Routine medical evaluations of well-trained endurance athletes frequently disclose electrocardiographic abnormalities suggestive of organic heart disease. First- and second-degree atrioventricular (AV) block, altered ventricular conduction, criteria for atrial enlargement or ventricular hypertrophy, and repolarization abnormalities are commonly found. On the basis of such abnormal tracings, the athlete may be advised to refrain from his customary strenuous exertion, even though the results of physical examination are normal and there is no history suggesting cardiovascular disease. In fact, such athletes are usually quite fit for the activity for which they train so vigorously. The electrocardiographic findings probably reflect the anatomic and electrophysiologic effects of training on the cardiovascular system. It is important for physicians to recognize these changes as normal variants when seen in well-trained athletes.
Lichtman J, O'Rourke RA, Klein A, Karliner JS. Electrocardiogram of the AthleteAlterations Simulating Those of Organic Heart Disease. Arch Intern Med. 1973;132(5):763-770. doi:10.1001/archinte.1973.03650110095021