Exercise Induced Left Bundle Branch Block Treated with Cardiac Rehabilitation: A Case Report and a Review of the Literature

Exercise induced bundle branch block is a rare observation in exercise testing, accounting for 0.5 percent of exercise tests. The best treatment of this condition and its association with coronary disease remain unclear. We describe a case associated with normal coronary arteries which was successfully treated with exercise training. While this treatment has been used previously, our case has a longer followup than previously reported and demonstrates that the treatment is not durable in the absence of continued exercise. 1. Introduction The patient was a 42-year-old woman who presented with exertional chest pain, palpitations, and dyspnea that resolved with rest. She had a normal physical exam and her only medication was an oral contraceptive. 12-lead electrocardiogram was normal with the following intervals: PR interval was 154 millisecond (msec), QRS was narrow at 82？msec, and QT interval was normal at 392？msec, corrected QT (QTc) using Bazett’s formula was 431？msec (Figure 1). Laboratory tests including hemoglobin and cardiac troponin T were normal. Figure 1: Baseline electrocardiogram demonstrating normal baseline conduction. She was referred for exercise stress testing using the Bruce protocol during which she developed a left bundle branch block (LBBB) with a QRS duration of 120？msec at a heart rate of 112 beats per minute (bpm) (Figure 2). During the aberrant conduction and at peak exercise, her symptoms of chest pain and palpitations returned. She was able to exercise through her discomfort, reaching a peak heart rate of 171？bpm and 10.4 metabolic equivalent (MET) at 9？:？11？min of exercise. The test was stopped due to limiting chest discomfort that persisted until her heart rate returned to 100？bpm at 2？:？30？min of recovery and normal conduction was restored. An echocardiogram was performed and revealed no structural abnormalities other than a small patent foramen ovale (PFO). Concerns regarding ischemia as the etiology for her conduction abnormalities prompted coronary angiography that demonstrated normal coronary arteries with no evidence of atherosclerosis. Figure 2: Electrocardiogram at peak exertion demonstrating left bundle branch block morphology. The patient was a military service member on active duty status, which would require passing a physical fitness test, something her symptoms had not permitted. In the absence of structural heart disease leading to her conduction abnormality at peak exercise, patient was prescribed an exercise program in an attempt to improve symptoms with physiologic conditioning and left ventricular