title: Time-frequency mapping of the QRS complex in normal subjects and in postmyocardial infarction patients.
abstract: The effect of myocardial infarction upon the frequency content of the QRS complex was analyzed. Three bipolar signal-averaged surface electrograms, recorded during the early (10-15 days) and late (6 months) chronic phases of myocardial infarction, were analyzed in 61 patients and 11 healthy subjects. All patients were free of ventricular arrhythmia during 6 months of follow-up examinations. Time-frequency analysis of the QRS complex was based on the modified Wigner distribution, which is well suited to examine nonstationary character of data. Standard time-domain analysis for the presence of late potentials was used for comparison. High-frequency (> or = 90 Hz) components, separable from the dominant low-frequency components (< 90 Hz), were found in all groups. They were present throughout the QRS complex and were peaking in its middle portion. The high-frequency components were found significantly higher in postinfarction patients in both early (P < .007) and late chronic stage myocardial infarction (P < .05) compared to healthy subjects. Patients who tested positive for late potentials (24%) also had elevated high-frequency components; however, a comparable increase was also observed in late potential negative patients. Furthermore, the high-frequency component increase occurred in all patients earlier in the QRS than in its terminal 40 ms, where late potentials are traditionally evaluated. It is concluded that high-frequency components are an integral part of the QRS complex under physiologic conditions and persist in variable amount throughout its duration. The high-frequency components are increased in patients after myocardial infarction not associated with ventricular arrhythmia, and their elevation is not limited to the terminal QRS complex.
authors.affiliation: Research Center, Hôpital du Sacré-Coeur de Montréal, Quebec, Canada.
authors.forename: P
authors.initials: P
authors.lastname: Novak
authors.forename: Z
authors.initials: Z
authors.lastname: Li
authors.forename: V
authors.initials: V
authors.lastname: Novak
authors.forename: R
authors.initials: R
authors.lastname: Hatala
mesh_terms: D000328:Adult; D004562:Electrocardiography / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D005583:Fourier Analysis; D006329:Heart Conduction System / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009200:Myocardial Contraction / Q000502:physiology; D009203:Myocardial Infarction / Q000175:diagnosis / Q000453:epidemiology / Q000503:physiopathology*; D010865:Pilot Projects; D012815:Signal Processing, Computer-Assisted; D013997:Time Factors