What is the typical cause of premature ventricular contractions?

• A. Delayed depolarization of atrial cells
• B. Premature depolarization of ventricular myocardium
• C. Normal conduction through the AV node
• D. Increased heart rate

Answer: (B)

Premature ventricular contractions (PVCs) are primarily caused by the premature depolarization of the ventricular myocardium. This occurs when an electrical impulse originates in the ventricles before the regular heartbeat is initiated by the sinoatrial (SA) node, leading to an early contraction of the ventricles. The resulting heartbeat can disrupt the usual rhythm of the heart and may manifest as a sensation of palpitations or skipped beats.

Other choices focus on different aspects of cardiac conduction or physiology. Delayed depolarization of atrial cells does not typically relate to PVCs, as PVCs stem from events that initiate in the ventricles, not the atria. Normal conduction through the AV node suggests that impulses are traveling through the heart in a standard manner, further diverging from the concept of PVCs which involve abnormal premature contractions. Lastly, while an increased heart rate can influence the occurrence of PVCs, it is not the direct cause; it may merely create a conductive environment where PVCs may be more noticeable. Thus, understanding that PVCs arise specifically from the ventricular myocardium helps clarify why the corresponding answer best defines the etiology of these contractions.