Circadian and Gender Effects on Repolarization in Healthy Adults: A Study Using Harmonic Regression Analysis

Background: Sudden cardiac death and myocardial infarction have a circadian variation with a peak incidence in the early morning hours. Increased dispersion of repolarization facilitates the development of conduction delay necessary to induce sustained arrhythmia. Both QT‐dispersion and T‐wave peak to T‐wave end (TpTe) have been proposed as markers of dispersion of myocardial repolarization. Methods: Forty healthy adults (20 women), age 35–67 years old, with normal EKGs, echocardiograms, stress tests, and tilt‐table tests were analyzed during a 27‐hour hospital stay. EKGs were done at eight different time points. QT‐intervals, QT‐dispersion, and TpTe were measured at each time point. Harmonic regression was used to model circadian periodicity, P < 0.05 was considered significant. Results: The composite QT‐interval was longer in women than in men (416 ± 17 msec vs 411 ± 20 msec, respectively, P = 0.006). The QT‐dispersion among all leads was greater in men than women (37 ± 13 msec vs 30 ± 11 msec, respectively, P < 0.0001); a similar difference was found in the precordial leads. Harmonic regression showed that QT‐dispersion had a significant circadian variation, primarily in men. In men, the maximum QT‐dispersion occurred at 6 AM (45 ± 15 msec). TpTe also had a significant circadian variation that was not affected by gender in the majority of leads. Conclusions: A circadian variation exists in the dispersion of myocardial repolarization, as measured by both TpTe and QT‐dispersion. Men and women have a different circadian variation pattern. Further studies regarding the mechanisms and clinical implications are needed. Ann Noninvasive Electrocardiol 2010;15(1):3–10