Laboratory Studies
In young, healthy patients without concerning concomitant symptoms, laboratory tests are not typically necessary. The following diagnostic measures may be necessary, depending on the patient's history and underlying illness(es):
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Obtain serum electrolyte levels, in particular potassium levels; consider checking the magnesium level, especially in patients with low potassium levels
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In selected patients, a drug screen may be helpful
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For patients taking medication with known proarrhythmic effects (eg, digoxin, theophylline), drug levels may be useful
Echocardiography
Echocardiography is useful not only in evaluating the ejection fraction, which is important in determining the prognosis and also in identifying valvular disease or ventricular hypertrophy.
Electrocardiography
Electrocardiography (ECG) allows characterization of the ventricular ectopy and determination of the cause. In addition to the standard 12-lead ECG, a 2-minute rhythm strip may help in determining the frequency of the ectopy and capturing infrequent premature ventricular contractions (PVCs). Findings may include the following:
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Left ventricular hypertrophy
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Active cardiac ischemia (ST-segment depression or elevation and or T-wave inversion)
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In patients with previous MI - Q waves or loss of R waves, bundle-branch block
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Electrolyte abnormalities (hyperacute T waves, QT prolongation)
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Drug effects (QRS widening, QT prolongation)
On ECG, PVCs may be premature in relation to the next expected beat of the basic rhythm. The pause after the premature beat is usually a fully compensatory one. The R-R interval surrounding the premature beat is equal to double the basic R-R interval, showing that the ectopic beat did not reset the sinus node. PVCs may appear in a pattern of bigeminy, trigeminy, or quadrigeminy (ie, may occur every other beat, every third beat, or every fourth beat). PVCs with identical morphologies on a tracing are called monomorphic or unifocal. PVCs demonstrating two or more different morphologies are referred to as multiform, pleomorphic, or polymorphic. (See the images below.)
ECG shows frequent, unifocal PVCs with a fixed coupling interval between the ectopic beat and the previous beat. These PVCs result in a fully compensatory pause; the interval between the 2 sinus beats surrounding the PVC are exactly twice the normal R-R interval. This finding indicates that the sinus node continues to pace at its normal rhythm despite the PVC, which fails to reset the sinus node.
On this ECG, the PVCs occur near the peak of the T wave of the preceding beat. These beats predispose the patient to ventricular tachycardia or fibrillation. This R-on-T pattern is often seen in patients with acute myocardial infarction or long Q-T intervals. In the latter case, the triggered arrhythmia would be torsade.
PVCs usually are described in terms of the Lown grading system for premature beats, as follows (the higher the grade, the more serious the ectopy):
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Grade 0 - No premature beats
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Grade 1 - Occasional (< 30/hr)
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Grade 2 - Frequent (>30/hr)
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Grade 3 - Multiform
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Grade 4 - Repetitive (A = couplets; B = salvos of ≥3)
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Grade 5 - R-on-T pattern
Holter 24-hour monitoring
Holter 24-hour monitors are useful in quantifying and characterizing ventricular ectopy. Holters also have been used to determine treatment efficacy in patients with frequent or complex PVCs. Suppression of ectopy on Holter monitoring is not always predictive of survival. The most important role for Holter monitoring is risk stratification of patients with a recent myocardial infarction (MI) or known left ventricular dysfunction. More than 60% of healthy, middle-aged men have ventricular ectopy on Holter monitoring.
Signal-averaged ECG
Signal-averaged ECG (SAECG) may have a future role in identifying patients at risk for complex ventricular ectopy and nonsustained ventricular tachycardia (NSVT). SAECG may have a role in identifying patients with complex ectopy who may benefit from electrophysiologic studies (EPS).
Procedures
Exercise stress testing (EST) is best used complementary to Holter monitoring. In patients with complex ectopy, EST can unmask NSVT triggered by increased catecholamines or myocardial ischemia.
The role of EPS in complex ventricular ectopy is an area of both intense research and debate. A joint American Heart Association (AHA)/American College of Cardiology (ACC) statement suggested the following [10, 11] :
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Routine EPS are not indicated in low-risk patients after MI; "low-risk" refers to simple ectopy, good left ventricular function, and low congestive heart failure (CHF) class
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EPS are indicated in high-risk patients with complex ectopy
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EPS are thought to be beneficial in patients with sustained ventricular tachycardia more than 48 hours after MI
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ECG shows frequent, unifocal PVCs with a fixed coupling interval between the ectopic beat and the previous beat. These PVCs result in a fully compensatory pause; the interval between the 2 sinus beats surrounding the PVC are exactly twice the normal R-R interval. This finding indicates that the sinus node continues to pace at its normal rhythm despite the PVC, which fails to reset the sinus node.
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On this ECG, the PVCs occur near the peak of the T wave of the preceding beat. These beats predispose the patient to ventricular tachycardia or fibrillation. This R-on-T pattern is often seen in patients with acute myocardial infarction or long Q-T intervals. In the latter case, the triggered arrhythmia would be torsade.
