A 51-year-old man who experienced syncope while exercising on the treadmill at the gym presented for further evaluation. He had no significant medical history. Results from basic laboratory testing, including serum electrolytes, troponin, and complete blood cell counts, were unremarkable. Routine electrocardiogram (ECG) at presentation (Figure 1A) revealed sinus rhythm with first-degree atrioventricular (AV) block, borderline right axis deviation, and right bundle branch block. The patient was sent for exercise stress echocardiography. Resting echocardiogram revealed normal left ventricular size and function, mild concentric left ventricular hypertrophy, and no significant valvular abnormalities. Shortly after the patient reached a peak heart rate of 130 beats per minute at 9 minutes 28 seconds of exercise (Figure 1B), his heart rate abruptly decreased to 95 beats per minute, with evidence of AV block (Figure 1C). Subsequent coronary angiogram revealed no obstructive epicardial coronary artery disease.
Prenner SB, Schimmel DR, Chicos AB. A 51-Year-Old Man With Exercise-Induced Syncope. JAMA Cardiol. Published online December 14, 2016. doi:10.1001/jamacardio.2016.3866