Elevated temporal lability of myocardial repolarization after coronary artery bypass grafting

Introduction

Ventricular arrhythmias are uncommon after coronary artery bypass grafting (CABG), but the incidence and mortality are high in certain subsets of patients during the early recovery after surgery. Elevated temporal lability of myocardial repolarization has been associated with sudden cardiac death. The aim of the current study was to explore temporal variability of myocardial repolarization during both early and longtime follow-up after CABG.

Methods and Results

Patients (n = 61) who had undergone CABG and healthy subjects (HS, n = 33) were examined. Electrocardiogram and beat-to-beat blood pressure were recorded at 5 weeks and 5 months after surgery. The QT variability index (QTVI) was calculated as the log ratio between the temporal variabilities of the QT and RR intervals. The QTVI and QT variances were elevated by 40% and 44%, whereas RR variances were reduced by 40% among patients 5 weeks after CABG compared to HS (−0.90 ± 0.59, 29 ± 30, and 1223 ± 1895 ms² vs −1.50 ± 0.29, 15 ± 16, and 2200 ± 2877 ms² for HS; P < .01 for all). The QTVI and QT variances decreased by 38% and 31% between 5 weeks and 5 months after CABG, whereas the RR variances increased by 51% (P < .01 for all). The QTVI values remained elevated among patients compared to HS at 5 months after CABG (P < .01), whereas QT and RR variances did not differ.

Conclusion

Elevated temporal lability of myocardial repolarization prevails particularly during the early recovery phase after CABG and may reflect increased susceptibility to ventricular arrhythmia.