Ethnic

differences in cardiac arrhythmia incidence have been reported, with higher incidence of sudden cardiac death and lower incidence of atrial fibrillation in African Americans compared with Americans of European ancestry.1–3 These differences have been independent of measured envi-ronmental and behavioral factors and therefore attributed to differences in genetic makeup, although the specific genetic determinants have not been identified.3,4 Rare nonsynonymous genetic variants in cardiac ion channel genes have been found more often in African Americans than in European Americans,5 some of which have been associated with arrhythmia risk and myocardial electrophysiological characteristics.6 Clinical Perspective on p 655 Background—Ethnic differences in cardiac arrhythmia incidence have been reported, with a particularly high incidence of sudden cardiac death and low incidence of atrial fibrillation in individuals of African ancestry. We tested the hypotheses that African ancestry and common genetic variants are associated with prolonged duration of cardiac repolarization,