Diurnal variation of RT dispersion in patients with and without coronary artery disease

QT dispersion defined as interlead QT variability in a 12-lead electrocardi ogram was proposed by Day and associates as a simple method to evaluate the repolarization heterogenicity of the ventricular myocardium. The frequency of onset of myocardial infarction and sudden death has been reported to ha ve a circadian variation, with a peak incidence in the early morning hours. The authors investigated whether there is diurnal variation of QT interval and QT interval dispersion in healthy subjects and in patients with corona ry artery disease. The study population consisted of two groups. Group I co nsisted of 62 subjects without coronary artery disease and group II consist ed of 82 patients with coronary artery disease. Twelve-lead ECG was recorde d for each patient in the morning (between 7 AM and 8 AM), afternoon (betwe en 3 PM and 5 PM) and at night (between 11 PM and 1 AM), On the day after p erformance of coronary angiography. QTc dispersion was significantly higher in patients with coronary artery disease than in healthy subjects in the m orning hours and afternoon (p < 0.001). Although the differences were much prominent in group I than group II, both QTc dispersion of morning and afte rnoon were significantly greater than those at night. There were no statist ically significant differences between group I and group II at nighttime wi th respect to maximum QTc, minimum QTc intervals, and QTc dispersion (p > 0 .05). In conclusion, QT dispersion shows diurnal variation with an increase in the morning hours in both patients with coronary artery disease and sub jects without coronary artery disease. The mechanism of diurnal variation o f QT dispersion in patients with coronary artery disease is quite different from that of healthy subjects.