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

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Signal-averaged electrocardiography (SAECG) in patients after myocardial infarction (MI) is widely used to identify patients at risk for ventricular tachycardia (VT) and sudden cardiac death (SCD). It is believed that ventricular late potentials when detected after day 5 after MI are relatively stable and carry the most significant relation to subsequent arrhythmic events. This study sought to determine if ventricular late potentials in patients after MI exhibit variability when recordings were made 10 to 12 hours apart on day 7 and to assess the clinical significance of this variability. 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 patients also had recordings 30 to 40 minutes apart to determine the 95% confidence interval of variability of each parameter of SAECG. The data were analyzed with the criteria of the American College of Cardiology policy statement. A prospective analysis for the clinical end points of VT and SCD was carried 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 parameters 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 SAECG on both occasions. Diabetes mellitus was an independent predictor of the variability of late potentials (P <.0001). A prospective analysis for the clinical end points of VT and SCD showed that the event rate was significantly higher in group 1 than in group 2 (P <.019). To improve the positive predictive value of SAECG in patients after 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.