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 microV 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 (less than 20 microV) in 21 of 50 patients (58%), and the signal-averaged vector complex was abnormal (greater than 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 ba...