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CLINICAL STUDIES

Improved diagnostic value of combined time and frequency domain analysis of the signal-averaged electrocardiogram after myocardial infarction

Rafael Vázquez, MD^*, Edward B. Caref, PhD, Francisco Torres, MD^*, Margarita Reina, RN^*, Aurora Espina, MD^* and Nabil El-Sherif, MD

^* Cardiology Unit of Valme University Hospital, Seville, Spain
Cardiology Divisions of the State University of New York Health Science and Veterans Administration Medical Centers, Brooklyn, New York, USA

Manuscript received December 8, 1997; revised manuscript received August 27, 1998, accepted October 15, 1998.

Reprint requests and correspondence: Nabil El-Sherif, MD, Cardiology Section (111A), VA Medical Center, 800 Poly Place, Brooklyn, New York 11209
el-sherif.nabil{at}brooklyn.va.gov

Background

Time domain analysis (TD) of the signal-averaged electrocardiogram (SAECG) presents a higher incidence of false positives in inferior myocardial infarction (MI), whereas spectral turbulence analysis (STA) suffers from a higher incidence of false positives in anterior MI. We investigated the hypothesis that a combined TD and STA (TD+STA) analysis of the SAECG could improve its predictive accuracy for major arrhythmic events (MAE) after MI.

Methods

Signal-averaged electrocardiograms were prospectively recorded 10.1 ± 2.6 days after acute MI in 602 patients. Time domain analysis and STA were performed using standard parameters and criteria for abnormality. For the combined TD+STA model, stepwise discriminant analysis was utilized to optimize prediction of MAE. Receiver operating characteristic curves were utilized to optimize cutoff values for each SAECG parameter separately, and also for the combined TD+STA model.

Results

During a one-year follow-up period, 38 patients had MAE: 14 sustained ventricular tachycardia, 2 resuscitated ventricular fibrillation and 22 sudden cardiac deaths. The total predictive accuracy of combined TD+STA (89.9%) was significantly higher than TD (75.1%) or STA (77.6%). The negative predictive accuracy of all three analyses was high (98%). The positive predictive accuracy of TD (19.6%) or STA (18.3%) was quite low, and significantly improved to 35.8% by combined TD+STA analysis. The positive predictive accuracy of TD+STA improved to 51.2% in patients with left ventricular ejection fraction <40%.

Conclusions

Combined TD+STA analysis of the SAECG significantly improves its prognostic ability for MAE in post-MI patients compared with TD or STA analyzed separately.

Abbreviations and Acronyms   CI = confidence interval   ISCM = interslice correlation mean   ISCSD = interslice correlation standard deviation   IVCD = intraventricular conduction defects   LAS40 = duration of terminal low amplitude signals <40 µV   LBBB = left bundle branch block   LSCR = low slice correlation ratio   MAE = major arrhythmic events   MI = myocardial infarction   QRSD = total filtered QRS duration   RBBB = right bundle branch block   RMS40 = root mean square voltage of the last 40 ms of the filtered QRS   ROC = receiver operating characteristic   SAECG = signal-averaged electrocardiogram   SE = spectral entropy   STA = spectral turbulence analysis   TD = time domain analysis

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