Influence of coronary artery bypass grafting on QT dispersion

Abstract

Background: Abnormal dispersion of the QT interval (QTd), measured as the interlead variability of QT, reflects an inhomogeneity of ventricular action potentials. In this study we observed both short- and long-term influences of coronary artery bypass grafting (CABG) on rest and exercise QTd in 64 male patients, having a mean age of 54+/-10 years, with coronary heart disease.

Material/methods: QTd was measured as the difference between QT maximum and minimum from 12 leads on an averaged ECG (25 mm/s). QTd and QTdc were measured at rest and at peak exercise during symptom-limited treadmill exercise (ET), which was performed before, 6 months after, and 2 years after CABG.

Results: There was a significant reduction in rest QTd from before CABG to 6 months and 2 years after (60+/-20 ms vs. 43+/-14 ms and 45+/-13 ms, respectively; p<0.001). Similarly, there was a significant reduction in peak QTd from before CABG to 6 months and 2 years after (66+/-22 ms vs. 38+/-11 ms and 36+/-11 ms, respectively; p<0.001). Two years after CABG, 17 patients had a recurrence of angina and ET provoked chest pain and/or >2 mm ST depression. The resting values did not distinguish patients with ischemia from nonischemic ones. In patients with ischemia, ET provoked an increase in QTdc.

Conclusions: Rest and exercise QTd is significantly reduced after CABG. It seems that the measurement of QT dispersion during ET can be helpful in distinguishing patients with a recurrence of ischemia.