Effect of obesity and regional adiposity on the QTc interval in women J-J Park 1 and PD Swan 2 1 Department of Kinesiology, University of Maryland, MD, USA and 2 Department of Exercise Science and Physical Education, Arizona State University, Tempe, AZ, USA OBJECTIVES: To determine whether differences in body fat composition and body fat distribution patterns are associated with a prolongation of the corrected QT interval for heart rate (QTc) on the electrocardiogram (EKG) during rest and exercise. DESIGN: Cross-sectional evaluation of the QTc interval in three groups of premenopausal women during rest and two exercise conditions (50% _ VO 2 max and _ VO 2 max). SUBJECTS: Thirty-one healthy women with a mean age of 35 y (27±44 y) were classi®ed as either obese (n  22; percent body fat [%BF] > 30%) or nonobese (NO; n  9; %BF  27%) by hydrostatic weighing. Obese subjects matched for age and %BF were grouped by waist to hip ratio (WHR) into two groups: upper body obesity (UBO; n  11; WHR  0.85) and lower body obesity (LBO; n  11; WHR  0.75). MEASUREMENTS: RR and QT intervals were measured in a double-blind design with the aid of calipers and magnifying lens for seven consecutive beats in lead II from a 12-lead EKG at a paper speed of 25 mm/sec. Five consecutive cardiac cycles excluding the longest and shortest RR and QT intervals were averaged and calculated for QTc interval using Bazett's formula. RESULTS: Mean QTc intervals were signi®cantly different (P < 0.001) across the groups for each condition. For all conditions, UBO had the longest QTc interval as compared to LBO and NO respectively (i.e., Rest: 0.426; 0.413; 0.399 sec 1/2 ; Mid50%: 0.447; 0.426; 0.409 sec 1/2 ; Max: 0.390; 0.374; 0.357 sec 1/2 ). CONCLUSIONS: The QTc interval is positively associated with UBO even at the same level of body fat in moderately obese women. It is clear that abdominal obesity may be one of the risk factors for a prolonged QTc interval in premenopausal women. Keywords: body fat distribution; electrocardiogram; exercise; waist±hip ratio Introduction Obesity has been implicated as a risk factor for sudden cardiac death as well as cardiovascular morbidity and mortality for several decades. 1±4 In the Framingham Heart Study, obesity was found to be a strong pre- dictor of sudden cardiac death. 1,3 A primary mechan- ism of sudden cardiac death in obesity has been shown to be malignant ventricular arrhythmias (MVA), which may relate to electrocardiogram (EKG) abnormalities. 2,5,6 Prolongation of the QT interval on the EKG, represents delayed repolarization of the ventricular myocardium and is considered a precursor of MVA and sudden cardiac death in obesity. 5,7±10 Prolongation of the QT interval is the most important electrocardio- graphic abnormality found in obesity. 11 Frank et al 12 found that 28.3% of their obese outpatients had a mild prolonged QT interval and 4% of them had a mark- edly prolonged QT interval. A prolonged QT interval has also been found in obese patients on very low calorie diets (VLCD) or after surgery for obesity. 6,13 From these results, however, it is impossible to distinguish whether obesity alone or other factors associated with obesity (for example, VLCD, meta- bolic abnormalities etc.) increases the risk for prolon- gation of the QT interval. 7,10 Since the duration of the QT interval is altered by the length of the preceding cardiac cycle, an adjust- ment for differences in heart rate (QTc) has been developed. 9,14 The length of the QTc interval was found to be exponentially related to the risk of developing MVA in patients with QT prolongation. In healthy obese subjects, El-Gamal et al 15 reported that prolongation of the QTc interval was signi®cantly associated with relative body mass and fatness, whereas Peiris et al, 16 found no signi®cant associa- tion. It has become increasingly evident that obesity is a heterogeneous disorder. Body fat location, speci®cally abdominal or visceral obesity, is a higher predictor of cardiovascular and metabolic disease risk, than the amount of body fat alone. 17±19 In addition, abdominal fat deposition has been suggested as an independent risk factor for prolongation of the QTc interval. 16 Peiris et al 16 found that increasing intra-abdominal deposition of fat was closely associated with prolon- Correspondence: Pamela D Swan, Ph. D., FACSM, Department of Exercise Science and Physical Education, Mail Code 870701, Arizona State University, Tempe, AZ, 85287-0701, USA. E-mail: pswan@asu.edu Received 16 January 1997; revised 2 July 1997; accepted 21 July 1997 International Journal of Obesity (1997) 21, 1104±1110 ß 1997 Stockton Press All rights reserved 0307±0565/97 $12.00