Paroxysmal Pause-Dependent Atrioventricular Block: An Often-Missed Medical Emergency

Pause-dependent atrioventricular (AV) block is a cause of syncope and cardiac arrest characterized by abrupt but transient conduction failure with ventricular standstill despite previous AV conduction. It is frequently under-recognized.

We describe 4 patients presenting with syncope. Baseline electrocardiograms were nondiagnostic, but continuous monitoring captured episodes of sudden high-grade AV block initiated by pauses or premature beats, without progressive PR prolongation. All patients underwent permanent pacemaker implantation, with resolution of symptoms during follow-up.

Pause-dependent AV block is thought to arise from the inability of diseased His-Purkinje tissue to sustain its resting potential during phase 4 of the cardiac action potential. It may mimic neurological or vasovagal events. Diagnosis depends on timely rhythm documentation. Early recognition is essential because pacing is highly effective in preventing recurrence.

Syncope with suspicion for a cardiac cause should prompt prolonged monitoring. Pacing of pause-dependent paroxysmal AV block can prevent further events.