Premature Ventricular Complex (PVC) occurs when

• A. Atrial site generates an impulse before next regular sinus beat.
• B. Ventricular site generates an impulse before next regular sinus beat.
• C. SA node fails temporarily.
• D. AV node blocks conduction.

Answer: (B)

Premature ventricular contraction happens when an impulse starts in a ventricular ectopic focus and triggers a beat earlier than the next expected sinus beat. This is exactly what the option states: a ventricular site generates an impulse before the next regular sinus beat. On ECG, you’d see a wide, bizarre QRS complex that often occurs without a preceding P wave and is followed by a compensatory pause.

If the impulse came from the atria, you’d expect a premature atrial contraction, which typically has a normal or narrow QRS because the ventricles are still activated through the normal pathway and often shows a preceding P wave. If the SA node failed temporarily, you’d get a pause or arrest rather than an early beat. If the AV node blocked conduction, you’d see a dropped beat or a markedly altered PR interval, not an early ventricular beat.