Paroxysmal atrioventricular block as an initial presentation of bicuspid aortic valve calcification: a case report.

Background: Atrioventricular (AV) conduction disturbances in bicuspid aortic valve (BAV) patients are typically attributed to age-related fibrosis or post-surgical trauma. Direct mechanical impingement of the conduction system by accelerated valvular calcification causing reversible, dynamic AV block is rarely reported. Case Summary: A 43-year-old male presented with syncope. Electrocardiograms revealed dynamic high-grade AV block and alternating bundle branch block (ABBB). Echocardiography and computed tomography identified a BAV with a calcified spur extending into the membranous interventricular septum, mechanically compressing the His bundle during the cardiac cycle. Additionally, a hypermobile mass-initially suspected as infective vegetation-was attached to the calcification. To prevent embolic events and address the root cause of the conduction block, surgical tissue-sparing resection was performed. Histopathology confirmed the mass as a reactive thrombus formed on the calcified nodule. Postoperatively, normal sinus rhythm was successfully restored, completely obviating the need for permanent pacemaker implantation. Discussion: This case highlights that dynamic conduction disturbances, such as ABBB, in BAV patients can stem from reversible mechanical compression rather than intrinsic irreversible fibrosis. Furthermore, calcific extensions can create local turbulence and surface irregularities, acting as a nidus for thrombus formation that mimics vegetation. When young BAV patients present with unexplained dynamic AV block, meticulous evaluation for calcific extension is essential. In selected cases, surgical resection targets the underlying pathology, offering a curative alternative to lifelong pacing while simultaneously eliminating embolic risks.