Circadian modulation of QT rate dependence in healthy volunteers - Gender and age differences

QT rate dependence is known to be linked with both circadian variations of the autonomic tone and gender. However, age and heart rate variability (HRV ) influences are not well established. The QT/RR relationship was evaluated , separately during the day and at night, on 24-hour electrocardiogram in 6 0 healthy subjects (30 men) divided into three homogeneous groups (group 1, 20-29; group 2 30-39; group 3, 40-50 years). QT rate dependence was larger during the day in both genders. Women showed stronger QT rate dependence ( 0.195 during the day vs 0.154 in men P < .0001). The circadian modulation d ecreased with increasing age (day/night slope differences: group 1, 0.038; group 2, 0.031; group 3, 0.001; analysis of variance P < .05). In addition, QT rate dependence increased as mean RR decreased (r = -0.58, P < .0001) a nd decreased as HRV parameters increased. Multiple influences on QT rate de pendence can be found: not only circadian and gender modulation, but also a ge, heart rate, and HRV interventions.