Short-term effect of coronary artery bypass grafting on the signal-averaged electrocardiogram

Ventricular late potentials at the end of the QRS can be detected on the body surface during sinus rhythm by recording a signal-averaged electrocardiogram (SAECG). In patients with coronary artery disease, these late potentials have been shown to be markers for spontaneous or inducible ventricular tachycardia, or both. The short-term (before and 10 ± 4 days after coronary revascularization) influence of coronary artery bypass grafting (CABG) on the quantitative SAECG variables was studied in 40 patients with chronic coronary artery disease. Twentyfive of these patients had a previous myocardial infarction. In the 15 patients without previous myocardial infarction, no abnormal SAECG indexes were recorded before CABG and no change in the quantitative SAECG variables was observed after surgery. In the patients with a previous myocardial infarction, 7 (28%) had a late potential before CABG. After CABG, 5 (71%) patients remained late potentialpositive, whereas the other 2 (29%) lost their late potential. The mean values of their SAECG variables improved after coronary revascularization. In the entire group of postmyocardial infarction patients, the high-frequency QRS duration had shortened (p < 0.01) after CABG (the other SAECG indexes did not change). The postoperative arrhythmic complications (transient atrial fibrillation, new onset of ventricular couplets) tended to be more frequent in the postmyocardial infarction group and in patients with late potentials. Our findings suggest that the reported increase in ventricular arrhythmias after CABG is probably not related to a change in the arrhythmogenic substrate for ventricular reentry but is associated with changes in the arrhythmogenic milieu.