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; and to describe the change in the QT interval during rapid weight loss with a very-low-calorie diet.

DESIGN

Retrospective and prospective review of charts and electrocardiograms.

SUBJECTS

Five hundred twenty-two 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.

MEASUREMENTS

We reviewed the EKGs of all patients and serially monitored the QTc if greater than 0.44 s or if more than 23 kg was lost during treatment. The QTc interval was calculated with Bazzett's formula using both a manual method and an automated software program. In some patients, body composition was measured by hydrodensitometry.

RESULTS

The QTc interval before treatment was 0.42 +/- 0.026 s by manual measurement and 0.41 +/- 0.021 s by automated measurement. Forty-one to 53% of patients showed a QTc interval of greater than 0.42 s and 10-24% demonstrated moderate prolongation (> 0.44 s). In those patients for whom repeat EKG were performed, QTc 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 +/- 0.003 to 0.40 +/- 0.003 s, p < 0.005 by automated program). Analyses were repeated excluding 179 patients with a cardiovascular-related diagnosis or intraventricular block and the results were similar. By regression analysis, gender and fat mass (FM) percentage above normal predicted the QTc.

CONCLUSIONS

QT Interval prolongation is common in obesity. For each 50% increase in FM% above normal, there is a 5 ms increase in the QTc above a 'normal' upper limit of 0.40 and 0.38 s in women and men, respectively. Moreover, the 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.