Transient Myocardial Tissue and Function Changes During a Marathon in Less Fit Marathon Runners

Background: Although regular physical activity improves health, strenuous exercise might transiently increase cardiac risk. Training and fitness might provide protection. Methods: We prospectively studied 20 recreational marathon runners without known cardiovascular disease or symptoms: at peak training before, immediately after, and 3 months after a 42.2-km marathon. Changes in global/segmental myocardial function, edema, resting perfusion, and fibrosis were measured. Results: At peak training, runners exercised 8.1 +/- 2.3 hours and 62 +/- 18 km per week with mean maximal oxygen consumption (VO(2)max) of 53.2 +/- 8.3 mL kg/min. In response to the marathon, global left ventricular and right ventricular ejection fraction decreased in half of the runners; these runners had poorer peak training distance, training time, and fitness level. Change in global left ventricular ejection fraction was associated with VO(2)max. Overall, 36% of segments developed edema, 53% decreased function, and 59% decreased perfusion. Significant agreement was observed between segment decreasing function, decreasing perfusion, and developing edema. Myocardial changes were reversible at 3 months. Conclusions: Completing a marathon leads to localized myocardial edema, diminished perfusion, and decreased function occurring more extensively in less trained and fit runners. Although reversible, these changes might contribute to the transient increase in cardiac risk reported during sustained vigorous exercise.