Exercise-induced bundle branch block

Exercise-induced bundle branch block (BBB) is poorly understood. An investigation was made of its clinical, electrocardiographic, coronary angiographic, and myocardial scintigraphic characteristics, with follow-up data in 16 patients, aged 59 ±9 (mean ± standard deviation) years, 11 who had left BBB and 5 who had right BBB. Fourteen had a preexisting baseline electrocardiographic abnormality; 11 had either incomplete BBB or nonspecific intraventricular conduction delay. Heart rates at onset of exercise BBB varied from 70 to 166 beats/min and in 9 patients the rates at BBB onset and offset appeared to be related, occurring within 8 beats/min of each other. Coronary artery disease (CAD) was diagnosed in 10 patients, cardiomyopathy in 2, and probable coronary spasm in 2. One patient had ventricular arrhythmias of uncertain origin, and 1 appeared to have no cardiac disease. Three patients had reversible thallium perfusion defects consistent with ischemia concurrent with developing BBB. The 3 patients in whom exercise BBB persisted all had CAD. Over a mean of 28 months of follow-up, only 1 patient had a morbid cardiac event—nonfatal myocardial infarction—and 2 died from noncardiac causes. Thus, exercise BBB primarily occurs in the context of cardiac disease, most commonly CAD, and concurrent ischemia may be demonstrable; the presence of “rate relation” does not militate against CAD.