07-ElectroCardEMPrint

C h apter e l eve n

Pericarditis, Myocarditis, and
Pericardial Effusions

Michael C. Bond, MD

Pericarditis the pericardium covers most of the heart (a
small portion of the left atrium is outside the
The diagnosis of pericarditis requires that pericardium), the ST-segment elevation should
the physician combine ECG interpretation be diffuse and without reciprocal changes.
skills with clinical assessment. Therefore, it is However, pericarditis can occur in a more
important to review the more common causes localized fashion (eg, after open heart surgery),
of pericarditis (Table 11-1)1 and the common resulting in an ECG with ST-segment elevation in
signs and symptoms seen in a patient with only a few leads and, rarely, reciprocal changes.
this condition (Table 11-2). Most patients In such localized cases, an echocardiogram
with pericarditis present to an emergency is often necessary to definitively distinguish
department with a complaint of chest pain and between pericarditis and acute myocardial
have ST-segment elevation on their ECGs. The ischemia/infarction. Echocardiographic clues
major challenge is to differentiate AMI from to pericarditis include absence of wall motion
pericarditis, because if an incorrect diagnosis abnormalities (their presence is typical of acute
of myocardial infarction is made, the patient myocardial ischemia/infarction) and sometimes
could be given thrombolytics or anticoagulants, the presence of pericardial effusion. Serial
leading to hemorrhagic pericardial effusion or measurements of cardiac enzyme concentrations
tamponade. A sound understanding of the ECG and serial ECGs are also helpful in making the
changes associated with pericarditis is critical distinction between these two diagnoses.
in order to reduce the chance of misdiagnosis.
Figure 11-1 demonstrates the ECG areas
The classic ECG changes seen in patients with of interest when evaluating patients for
pericarditis are diffuse ST-segment elevation pericarditis: the PR segment, the ST segment,
and PR-segment depression. These changes are and the TP segment. The TP segment, the
caused by inflammation of the pericardium, isoelectric point on the ECG, is the portion
extending to the epicardial layer. Inflammation used as the “baseline” of the ECG and the
of the ventricles results in ST-segment elevation, area of reference when judging the PR and
while the PR-segment depression represents ST segments for elevation or depression.
subepicardial injury to the atrium.1 Because
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PR-segment depression is the first ECG sign PR-segment elevation in other leads suggests
of acute pericarditis and is often found to occur atrial infarction, a relatively rare entity.
prior to ST-segment elevation.2 PR-segment
depression of more than 0.8 mm is specific The ST-segment elevation in pericarditis
but not highly sensitive for pericarditis3 and should be upwardly concave (analogous to a cup
tends to be greatest in the inferior leads (II, holding water). Additionally, the ST-segment
aVF) and lateral precordial leads (V4 to V6). elevation should not follow any specific arterial
PR-segment depression is not seen in leads distribution (ie, it should be diffuse). Common
aVR or V1. Although PR-segment depression exceptions occur in postoperative pericarditis
is commonly taught as a classic finding in all and in patients with pericardial adhesions from
types of pericarditis, it is most commonly found previous surgery or injury. These patients can
in cases of viral pericarditis, and its presence is have pericarditis localized to specific regions
often transient. PR-segment elevation in aVR of of the heart, resulting in ST-segment elevation
more than 0.5 mm is highly suggestive of, but limited to fewer leads. If the ST segment
not specific for, pericarditis, and it can be seen plateaus (becomes horizontal) or is convex
in patients with myocardial infarctions. PR- upward (tombstone-shaped), one must consider
segment elevation can also be seen in lead V1.4 myocardial ischemia as the cause, as these
findings essentially exclude pericarditis.1 The

Table 11-1. Neoplastic
Causes of pericarditis • primary
– sarcoma
Drugs – mesothelioma
• hydralazine • metastatic
• procainamide – breast
• methyldopa – lung
• penicillin – lymphoma
Infectious Rheumatologic
• bacterial • sarcoidosis
– Staphylococcus • systemic lupus erythematosus
– Haemophilus • rheumatoid arthritis
– Pneumococcus • dermatomyositis
– Salmonella • scleroderma
– tuberculosis • polyarteritis nodosa
– Meningococcus • vasculitis
– syphilis • ankylosing spondylitis
• viral Other
– Coxsackievirus • chest trauma
– echovirus • cardiac surgery
– Epstein-Barr virus • uremia
– HIV • myxedema
– mumps • aortic dissection
• parasites and fungi • radiation therapy
– histoplasmosis • myocardial infarction
– blastomycosis • Dressler syndrome
– coccidioidomycosis • pregnancy
– aspergillosis Idiopathic
– echinococcosis
– amebiasis
– rickettsiosis

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ST-segment elevation in pericarditis is usually to see patients beyond stage 1.9 Most patients
less than 5 mm in amplitude and tends to be are seen and treated promptly during stage 1,
greatest in leads II and V5 because the ST-segment so they never progress through the remaining
axis is typically leftward/anterior/inferior (over stages. If the ECG findings of stages 2 through
the left ventricle). ST-segment elevation in lead 4 do occur, they should be found in the same
II usually exceeds the ST-segment elevation in leads in which the stage 1 changes occurred.
lead III. If the reverse is true, cardiac ischemia
should be strongly suspected. The ST-segment T-wave flattening, T-wave inversion, and
elevation in pericarditis tends to decrease notched T waves have all been described in
across the precordial leads from lead V4 to lead patients who evolve through the later stages
V1 and in the limb leads from inferior (aVF) to of pericarditis. These changes never occur in
lateral (aVL) leads.5 A final clue suggestive of pericarditis until after the ST-segment elevation
acute pericarditis is based on a comparison of has resolved. Simultaneous T-wave inversion with
the height of the ST-segment elevation with the ST-segment elevation should always be considered
height of the T wave in lead V6. Both should cardiac ischemia until proved otherwise.
be measured from the isoelectric point, the TP
segment, in millimeters. An ST:T ratio greater Arrhythmias are uncommon in patients
than 0.25 in V6 suggests acute pericarditis.6 with simple pericarditis. Sinus tachycardia and
supraventricular arrhythmias are uncommon,
ST-segment depression is commonly seen in except in the presence of pericardial effusion
leads aVR and V1 in acute pericarditis, although or myocarditis. Intraventricular conduction
rarely more than 0.5 mm. ST-segment depression delays are most often found in myocarditis
in any leads other than aVR and V1, especially and should not occur if the inflammation
aVL, suggests acute myocardial ischemia or is limited to the pericardium.10
infarction until it is proved otherwise.7-9 ST-
segment elevation should never be found in Figure 11-2 shows the typical ECG of a patient
lead aVR in patients with acute pericarditis. with acute pericarditis. Diffuse ST-segment
ST-segment elevation in lead aVR is worrisome elevation is present in all leads except aVR, aVL,
for underlying ischemia. The ECG findings of and V1, and the magnitude of the ST-segment
acute pericarditis are summarized in Table 11-3. elevation in lead II is greater than the ST-
segment elevation in lead III. The PR segments
The ECG changes of pericarditis were slope downward and are depressed compared
described by Spodick7,8 as occurring in four stages with the TP segment. PR elevation is present
(Table 11-4). Progression through the stages tends in lead aVR. Finally, no reciprocal ST-segment
to occur in untreated patients. Today, except depressions are seen in any leads except aVR.
for patients with purulent pericarditis, it is rare
Figure 11-3 demonstrates localized
Table 11-2. pericarditis in a patient who had recent
Symptoms and signs of pericarditis cardiac surgery. The ECG abnormalities are
much more difficult to distinguish from
Symptoms acute myocardial ischemia because of the
• chest pain: might be positional (worse supine, absence of diffuse ST-segment elevation and
better when sitting up) or pleuritic and often is felt PR depression. The diagnosis of acute cardiac
along the trapezius ridge ischemia is also uncertain in this patient
• nonproductive cough because of the absence of reciprocal ST-segment
• shortness of breath depression. Echocardiography and cardiac
• low-grade fever biomarker testing were necessary to confirm
the diagnosis of postoperative pericarditis.
Signs
• tachycardia Figure 11-4 is the ECG of a patient with an
• three-phase pericardial friction rub (rare to hear all acute anterior lateral wall myocardial infarction
three phases) that was misdiagnosed as pericarditis. This
ECG shows ST-segment elevation in limb leads

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I and aVL and precordial leads V2 through 11-5 lists some of the symptoms and signs
V6. PR-segment elevation is present in lead commonly found in patients with myocarditis.12
aVR, suggestive of acute pericarditis. The most
important finding, however, is the presence Patients with myocarditis often present
of reciprocal ST-segment depression in leads with chest pain and shortness of breath, and
II, III, and aVF. This change alone should they can have an ECG that demonstrates ST-
rule out acute pericarditis. PR elevation in segment elevation or depression, suggesting
aVR has been seen on approximately 80% acute myocardial ischemia. These “pseudo-
of ECGs from patients with pericarditis, ischemia” patterns can be very difficult to
but it can be seen in AMI and should not be differentiate from true myocardial ischemia
considered pathognomonic for pericarditis.4 or infarction on a single ECG. ST- and T-wave
changes that occur with myocarditis do not
Figure 11-5 demonstrates an ECG from tend to evolve over the course of hours as they
another patient who was misdiagnosed with do with acute myocardial ischemia/infarction,
pericarditis because of the presence of PR- so serial ECG testing to evaluate for developing
segment depression in multiple leads. However, reciprocal ST-segment depression or developing
concurrent ST-segment elevation is absent. In infarction Q waves should be helpful. However,
contrast, ST-segment depression in the inferior there are no reliable criteria to help make a
leads is present, confirming that this patient clear distinction between myocarditis and
has acute cardiac ischemia. Any ST-segment myocardial ischemia on a single initial ECG.
depression in leads other than aVR and V1 Further complicating the distinction between
must be diagnosed as acute cardiac ischemia. myocarditis and myocardial ischemia is the
frequent presence of elevated cardiac biomarkers
Myocarditis early on in both conditions. Echocardiography
is often needed to make the diagnosis. Diffuse
Myocarditis is an inflammatory process wall motion abnormalities, often with global
involving the entire myocardium. The causes hypokinesis, are found in myocarditis, whereas
of pericarditis and myocarditis are very similar; regional wall motion abnormalities are found
however, myocarditis is also commonly in patients with myocardial infarction.
associated with Kawasaki disease, the peripartum
state, and cardiac transplant rejection. In the It is rare to find a patient with myocarditis
Myocarditis Treatment Trial,11 89% of patients who has a completely normal ECG. Many
reported having a viral-like prodrome, and types of ECG patterns have been reported in
50% of patients reported having a recent upper these patients (Table 11-6), although none
respiratory or gastrointestinal infection. Table are highly specific for myocarditis. Sinus

Table 11-3.
Common ECG findings in acute pericarditis

PR-segment depression Usually early finding and transient
Depression >0.8 mm is specific but not sensitive
Greatest in leads II, aVF, V4 through V6
ST-segment elevation Upwardly concave
Diffuse
Does not correspond to any arterial distribution
Usually <5 mm compared with the PR segment and tends to be greatest in leads II and V5
An ST:T ratio >0.25 in V6 suggests acute pericarditis
Never found in aVR
ST-segment elevation in lead II is generally greater than the ST-segment elevation in lead III
ST-segment depression Commonly found in aVR and V1

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tachycardia is the most common arrhythmia, on physical examination. Pulsus paradoxus
although other tachyarrhythmias are well is only 77% sensitive in patients with cardiac
reported as well. Diffuse nonspecific T-wave tamponade, and the Beck triad of hypotension,
inversions tend to be the most common elevated central venous pressure, and quiet heart
abnormality.10,12–14 Atrioventricular blocks and sounds is seen so infrequently that its absence
ST abnormalities are common during the first does not rule out the diagnosis. Because the
month of symptoms, whereas left bundle- physical examination is so unreliable, ancillary
branch blocks, atrial fibrillation, and left testing is usually needed to secure the diagnosis
ventricular hypertrophy are more common of pericardial effusion or cardiac tamponade.
in late disease.15 The ECG abnormalities of Echocardiography is the diagnostic test of choice
myocarditis are often transient (eg, there to visualize the presence of pericardial effusion
should be no residual Q waves) and tend to and to evaluate for the evidence of pericardial
resolve as the underlying condition resolves. tamponade. Tamponade is diagnosed when
pericardial fluid pressure causes right atrial
Figure 11-6 is an ECG from a patient with or right ventricular collapse, most commonly
myocarditis, showing the most common during diastole. Right heart catheterization can
arrhythmia, sinus tachycardia. The patient was also accurately diagnose pericardial tamponade
a young man who presented with a low-grade when there is near equalization (within 5 mm
fever, tachycardia out of proportion to the fever, Hg) of the right atrial, right ventricular diastolic,
and mild evidence of heart failure—the classic pulmonary arterial diastolic, and pulmonary
presentation of acute myocarditis. The clinical capillary wedge pressures. However, right heart
presentation and the ECG prompted additional catheterization does not diagnose pericardial
cardiac evaluation to secure the proper diagnosis. effusions that are not causing tamponade.16

Figure 11-7 is an ECG from an older patient Echocardiography and right heart
who presented after a syncopal episode; she catheterization are often not available in an
has third-degree atrioventricular heart block, emergency department. Consequently, physicians
which was initially presumed to be caused by should be familiar with the ECG findings that
coronary artery disease. An echocardiogram suggest large pericardial effusions. The triad of
demonstrating diffuse hypokinesis and electrical alternans, low QRS voltage, and PR-
new heart failure prompted an extensive segment depression are often taught as classic
workup, resulting in a final diagnosis of for the diagnosis, but a recent review of these
myocarditis induced by Lyme disease. findings found that, although the specificity
was very good (89%–100%), the sensitivity of
Pericardial Effusion and this triad was poor (1%–17%) in diagnosing
Cardiac Tamponade pericardial effusions and cardiac tamponade.17
The primary limitation of this triad is that it
The diagnosis of pericardial effusion and
cardiac tamponade is difficult to make based

Table 11-4.
Stages of pericarditis

Stage 1 Diffuse concave-upward ST-segment elevation with concordance of T waves
PR-segment depression, generally present in same leads as those with ST-segment elevation; most
prominent in viral pericarditis
ST-segment depression in aVR and V1 is common
Absence of reciprocal ST-segment depression in any other leads
Stage 2 ST segments return to baseline; T-wave flattening
Stage 3 T-wave inversion, primarily in leads in which prior ST-segment elevation occurred
Stage 4 Gradual resolution of T-wave inversion and return to baseline ECG

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assumes that the pericardial effusion is caused is low. However, when the low voltage is new
by viral pericarditis. Other causes of pericardial compared with recent ECGs and concurrently
effusion are not reliably associated with PR- associated with sinus tachycardia, the specificity
segment depression. The presence of electrical for large pericardial effusions is more than 80%.18
alternans is also less common than was once
thought, with a sensitivity of approximately Electrical alternans is a cyclic beat-to-beat
30% in patients with pericardial effusions.18 variation in the amplitude or axis of the electrical
complexes on the ECG. This can be caused by the
The most common abnormalities found in heart swinging within the pericardial sac, as seen
patients with large pericardial effusions are in patients with pericardial effusion. Numerous
sinus tachycardia and low voltage on the ECG. other potential causes (eg, myocardial infarction,
Both findings are present in well over 50% of cardiomyopathy, supraventricular and ventricular
patients.18 The definition of low QRS voltage tachycardias, hypothermia, atrial fibrillation, and
varies among authors, but a simple method of electrolyte disturbances) have been described
defining low voltage is as follows: when the total as well.18–23 The most common type of electrical
amplitude of the QRS complexes in leads I, II, alternans involves the QRS complex (Figure 11-9).
and III adds up to less than 15 mm or when the Electrical alternans involving the P wave or the T
total amplitude of the QRS complexes in leads wave is also well described, although it is much
V1, V2, and V3 adds up to less than 30 mm, less common. Patients with large pericardial
then low voltage is diagnosed (Figure 11-8). effusions might also demonstrate total electrical
Low voltage is found not only in patients with alternans, in which cyclic beat-to-beat variations
pericardial effusions but also in patients with in the P-wave, QRS, and T-wave axes all occur
amyloidosis, sarcoidosis, myxedema, chronic together. Total electrical alternans is more than
obstructive pulmonary disease, pleural effusion,
obesity, anasarca, and pneumothorax and after Table 11-6.
open heart surgery. As a result, the specificity of Common ECG findings in myocarditis
low voltage alone for large pericardial effusions
Sinus tachycardia
Table 11-5. Supraventricular or ventricular arrhythmias
Symptoms and signs of myocarditis Incomplete atrioventricular and intraventricular blocks
are most common; complete atrioventricular block is
Symptoms less common.
• fever Left and right bundle-branch block
• myalgia T-wave inversions
• cough Prolonged QT interval
• shortness of breath (orthopnea, dyspnea on ST-segment elevation or depression (often
exertion, paroxysmal nocturnal dyspnea) misdiagnosed as acute cardiac ischemia/infarction)
• weakness PR-segment depression (if myopericarditis is present)
• dizziness Low-voltage QRS complexes may be present.
• chest pain: may be positional, pleuritic, or
substernal pressure Table 11-7.
• syncope ECG findings in pericardial effusion and tamponade

Signs Electrical alternans
• tachycardia Low voltage
• hypotension or cardiogenic shock PR-segment depression, especially if precipitated by
• rales acute pericarditis; can be transient
• cardiac gallop (S3, S4, or both) Sinus tachycardia
• displaced point of maximal impulse (due to Nonspecific T-wave abnormalities
cardiomegaly)
• pedal edema

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90% specific for large pericardial effusions,18 changes other than those already described
but it is a rare finding. In patients with large for pericardial effusion; however, it is more
pericardial effusions, the sensitivity of electrical common to see tachycardia as the heart tries to
alternans is only 30%. However, when electrical compensate for the diminished cardiac output.
alternans occurs in combination with low voltage Table 11-7 summarizes the typical ECG findings
and tachycardia, it is almost pathognomonic for in patients with large pericardial effusions and
the presence of a large pericardial effusion. PR- tamponade. A detailed clinical examination
segment depression can also occur in patients and judicious use of ancillary tests will assist
with large pericardial effusions, especially when the clinician in making the correct diagnosis.
the effusion is caused by viral pericarditis,
malignancy, or connective tissue disorders.24

Pericardial tamponade has no specific ECG

Key Facts

Acute Pericarditis
• The combination of PR-segment depression with ST-segment elevation is virtually diagnostic of

acute pericarditis.
• PR-segment elevation in aVR is suggestive of, but not pathognomonic for, acute pericarditis. It can

be found in the setting of myocardial infarction as well.
• ST-segment elevation should be concave-upward. ST-segment elevation that is convex-upward

(tombstone-shaped) or horizontal is highly suggestive of cardiac ischemia or acute myocardial
infarction.
• ST-segment elevation in lead aVR strongly virtually excludes the diagnosis of acute pericarditis.
• ST-segment depression can be found in leads aVR and V1. The presence of ST-segment depression
in any other leads suggests cardiac ischemia.
• ST-segment elevation in lead III greater than that found in lead II suggests cardiac ischemia.
• Simultaneous ST-segment elevation and T-wave changes suggest ischemia.
Myocarditis
• By far, the most common ECG abnormality found in acute myocarditis is sinus tachycardia.
• Nonspecific ST/T-wave changes are the most common abnormality noted.
• Arrhythmias and conduction delays tend to be transient.
• PR-segment depression is common with myopericarditis.
• Distinction from acute cardiac ischemia/infarction can be extremely difficult in the early stages. The
ECG is often limited here; historic information and serial ECGs are helpful but often not definitive.
• Evolving Q waves suggest myocardial infarction.
• Echocardiography is often needed to help differentiate myocarditis from myocardial infarction when
there are ST-segment elevations and depressions.
Pericardial Effusion/Tamponade
• Electrical alternans occurs in the minority of patients, so its absence should not be used to rule out
the diagnosis.
• Low voltage is common but nonspecific for large pericardial effusions.
• The presence of tachycardia plus new low voltage on the ECG, compared with a previous ECG, is
highly specific for large pericardial effusions.
• Pericardial tamponade is a clinical or echocardiographic diagnosis and should not be ruled in or ruled
out based on the ECG.

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References 13. Oakley CM. Myocarditis, pericarditis and other
pericardial diseases. Heart. 2000;84(4):449-454.
1. Marinella MA. Electrocardiographic manifestations
and differential diagnosis of acute pericarditis. 14. Ander DS, Heilpern KL. Myocarditis. In: Chan TC, Brady W,
Am Fam Phys. 1998;57(4):699-704. Harrigan R, et al, eds. ECG in Emergency Medicine and Acute
Care. St Louis, MO: Mosby-Year Book; 2004:204-206.
2. Baljepally R, Spodick DH. PR-segment deviation as
the initial electrocardiographic response in acute 15. Morgera T, Di Lenarda A, Dreas L, et al. Electrocardiography
pericarditis. Am J Cardiol. 1998;81(12):1505-1506. of myocarditis revisited: clinical and prognostic significance of
electrocardiographic changes. Am Heart J. 1992;124(2):455-467.
3. Charles MA, Bensinger TA, Glasser SP. Atrial injury current
in pericarditis. Arch Intern Med. 1973;131(5):657-662. 16. Scarpinato L. Pericardial effusion and cardiac
tamponade diagnostic methods: where are we
4. Pericarditis and myocarditis. In: Smith SW, Henry TD, headed? Chest. 1996;110(2):308-310.
Sharkey SW, et al, eds. ECG in Acute MI: An Evidence-
Based Manual on Reperfusion Therapy. Philadelphia, 17. Eisenberg MJ, de Romeral LM, Heidenreich PA, et al. The
PA: Lippincott William & Wilkins; 2002. diagnosis of pericardial effusion and cardiac tamponade by 12-
lead ECG: a technology assessment. Chest. 1996;110(2):318-324.
5. Spodick DH. Electrocardiogram in acute pericarditis:
distributions of morphologic and axial changes 18. Surawicz B, Knilans TK. Chou’s Electrocardiography In Clinical
by stages. Am J Cardiol. 1974;33(4):470-474. Practice. 5th ed. Philadelphia, PA: WB Saunders; 2001.

6. Ginzton LE, Laks MM. The differential diagnosis of acute 19. Cheng TC. Electrical alternans: an association with coronary
pericarditis from the normal variant: new electrocardiographic artery spasm. Arch Intern Med. 1983;143(5):1052-1053.
criteria. Circulation. 1982;65(5):1004-1009.
20. Crosson JE, Dunnigan A. Propranolol induced electrical and
7. Spodick DH. Pericardial diseases. In: Braunwald mechanical alternans in orthodromic reciprocating tachycardia.
E, Lippy P, eds. Heart Disease. 6th ed. Philadelphia, Pacing Clin Electrophysiol. 1993;16(3 Pt 1):496-500.
PA: WB Saunders; 2001:823-1866.
21. Konno T, Araki T, Soma R, et al. Electrical and mechanical
8. Spodick DH. Diagnostic electrocardiographic sequences alternans during percutaneous transluminal coronary
in acute pericarditis: significance of PR segment and PR angioplasty in a patient with acute myocardial infarction—a
vector changes. Circulation. 1973;48(3):575-580. case report. Angiology. 2004;55(5):569-571.

9. Spodick DH. Acute pericarditis: current concepts 22. Lau TK, Civitello AB, Hemandez A, et al. Cardiac tamponade
and practice. JAMA. 2003;289(9):1150-1153. and electrical alternans. Tex Heart Inst J. 2002;29(1):66-67.

10. Demangone D. ECG manifestations: noncoronary heart 23. Wasir HS, Mohan JC. Exercise induced QRS, ST, T electrical
disease. Emerg Med Clin North Am. 2006;24(1):113-131,vi. alternans in a normal person. Indian Heart J. 1987;39(1):69-70.

11. Mason JW, O’Connell JB, Herskowitz A, et al. A clinical trial of 24. Kudo Y, Yamasaki F, Doi T, et al. Clinical significance of low
immunosuppressive therapy for myocarditis. The Myocarditis voltage in asymptomatic patients with pericardial effusion
Treatment Trial Investigators. N Engl J Med. 1995;333(5):269-275. free of heart disease. Chest. 2003;124(6):2064-2067.

12. Brady WJ, Ferguson JD, Ullman EA, et al. Myocarditis:
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Emerg Med Clin North Am. 2004;22(4):865-885.

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Figures

Figure 11-1.
ECG reference: areas of interest in the evaluation of patients for pericarditis.

Figure 11-2.
Acute pericarditis. This ECG shows a classic example of the changes seen in pericarditis. PR segments
are depressed and slope downward compared with the TP segment; there is diffuse concave-upward ST-
segment elevation in many leads. PR-segment elevation in lead aVR is suggestive, but not diagnostic, of acute
pericarditis. The PR- and ST-segment changes are more pronounced in lead II than in lead III, another finding
typical of acute pericarditis compared with acute cardiac ischemia. Image courtesy of Amal Mattu, MD.

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Figures

Figure 11-3.
Localized pericarditis. ST-segment elevation is localized to the anterior leads. The patient developed chest
pain 2 days after cardiac surgery. Echocardiography and serial cardiac biomarker testing was used to confirm
the diagnosis. Note the absence of PR-segment depression, a finding that is primarily present in viral cases of
acute pericarditis. Image courtesy of Amal Mattu, MD.

Figure 11-4.
Acute myocardial infarction. ST segment elevation is present in the precordial leads (V2 to V6) and limb leads I
and aVL. The ST-segment depression in leads II, III, and aVF represents reciprocal changes, essentially ruling
out acute pericarditis. Note the presence of PR-segment elevation in lead aVR, a finding often misinterpreted
as being pathognomonic for acute pericarditis. Image courtesy of Amal Mattu, MD.

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Figures

Figure 11-5.
Acute cardiac ischemia. This ECG was misinterpreted as acute pericarditis because of the presence of PR-
segment depression in multiple leads and the presence of PR-segment elevation in lead aVR. However, the
physician was misled into thinking that ST-segment elevation was present, because he used the PR segment
as the ECG baseline. Instead, by using the TP segment as the baseline, one can easily see that ST-segment
elevation is not present. In fact, ST-segment depression is present in leads II, III, and aVF, a finding that
excludes the diagnosis of acute pericarditis. Image courtesy of Amal Mattu, MD.

Figure 11-6.
Acute myocarditis: extreme sinus tachycardia. Image courtesy of Amal Mattu, MD.

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Figures

Figure 11-7.
Myocarditis. Sinus tachycardia is present with a new incomplete right bundle-branch block and complete
heart block. The patient was found to have Lyme disease. Image courtesy of Amal Mattu, MD.

Figure 11-8.
Large pericardial effusion. The combination of tachycardia plus low voltage (a new finding in this patient) is
highly suggestive of the diagnosis. Low voltage in this patient is diagnosed based on the QRS amplitudes in
leads V1 to V3. Image courtesy of Amal Mattu, MD.

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Figures

Figure 11-9.
Large pericardial effusion. The classic triad of sinus tachycardia, low voltage, and electrical alternans (best
seen in the precordial leads) is present. The patient also had hypotension and echocardiographic evidence of
pericardial tamponade. Image courtesy of Amal Mattu, MD.

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154

C h apter t w e l ve

Preexcitation and Accessory Pathway
Syndromes

Stephen Y. Liang, MD, and Edward B. Bolgiano, MD

In the normal heart, electrical impulses Anatomic Substrate
generated in the sinuatrial node pass through the
atrioventricular (AV) node, where the impulse Anomalous bundles of conducting tissue that
is slowed before conduction to the His-Purkinje bypass all or part of the normal atrioventricular
system and the ventricular muscle. The normal conduction system form the anatomic substrate
PR interval represents the time taken for the for preexcitation.2 Several types of accessory
impulse to depolarize the atria and pass through pathways exist. An AV bypass tract, or Kent
the AV node and the His-Purkinje system. bundle, is the most common type, directly
connecting atrial and ventricular myocardium,
Preexcitation refers to activation of the circumventing the AV node and the His-Purkinje
ventricular myocardium by a supraventricular system altogether. Concurrent activation
impulse earlier than would occur by the normal of the ventricular myocardium via this AV
path through the AV node. This early activation bypass tract as well as via the normal AV
occurs via an additional or alternative pathway conduction pathway creates the characteristic
that connects the atria and ventricle and bypasses QRS complex or fusion beat of the WPW
the AV node. This accessory pathway may have ECG pattern and syndrome (Figure 12-1).
several possible types of anatomic substrate and
can conduct impulses in one or both directions. James fibers (intranodal or atrionodal tracts)
have historically been associated with the
The Wolff-Parkinson-White (WPW) syndrome, Lown-Ganong-Levine (LGL) syndrome, a rare
first described in 1930,1 is the most common accessory pathway syndrome. Mahaim fibers
accessory pathway syndrome. The syndrome have AV node-like properties and connect the
consists of paroxysmal tachycardia, a short atrium (atriofascicular or Brechenmacher tract)
PR interval, and an abnormal QRS complex. to the right ventricle through a Purkinje-like
The characteristic ECG features in patients network. All of these pathways are congenital
without the associated preexcitation-dependent in origin and are a result of incomplete
tachycardia is termed a WPW pattern. Variants of separation of the atria and ventricles.
the WPW syndrome have also been described.

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Associated Abnormalities and conducting system or within the ventricular
Epidemiology myocardium close to the conducting system.

The WPW pattern is present in 0.15% In the presence of a bypass tract,
to 0.25% of the general population.3,4 Men supraventricular impulses might be conducted
are affected twice as often as women. The only through the AV node, only through
incidence of the other types of preexcitation the bypass tract (full preexcitation), or
is much lower. Substantially less than 50% simultaneously through both the AV node
of patients with the WPW pattern become and bypass tract, causing a variety of fusion
symptomatic (reported numbers vary).5,6 complexes. ECG findings are determined by
the relative timing and direction of impulse
Although most patients with the WPW flow. With increasing relative contribution of
pattern have no associated organic heart disease, conduction through the bypass tract, the PR
a variety of conditions are associated with interval shortens, the delta wave becomes more
WPW, including Ebstein anomaly, hypertrophic prominent, and the QRS complex widens (Figure
cardiomyopathy, mitral valve prolapse, tricuspid 12-3). Conversely, with increasing relative
atresia, endocardial fibroelastosis, rheumatic contribution of conduction through the AV node,
heart disease, and hyperthyroidism. A familial the PR interval lengthens, the delta wave becomes
component is suggested by an increased less prominent, and the QRS complex shortens.8
prevalence among first-degree relatives. With However, it is important to remember that the
coexistent age-related conditions such as ECG is normal in many patients with WPW.
coronary or hypertensive heart disease, the
WPW pattern is an unrelated finding. Several other factors influence the degree
of PR-interval shortening and QRS-interval
The ECG Pattern widening—the site of origin of the atrial
impulse, interatrial conduction time, atrial
The classic ECG pattern in WPW syndrome refractoriness, and the conduction properties
(Figure 12-2) has four elements, as follows: of both the accessory pathway and the normal
pathway (AV node/His-Purkinje system).
• PR interval less than 0.12 second, with a
normal P wave The autonomic nervous system affects
the conduction properties of both pathways.
• wide QRS complex with a duration of 0.11 During sinus tachycardia, when sympathetic
second or more tone is increased and vagal tone is decreased,
preexcitation can be less apparent.
• initial slurring of the QRS complex (the
delta wave) Secondary repolarization abnormalities (ST-
segment and T-wave changes) occur in patients
• secondary ST-segment and T-wave changes with the WPW pattern as a consequence of
the altered sequence of ventricular activation.
Because the supraventricular impulse bypasses Similar to the repolarization changes of
the AV node (avoiding the associated delay), the ventricular hypertrophy or bundle-branch
onset of ventricular activation occurs earlier block, the direction of the ST segment and
than expected and the preexcited PR interval T wave are opposite the direction of the
is shortened. In most cases, the PR interval is delta wave and the main QRS complex.
0 to 0.11 second.7 Unless there is coexistent
atrial pathology, the P-wave morphology is Related ECG Phenomena
normal. Direct depolarization of nonspecialized
ventricular myocardium (which conducts at Concealed Accessory Pathway
a slower rate than the His-Purkinje system)
at the site of bypass tract insertion generates Although accessory pathways usually
an initial slurring of the QRS complex (the conduct in both directions, most tracts are
delta wave). Delta waves are not seen with capable of only retrograde conduction. Because
non-WPW types of preexcitation in which
the accessory pathways terminate in the

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Preexcitation and Accessory Pathway Syndromes

these concealed accessory pathways do not Type A and Type B Wolff-Parkinson-White
preexcite the ventricles, the ECG during A left-sided accessory pathway produces a
sinus rhythm is normal. Concealed bypass
tracts can serve as a conduit in the retrograde QRS complex mostly positive in V1 (type A), and
direction in an AV reentrant circuit and thus a right-sided accessory pathway produces a QRS
are associated with reentrant arrhythmias. complex mostly negative in V1 (type B). Type
A WPW is more common. This classification
Lown-Ganong-Levine Syndrome scheme is of no significant clinical importance
in the emergency setting and is considered
The LGL syndrome is a rare accessory pathway outdated by most electrophysiologists.
syndrome characterized by a short PR interval
(≤0.12 sec), a normal QRS complex without Pseudoinfarction and the Diagnosis of
a delta wave, and paroxysmal tachycardia. Myocardial Infarction in the Presence of
Identified as a syndrome prior to the era of the Wolff-Parkinson-White Pattern
electrophysiologic studies, LGL is now generally
considered an outdated clinical diagnosis. Data When the delta wave is negative, it can
from electrophysiologic studies have cast doubt resemble an abnormal Q wave associated
on the existence of LGL as a separate entity, with myocardial infarction (MI).9 Negative
revealing that the short PR interval of the LGL delta waves in the right precordial leads can
syndrome is on the end of the spectrum of cause a pseudoinfarction pattern, suggesting
normal variants and that most patients with LGL anterior myocardial infarction; a negative
syndrome have another cause for paroxysmal delta wave in lead aVL suggests lateral MI;
tachycardia, usually AV nodal reentrant and negative delta waves in leads II, III,
tachycardia or a concealed accessory pathway. and aVF suggest inferior MI (Figure 12-6).
An upright delta wave in lead V1 suggests
Intermittent Preexcitation and posterior MI or right bundle-branch block.
Preexcitation Alternans
The abnormal Q waves of true MI are
In most patients with the WPW pattern, frequently obscured by the preexcitation
the ECG changes appear intermittently. The pattern. Secondary repolarization abnormalities
change from the preexcitation pattern to a are common in WPW and can mimic acute
normal conduction pattern (and back again) ischemic changes. With the WPW pattern,
can occur in the same continuous tracing. This in leads with an upright QRS complex, the
occurs in the absence of any appreciable change ST segment should be either isoelectric or
in heart rate and is usually associated with depressed; ST-segment elevation in this situation
an accessory pathway with a relatively long usually indicates acute injury (Figure 12-7).
antegrade refractory period. In preexcitation
alternans, the preexcitation pattern alternates Clinical Significance
with a normal conduction pattern (Figure 12-4).
Tachyarrhythmias
Concertina Effect The most important clinical features

The degree of preexcitation can show a cyclic of the accessory pathway syndromes are
pattern, with progressive shortening of the PR their association with and propensity for
interval and corresponding widening of the tachyarrhythmias. The accessory pathways are
QRS complex over several cycles, followed by a capable of rapid conduction and recovery and
gradual decrease in the degree of preexcitation can, in rare cases, conduct atrial flutter 1:1 to
over several cycles, despite a constant heart the ventricles (300 beats/min). Atrial fibrillation
rate. The P end of the QRS interval remains can be conducted even more rapidly, with
constant. This “concertina effect” produces a possible degeneration into ventricular fibrillation.
characteristic pattern on the ECG (Figure 12-5). Standard pharmacologic management of certain
tachyarrhythmias inappropriately applied

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in this setting can have dire consequences. the presence of a preexisting or rate-related
An understanding of the mechanisms of bundle-branch block, the QRS complex can be
tachyarrhythmias associated with accessory wide in orthodromic AVRT.) The tachycardia
pathways is fundamental to proper management. is rapid (150–250 beats/min). P waves can
be found within the ST/T-wave segment.
Paroxysmal supraventricular tachycardia
is the most common rhythm in symptomatic Less commonly, the anterograde limb is the
patients with the WPW syndrome (70%– accessory pathway and the retrograde limb is
80%). Atrioventricular reentrant (or the normal AV conduction system (antidromic
reciprocating) tachycardia (AVRT) and AVRT); the QRS complex is wide, and a delta
atrioventricular nodal reentrant tachycardia wave is present. Retrograde P waves are usually
are the two most common forms of paroxysmal obscured by the wide preexcited QRS complex
supraventricular tachycardia. Atrial and ST/T-wave segment but sometimes can be
fibrillation is less common (10%–30%).10 identified within the ST/T-wave segment.

The mechanisms of tachycardia associated Tachycardias in Which the Accessory
with accessory pathway syndromes can best be Pathway Facilitates Rapid Transmission
understood by classification into two groups:
In some types of tachycardias associated with
1. Tachycardias requiring an accessory accessory pathway syndromes, the bypass tract
pathway for initiation and maintenance, eg, is not required for initiation and maintenance
AVRT. of the arrhythmia but can “facilitate” rapid
transmission of impulses to the ventricles. This
2. Tachycardias in which the accessory group includes atrial fibrillation and atrial flutter.
pathway might act only as a “facilitator,”
providing a rapid route of conduction, eg, Atrial Fibrillation. Atrial fibrillation occurs
atrial fibrillation and atrial flutter. in 10% to 30% of individuals with the WPW
syndrome. Coexistent structural heart disease
Tachycardias Requiring an Accessory (a common cause of atrial fibrillation in patients
Pathway for Initiation and Maintenance without accessory pathways) is uncommon in
the WPW syndrome and cannot explain the
The accessory path(s), together with high frequency of atrial fibrillation. Fibrillation
the normal AV conduction system, atrial is often preceded by AVRT in WPW.
myocardium, and ventricular myocardium, form
a reentrant pathway that produces and sustains Atrial fibrillation originates in the atria,
the tachycardia. Differences in conduction time independent of the accessory pathway. Atrial
and refractoriness between the bypass tract impulses can be conducted down both the
and the normal AV conduction system permit a normal AV conduction system and the accessory
properly timed premature impulse (premature pathway. The accessory pathway can function
atrial contraction, premature junctional complex, as a route for rapid conduction of atrial
or premature ventricular contraction) to initiate impulses to the ventricles, producing wide
reentry and establish a circus movement. QRS complexes with rapid ventricular rates
(Figure 12-8). The irregularity of the ventricular
Two forms of conduction can occur in response helps differentiate atrial fibrillation
this type of arrhythmia: orthodromic AVRT in WPW from ventricular tachycardia. When
and antidromic AVRT (Figure 4-1E, 4-1F). In the ventricular rate exceeds 200 beats/min,
orthodromic AVRT, anterograde conduction however, the irregularity of atrial fibrillation
(toward the ventricle) occurs through the can become less apparent. Atrial fibrillation
normal AV conduction system, and retrograde with rapid ventricular response rates in WPW
conduction (toward the atrium) occurs through can degenerate into ventricular fibrillation.
the accessory pathway. The ventricle is activated
via the normal pathway, and there is no degree Atrial Flutter. An atrial reentrant circuit,
of ventricular preexcitation; the QRS complex independent of the accessory pathway,
is narrow and the delta wave is absent. (In

158

Preexcitation and Accessory Pathway Syndromes

causes atrial flutter. Atrial impulses are radiofrequency ablation is appropriate for all
usually conducted to the ventricles through
the accessory pathway, causing wide QRS symptomatic patients with WPW syndrome.
complexes. The conduction ratio can be 2:1
or 1:1. The regular rhythm and wide QRS Although hospital admission is not always
complexes can mimic ventricular tachycardia.
necessary for symptomatic patients, appropriate
Treatment Considerations
consultation with a cardiologist should
Emergency
Proper emergency management of patients usually be obtained prior to discharging the

with preexcitation syndromes who present patient from the emergency department.
with tachyarrhythmias requires an assessment
of both clinical and ECG features: References

• symptoms of instability 1. Wolff L, Parkinson J, White PD. Bundle-branch block
with short PR interval in healthy young people prone to
• QRS duration paroxysmal tachycardia. Am Heart J. 1930;5:685.

• QRS regularity or irregularity 2. Becker AE, Anderson RH, Durrer D, et al. The
anatomic substrates of Wolff-Parkinson-White
Cardioversion is the treatment of choice for all syndrome: a clinicopathologic correlation in seven
unstable patients, regardless of ECG findings. patients. Circulation. 1978;57:870-879.

Regular orthodromic tachycardia (narrow 3. Chung KY, Walsh TJ, Massie E. Wolff-Parkinson-
QRS complex, no delta wave) can be treated White syndrome. Am Heart J. 1965;69:116-133.
in the usual manner: vagal maneuvers
followed by adenosine, calcium channel 4. Krahn AD, Manfreda J, Tate RB, et al. The natural history
blockers, or -blockers. Amiodarone, of electrocardiographic preexcitation in men: the Manitoba
procainamide, and digoxin are alternatives. follow-up study. Ann Intern Med. 1992;116:456-460.

Regular antidromic tachycardia (wide QRS 5. Fitzsimmons PJ, McWhirter PD, Peterson DW, et
complex) or any irregular tachycardia (regardless al. The natural history of Wolff-Parkinson-White
of QRS duration) requires special consideration. syndrome in 228 military aviators: a long-term follow-
All drugs that block the AV node (calcium up of 22 years. Am Heart J. 2001;142:530-536.
channel blockers, -blockers, adenosine, and
digoxin) are contraindicated in this situation. 6. Munger TM, Packer DL, Hammill SC, et al. A population
AV nodal blockade might actually create a faster study of the natural history of Wolff-Parkinson-
ventricular response rate and cause degeneration White syndrome in Olmstead County, Minnesota,
into ventricular fibrillation.11 Atrial fibrillation 1953 to 1989. Circulation. 1993;87:866-873.
and the WPW syndrome must be suspected with
any wide complex irregular tachycardia. At very 7. Gallagher JJ, Pritchett ELC, Sealy WC, et al. The preexcitation
fast rates (>250 beats/min), irregularity can be syndromes. Prog Cardiovasc Dis. 1978;20:285-327.
difficult to detect. Electrical cardioversion should
be considered early in this setting. If drug therapy 8. Wellens HJJ, Atie J, Penn OC, et al. Diagnosis and treatment of
is used, procainamide has been a treatment patients with accessory pathways. Cardiol Clin. 1990;8:503-521.
mainstay, although the most recent advanced
cardiac life support guidelines recommend 9. Wang K, Asinger R, Hodges M. Electrocardiograms
amiodarone as an effective treatment as well.12 of Wolff-Parkinson-White syndrome simulating other
conditions. Am Heart J. 1996;132:152-155.
Beyond the Emergency Department
Referral to a cardiologist for electrophysiologic 10. Yee R, Klein GJ, Sharma AD, et al. Tachycardia associated with
accessory atrioventricular pathways. In: Zipes DP, Jalife J, eds.
studies, risk stratification, and possible Cardiac Electrophysiology. Philadelphia, PA: WB Saunders; 1990.

11. McGovern B, Garan H, Ruskin JN. Precipitation of ventricular
fibrillation by verapamil in patients with Wolff-Parkinson-
White syndrome. Ann Intern Med. 1986;104:791-794.

12. 2005 American Heart Association Guidelines for
Cardiopulmonary Resuscitation and Emergency
Cardiovascular Care. Circulation. 2005;112:67-77.

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Electrocardiography in Emergency Medicine

Figures

Figure 12-1.
Relationship between an anatomic Kent bundle and physiologic preexcitation of the ventricular myocardium
(top) and the typical ECG changes of ventricular preexcitation (bottom). A: Normal condition. B: Abnormal
condition. Modified from: Wagner GS, Waugh RA, Ramo BW. Cardiac Arrhythmias. New York, NY: Churchill
Livingstone; 1983:13. Used with permission.

Figure 12-2.
The WPW ECG pattern.

160

Preexcitation and Accessory Pathway Syndromes

Figures

Figure 12-3.
Intermittent WPW syndrome. A: Intermittent preexcitation mimicking frequent preventricular contractions.
B: Intermittent preexcitation from same patient simulating accelerated idioventricular rhythm. C: Tracing
taken simultaneously with tracing B with different lead reveals short PR interval with delta wave and confirms
intermittent preexcitation. From: Wang K, Asinger R, Hodges M. Electrocardiograms of Wolff-Parkinson-White
syndrome simulating other conditions. Am Heart J. 1996;132:152-155. Used with permission.

Figure 12-4.
Preexcitation in alternate beats simulating electrical alternans. From: Wang K, Asinger R, Hodges M.
Electrocardiograms of Wolff-Parkinson-White syndrome simulating other conditions. Am Heart J.
1996;132:152-155. Used with permission.

Figure 12-5.
ECG lead II of a patient with intermittent WPW preexcitation demonstrates a “concertina” effect, in which
increasing preexcitation shortens the PR interval and lengthens the QRS complex, with the interval from P
to the end of QRS remaining constant. This tracing also is an example of secondary T-wave changes, with
the T wave becoming more negative as the QRS duration increases. Of the six consecutive complexes, the
first is conducted through the AV node alone and the sixth presumably through the accessory pathway alone
(fully preexcited), whereas the second, fourth, fifth, and third complexes show increasing degrees of fusion
between the AV nodal and accessory pathway conduction. From: Ventricular preexcitation (Wolff-Parkinson-
White syndrome and its variants). In: Surawicz B, Knilans TK, eds. Chou’s Electrocardiography in Clinical
Practice. Philadelphia, PA: WB Saunders; 2001:463. Used with permission.

161

Electrocardiography in Emergency Medicine

Figures

Figure 12-6.
Pseudoinfarction pattern with negative delta waves in leads II, III, and aVF suggestive of inferior myocardial
infarction.

Figure 12-7.
Acute myocardial infarction in the presence of a WPW pattern in a 49-year-old man with the typical symptoms
and enzyme changes of acute MI. The tracing shows a WPW pattern. The presence of acute injury is indicated
by the ST-segment elevation in leads V3 through V5. In uncomplicated cases of WPW pattern, the ST segment
is either isoelectric or depressed in leads with an essentially upright QRS complex. From: Ventricular
preexcitation (Wolff-Parkinson-White syndrome and its variants). In Surawicz B, Knilans TK, eds. Chou’s
Electrocardiography in Clinical Practice. Philadelphia, PA: WB Saunders; 2001:487. Used with permission.

162

Preexcitation and Accessory Pathway Syndromes

Figures

Figure 12-8.
Atrial fibrillation in WPW. Image courtesy of Amal Mattu, MD.

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Electrocardiography in Emergency Medicine
164

C h apter t h i rtee n

Inherited Syndromes of Sudden Cardiac
Death

Benjamin S. Abella, MD, MPhil, and Salem Kim, BA

Sudden cardiac death (SCD) is most from undiagnosed cardiac conditions that
commonly seen in the setting of ischemic heart predisposed them to SCD. In this chapter, the
disease, in which patients suffer the acute clinical aspects and ECG findings associated with
onset of a lethal rhythm in response to new these syndromes are described (Table 13-1).
ischemia or as a result of a myocardial injury
from an old ischemic event. This common Brugada Syndrome
scenario is a widespread cause of mortality
in the developed world, leading to more than Brugada syndrome is an inherited
250,000 deaths in the United States per year.1 arrhythmogenic disease characterized by a
Despite recent advances in cardiopulmonary right bundle-branch–like pattern on the ECG,
resuscitation and defibrillation techniques, associated with ST-segment elevation in leads
survival remains poor and survivors often suffer V1 and V2 and, less commonly, V3.2,3 The ST
long-term morbidity, including neurologic segment is typically downsloping and often
disability. It is therefore important to identify followed by an inverted T wave. This pattern has
patients at risk for SCD whenever possible. been associated with a high incidence of sudden
death among previously healthy individuals,
A variety of inherited conditions predispose particularly Asian men.4,5 Brugada syndrome is
patients to SCD even in the absence of believed to be responsible for 4% to 12% of all
ischemic heart disease; these include Brugada nonischemic SCD and for approximately 20% of
syndrome, hypertrophic cardiomyopathy SCD in patients with structurally normal hearts.
(HCM), arrhythmogenic right ventricular Brugada syndrome has recently been shown to
dysplasia (ARVD), and long QT syndrome be identical to the disorder known as sudden
(LQTS). Patients with these genetic conditions unexplained nocturnal death syndrome.6
might remain asymptomatic and never suffer
a cardiac event, or they might suffer SCD at Patients with Brugada syndrome are
a young age. Genetic predisposition to SCD predisposed to episodes of ventricular
has received some notoriety in recent years, tachycardia, usually polymorphic in nature.
since several prominent athletes have died If the arrhythmia terminates spontaneously,
the patient is likely to present with complaints

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Electrocardiography in Emergency Medicine

of syncope. Alternatively, if the arrhythmia with Brugada syndrome are at relatively low
is prolonged, SCD results. The average age risk for SCD.11 Intravenous administration of
at the time of diagnosis is in the 4th or 5th class 1C antiarrhythmics (eg, flecainide or
decade of life, although the original report by propafenone) can lead to adverse cardiovascular
Brugada described adolescents. Bradycardia effects in most patients with the syndrome.
resulting from altered autonomic balance or
other factors can contribute to initiation of Genetic predisposition to Brugada syndrome
the arrhythmia.7,8 In most cases, malignant is most commonly a result of autosomal
arrhythmias occur during sleep. It is believed that dominant mutations in the cardiac sodium
circadian variation of sympathovagal balance, channel gene SCN5A. However, only 18% to
hormonal fluctuation, and other metabolic 30% of patients with clinically diagnosed
factors contribute to this circadian pattern.9,10 Brugada syndrome are found to have these
genetic mutations, suggesting the possible
It was originally thought that asymptomatic involvement of other genes as well.12 The high
patients with Brugada syndrome had a high risk incidence of ventricular arrhythmias is associated
of sudden death, but recent research disputes with mutation of the sodium channel, which
this claim. Patients initially presenting with shortens the cardiac action potential, making
aborted sudden death are at the highest risk cardiac tissue vulnerable to reentry circuits.
for recurrence, whereas patients presenting
with syncope and asymptomatic patients who Noninvasive methods of risk stratification
were found by chance to have ECGs consistent involve detection of spontaneous changes in
the ST segment on the ECG combined with

Table 13-1.
Congenital arrhythmic syndromes

Brugada ECG Symptoms, diagnosis Genetic factors Treatment
ST elevation in V1 to V3; Definitely diagnosed when SCN5A — missense Implantable
Arrhythmogenic PR prolongation ST-segment elevation is and deletion defibrillator
right ventricular observed in more than one mutations; autosomal
cardiomyopathy “Epsilon” waves and precordial lead (V1 to V3) dominant
(ARVD) inverted T waves in V1 and in conjunction with one Leading cause of
Long QT through V3 of the following: death in middle-aged
Hypertrophic Prolonged QTc a) documented VF or VT; Asian men
cardiomyopathy Findings consistent b) family history of SCD at
(HCM) with left ventricular <45 years of age; Autosomal dominant Implantable
hypertrophy; deep c) inducibility of VT with disorder defibrillator
narrow Q waves in electrical stimulation;
inferior and/or lateral d) syncope Mutations in KCNQ1 -Blockers
leads Should be considered in and KCNQ2 are
young patients presenting responsible for this
with syncope, VT, or version of syndrome,
cardiac arrest and in adults which is accompanied
with CHF by deafness
Syncope, sudden death; 12 genes identified; -Blockers or
common in young children most common genetic calcium channel
and adolescents. Many autosomal dominant blockers
patients are asymptomatic cardiovascular disease
until onset of their first
cardiac arrest.
Syncope, chest pain,
sudden death

166

Inherited Syndromes of Sudden Cardiac Death

a history of syncopal episodes or a family changes consistent with Brugada syndrome.18
history consistent with SCD.13,14 The three ECG Patients should be monitored with a continuous
patterns associated with Brugada syndrome are ECG recording while the drugs are being
described in Table 13-2. All types have ECG administered; administration should be
findings suggestive of right bundle-branch block terminated when the diagnostic arrhythmia
(RBBB) or incomplete RBBB, with ST-segment is observed. Such testing should be reserved
elevations in V1 through V3 (Figure 13-1). No for the experienced electrophysiologist.
reciprocal ST-segment depression is usually
observed in ECGs from patients with Brugada S-wave duration of more than 80 msec in V1
syndrome. Additionally, there is often slight or ST-segment elevation of 80 msec or more in V2
prolongation of the PR interval. Recent work measured from the J point is indicative of a high
suggests that the ECG in Brugada syndrome risk for ventricular arrhythmias in patients with
is dynamic, with day-to-day changes under a Brugada syndrome.19 Proper treatment strategies
variety of hormonal and other influences. In are urgently needed to treat symptomatic patients
fact, the ECG normalizes at some point in up to at high risk of sudden death. Despite a growing
40% of cases. Signal-averaged ECG techniques body of knowledge regarding this condition,
are useful to more accurately determine clinical management of Brugada syndrome is
whether a patient exhibits Brugada syndrome. limited by the lack of pharmacologic therapies.
At the Second Consensus Conference on
Diagnostic criteria for Brugada syndrome Brugada syndrome,7 it was recommended that
include characteristic ECG patterns in a symptomatic individuals be offered implantable
patient without structural heart disease, a cardiac defibrillators (ICDs). The mortality rate
family history of SCD, the presence of syncope associated with Brugada syndrome from the time
of unknown origin, a documented episode of first clinical manifestation is 10% per year.
of ventricular tachycardia or fibrillation, Medical therapy has not been demonstrated to
inducibility during electrophysiological improve the outcome; however, ICD placement
study, and definitive molecular analysis.15 has been shown to decrease the mortality rate
from Brugada syndrome to nearly zero.2
Placement of the right precordial leads in a
more rostral position (up to the second intercostal Hypertrophic Cardiomyopathy
space) can increase the sensitivity of the ECG
for detecting the Brugada phenotype in some HCM, a genetic disorder caused by an
patients, both in the presence and absence autosomal dominant mutation in 1 of at least 12
of drugs used to unmask it. Sodium channel genes, is the most common cause of SCD in the
blockers and vagotonic agents can be used young.20 Some HCM patients present for the first
to unmask concealed ECG manifestations of time as cardiac arrest victims; others present
Brugada syndrome.16,17 Potent sodium channel with episodes of syncope and angina pectoris.21
blockade, achieved with type 1C antiarrhythmic HCM is characterized by a hypertrophy of the
agents, can provoke the characteristic ECG left ventricle in the absence of another cardiac

Table 13-2.
Types of Brugada syndrome by ECG analysis

Type Description
I ST-segment elevation is triangular (“coved” or “convex upward” pattern) and the T waves can be inverted in
leads V1 to V3
II Downward displacement of the ST segment lies between the two elevations of the segment in leads V1 to V3
(“concave upward”) but does not reach the baseline
III Downward displacement of the ST segment lies between the two elevations of the segment in leads V1 to V3,
and the middle part of the ST segment touches the baseline

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Electrocardiography in Emergency Medicine

or systemic disease capable of producing this with these clinical symptoms include left
magnitude of hypertrophy. In most patients, ventricular (LV) diastolic dysfunction,
HCM goes clinically unrecognized.20 The impaired coronary reserve, myocardial
low rate of diagnosis is partially attributed to ischemia, and supraventricular or ventricular
the fact that most patients are asymptomatic tachyarrhythmias.23 LV hypertrophy is
until the condition manifests in SCD. commonly asymmetric, with disproportionate
thickening of the intraventricular septum.24
The diagnosis of HCM can be entertained on In a minority of HCM patients, progression to
the basis of typical clinical, echocardiographic, dilated cardiomyopathy can occur, characterized
hemodynamic, and ECG features. Individuals by thinning of the ventricular wall and LV
with HCM can express a variety of symptoms, dysfunction.25 Another histopathologic feature
including chest pain, that can be typical of angina of HCM is small vessel disease, or arterial
and symptoms related to pulmonary congestion. dysplasia, characterized by narrowing of the
Additionally, HCM patients often experience intramural coronary arterioles secondary to wall
exertional angina, despite the absence of thickening from increased intimal and medial
coronary artery disease. Abnormal blood pressure collagen deposition. Consequent tissue death
changes during exercise testing can identify HCM leads to myocardial scarring and fibrosis, which
patients at increased risk of sudden death.22 exacerbate transition from the compensated HCM

Pathophysiologic changes that coincide

Table 13-3.
Criteria for diagnosis of right ventricular dysplasia

Global or regional Major Minor
dysfunction and Severe dilation and reduction of Mild global RV dilation or ejection fraction reduction
structural alterations RV ejection fraction with no LV with normal left ventricle
impairment28 Mild segmental dilation of the right ventricle
Localized RV aneurysms (akinetic Regional RV hypokinesis
or dyskinetic areas with diastolic
bulging)
Severe segmental dilation of the
right ventricle

Tissue Fibrofatty replacement of the
characterization of myocardium on endomyocardial
wall biopsy

Repolarization Epsilon waves or localized Inverted T waves in right precordial leads (V2 and V3)
abnormalities prolongation (>110 msec) of the (people older than 12 years; in absence of RBBB)
Depolarization/ QRS complex in right precordial Late potentials (signal-averaged ECG)
conduction leads (V1 to V3)
abnormalities Left bundle-branch block type ventricular tachycardia
(sustained and nonsustained) (ECG, Holter, exercise
Arrhythmias testing)
Frequent ventricular extrasystoles (more than
1,000/24 hr) (Holter)

Family history Familial disease confirmed at Familial history of sudden premature death (<35 yr)
168 necropsy or during surgery due to suspected RV dysplasia
Familial history (clinical diagnosis based on present
criteria)

Inherited Syndromes of Sudden Cardiac Death

phase to the decompensated, dilated phase.26 with Q waves that are at least 0.04 seconds
HCM is usually diagnosed based on the wide (1 mm), whereas the Q waves of HCM
tend to be deep but very narrow. The deep
results of electrocardiography and Doppler narrow Q waves of HCM tend to be especially
echocardiography. The latter technique is prominent in the lateral leads (Figure 13-2A),
recognized as generally being more reliable, although these Q waves might not be found in
providing detailed information regarding the all of the lateral leads (Figure 13-2B) or at all.
distribution and severity of hypertrophy and
LV size and function.23 Other methods that are Traditionally, it was recommended that
helpful in confirming a diagnosis of HCM or symptomatic HCM patients receive negative
identifying individuals at high risk for sudden inotropic agents, including -blockers, verapamil,
death include exercise testing and ambulatory and disopyramide.27 A small minority of patients
Holter monitoring; a history of cardiac events are unreceptive to pharmacologic treatment and
in other family members contributes to the are consequently eligible for major therapeutic
diagnosis.23 The ECG is normal in 5% to 10% of interventions that target relief of obstruction
HCM patients, but more commonly it exhibits and mitral regurgitation.27 During the past 50
findings of LV hypertrophy, including left- years, the “gold standard” intervention was
axis deviation, increased QRS voltage (nearly considered to be ventricular septal myectomy.
universally present), and T-wave changes However, percutaneous septal ablation has
consistent with a “strain pattern” (Figure recently been shown to be a promising alternative
13-2). Septal hypertrophy is often reflected to surgery and is being performed at increasing
as abnormal Q waves, most commonly in the rates.27 The long-term consequences of the
lateral leads and less commonly in the inferior intramyocardial septal scar (often transmural)
leads, which can mimic myocardial infarction. intentionally produced during the procedure
However, infarction-related Q waves can be are unknown. Because these patients already
distinguished from HCM Q waves by their harbor an electrically unstable myocardial
duration: myocardial infarction is associated substrate that is prone to reentrant arrhythmias,

Table 13-4.
Long QT syndrome diagnostic criteria. Based on: Schwartz PJ, Moss AJ, Vincent GM, Crampton RS. Diagnostic
criteria for the long QT syndrome: an update. Circulation. 1993;88(2):782-784. Used with permission from
Lippincott Williams & Wilkins.

ECG finding ≥480 msec Points
QTc 460–470 msec 3
450 msec 2
Torsade de pointes 1
T-wave alternans Syncope with stress 2
Notched T wave in three leads 1
Low heart rate for age 1
(bradycardia) 0.5
Clinical history
2

Syncope without stress 1

Congenital deafness 0.5

Family history Family members with definite LQTS 1

Unexplained sudden cardiac death among immediate family 0.5
members younger than 30 years

A total point score of 2 or 3 suggests intermediate probability of LQTS, requiring serial ECG measurements. If the
score is higher than 3.5 points, the probability of LQTS is high.

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Electrocardiography in Emergency Medicine

there is a possibility that the septal infarct condition is treated, for example, with an ICD.
could increase the likelihood of sudden death. ECG findings in ARVD include T-wave

Arrhythmogenic Right inversions in V1 through V3 in the absence
Ventricular Dysplasia of complete RBBB (Figure 13-3). However,
RBBB occurs in up to 15% of cases. Selective
ARVD is a genetic cardiomyopathy prolongation of the QRS complex in V1 through
characterized by ventricular arrhythmias and V3 compared with V6 is another hallmark of
structural abnormalities of the right ventricle. ARVD. “Epsilon” waves, small-amplitude waves
ARVD is believed to be responsible for up to that immediately follow the QRS complex, are
20% of SCD in young people. Histologically, a specific finding in the condition and likely
ARVD is typified by the gradual replacement reflect delayed right ventricular conduction.
of myocytes with adipose and fibrous tissue.28 Sometimes biatrial enlargement can also be
Although early reports emphasized localized discerned, with biphasic or notched P waves
right ventricular (RV) involvement, it is now in V1. When arrhythmia occurs in ARVD, it is
recognized that ARVD can progress to diffuse typically monomorphic ventricular tachycardia,
RV and LV involvement and can result in which is rarely initiated by complexes of
biventricular heart failure. If it progresses to that different configurations, suggesting the
extent, ARVD is difficult to distinguish from tachycardia originates from a single focus.28
dilated cardiomyopathy.28 The regions of the right
ventricle most frequently affected are the RV Patients with ARVD can develop isolated
inflow area, the apex, and the infundibulum—the right heart failure or biventricular failure,
three areas that form the “triangle of dysplasia.” which typically presents during the fourth
and fifth decades of life. Arrhythmogenic RV
ARVD is typically inherited as an autosomal cardiomyopathy is one of the few myocardial
dominant trait with variable penetrance and diseases that cause RV heart failure without
incomplete expression. The prevalence of ARVD pulmonary hypertension. Rather, the
in the general population is approximately 1 in mechanisms of RV failure are dilation, thinning
5,000, but the disease is often not recognized of the wall, and progressive loss of contractile
because of the difficulty of diagnosis.28 ARVD function because of myocardial atrophy.
should be considered in young patients presenting Arrhythmogenic RV cardiomyopathy can also
with syncope, ventricular tachycardia (VT), and involve the left ventricle, resulting in mild
cardiac arrest and in select adult patients with decreases in its function. LV failure is uncommon;
idiopathic congestive heart failure (Table 13-3).28 when it does occur, it is commonly misdiagnosed
Patients with ARVD who demonstrate functional as idiopathic or viral dilated cardiomyopathy.
and structural worsening of RV performance
are at high risk for SCD.28 The progressive If noninvasive testing suggests ARVD, invasive
deterioration of cardiac function is one of the testing with an RV angiogram, biopsy, and
key indicators for diagnosing this condition, electrophysiology study are recommended.29
and the ECG often evolves concomitantly with Endomyocardial biopsy can eliminate the
these functional changes. The isolated patches possibility of other conditions that mimic ARVD
of fibrofatty tissue found in ARVD generate
macroreentry electrical circuits and form the Table 13-5.
arrhythmogenic substrate for the malignant Nongenetic causes of QTc prolongation
cardiac arrhythmias responsible for sudden
death. Because these arrhythmias are typically Electrolyte disorders: hypokalemia, hypomagnesemia,
induced by adrenergic stimulation such as hypocalcemia
physical exercise, it is recommended that young Acute cardiac ischemia
subjects with this condition be prohibited from Hypothermia
vigorous athletic competition, even after their Elevated intracranial pressure
Sodium channel–blocking medications
170

Inherited Syndromes of Sudden Cardiac Death

such as myocarditis involving the right ventricle.30 overt evidence of AVRD, particularly if the
However, diagnosis by endomyocardial biopsy electrophysiology study is abnormal or if there
is difficult because the disease is segmental and is a family history of sudden death. Defibrillator
because the target of biopsy, the interventricular implantation poses risks to these patients: the
septum, is often spared as the disease progresses. thinned and weakened RV myocardial wall
could be penetrated and the device could fail
Once the diagnosis of ARVD is established, to adequately sense arrhythmias because of
the main treatment decision involves whether the sclerotic nature of the right ventricle.
to implant an ICD. These devices are generally
recommended for patients who have experienced
syncope or cardiac arrest or who have sustained
ventricular arrhythmias and for patients with

Key Facts

Brugada Syndrome
• ST-segment elevation is observed in leads V1 to V3 with no reciprocal ST depression.
• ST segment is typically downsloping and often followed by an inverted T wave.
• The PR interval may be slightly prolonged.
• Sodium channel blockers and vagotonic agents can be used to unmask concealed ECG

manifestations of Brugada syndrome.
• S-wave duration of more than 80 msec in V1 or ST-segment elevation of 80 msec or more in V2

measured from the J point often indicates a high risk of ventricular fibrillation in patients with
Brugada syndrome.
Hypertrophic Cardiomyopathy
• Patients can exhibit findings of LV hypertrophy, including left-axis deviation, increased QRS voltage,
and T-wave changes consistent with a “strain pattern.”
• T-wave inversions in HCM tend to be pronounced, especially in the precordial leads.
• Septal hypertrophy is often reflected as abnormal Q waves, which can mimic myocardial infarction,
although infarction-related Q waves are wider.
Arrhythmogenic Right Ventricular Dysplasia
• The ECG often indicates progressive deterioration of cardiac function, which is one of the key
indicators for diagnosing this condition.
• “Epsilon” waves, small-amplitude waves that immediately follow the QRS complex, are a specific
finding in the condition and likely reflect delayed RV conduction.
• T-wave inversions in V1 through V3 in the absence of complete RBBB as well as selective
prolongation of the QRS complex in V1 through V3 compared with V6 are hallmarks of this condition.
• When arrhythmia occurs in ARVD, it is typically monomorphic ventricular tachycardia, which is
rarely initiated by complexes of different configurations.
Long QT Syndrome
• A QTc interval greater than 440 msec (using the Bazett formula) is observed.
• Lead II is generally regarded as the best single lead for measuring the QT interval.
• Other diagnostic features on the ECG include notched T waves on several leads and a tendency
toward bradycardia.
• Torsade de pointes variant of ventricular tachycardia is suggestive of underlying LQTS.
• Multiple ECGs are recommended if an asymptomatic patient has a family history suggestive of
LQTS.

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Electrocardiography in Emergency Medicine

Long QT Syndrome pointes variant of ventricular tachycardia is
suggestive of underlying LQTS (Table 13-4).
Prolongation of the QT interval (measured
from the beginning of the Q wave to the end The most common mutation implicated
of the T wave) is associated with a higher in LQTS is associated with a higher risk of
risk of mortality from sudden cardiac arrest.31 cardiac events in men until puberty and in
Congenital LQTS is a clinical disorder women during adulthood.36 Recently, Shimizu
characterized by prolongation of the QT and colleagues reported that an epinephrine
interval on the ECG (Figure 13-4) and by the infusion (0.1 mcg/kg/min) is a sensitive means
occurrence of sudden death or of life-threatening of identifying asymptomatic carriers of this
arrhythmias caused by torsade de pointes mutation, who can then undergo management
ventricular tachycardia.32 A variety of hereditary to prevent emergence of symptoms.37
mutations in genes encoding for myocardial
membrane channels is believed to be the source Therapies for the management of LQTS, in
of the QT-interval prolongation. Two hereditary order of increasing severity of the condition, are
variants exist: one is associated with deafness administration of -blockers, cardiac pacing, left
(Jervell and Lange-Nielson syndrome), and cardiac sympathetic denervation, and finally, for
the other is not (Romano-Ward syndrome). the most severe cases, implantation of an ICD.
Cardiac pacing might be beneficial for high-risk
LQTS often clinically manifests in otherwise LQTS patients by preventing pauses; however,
healthy young individuals, mostly children pacing should always be used in conjunction
and adolescents, when they are under physical with -blockers and should never be considered
or emotional stress. The arrhythmia-induced a sole treatment for LQTS, especially because
loss of consciousness might be misdiagnosed pacemaker problems attributed to T-wave sensing
as epileptic convulsions.33 The disease also and rate adjusting are relatively common.38
dramatically manifests as syncopal episodes,
which often result in cardiac arrest. When Recent developments have made gene-specific
diagnosed, however, LQTS can be effectively therapies for LQTS treatment increasingly viable.
treated and cardiac arrest can be averted. The genotype of LQTS patients is generally
identified after -blocker therapy has started.
A widely accepted method for correcting the An experienced cardiologist should be able
QT interval for rate is the Bazett formula34: to guess the genotype of his or her patients
on the basis of clinical history, circumstances
QTc = QT/√R-R interval associated with the cardiac events, and
A corrected QT interval (QTc) longer than sometimes according to the T-wave morphology
440 msec is considered prolonged.35 However, on the ECG; nevertheless, confirmation must
a minority of patients with LQTS have a QTc be sought from the molecular laboratory.
less than the 440 msec cutoff on their initial
ECG. The greatest risk of development of torsade Physicians should be aware of the
de pointes is believed to occur when the QTc nongenetic causes of QTc prolongation
exceeds 500 msec. It is recommended that (Table 13-5), many of which can be
multiple ECGs be obtained if LQTS is suspected treated in the emergency department.
from family history or clinical presentation.35
Lead II is generally regarded as the best single References
lead for measuring the QT interval because
the end of the T wave is usually discrete and 1. Thom T, Haase N, Rosamond W, et al. Heart disease and
the QT interval obtained from this lead is stroke statistics—2006 update: a report from the American
usually well correlated with the maximal QT Heart Association Statistics Committee and Stroke Statistics
measured from the remainder of the ECG. Subcommittee. Circulation. 2006;113(6):e85-151.
Other diagnostic features on the ECG include
notched T waves in several leads and a tendency 2. Scheinman M. Brugada syndrome. BUMC Proc. 2001;14:127-129.
toward bradycardia. Finally, the torsade de
3. Klijn CJ, Hankey GJ. Management of acute ischaemic stroke:
172 new guidelines from the American Stroke Association and
European Stroke Initiative. Lancet Neurol. 2003;2(11):698-701.

4. Hong K, Antzelevitch C, Brugada P, et al. Brugada syndrome: 12
years of progression. Acta Med Okayama. 2004;58(6):255-261.

Inherited Syndromes of Sudden Cardiac Death

5. Juang J, Huang S. Brugada syndrome: an under- 22. Yoshida N, Ikeda H, Wada T, et al. Exercise-induced
recognized electrical disease in patients with sudden abnormal blood pressure responses are related to
cardiac death. Cardiology. 2004;101(4):157-169. subendocardial ischemia in hypertrophic cardiomyopathy.
J Am Coll Cardiol. 1998;32:1938-1942.
6. Vatta M, Dumaine R, Varghese G, et al. Genetic and
biophysical basis of sudden unexplained nocturnal 23. Doolan A, Nguyen L, Semsarian C. Hypertrophic
death syndrome (SUNDS), a disease allelic to Brugada cardiomyopathy from “heart tumor” to a complex molecular
syndrome. Hum Mol Genet. 2002;11(3):337-345. genetic disorder. Heart Lung Circ. 2004;13(1):15-25.

7. Antzelevitch C, Brugada P, Borggrefe M, et al. 24. Davies MJ, McKenna WJ. Hypertrophic cardiomyopathy:
Brugada syndrome: report of the Second Consensus pathology and pathogenesis. Histopathology. 1995;26:493-500.
Conference. Circulation. 2005;111:659-670.
25. Biagini E, Coccolo F, Ferlito M, et al. Dilated-
8. Kasanuki H, Onishi S, Ohtuka M, et al. Idiopathic ventricular hypokinetic evolution of hypertrophic cardiomyopathy.
fibrillation induced with vagal activity in patients without J Am Coll Cardiol. 2005;46(8):1543-1550.
obvious heart disease. Circulation. 1997;95:2277-2285.
26. Hatcher CJ, Basson CT. Taking a bite out of
9. Nogami A, Nakao M, Kubota S, et al. Enhancement of J-ST- hypertrophic cardiomyopathy: soy diet and
segment elevation by the glucose and insulin test in Brugada disease. J Clin Invest. 2006;116(1):16-19.
syndrome. Pacing Clin Electrophysiol. 2003;26(1 Pt 2):332-337.
27. Kimmelstiel C, Maron B. Role of percutaneous
10. Nishizaki M, Sakurada H, Ashikaga T, et al. Effects of glucose- septal ablation in hypertrophic obstructive
induced insulin secretion on ST segment elevation in the Brugada cardiomyopathy. Circulation. 2004;109:452-455.
syndrome. J Cardiovasc Electrophysiol. 2003;14(3):243-249.
28. Gemeyal C, Pelliccia A, Thompson P.
11. Brugada P, Brugada R, Mont L, et al. Natural history Arrhythmogenic right ventricular cardiomyopathy.
of Brugada syndrome: the prognostic value of J Am Coll Cardiol. 2001;38(7):1773-1781.
programmed electrical stimulation of the heart. J
Cardiovasc Electrophysiol. 2003;14(5):455-457. 29. Prakasa K, Calkins H. Arrhythmogenic right
ventricular dysplasia/cardiomyopathy. Curr Treat
12. Shimizu S, Aiba T, Kamakura S. Mechanisms of disease: Options Cardiovasc Med. 2005;7(6):467-475.
current understanding and future challenges in Brugada
syndrome. Nat Clin Pract Cardiovasc Med. 2005;2(8):408-414. 30. Chimenti C, Pieroni M, Maseri A, et al. Histologic
findings in patients with clinical and instrumental
13. Ikeda T, Takami M, Sugi K, et al. Noninvasive diagnosis of sporadic arrhythmogenic right ventricular
risk stratification of subjects with a Brugada-type dysplasia. J Am Coll Cardiol. 2004;43(12):2305-2313.
electrocardiogram and no history of cardiac arrest. Ann
Noninvasive Electrocardiol. 2005;10(4):396-403. 31. Dekker J, Crow R, et al. Heart rate-corrected QT
interval prolongation predicts risk of coronary heart
14. Grillo M, Napolitano C, Bloise R, et al. Brugada’s disease in black and white middle-aged men and
syndrome: epidemiology, risk stratification, and clinical women. J Am Coll Cardiol. 2004;43:565-571.
management. Ital Heart J Suppl. 2002;3(9):919-927.
32. Schwartz P. The congenital long QT syndromes from genotype to
15. Di Grande A, Tomaselli V, Massarelli L, et al. Brugada- phenotype: clinical implications. J Intern Med. 2006;259:39-47.
like electrocardiographic pattern: a challenge for
the clinician. Eur J Intern Med. 2006;17:3-7. 33. Schwartz P, Zaza A, Locati E, et al. Stress and
sudden death: the case of the long QT syndrome.
16. Brugada P, Brugada J, Brugada R. Arrhythmia Circulation. 1991;83(4 suppl):II71-II80.
induction by antiarrhythmia drugs. Pacing Clin
Electrophysiol. 2000;23(3):291-292. 34. Bazett H. An analysis of the time-relations of
electrocardiograms. Heart. 1920;7:353-370.
17. Brugada R, Brugada J, Antzelevitch C, et al. Sodium channel
blockers identify risk for sudden death in patients with 35. Chiang C, Roden DM. The long QT syndromes: genetic basis
ST-segment elevation and right bundle branch block but and clinical implications. J Am Coll Cardiol. 2000;36(1):1-12.
structurally normal hearts. Circulation. 2000;101:501-515.
36. Zareba W, Moss A, Locati EH, et al. Modulating effects of
18. Antzelevitch C, Olivia A. Amplification of spatial dispersion age and gender on the clinical course of long QT syndrome
of repolarization underlies sudden cardiac death associated by genotype. J Am Coll Cardiol. 2003;42:103-109.
with catecholaminergic polymorphic VT, long QT, short QT
and Brugada syndromes. J Intern Med. 2006;259:48-58. 37. Shimizu W, Noda T, Takaki H, et al. Epinephrine unmasks
latent mutation carriers with LQT1 form of congenital
19. Atarashi H, Ogawa S, for the Idiopathic Ventricular long-QT syndrome. J Am Coll Cardiol. 2003;41:633-642.
Fibrillation Investigators. New ECG criteria for high-
risk Brugada syndrome. Circulation. 2003;67:8-10. 38. Eldar M, Griffin J, Van Hare GF, et al. Combined
use of beta-adrenergic blocking agents and long-
20. Poliac L, Barron M, Maron B. Hypertrophic term cardiac pacing for patients with the long QT
cardiomyopathy. Anesthesiology. 2006;104:183-192. syndrome. J Am Coll Cardiol. 1992;20(4):830-837.

21. Wigle E, Rakowski H, Kimball B, et al. Hypertrophic
cardiomyopathy: clinical spectrum and treatment.
Circulation. 1995;92:1680-1692.

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Figures

Figure 13-1.
ECGs from patients with Brugada syndrome. A: The ST segments in lead V1 demonstrate a “coved” or
“convex upward” pattern, commonly referred to as the Brugada Type I pattern. B: The ECG demonstrates an
incomplete RBBB pattern with ST-segment elevation. Lead V2 especially demonstrates the Brugada Type II
pattern with convex-upward ST-segment elevation. Image 13-1B courtesy of Amal Mattu, MD.

A

B

174

Inherited Syndromes of Sudden Cardiac Death

Figures

Figure 13-2.
ECG from a patient with hypertrophic cardiomyopathy. A: The ECG demonstrates the classic findings of HCM:
large-amplitude QRS complexes and deep narrow Q waves in all lateral leads (I, aVL, V5, V6). B: The ECG
demonstrates large-amplitude QRS complexes and deep narrow Q waves limited to lateral leads I and aVL.
Images courtesy of Amal Mattu, MD.

A

B

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Electrocardiography in Emergency Medicine

Figures

Figure 13-3.
ECG from a patient with arrhythmogenic right ventricular dysplasia. In the enlargement, the arrows indicate
the epsilon waves following the QRS complexes in lead V1.

176

Inherited Syndromes of Sudden Cardiac Death

Figures

Figure 13-4.
ECG from a patient with long QT syndrome. Image courtesy of Amal Mattu, MD.

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Electrocardiography in Emergency Medicine
178

C h apter f o u rtee n

Pacemakers and Pacemaker
Dysfunction

Steven A. Pace, MD, and Jeffrey A. Tabas, MD

Approximately 5 million people in the implanted generator through the left subclavian
United States have permanent pacemakers. or cephalic vein into the right atrium and
Six hundred new pacemakers, most of which ventricle. The generated impulse is conducted
are dual-chamber devices, are implanted per through the lead to the myocardium (Figure 14-
million people each year. Pacemakers were 1). These leads also allow sensing of myocardial
originally introduced to treat symptomatic depolarizations, and electronic circuitry
bradycardia, and the most common indications modulates pacemaker response to sensing.3
for pacemaker placement are sinus node The circuitry and battery are enclosed in a
dysfunction (more than 50%) and atrioventricular hermetically sealed metal container, 9 to 45 cm3.
(AV) conduction abnormalities. As pacing
systems have gained function and complexity, Pacemaker Nomenclature/
broader indications for them have been Modes
identified such as prevention of atrial fibrillation,
neurocardiogenic syncope, and cardiomyopathy.1 Nomenclature for pacemaker capabilities has
Selection of a patient for pacemaker placement been developed and standardized by the North
is a complex decision. A joint task force of American Society of Pacing and Electrophysiology
the American College of Cardiology and and the British Pacing and Electrophysiology
the American Heart Association developed Group. A series of five letters describes the
guidelines listing indications, with further abilities of each pacemaker (Table 14-1). The first
recommendations specifying the circumstances letter indicates the chamber being paced and
in which a pacemaker is generally necessary, the second letter the chamber being sensed (A,
perhaps helpful, or generally not necessary.2 atrial; V, ventricle; D, dual). The third letter is
the response to sensing. “I” indicates “inhibited,”
Current devices consist of the generator, which means that output is suppressed when
which contains a lithium-iodide battery, and depolarization is sensed. For example, in a
the lead(s). Batteries have a life of 4 to 12 patient with AV nodal block, the atrial chamber
years, depending on pacemaker and patient is inhibited when the patient’s own intrinsic
characteristics. The leads typically run from the sinus beats are sensed. “T” indicates “triggered,”

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Electrocardiography in Emergency Medicine

which means that an impulse is generated inappropriate impulse generation when
when depolarization is sensed. In the above the pacemaker should be suppressed (the
example, a pacing impulse would be delivered pacemaker is “inappropriately turned on”).
to the ventricle in response to a sensed p wave,
which is either intrinsic or paced. “D” indicates Pacemaker output involves generation and
both functions are available. The fourth and delivery of an electrical impulse. This is seen
fifth letters indicate programmability/rate on the ECG as a sharp narrow spike. The
adaptability and antitachydysrhythmia functions.4 amplitude of this spike can vary, based on
In general, dual-chamber pacing systems are device type, lead location, and the axis of the
programmed to the DDD or VDD pacing mode. ECG recording lead. Unipolar pacing generates
a current between the lead tip and the generator
Generation and Pattern of a unit, and bipolar pacing generates a current
Normally Paced Complex between points that are close to the end of the
lead tip. In general, unipolar leads record a
For the pacemaker to generate an impulse, large-amplitude spike on the surface ECG, and
which in turn generates a myocardial contraction, bipolar leads record a small-amplitude spike that
the device must sense, deliver an impulse, can sometimes be seen only in the anterolateral
and capture. Normal sensing occurs when a leads lying closest to the lead poles, V3 to V6.
pacemaker lead detects chamber depolarization;
pacemaker output is then suppressed (Figure Capture represents depolarization of the
14-1). If no event is sensed before the stimulated chamber. In the atrium, this generates
programmed lower rate limit expires, then a p wave. The morphology of the p wave depends
an impulse is generated. This prevents the on the location of the right atrial lead and is
pacemaker from firing needlessly or from variable. It can have a sinus appearance (upright
firing during the repolarization phase of an in lead II and inverted in lead aVR) but most
intrinsic ventricular beat, causing the “R- often appears ectopic. The PR interval, when
on-T” phenomenon (which can generate the atrial depolarization is conducted, can be
ventricular fibrillation). The presence of an normal or prolonged.4 In the right ventricle,
intrinsic event that appropriately delays the the impulse generates a QRS complex, which
next paced beat suggests that the pacemaker is typically displays a left bundle-branch pattern.
sensing appropriately. Oversensing represents There is a large, widened R wave in lead I and a
inappropriate suppression of pacemaker large, widened S wave in V1. There is minimal
impulses (the pacemaker is “inappropriately R-wave progression across the precordium
turned off”), and undersensing represents (Figures 14-2 and 14-3).5 The presence of a right
bundle-branch block pattern raises concern that

Table 14-1.
Standardized pacemaker nomenclature

I II III IV V
Chamber paced Chamber sensed Antitachycardia
Response to sensing Rate modulation, features
0 = none 0 = none programmability 0 = none
A = atrium A = atrium P = anti-tachycardia
0 = none 0 = none pacing
V = ventricle V = ventricle S = shock
I = inhibited S = simple
D = dual D = dual programmable D = dual

T = triggered M = multi-
programmable

D = dual C = communicating

R = rate modulation

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pacemakers and pacemaker dysfunction

the pacing lead has perforated the septum and used primarily for patients with chronic atrial
is initiating impulses from the left side of the fibrillation. The response to sensing ventricular
heart. However, in most cases, this is caused by depolarization is to inhibit pacemaker discharge
atypical lead location in the right ventricle in the until a preprogrammed interval has elapsed.
absence of perforation.4 Chest radiography can Single-chamber sensing and pacing reduce
provide a clue, although advanced expertise is complexity, cost, and frequency of followup
ultimately required to make the determination, and prolong battery life. However, this type
often with the assistance of echocardiography. of pacemaker lacks versatility and is less well
tolerated.1 VVI pacing, or “demand mode,” is
Biventricular pacing, also known as cardiac also used with temporary transcutaneous or
resynchronization, is recommended to decrease transvenous pacing during the resuscitation
mortality and improve cardiac function in heart of a patient with symptomatic bradycardia.
failure patients with severely depressed ejection
fraction (<35%) and prolonged QRS duration AAI pacemakers are occasionally implanted
(>120 msec). In this case, both ventricles are in patients with sinus node dysfunction
paced in coordination, eliminating the delay and intact atrioventricular conduction. The
in activation of the left ventricular free wall atrium contains one lead that both senses and
and leading to improved cardiac output. The paces in response to atrial depolarization. An
ECG frequently displays a QRS interval that impulse is delivered when depolarization does
is decreased from baseline6 (Figure 14-4). not occur after a programmed interval but is
inhibited when an intrinsic P wave is sensed.1
Common Pacemaker Modes
Finally, rate-adaptive pacemakers (XXXR)
A pacemaker with DDD (dual chamber paced, allow rates to change according to the patient’s
dual sensed, dual response to sensing) pacing physiologic demands. Various types of sensors
is the type most commonly implanted today. respond to physical, electrical, or chemical
Both atrial and ventricular chambers contain stimuli. Most commonly, body motion is
pacing and sensing leads and are either inhibited sensed, triggering an increase in the rate of
or triggered in response to sensing signals pacer impulses. Exercise changes in the QT
(Figures 14-2 and 14-3). Dual-chamber pacing interval, changes in respiratory rate, or even
and sensing allow versatility and synchrony the temperature of venous blood are examples
between atrial contraction and ventricular filling. of sensed input.1 Increases in the pacing rate
Exercise responsiveness is maintained, when can occur transiently if the device is stimulated
sinus node function is preserved, by triggering
ventricular rates to increased sinus rates. Table 14-3.
Causes of oversensing
VVI (ventricular chamber, ventricular
sensing, inhibition) pacing involves a single Sensed intracardiac signals: T waves, R waves,
lead that both senses and paces. This mode is concealed extrasystoles
Muscle potentials (diaphragm, pectoral, seizure, shiver)
Table 14-2. Electromagnetic interference
Causes of undersensing (failure to sense) Electrocautery
Magnetic resonance imaging
Poor intracardiac signal Cardioversion/defibrillation
Intracardiac signal occurs in pacemaker refractory period Transcutaneous pacing
Lead dislodgement/loose connection Electrotherapy
Conductor wire fracture/insulation failure
Improper programming • transcutaneous nerve stimulation
Generator end of life • implanted neuromuscular stimulators
Hyperkalemia Cross-talk (sensing of the electrical event in one
chamber by the other; for example, sensing of the atrial
output by the ventricular lead)

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Electrocardiography in Emergency Medicine

inadvertently, for example, with compression In this case, repeated movements of the
by a clinician during physical examination. underlying muscle, for example, each brush
stroke during house painting, can cause
ECG Findings in Pacer inhibition. Electrocautery within inches of
Malfunction the pulse generator can have a similar effect.
Modern systems are not inhibited by microwave
Inappropriately Paced Complexes ovens and weapon detector equipment.
When a pacemaker completely loses its ability
The other cause of failure to pace is output
to sense, called “undersensing,” it performs failure, resulting from failure of the unit to
like a fixed-rate pacer. Undersensing will be either generate an impulse (eg, battery failure)
evident if a spontaneous ventricular complex or deliver a generated impulse (eg, lead
does not result in an escape interval (the delay fracture). Causes of output failure are listed in
to the next paced impulse) that is the same as or Table 14-4. An ECG with an intrinsic rate that
longer than the spike-to-spike intervals (Figure exceeds the pacemaker’s lower rate timer would
14-5). Undersensing cannot be excluded on the not be expected to demonstrate pacemaker
resting ECG when all of the complexes are paced. impulses, so pacemaker failure cannot be
Causes of undersensing are listed in Table 14-2. excluded. In a patient who has experienced
Failure to sense can be intermittent, resulting symptoms consistent with bradycardia but is
in occasional inappropriate impulse delivery.5 now asymptomatic, exclusion of pacemaker
failure requires further evaluation (see below).
Pacing Failure
Failure to pace can be either complete or Pacemaker Spikes Without Generated
Complexes
incomplete. An inappropriately slow pacing rate
is most commonly a sign of battery depletion Failure to capture is evident when pacemaker
and is an indication for urgent replacement. spikes do not generate depolarization (Figures
Complete failure to pace is diagnosed when 14-5 and 14-7). Causes of failure to capture
the ECG demonstrates an intrinsic bradycardia are listed in Table 14-5. Note that failure to
below the pacemaker’s lower rate timer without
evidence of pacemaker impulses. Pacing Table 14-5.
failure has two causes: oversensing or output Causes of failure to capture
failure. Oversensing results in inappropriate
inhibition of pacing stimuli (Figure 14-6 and Tissue is refractory, eg, prior depolarization
Table 14-3). In a ventricular lead, this can Metabolic disturbance, eg, hyperkalemia, acidosis,
be observed as inappropriately long pauses alkalosis, hyperthyroidism
between pacing spikes. Occasionally, P or Myocardial infarction/myocarditis
T waves can be sensed as R waves, causing Medications (antidysrhythmics)
impulse generation to be suppressed.7 Another Lead insulation break or dislodgement
oversensing scenario occurs when myopotentials Inappropriately low programmed output
are sensed from the pectoralis muscle, most Generator end of life
commonly in patients with unipolar pacers.
Table 14-6.
Table 14-4. Uses of a magnet
Causes of output failure (other than oversensing)
Assess capture
Lead dislodgement/loose connection Assess end-of-life battery function
Conductor wire fracture/insulation failure Break pacemaker-mediated tachycardia and other
Generator end of life causes of rapid paced ventricular rates
Treat cross-talk inhibition
182 Treat oversensing

pacemakers and pacemaker dysfunction

capture can occur when pacing impulses fall A normally functioning pacemaker is set to sense
during the refractory period of an intrinsic an atrial impulse, either intrinsic or generated,
beat, which can occur during sensing failure and sequentially deliver a ventricular impulse
or magnet placement. Exclusion of failure to at the appropriate PR interval. When cross-talk
capture can require further evaluation if no occurs, the ventricular stimulus is conducted
pacemaker impulses are recorded on the ECG. retrograde through the AV node. The impulse is
sensed by the atrial lead, and the pacer generates
Irregularity in the Paced Rate a ventricular impulse after an appropriate PR
interval in response. This will cause tachycardia
Apparent pauses or irregularity in the at the upper rate limit programmed for the unit.
pacemaker rhythm can be the result of Again, the pacemaker functions appropriately
“pseudomalfunction,” that is, appropriately as programmed, but the programming must be
functioning advanced programming algorithms. changed to correct the problem (Figure 14-9).
This term also refers to appropriately paced
complexes for which the pacemaker impulse Use of a Magnet
is not evident on the surface ECG, as can
occur with bipolar leads. Algorithms such as If the resting ECG indicates no clear
adaptive AV delay and mode switching can abnormality, a magnet can be used to further
lead to irregularity of the paced rhythm. assess pacemaker function (Table 14-6). Placing
a magnet over most pacemakers will inhibit
Rapid Paced Ventricular Rates all sensing and therefore induce unsuppressed
pacing, known as fixed-rate or asynchronous
Patients can present with a rapid paced mode, from each lead until the magnet is removed
ventricular rate, which is most commonly (Figures 14-3 and 14-10). Pacing spikes will be
caused by a rapid sensed atrial rate or, possibly, seen at the default rate set by the manufacture,
pacemaker tachycardia. In a patient with a and appropriate capture should be seen. If
dual-chamber pacemaker, any atrial tachycardia spontaneous complexes occur, there might be
such as atrial fibrillation or sinus tachycardia intermittent capture if the pacer impulses occur
can result in pacing at the upper programmed during the ventricular refractory period.
limit of the ventricular rate (Figure 14-8).
This rate is usually less than 130 beats/min, Emergency physicians should consider
although it can be as high as 180 beats/min in the use of a magnet in consultation with a
a young athlete. This tachycardia is not due cardiologist in three situations as follows:
to inappropriate pacemaker function, but it is
undesirable if it causes symptoms or if it persists. 1) A patient reports having symptoms
consistent with bradycardia but is now
Pacemaker-mediated tachycardia occurs in asymptomatic. If pacing impulses are absent
dual-chamber devices because of cross-talk, when the intrinsic rhythm is of sufficient
the inappropriate sensing by one channel of rate to suppress these impulses, neither
electrical events generated in the other chamber.4 oversensing nor failure to output can be

Table 14-7.
Reliable criteria for ECG diagnosis of acute myocardial infarction. From: Sgarbossa EB, Pinski SL, Gates KB,
Wagner GS. Early electrocardiographic diagnosis of acute myocardial infarction in the presence of ventricular
paced rhythm. GUSTO-I investigators. Am J Cardiol. 1996;77(5):423-424. Used with permission.

Relation to QRS polarity Sensitivity (%) Specificity (%) Likelihood

≥5 mm ST-segment elevation when discordant 53 88 4.4

≥1 mm ST-segment elevation when concordant 18 94 3.1

≥1 mm concordant ST depression in V1 to V3 29 82 1.8

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excluded. In the normally functioning retrograde p wave and therefore interrupts
pacemaker, application of a magnet will the reentrant circuit between the atrial and
demonstrate the presence of unsuppressed ventricular chambers.
pacing impulses with capture. If no pacing
spikes are seen with magnet application, Another indication for magnet application
oversensing is excluded and causes of in the emergency setting is for suppression of
output failure should be considered (Table an implantable cardioverter-defibrillator with
14-4). inappropriate recurrent discharges, which
is beyond the scope of this discussion. A
2) A patient presents with significant theoretical concern with magnet application is
bradycardia, and there is no pacemaker that a pacing impulse will fall on the T wave
activity on the ECG. If application of the (ventricular repolarization) of a ventricular
magnet causes impulse delivery with complex. Although this R-on-T phenomenon
capture, the problem is oversensing. If no could induce ventricular tachycardia, it is
pacing spikes are seen, failure to output is exceedingly rare with today’s devices.
the cause of symptoms, and the causes listed
in Table 14-3 should be considered. Diagnosis of Acute
Myocardial Infarction
3) A patient presents with pacemaker-
mediated tachycardia (Figure 14-9). This Acute myocardial infarction is difficult to
occurs, though infrequently, in patients diagnose in the presence of a paced rhythm.
with DDD pacemakers. Application of the Assessment of the ventricular complex for
magnet suppresses atrial lead sensing of the Q waves lacks diagnostic value, but certain

Key Facts

• Normal appearance of the paced complex:
• In patients with bipolar pacing, pacemaker spikes can be poorly visualized in some or all ECG
leads.
• Because of right ventricular lead placement, almost all paced complexes have a left bundle-
branch pattern.
• The ST segments of a paced ventricular complex exhibit repolarization changes similar to those
seen in left bundle-branch block.

• Approach to pacemaker dysfunction:
• Consider whether the pacemaker is actually functioning appropriately but only appears
abnormal because of the complicated nature of equipment and programming (termed
“pseudomalfunction”).
• Consider whether the pacemaker is inappropriately programmed and requires reprogramming
(eg, pacemaker tachycardia or oversensing of myopotentials).
• Consider whether the pacemaker is malfunctioning because of hardware problems (eg, end of
battery life or lead fracture) or changes in the patient’s underlying condition (eg, hyperkalemia or
myocardial ischemia).

• Considerations for magnet application:
• Symptomatic bradycardia in a patient with an implanted pacemaker that is not firing
• Pacemaker-mediated tachycardia
• Previous symptoms that can be attributable to bradycardia in an asymptomatic patient with a
normal rhythm on ECG that appropriately suppresses pacemaker impulses
• Inappropriate, recurrent implantable cardioverter-defibrillator discharges

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pacemakers and pacemaker dysfunction

patterns of ST-segment changes are predictive.
ST segments in paced complexes are normally
discordant with (in the direction opposite to)
the primary direction of the QRS complex.
The ST-segment criteria that are of diagnostic
value for AMI in left bundle-branch block
appear to be of value in right ventricular pacing
as well8,9: 1) 5 mm of ST-segment elevation
discordant with the QRS complex or 2) 1 mm
of ST-segment deviation that is concordant with
(in the same direction as) the QRS complex.
The presence of either anomaly has specificity
approaching 90% (Table 14-7; Figure 14-10).

References

1. Kusumoto FM, Goldschlager N. Cardiac
pacing. N Engl J Med. 1996;334:89-97.

2. Gregoratos G, Cheitlin MD, Conill A, et al. ACC/AHA
guidelines for implantation of cardiac pacemakers and
antiarrhythmia devices: executive summary—a report
of the American College of Cardiology/American Heart
Association Task Force on Practice Guidelines (Committee on
Pacemaker Implantation). Circulation. 1998;97:1325-1335.

3. Kusumoto FM, Goldschlager N. Device therapy for
cardiac arrhythmias. JAMA. 2002;287:1848-1852.

4. Surawicz B, Knilans TK, Chou T-C. Chou’s
Electrocardiography in Clinical Practice: Adult and
Pediatric. Philadelphia, PA: Saunders; 2001:xiv,709.

5. Chan TC, Cardall TY. Electronic pacemakers. Emerg
Med Clin North Am. 2006;24:179-194,vii.

6. Jarcho JA. Biventricular pacing. N Engl J Med. 2006;355:288-294.
7. Harper RJ, Brady WJ, Perron AD, et al. The paced

electrocardiogram: issues for the emergency
physician. Am J Emerg Med. 2001;19:551-560.
8. Brandt RR, Hammill SC, Higano ST. Images in
cardiovascular medicine: electrocardiographic diagnosis
of acute myocardial infarction during ventricular
pacing. Circulation. 1998;97:2274-2275.
9. Sgarbossa EB, Pinski SL, Gates KB, et al. Early
electrocardiographic diagnosis of acute myocardial
infarction in the presence of ventricular paced rhythm.
GUSTO-I investigators. Am J Cardiol. 1996;77:423-424.

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Figures

Figure 14-1.
Dual-chamber pacing function. A: Schematic of a dual-chamber pacemaker. The atrial and ventricular leads
run from the implanted generator through the subclavian or cephalic vein and enter the appropriate chambers
through the superior vena cava. Leads transmit electrical impulses to the myocardium (pacing) and detect
electrical cardiac activity (sensing). B: This initial tracing from a patient with sinus node dysfunction shows
sinus p waves with normal conduction resulting in intrinsic ventricular activity. After the second complex,
ventricular activity is absent as a result of failure of the sinus node. In the second tracing, a dual-chamber
pacemaker has been implanted. Sinus p waves with normal AV conduction result in intrinsic ventricular
activity and both are sensed, appropriately suppressing pacemaker function. A pause in atrial activity exceeds
the lower rate timer and results in an atrial pacing stimulus. This conducts appropriately through the AV node
and generates intrinsic ventricular depolarization, which is sensed, and suppresses ventricular pacing. C:
This initial tracing from a patient with complete AV nodal block shows an atrial rate that is unrelated to the
junctional escape rate that generates ventricular activity. In the second tracing, a dual-chamber pacemaker
has been implanted. The intrinsic atrial activity is sensed and a paced ventricular impulse is delivered after
a programmed AV delay expires without sensed ventricular activity. From: Kusumoto FM, Goldschlager N.
Device therapy for cardiac arrhythmias. JAMA. 2002;287:1848-1852. Copyright (c) 2002 American Medical
Association. All rights reserved. Used with permission.

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pacemakers and pacemaker dysfunction

Figures

Figure 14-2.
DDD pacemaker with ventricular ectopy. Ventricular pacing as well as dual-chamber sensing are demonstrated
on this ECG. Intrinsic sinus p waves (p) are sensed, suppressing atrial pacing. A paced ventricular impulse
is delivered in response to the sensed p wave after a programmed AV interval expires without intrinsic
ventricular response (bar). A premature ventricular beat (star) is sensed and appropriately suppresses both
atrial and ventricular pacing. A subsequent sinus p wave occurs before the pacemaker fires at its lower rate
limit, again triggering a ventricular pacing impulse after the appropriate AV delay. Note that the amplitude of
the pacer spike from the bipolar ventricular lead is small and is best seen in leads V2 to V4. Although pacing
spikes are absent in two of the paced complexes, these have the same QRS morphology as the other paced
complexes and can be assumed to be paced.

Figure 14-3.
DDD pacing. This ECG demonstrates 100% atrial and ventricular pacing with sensing turned off by application
of a magnet. The recorded amplitude of the pacemaker impulses is small, requiring a thorough examination of
all leads. Image courtesy of Nora Goldschlager, MD.

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Electrocardiography in Emergency Medicine

Figures

Figure 14-4.
Biventricular pacing or cardiac resynchronization therapy. A: ECG of a patient with symptoms of severe heart
failure—atrial fibrillation at a rate of 58 beats/min and left bundle-branch block with a QRS duration of 194
msec. B: ECG of the same patient after cardiac resynchronization therapy. A ventricular pacer spike represents
simultaneous impulse delivery from right and left ventricular leads. The QRS is narrowed to 168 msec, and the
left bundle-branch pattern is no longer present. Image courtesy of Nora Goldschlager, MD.

A

B

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pacemakers and pacemaker dysfunction

Figures

Figure 14-5.
Undersensing (failure to sense). This rhythm strip from lead V1 shows pacemaker impulses at a fixed rate of 60
beats/min despite intrinsic ventricular activity. Normal sensing would detect intrinsic ventricular activity that
occurs before expiration of the lower rate limit and suppress impulse delivery. The first paced impulse results
in capture (star), while subsequent paced impulses that occur during the refractory period of conducted
ventricular beats fail to capture (arrows). This is an example of magnet application to a VVI pacemaker in a
patient with underlying atrial fibrillation.

Figure 14-6.
Oversensing. Tracing reveals background artifact that is sensed inappropriately, thereby suppressing
pacemaker impulses. Occasional intrinsic ventricular complexes are seen. Image courtesy of Nora
Goldschlager, MD.

Figure 14-7.
Failure of ventricular capture. The rhythm strip from lead V1 shows normal paced ventricular complexes at a
rate of 80 beats/min until a paced impulse (star), which fails to capture, is recorded. A junctional escape beat
(arrow) follows the delay in ventricular activity. Image courtesy of Nora Goldschlager, MD.

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ElEctrocardiography in EmErgEncy mEdicinE

Figures

Figure 14-8.
Rapid paced ventricular rate caused by atrial fibrillation in a patient with a DDD pacemaker. A: Recording of
the presenting rhythm (lead V1) in a patient with rapid (100 beats/min) irregular pacemaker discharges and
ventricular capture. This is most likely the result of atrial fibrillation waves sensed by the atrial lead, resulting
in delivery of a paced ventricular impulse after expiration of the programmed AV interval. This leads to rapid
ventricular response with rates as fast as the upper rate limit of the pacemaker. The shortest R-R interval in
this strip is at a rate of 115 beats/min. There are no discernible P waves, and there is a ventricular complex
that could represent a fusion complex between a conducted atrial and a generated ventricular impulse. B:
Recording from the same patient after he spontaneously reverted to sinus rhythm. Sensed atrial sinus beats
trigger ventricular pacing with appropriate capture. The pacemaker was subsequently reprogrammed to
decrease the maximum ventricular pacing rate. Some devices use internal logic that will analyze and detect
atrial fibrillation, thus avoiding excessively rapid ventricular responses.

a

B

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