Mechanism of Syncope in Patients With Bundle Branch Block and Negative Electrophysiological Test

TLDR

Syncope in patients with bundle branch block is thought to arise from paroxysmal atrioventricular block, yet its mechanism remains poorly understood when electrophysiological studies are negative. An implantable loop recorder was used in 52 patients with bundle branch block and negative conventional workup to capture arrhythmic events. During 3–15 months of follow‑up, 42 % of patients had recurrent syncope, most of which were sudden‑onset prolonged asystolic pauses due to paroxysmal AV block (median 47 s, often preceded by ventricular premature beats), with no injuries reported.

Abstract

Background In patients with syncope and bundle branch block (BBB), syncope is suspected to be attributable to a paroxysmal atrioventricular (AV) block, but little is known of its mechanism when electrophysiological study is negative. Methods and Results We applied an implantable loop recorder in 52 patients with BBB and negative conventional workup. During a follow-up of 3 to 15 months, syncope recurred in 22 patients (42%), the event being documented in 19 patients after a median of 48 days. The most frequent finding, recorded in 17 patients, was one or more prolonged asystolic pause mainly attributable to AV block; the remaining 2 patients had normal sinus rhythm or sinus tachycardia. The onset of the bradycardic episodes was always sudden but was sometimes preceded by ventricular premature beats. The median duration of the arrhythmic event was 47 seconds. An additional 3 patients developed nonsyncopal persistent III-degree AV block, and 2 patients had presyncope attributable to AV block with asystole. No patients suffered injury attributable to syncopal relapse. Conclusions In patients with BBB and negative electrophysiological study, most syncopal recurrences have a homogeneous mechanism that is characterized by prolonged asystolic pauses, mainly attributable to sudden-onset paroxysmal AV block.