Circadian variations of QTc dispersion: Is it a clue to morning increase of sudden cardiac death?

Background: Several studies related to cardiac events including sudden deat h have shown a peak incidence in the early morning hours. It has also been known that acute ischemia is a potent stimulus to increased dispersion of r epolarization and development of malignant arrhythmias. Hypothesis: The purpose of the present study was to investigate diurnal var iations of corrected QT dispersion (QTcD) in patients with coronary artery disease (CAD) (Group 1) compared with controls with normal coronary angiogr ams (Group 2). Methods: We investigated a total of 110 patients who had been referred for coronary angiography, of whom 62 (42 men, 20 women; age 55 +/- 7 years) had double- or triple vessel disease, and of whom 48 (31 men, 17 women; age 54 +/- 9 years) had normal coronary angiograms. QTcD measurements were calcul ated from a 12-lead resting electrocardiogram (ECG) during sinus rhythm. Th ese ECGs were obtained for each patient in the morning, at noon, in the eve ning, and at night on the day after performance of coronary angiography. QT cD was significantly greater in patients with abnormal coronary angiograms (Group 1) than in patients with angiographically documented normal coronary arteries (Group 2). This difference appeared to be more prominent in the m orning hours (p < 0.001) than at other times. QTcD in the evening and night hours was not statistically different (p > 0.05) between both groups. We a lso compared intragroup QTcD values: QTcD values were significantly increas ed in the morning hours and were more prominent in Group 1 than in Group 2. Conclusions: Our data suggest that QTcD has a circadian variation with an i ncrease in the morning hours, especially in patients with coronary artery d isease. This finding was thought to be an explanation for the role played b y sympathetic nervous system in the occurrence of acute cardiac events and sudden death during these hours.