Time Course and Prognostic Implications of QT Interval in Patients with Coronary Artery Disease Undergoing Coronary Bypass Surgery

Abstract

The aim of the present study was to determine the prognostic implication of preoperative QT interval in relation to overall death and sudden cardiac death after coronary bypass surgery and to investigate the course of QT interval after surgery. Of 812 consecutive patients undergoing isolated off-pump coronary surgery, 656 were retrospectively analyzed after excluding the 48 patients who were taking QT prolonging drugs and the 108 patients who had any of the following electrocardiographic findings: atrial fibrillation, pacemaker, QRS of >120 milliseconds, bundle branch block. QT intervals were corrected for heart rate (QTc) using Bazett's formula. Prolonged QTc was defined as QTc of ≥450 milliseconds in men (n = 144) and ≥470 milliseconds in women (n = 36). The 5-year cumulative rate of sudden cardiac death in patients with prolonged QTc was 25% against 4% for those with normal QTc (P = 0.01). The risk-adjusted hazard ratio (95% confidence interval) for the association between preoperative QTc and overall death was 1.47 (1.21-1.74) per 1-SD increase in QTc; and 2.38 (1.50-3.45) for prolonged versus normal QT. For sudden cardiac death, the respective ratios were 1.63 (1.32-2.25) per 1-SD increase in QTc; and 3.32 (2.14-4.23). QTc interval did not change during the first year after surgery, but increased significantly during the subsequent years. Patients with prolonged QTc before surgery had consistently longer QTc even after revascularization than those with normal QTc. Preoperative QT interval was an independent predictor of overall death and sudden cardiac death after isolated coronary bypass surgery.