Effect of obesity and subsequent weight reduction upon QT intervals

Electrocardiograms of 48 men and women were examined to determine if obesity is associated with QT interval prolongation. When corrected for heart rate, the QTc was slightly but significantly prolonged in 31 morbidly obese subjects as compared to the QTc in a control group of 17 lean subjects (0.43 ± 0.01 vs. 0.40 ± 0.01 s, mean ± SEM). Pathologic QTc prolongation (i.e., greater than 0.44 s) was present in 35% of the obese group and in none of the lean controls. For the entire group of 48 subjects, a strongly positive correlation was found between body weight and QTc (r = 0.69; p < 0.0001). Using multivariate analysis, other factors such as serum potassium, diastolic arterial pressure, caffeine intake, and cigarette smoking had little or no correlation with QTc. We subsequently studied the relationship between weight loss and QTc changes in a separate group of 16 patients entering a weight reduction program. Based upon the initial electrocardiogram, a positive correlation between obesity and QTc prolongation was reconfirmed (r = 0.67; p < 0.005). A significant reduction of the QTc (0.02 ± 0.01 s) occurred in these 16 patients, in whom the mean weight loss was 35 kg. Furthermore, a positive correlation between weight reduction and shortening of QTc was apparent (r = 0.67; p < 0.004). These data indicate a stronger relationship between obesity and QTc prolongation than has been previously reported. A relationship between weight loss and shortening of the QT interval in the morbidly obese is also evident.