The frequency of onset of acute coronary syndromes and sudden cardiac death has been reported to have circadian variations, with a peak incidence in early morning hours. It has also been known that acute ischemia is a potent stimulus to increased dispersion of repolarization and development of malignant arrhythmias. QT dispersion (QTd) is used as an index of heterogenity of the ventricular repolarization and increases in patients with ischemic heart disease. The aim of the study was to investigate diurnal variations of QTd in patient with triple-vessel coronary artery disease (CAD) with and without diabetes mellitus type 2 (DM).
Material and methods: We investigated of 28 patients with stable triple-vessel CAD and 32 patients with similar advancement of changes in coronary circulation with co-existing DM. We excluded patients with prior myocardial infarction, taking oral medications which might alter QT interval and patients in which measurements of QT were difficult to perform or impossible. QTd measurements were taken semi-automatically every hour from 24 hours 12 leads Holter monitoring system (SUPRIMA 12). Measurements were verified independently by three observers.
Results: CAD patients without DM had QTd significantly greater in the morning hours (6 a.m. to 9 a.m.) in comparison with the other times (p < 0.01). The shortest QTd was measured during the night between 10 p.m. and 1 a.m. We did not observed circadian variations of QTd in patients with co-existent DM and values of QTd in this group was significantly greater then in CAD without DM group (p < 0.001).
Conclusions: Our data proved that QTd in patients with CAD had a circadian variation with a peak value in the morning hours shortly after awakening. Patients with DM and CAD had not circadian variation of QTd but QTd values, during whole day and night, were significantly greater then patients without DM.