Premature Ventricular Contraction (PVC)

01Pathophysiology

Premature ventricular contractions originate from an ectopic focus in the ventricular myocardium that depolarizes before the sinoatrial (SA) node can deliver its next impulse through the normal conduction system. Because the impulse arises below the His bundle, it does not travel through the rapid His-Purkinje network. Instead, it spreads slowly through ordinary ventricular muscle fibers cell to cell. This abnormal, sluggish conduction produces the hallmark finding: a wide, bizarre-looking QRS complex on the electrocardiogram.

Three primary electrophysiological mechanisms generate PVCs. Enhanced automaticity occurs when ventricular myocytes develop a faster-than-normal spontaneous depolarization rate, often driven by catecholamine surges, ischemia, or electrolyte disturbances. Triggered activity results from afterdepolarizations, which are abnormal oscillations in the membrane potential that follow a preceding action potential. Early afterdepolarizations (EADs) occur during phase 2 or 3 of the action potential and are often linked to prolonged QT states, while delayed afterdepolarizations (DADs) occur after full repolarization and are classically associated with intracellular calcium overload, as seen in digoxin toxicity. Finally, re-entry requires a circuit with two pathways differing in conduction velocity and refractory periods, often arising from scarred myocardium after infarction.

The reason the patient feels a "skipped beat" connects directly to hemodynamics. The premature ventricular beat contracts the ventricle before it has had time to fill adequately with blood. This produces a weak or absent pulse for that beat. The subsequent compensatory pause (the next sinus impulse finds the ventricle still refractory, so the patient must wait for the following sinus beat) allows extra filling time. The beat after the pause is therefore more forceful than usual, and this is the "thud" the patient often notices.

Hypokalemia is the single most important electrolyte disturbance linked to PVCs. Low extracellular potassium hyperpolarizes the resting membrane potential and prolongs repolarization, creating conditions favorable for both automaticity and afterdepolarizations. Similarly, hypomagnesemia destabilizes the membrane by impairing the function of the Na-K-ATPase and potassium channels. This is why any vignette describing a patient on loop diuretics who develops palpitations should immediately raise suspicion for electrolyte-driven PVCs.

02Classification and Clinical Manifestation

By Morphology

By Pattern and Frequency

By PVC Burden

03Diagnostic Workup

The best initial test is a standard 12-lead ECG. This immediately identifies the PVC by its wide QRS complex occurring earlier than the expected sinus beat, with no preceding P wave. The morphology of the PVC on the ECG is important for localization. A PVC with a left bundle branch block (LBBB) pattern (dominant S wave in V1) indicates the ectopic focus is in the right ventricle, most commonly the right ventricular outflow tract (RVOT). A PVC with a right bundle branch block (RBBB) pattern (dominant R wave in V1) indicates a left ventricular origin. This localization matters because RVOT PVCs in a structurally normal heart are the most common type and carry a benign prognosis with excellent response to ablation.

One key ECG feature that distinguishes a PVC from a premature atrial contraction (PAC) with aberrant conduction is the compensatory pause. After a PVC, the interval from the beat before the PVC to the beat after the PVC equals exactly two normal R-R intervals. This is because the sinus node is not reset by the PVC (the retrograde impulse usually does not penetrate the AV node to reach the SA node). In contrast, a PAC typically resets the sinus node, producing a non-compensatory pause (the total interval is less than two R-R cycles).

If the ECG confirms PVCs, the next step is a Holter monitor for 24 to 48 hours to quantify the PVC burden. This is the most important number for clinical decision-making. A burden exceeding 10 to 15% of total heartbeats is the threshold at which PVC-induced cardiomyopathy becomes a concern. The Holter also captures patterns (bigeminy, couplets, runs of NSVT) and correlates the patient's reported symptoms with the actual rhythm.

Echocardiography should be ordered for any patient with frequent PVCs to assess baseline left ventricular function and rule out structural abnormalities. This is critical because the presence or absence of structural heart disease fundamentally changes risk stratification and treatment selection (for example, flecainide is contraindicated in structural heart disease).

Laboratory workup targets reversible causes. Serum potassium, magnesium, thyroid function, and digoxin levels (when applicable) should be checked in every patient presenting with new or worsening PVCs. Correcting these abnormalities alone may eliminate the arrhythmia entirely.

An exercise stress test is ordered when there is concern that PVCs may be triggered by ischemia. The key teaching point is the behavioral pattern: PVCs that disappear during exercise are generally benign (they are suppressed by the faster sinus rate), while PVCs that increase or first appear during exercise suggest underlying ischemia or a catecholaminergic trigger that warrants further evaluation.

Cardiac MRI is reserved for cases where structural heart disease is suspected but echocardiography is not definitive. It is the gold standard for diagnosing arrhythmogenic right ventricular cardiomyopathy (ARVC), which classically presents with PVCs of LBBB morphology (right ventricular origin) in a young patient, and shows fibrofatty replacement of the RV myocardium.

04Management and Treatment

The first and most important step in managing any patient with PVCs is to identify and correct reversible causes. Replete potassium to a target of $4.0mEq\mathrm{/}L4.0\backslash \; mEq/L$ or higher and magnesium to a target of $2.0mg\mathrm{/}dL2.0\backslash \; mg/dL$ or higher. Discontinue or reduce stimulants, including caffeine, tobacco, and sympathomimetic medications. If the patient is on digoxin and the level is elevated, hold the drug and consider digoxin-specific antibody fragments (Digibind) if toxicity is severe with hemodynamic instability. Treat hyperthyroidism if present. In many cases, correcting these factors alone resolves the arrhythmia.

For patients who are asymptomatic with a structurally normal heart and low PVC burden, the correct answer is reassurance and lifestyle counseling. No antiarrhythmic medication is needed. This is a frequently tested concept: the exam wants you to recognize that isolated, infrequent PVCs in an otherwise healthy individual do not require pharmacologic therapy.

When PVCs are symptomatic and bothersome, the first-line pharmacologic agent is a beta-blocker. Metoprolol succinate (starting at 25 mg daily, titrated up to 200 mg daily) is the most commonly used agent. Beta-blockers work by reducing adrenergic stimulation of the ectopic focus and slowing the sinus rate, which allows less opportunity for ectopic beats to emerge. If beta-blockers are not tolerated (for example, in a patient with severe asthma or symptomatic bradycardia), non-dihydropyridine calcium channel blockers such as verapamil or diltiazem are the alternative. These are particularly effective for PVCs originating from the fascicles or the outflow tract.

If symptoms persist despite beta-blocker therapy in a patient with a structurally normal heart, Class IC antiarrhythmics such as flecainide or propafenone may be used. The critical teaching point here relates to the CAST trial (Cardiac Arrhythmia Suppression Trial), which demonstrated that flecainide and encainide increased mortality in patients with prior myocardial infarction and structural heart disease. Therefore, Class IC agents are absolutely contraindicated in patients with ischemic heart disease, heart failure, or any form of structural cardiac abnormality. This is one of the most tested contraindications in cardiology.

For patients with structural heart disease who require antiarrhythmic therapy beyond a beta-blocker, amiodarone (a Class III agent) is the preferred drug. Amiodarone is loaded at 400 mg PO twice daily for one to two weeks, then reduced to a maintenance dose of 200 mg PO daily. It is effective but carries a well-known toxicity profile: pulmonary fibrosis, thyroid dysfunction (both hypo- and hyperthyroidism), hepatotoxicity, corneal microdeposits, and blue-gray skin discoloration. Baseline and periodic monitoring of thyroid function, liver enzymes, pulmonary function, and ophthalmologic exams are required. Sotalol (80 to 160 mg PO twice daily) is an alternative Class III agent that also has beta-blocking properties, but it carries a risk of QT prolongation and torsades de pointes, requiring QTc monitoring during initiation.

Catheter ablation is the treatment of choice for PVC-induced cardiomyopathy (high PVC burden causing reduced ejection fraction). It is also indicated for patients with frequent, symptomatic PVCs refractory to medical therapy. RVOT PVCs, the most common type in structurally normal hearts, have ablation success rates exceeding 90%. After successful ablation, the left ventricular ejection fraction typically recovers over weeks to months, confirming the reversibility of the cardiomyopathy.

A notable contraindication to keep in mind: do not use prophylactic antiarrhythmics to suppress PVCs in the post-myocardial infarction setting. The CAST trial proved this increases mortality. If PVCs occur in the context of an acute MI, the correct approach is to optimize ischemia management (reperfusion, beta-blockers, electrolyte correction), not to add flecainide or encainide.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The single most common trap with PVC questions involves PVC-induced cardiomyopathy. The vignette presents a patient with a newly reduced ejection fraction and frequent PVCs, and the student is tempted to diagnose primary dilated cardiomyopathy and start heart failure therapy alone. The correct answer recognizes that a PVC burden exceeding 10 to 15% can be the sole cause of the LV dysfunction, and the appropriate next step is catheter ablation (or at minimum, aggressive PVC suppression). The cardiomyopathy is reversible once the PVC burden is eliminated. If you see a patient with a low EF and frequent PVCs, always consider PVCs as the cause, not just a bystander.

The second major trap is the CAST trial principle. A post-MI patient develops frequent PVCs, and the question asks for the best pharmacologic therapy. Students who remember that flecainide suppresses PVCs may select it. The correct answer is that Class IC antiarrhythmics are contraindicated after MI because they increase mortality despite effectively suppressing PVCs on the Holter monitor. Beta-blockers are the correct choice in this setting.

The third trap involves distinguishing PVCs from PACs with aberrancy. Both can produce wide QRS complexes on ECG. The exam will often hide a subtle P wave in the preceding T wave (changing the T wave morphology compared to baseline) to indicate a PAC rather than a PVC. Always compare the T wave preceding the wide complex to the patient's baseline T waves. If the T wave shape has changed, a hidden P wave is likely present, and the beat is a PAC, not a PVC.

Finally, never suppress a ventricular escape beat. If the vignette describes a patient with a slow heart rate and intermittent wide QRS complexes occurring after a long pause, those are escape beats, not PVCs. Suppressing them removes the only remaining pacemaker and can lead to asystole. The treatment is to address the underlying bradycardia (atropine, transcutaneous pacing), not to administer an antiarrhythmic.

The core competency being tested across PVC questions is the ability to risk-stratify based on the presence or absence of structural heart disease, quantify burden, recognize reversible causes, select the correct antiarrhythmic (and know which ones to avoid), and understand that PVCs themselves can be the primary disease, not merely a symptom.