Quantitative analysis of the high-frequency components of the signal-averaged QRS complex in patients with acute myocardial infarction: A prospective study

We performed a prospective study of the high-frequency components of the terminal portion of the QRS complex in 50 patients with acute myocardial infarction (AMI) (mean age 63 ± 10 years) within 3.25 ± 2.45 days of the acute event. Signal averaging (400 beats) at a filter setting of 80 to 300 Hz was performed and the duration of the low-amplitude signals of less than 40 μV in the terminal portion of the QRS, the root-mean-square (RMS) voltage of the terminal 40 msec of the QRS complex, and the total duration of the signal-averaged QRS vector complex were measured. The low-amplitude signals were abnormally prolonged in 22 of 50 patients (44%); the RMS-V was abnormal (<20 μV) in 21 of 50 patients (58%), and the signal-averaged vector complex was abnormal (>120 msec) in 15 of 46 patients (33%) without bundle branch block. There was no significant correlation, between any of the signal-averaged parameters and site of AMI or total creatine kinase (CK) and CK-MB values. On the basis of the occurrence of spontaneous ventricular tachycardia in the acute and postcoronary care phase of AMI, the patients were divided into two groups. Group I consisted of 31 patients (62%) who had no documented ventricular tachycardia and group II consisted of 19 patients (38%) who had one or more runs of ventricular tachycardia. Fourteen of the 19 patients in group II (73.6%) had nonsustained ventricular tachycardia and five patients (26.3%) suffered sustained ventricular tachycardia/ventricular fibrillation or sudden death. The low-amplitude signals and the signal-averaged QRS complex duration were significantly longer in group II than group I. The RMS voltage was significantly lower in group II than group I. In addition, in five of the patients (10%) who had sustained ventricular tachycardia/fibrillation and/or sudden death the low-amplitude signals were 50 msec or greater and the RMS voltage was 13 μV or less; the signal-averaged QRS vector complex was greater than 120 msec in four of these patients. We conclude the following: (1) Abnormal signal-averaged parameters are seen in 33% to 58% of patients with AMI. (2) There is no correlation between any of the signal-averaged parameters and site of AMI or CK and CK-MB values. (3) Low-amplitude signals and the duration of the signal-averaged QRS complex are significantly longer and the RMS voltage significantly lower in patients with AMI who had spontaneous ventricular tachycardia in the acute and postcoronary care phase of AMI. (4) Signal-averaged parameters may be valuable in predicting arrhythmic events in patients with AMI.