Exercise-Induced Left Bundle Branch Block in a Patient With Syncope: A Case Report

Exercise-induced left bundle branch block (EI-LBBB) is a rare phenomenon, particularly in patients without structural heart disease. Its pathophysiology remains poorly understood and there are no defined treatment protocols. We report a 77-year-old man with a history of syncope who developed EI-LBBB during a cardiac stress test, with transient electrocardiographic changes that resolved at rest. Coronary angiography revealed only a mild-moderate (approximately 25%-50%) proximal left anterior descending artery stenosis, and the rest of his cardiac evaluation was unremarkable. The patient was commenced on an aerobic exercise program, and reported symptomatic improvement on follow-up. Although EI-LBBB is often linked to underlying structural heart disease and coronary artery disease, it can occur in patients with normal cardiac structure. This report summarizes an approach to evaluation and follow-up of EI-LBBB and reviews management strategies described in the literature, including exercise training in selected patients.