Influence of underlying coronary artery disease on the natural history and prognosis of exercise-induced left bundle branch block.

The long-term prognosis of exercise-induced left bundle branch block (BBB) in patients with and without underlying coronary artery disease (CAD) was examined by following 15 patients (7 with normal coronary arteries and 8 with CAD) for an average of 6.6 years (range 2.2 to 11.2). Over the follow-up interval, permanent left BBB developed in 8 of the 15 patients. Seven of these 8 had underlying CAD, compared to 0 of 6 patients with normal coronary arteries and normal left ventricular function (p less than 0.002). In 1 patient with normal coronary arteries and a left ventricular ejection fraction of 0.34, permanent left BBB developed. During follow-up, 4 patients died; 3 had significant CAD and 1 had depressed left ventricular function. In no patient did high-grade atrioventricular block develop and no patient required pacing. Thus, development of permanent left BBB in patients with exercise-induced left BBB is related to presence or absence of underlying CAD or myocardial disease. When left BBB is found in the absence of underlying heart disease, there does not tend to be progression of the conduction disturbance and the prognosis is excellent.