Objective: although the isolated effects of age on QT interval and QT dispersion (QTd) have been previously investigated, no data are available on the simultaneous effects of age and other physiological or lifestyle factors on QT interval and QTd in healthy subjects. We studied the effects of age, gender, body mass index, smoking status, and blood pressure on these electrocardiographic parameters.
Design: observational study.
Setting: academic medical centre.
Participants and measurements: age, gender, body mass index, smoking status, and blood pressure were obtained from 191 consecutive healthy subjects (101 males and 90 females, age range 19-89 years). The subjects were divided into three groups according to their age: <30 (n=56), 30-65 (n=49), and >65 years (n=86).
Results: heart-rate corrected QT interval (QTc, Bazett's formula) progressively increased with advancing age (389+/-3 vs. 411+/-4 vs. 418+/-3 ms, means+/-SEM; P<0.01). By contrast, no differences in QTd were observed across the three groups (36+/-2 vs. 35+/-3 vs. 40+/-2 ms, P=NS). A multivariate regression analysis showed that age (P<0.01) and body mass index (P=0.04) independently predicted QT interval while gender was a weak (P=0.09) predictor of QTd.
Conclusions: after adjusting for gender, smoking status, and blood pressure, age and body mass index independently predicted QT interval in healthy subjects. By contrast, age is not a predictor of QTd. The increase of QT interval associated with ageing and body mass index might be secondary to cardiac hypertrophy and myocardial action potential prolongation.