Which of the following might be a sign of ventricular pacing failure?

In the context of ventricular pacing failure, increased signs of syncope and fatigue serve as significant indicators. When a pacemaker designed to stimulate the ventricles is not functioning correctly, the heart may not generate adequate electrical impulses or may fail to adequately pace the ventricles, leading to a decreased cardiac output. This can manifest as symptoms like syncope (fainting) and increased fatigue, as the heart struggles to maintain effective blood circulation and meet the body's metabolic demands.

These symptoms arise because when the pacing is insufficient, the heart might not contract effectively or at an appropriate rate, making it difficult for the body to receive enough blood flow, especially during physical activity or when experiencing stress. Monitoring for these signs is essential in patients with a pacemaker, as they indicate that the mechanical support provided by the device is inadequate.

Frequent normal heartbeats and normal exercise tolerance would suggest that the pacing system is functioning correctly, while decreased heart rate variability is a nonspecific sign that does not directly indicate pacing failure. In this context, the signs of syncope and fatigue are more directly related to the performance of the pacemaker and the adequacy of cardiac output.