Abstract

Women have a slower cardiac repolarization than men, which manifests as longer heart rate corrected QT interval (QTc) on the ECG. This study was undertaken to identify cyclical variations of QTc and to detect whether it can further be modulated by handgrip exercise. ECG changes were recorded before and after handgrip exercise during different phases of menstrual cycle in 30 healthy women (25-40 yrs) with a regular menstrual cycle. The different menstrual cycle phases were assigned on the basis of dates and confirmed by plasma levels of estrogen and progesterone. Daily basal body temperature was recorded to confirm the ovulatory phase. ECG parameters (in lead II) were recorded before and immediately after release of handgrip. During the menstrual phase, the basal RR interval was 0.765 ± 0.03 sec and after handgrip exercise, it increased to 0.829 ± 0.02 sec (p < 0.05). The QTc interval was maximal in the menstrual phase (0.44 ± 0.007). There was a significant decrease in QTc interval in the menstrual phase (0.41 ± 0.009 sec, p < 0.05) after handgrip exercise. This study confirms the cyclic variation of the QTc interval. The prolonged QTc interval during the menstrual phase is likely to produce arrhythmias if women are exposed to agents which further prolong the refractory period. A fall in the QTc interval was seen after handgrip exercise during the menstrual phase, females may be advised to engage themselves in isometric activities so as to decrease their susceptibility to arrhythmias.

Keywords: Electrocardiogram, handgrip exercise, menstrual cycle, ovarian sex steroids