DEFINITION OF THE BEST PREDICTION CRITERIA OF THE TIME-DOMAIN SIGNAL-AVERAGED ELECTROCARDIOGRAM FOR SERIOUS ARRHYTHMIC EVENTS IN THE POSTINFARCTION PERIOD

Objectives. The goal of this study was to establish guidelines for the prognostic use of the time domain signal-averaged electrocardiogram ( ECG) after myocardial infarction. Background. Previous studies of the prognostic use of the signal-averaged ECG in postinfarction patients h ad one or more of the following limitations: a small study group, empi ric definition of an abnormal recording and possible bias in the selec tion of high risk groups or classification of arrhythmic events, or bo th. To correct for these limitations, a substudy was conducted in conj unction with the Cardiac Arrhythmia Suppression Trial (CAST). Methods. Ten centers recruited 1,211 patients with acute myocardial infarction without application of the ejection fraction or Holter criteria restr ictions of the main CAST protocol. Several clinical variables, ventric ular arrhythmias on the Holter recording, ejection fraction and six si gnal-averaged ECG variables were analyzed. Patients with bundle branch block were excluded from the analysis, and the remaining 1,158 were f ollowed for up to 1 year after infarction. The classification of arrhy thmic events was reviewed independently by the CAST Events Committee. Results. During an average (+/-SD) follow-up of 10.3 +/- 3.2 months, 4 5 patients had a serious arrhythmic event (nonfatal ventricular tachyc ardia or sudden cardiac arrhythmic death). A Cox regression analysis w ith only the six signal-averaged ECG variables indicated that the filt ered QRS duration at 40 Hz greater than or equal to 120 ms (QRSD-40 Hz ) at a cutpoint greater than or equal to 120 ms was the most predictiv e criterion of arrhythmic events. In a regression analysis that includ ed all clinical, Holter and ejection fraction variables, a QRSD-40 Hz greater than or equal to 120 ms was the most significant predictor (p < 0.0001). The positive, negative and total predictive accuracy and od ds ratio for QRSD-40 Hz greater than or equal to 120 ms were 17%, 98%, 88% and 8.4, respectively, and improved to 32%, 97%, 94% and 16.7, re spectively, after combination with ejection fraction less than or equa l to 40% and complex ventricular arrhythmias on the Holter recording. Conclusions. The signal-averaged ECG predicts serious arrhythmic event s in the first year after infarction better than do clinical, ejection fraction and ventricular arrhythmia variables, and QRSD-40 Hz greater than or equal to 120 ms provides the best predictive criterion in thi s clinical setting.