Heart's Hidden Signal: A Rare Case of Alternating Bundle Branch Block and Atrioventricular Block

Alternating bundle branch block (ABBB) is a rare cardiac rhythm disorder characterized by alternating occurrence of right BBB and left BBB patterns in consecutive beats. The presence of ABBB in conjunction with atrioventricular block is even more rare.

A 69-year-old man with no significant medical history presented to the emergency department with dyspnea on exertion, lightheadedness, and dizziness for 3 weeks. His heart rate was 31 beats/min, blood pressure was 147/67 mm Hg, and Spo₂ was 96% on room air. An electrocardiogram obtained in the emergency department showed ABBB with atrioventricular block. The patient underwent emergency transvenous transcutaneous pacing in the intensive care unit for symptomatic bradycardia. An echocardiogram was performed that showed a left ventricular ejection fraction of 45% to 50%, a mildly thickened left ventricular wall, and a mildly enlarged left atrium. An electrophysiology consult was placed, and the patient underwent implantation of a permanent pacemaker.

ABBB with atrioventricular block is indicative of an advanced degree of conduction system disease and is associated with significant clinical implications. Pacemaker implantation is the definitive treatment of choice for ABBB.