Noninvasive Risk Modeling After Myocardial Infarction*

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Abstract

The aim of this study was to extract and combine non-invasive risk parameters from the signal-averaged electrocardiogram (SAECG) and heart rate variability (HRV) based on 24-hour ambulatory electrocardiography to optimize the prognostic value for arrhythmic events after acute myocardial infarction. A prospective series of 553 men <66 years of age enrolled in the Post-Infarction Late Potential study were analyzed. Within 2 to 4 weeks after acute myocardial infarction, all patients underwent SAECG and 24-hour ambulatory electrocardiography before hospital discharge. During 6 months of follow-up, 25 patients (4.5%) experienced arrhythmic events (sustained ventricular tachycardia, n = 11; ventricular fibrillation, n = 7; sudden cardiac death, n = 7). The predictive power of SAECG and HRV parameters was assessed using a Cox proportional-hazards model. In HRV analysis, the most significant differences between patients with and without arrhythmic events were observed for the beat-to-beat parameter root-mean-square of successive RR differences [RMSSD]): 25.7 ± 16.9 ms in patients with arrhythmic events versus 34.1 ± 18.6 ms in patients free of arrhythmic events (p = 0.004). Time domain analysis of the SAECG showed the QRS duration to be most significantly different in both patient groups: 106.4 ± 18.7 ms (arrhythmic events) versus 95.3 ± 18.7 ms (no arrhythmic events) (p = 0.001). Based on the Cox regression model, RMSSD and QRS duration were demonstrated to be independent significant risk factors (regression coefficient for QRS duration: cq = 0.014 ± 0.006 ms−1, p = 0.014; for RMSSD: cr = −0.041 ± 0.016 ms−1, p = 0.009). Based on the regression coefficients, an analytic risk model was developed describing the arrhythmic risk as a function of QRS duration, RMSSD, and time after infarction. We conclude that the combination of beat-to-beat changes of heart rate measured by RMSSD and QRS duration from the SAECG enhances noninvasive risk stratification after myocardial infarction. (Am J Cardiol 1996;78:627–632)

Section snippets

METHODS

Patient population: This study included 553 patients who participated in the Post-Infarction Late Potential (PILP) study. The PILP study represents a noninterventional study to assess the prognostic value of ventricular late potentials detected by signal-averaging technique.14, 15All patients were admitted to the participating 17 hospitals with suspected acute myocardial infarction. Only male patients aged <66 years who had survived the acute period of myocardial infarction were evaluated for

RESULTS

Study population: In all, 553 patients were included in the analysis. The mean age was 53 ± 8 years (range 22 to 65). Seventy-nine patients (14.3%) had had a previous myocardial infarction. There were 249 patients (45.0%) presenting with anterior wall myocardial infarction. In 301 patients (54.4%), the site of infarction was inferior, and in the remaining 3 patients (0.5%), the site of myocardial infarction remained undefined. In 164 cases (29.7%), intravenous thrombolytic therapy was applied

DISCUSSION

In the present study, the combination of different parameters obtained from 24-hour HRV and SAECG was investigated to create a statistical model for noninvasive risk stratification after myocardial infarction. It is shown that beat-to-beat changes of heart rate together with QRS duration from the SAECG yield the best combination for prediction of serious arrhythmic events during the first 6 months after acute myocardial infarction. Based on these findings, a continuous risk model was developed

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    *

    This study was supported in part by Deutsche Forschungsgemeinschaft (DFG), Förderkennzeichen Br 759/2–2, Bonn; Bundesministerium für Forschung und Technologie (BMFT), Förderkennzeichen HKP314, Bonn; Deutscher Akademischer Austauschdienst (DAAD), Bonn, Germany; Academy of Finland (SA), Helsinki, Finland; European Union Human Capital and Mobility Programme (BIRCH-European Large Scale Facility in Biomagnetic Research at Helsinki University of Technology), Brussels, Belgium; and Franz-Loogen-Stiftung for Cardiological Research, Düsseldorf, Germany

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