Clinical significance of variability of ventricular late potentials detected before discharge in patients after myocardial infarction

Background Signal-averaged electrocardiography (SAECG) in patients after my ocardial infarction (MI) is widely used to identify patients at risk for ve ntricular tachycardia (VT) and sudden cardiac death (SCD). It is believed t hat ventricular late potentials when detected after day 5 after MI are rela tively stable and carry the most significant relation to subsequent arrhyth mic events. This study sought to determine if ventricular late potentials i n patients after MI exhibit variability when recordings were mode 10 to 12 hours apart on day 7 and to assess the clinical significance of this variab ility. Methods and Results SAECG was recorded in 261 patients on the 7th day after MI at 7 to 10 AM (morning) and 6 to 8 PM (evening). Forty of these patient s also had recordings 30 to 40 minutes apart to determine the 95% confidenc e interval of variability of each parameter of SAECG. The data were analyze d with the criteria of the American College of Cardiology policy statement. A prospective analysis for the clinical end points of VT and SCD was carri ed out for a period of 1 year. We identified 3 groups of patients. Group 1 (54, 20.7%) had consistently positive SAECG by at least 2 abnormal paramete rs in both morning and evening. Group 2 (37, 14.2%) had positive SAECG at 1 time only, either morning or evening. Group 3 (170, 65.1%) had negative SA ECG on both occasions. Diabetes mellitus was an independent predictor of th e variability of late potentials (P < .0001). A prospective analysis for th e clinical end points of VT and SCD showed that the event rate was signific antly higher in group 1 than in group 2 (P < .019). Conclusions To improve the positive predictive value of SAECG in patients o ffer MI, we advise that all positive tests be repeated 10 to 12 hours later , especially in patients with diabetes mellitus. Such testing will identify patients with consistently positive SAECG who appear to be at the highest risk for VT and SCD.