UC San Diego

BACKGROUND: Conduction system disturbance is a leading complication of transcatheter aortic valve replacement (TAVR). Conventional predictors of post-TAVR pacing include preexisting right bundle branch block, new left bundle branch block, and annular calcification. CASE SUMMARY: A 71-year-old woman with severe aortic stenosis and left bundle branch block (PR: 160 ms, QRS: 138 ms) underwent TAVR. The QRS paradoxically narrowed postprocedure (104 ms), and inpatient telemetry showed no high-grade atrioventricular block before discharge. Five days later, an outpatient real-time monitor captured 71 seconds of asystole due to complete heart block. She presented with syncope and underwent pacemaker implantation. DISCUSSION: The paradoxical QRS narrowing reflects His-bundle injury producing a proximal conduction delay in the His bundle, with recovery of conduction in the left bundle branch indicative of gap phenomenon. The recovery of conduction in the left bundle also highlights the dynamic nature of a diseased left bundle that can facilitate prolonged, pause-dependent complete heart block without a stable escape rhythm. TAKE-HOME MESSAGES: Delayed complete heart block after TAVR is rare, life-threatening, and may occur in the absence of conventional predictors. Real-time ambulatory monitoring enables timely diagnosis.