Decision to implant a cardioverter defibrillator after myocardial infarction: The role of ejection fraction v. other risk factor markers

Background. The Multicenter Automatic Defibrillator Implantation Trial showed that in post-myocardial infarction patients with a left ventricular ejection fraction (EF) ≤ 0.30, an implantable cardioverter defibrillator (ICD) resulted in a 31% relative reduction in the risk of death when compared with a conventional therapy group. Whether further refinement in risk estimation could be achieved with additional clinical testing to qualify patients for primary prevention with ICDs remains problematic. Methods. The authors analyzed Cardiac Arrhythmia Suppression Trial registry data to estimate sensitivity and specificity of EF, ventricular premature frequency, and nonsustained ventricular tachycardia for predicting death. They combined the results with similar data from the literature and used summarizing receiver operating characteristic (meta-ROC) curves to estimate overall operational values for sensitivity and specificity for each clinical test. They estimated aggregate values for prior probability to project risks when tests were used singly and in combination. Results. The authors used arrhythmia markers and heart rate variability to further stratify low-EF patients (prior risk = 20.3%); proportionately, 20.4% were predicted at high risk (>30%) and 40.5% at low risk (<10%). When heart rate variability is normal, those at high risk reduced proportionately to 9.2%, and those at low risk increased to 51.6%. Conclusions. The combined use of noninvasive markers for arrhythmia substrate and altered autonomic tone can improve risk stratification in low EF without optimal beta-block therapy, whereas for those with optimal beta-block therapy, markers for arrhythmia substrate alone work. Ancillary use of electrophysiologic stimulation can improve results.