Effect of obesity and regional adiposity on the QTc interval in women

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.

Cross-sectional evaluation of the Qtc interval in three groups of premenopausal women during rest and two exercise conditions (50% VO2 max and VO2 max).

Thirty-one healthy women with a mean age of 35 y (27-44 y) were classified as either obese (n = 22; percent body fat [%BF] > 30%) or nonobese (NO; n = 9; %BF < or = or 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 > or = 0.85) and lower body obesity (LBO; n = 11; WHR < or = 0.75.

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.

Mean QTc intervals were significantly 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; 0.399sec1/2, Mid50%: 0.447; 0.426; 0.409sec1/2; Max: 0.390; 0.374; 0.357sec1/2).

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.