ATHLETIC HEART SYNDROME IN DOGS COMPETING IN A LONG-DISTANCE SLED RACE

The cardiac effects of endurance training were evaluated by cardiac au scultation and electrocardiographic examination of 48 heavily trained sled dogs (3,000-5,000 km of training), 18 lightly trained sled dogs ( 300-800 km of training), 19 untrained sled dogs, and 14 mongrel dogs. A grade I-II/VI early- to midsystolic cardiac murmur was auscultated w ith increasing frequency as training level increased. The QRS duration (66.1 +/- 7.4 ms) and QT interval (236 +/- 20 ms) were significantly (P < 0.05) longer in heavily trained sled dogs than in mongrel dogs (Q RS, 60.6 +/- 4.6; QT, 219 +/- 11 ms). A long QT interval (>250 ms) was observed in 8 (16.7%) heavily trained dogs but not in the other group s. A significant rightward shift in the mean electrical axis of ventri cular depolarization in the frontal plane was observed in heavily trai ned sled dogs. The auscultatory and electrocardiographic findings in h eavily trained sled dogs were remarkably similar to those reported in elite human endurance athletes, suggesting that endurance-trained sled dogs provide a naturally occurring model for the athletic heart syndr ome.