OBESITY, ADIPOSITY, AND LENGTHENING OF THE QT INTERVAL - IMPROVEMENT AFTER WEIGHT-LOSS

OBJECTIVES: To determine the prevalence of QT interval prolongation in patients referred to an outpatient clinic for treatment of obesity; a nd to describe the change in the QT interval during rapid weight loss with a very-low-calorie diet. DESIGN: Retrospective and prospective re view of charts and electrocardiograms.SUBJECTS: Five hundred twenty-tw o obese patients (411 female, 112 males) with a mean age 44 (18-78 y) and a mean initial weight of 116 kg (63-285 kg) completing 26 weeks of treatment between September, 1989 through to December, 1993. MEASUREM ENTS: We reviewed the EKGs of all patients and serially monitored the QT(c) if greater than 0.44 s or if more than 23 kg was lost during tre atment. The QT(c) interval was calculated with Bazzett's formula using both a manual method and an automated software program. In some patie nts, body composition was measured by hydrodensitometry. RESULTS: The QT(c) interval before treatment was 0.42 +/- 0.026 s by manual measure ment and 0.41 +/- 0.021 s by automated measurement. Forty-one to 53% o f patients showed a QT(c) interval of greater than 0.42 s and 10-24% d emonstrated moderate prolongation (> 0.44 s). In those patients for wh om repeat EKG were performed, QT(c) showed shortening with weight loss by both methods (mean +/- s.e. of 0.42 +/- 0.003 to 0.41 +/- 0.003 s, P < 0.01 manually and 0.41 +/- 0.093 to 0.40 +/- 0.003 s, p < 0.005 b y automated program). Analyses were repeated excluding 179 patients wi th a cardiovascular-related diagnosis or intraventricular block and th e results were similar. By regression analysis, gender and fat mass (F M) percentage above normal predicted the QT(c). CONCLUSIONS: QT interv al prolongation is common in obesity. For each 50% increase in FM% abo ve normal, there is a 5 ms increase in the QT(c) above a 'normal' uppe r limit of 0.40 and 0.38 s in women and men, respectively. Moreover, t he QT interval shortens with weight loss. This change may represent an additional benefit of weight loss along with the improvement in other cardiovascular risk factors.