During which phase of the cardiac cycle is the risk for ventricular fibrillation greatest in a client with frequent PVCs?

The correct response identifies that the risk for ventricular fibrillation is greatest during the T wave phase of the cardiac cycle. This is due to the fact that the T wave represents the repolarization of the ventricles, a critical period in the cardiac cycle when the myocardium is recovering and preparing for the next contraction.

During this phase, the heart is particularly vulnerable to disruption in the electrical activity. If a premature ventricular contraction (PVC) occurs during the T wave, it can lead to uncoordinated or chaotic electrical signals, increasing the risk of ventricular fibrillation. This is a dangerous arrhythmia where the ventricles quiver ineffectively instead of pumping blood, which can lead to sudden cardiac arrest.

In contrast, the P wave represents atrial depolarization and does not relate directly to ventricular contraction or repolarization. The QRS complex indicates ventricular depolarization, where the ventricles are contracting and pumping blood. The resting phase, or diastole, occurs after the T wave when the heart muscle is relaxed and there is less risk of arrhythmias connected to PVCs. Understanding the characteristics of each phase of the cardiac cycle reveals why the T wave is a critical point for assessing risk in patients with frequent PVCs