QT dispersion in exercise-induced myocardial hypertrophy

Background The measurement of QT dispersion in the surface electrocardiogra m is a noninvasive method used for assessing inhomogeneity of myocardial re polarization. Elevated QT dispersion is found in myocardial disease and is associated with an increased incidence of arrhythmic events. QT dispersion is also increased in myocardial hypertrophy secondary to systemic hypertens ion. However, the relation between left ventricular (LV) enlargement in end urance trained subjects and QT dispersion is unknown. Methods and Results In this study, IV mass (2-dimensional echocardiography) and QT dispersion (12-lead resting electrocardiogram) were assessed in 26 normotensive endurance trained subjects and 26 matched, less trained contro l subjects. Endurance trained subjects had a significantly greater LV mass (216 +/- 39 g vs 155 +/- 30 g, P <.001) but lower heart rate-corrected QTc dispersion (42 +/- 13 ms vs 51 +/- 15 ms, P =.012) than less trained contro l subjects. When all individuals were included, IV mass was inversely corre lated with QT dispersion (r = -0.38; P =.002) and heart rate-corrected QTc dispersion (r = -0.53, P<.0001). Conclusions These data show that myocardial hypertrophy induced by exercise training is not associated with increased QT dispersion as observed in sys temic hypertension. The reduced QT dispersion reflects homogeneous myocardi al repolarization and may help to explain the reduced mortality rate in reg ularly exercising subjects. If confirmed in further studies, the measuremen t of QT dispersion could provide a simple and inexpensive screening method for differentiating between physiologic and pathologic myocardial hypertrop hy.