Ventricular electrical instability: a predictor of death after myocardial infarction.

The results of a prospective study of ventricular electrical instability after myocardial infarction (MI) are presented. Ventricular electrical stability was assessed using a standardized protocol of programmed stimulation in 165 hemodynamically stable patients 6 to 28 days after acute MI. Ventricular electrical instability was defined as induction at programmed stimulation of ventricular fibrillation (VF) or ventricular tachycardia (VT) lasting at least 10 seconds. Of 165 MI survivors, 38 (23%) had ventricular electrical instability. No significant differences were noted between stable and unstable patients in terms of coronary prognostic index, elevation of serum creatine phosphokinase, coronary anatomy, site of MI, or frequency of VT within 48 hours of MI. The mean follow-up period was 8 months (range 0 to 12). There were 7 deaths in stable patients (5 from cardiogenic shock, 1 from septicemia, and 1 unwitnessed) and 10 deaths in unstable patients (8 instantaneous, 1 from cardiogenic shock, and 1 unwitnessed) during the subsequent year. In addition, 2 of 127 stable patients and 4 of 38 unstable patients had spontaneous VT from which they were satisfactorily resuscitated. Thus, the sensitivity of ventricular electrical instability as a predictor of instantaneous death or spontaneous VT was 86% and the specificity 83%. The predictive accuracy of the absence of ventricular electrical instability as an indicator for the absence of instantaneous death or spontaneous VT was 98%. The predictive accuracy of the presence of ventricular electrical instability as a predictor of instantaneous death or spontaneous VT was 32%. Thus, patients with ventricular electrical instability after MI have a high risk of instantaneous death within 1 year; patients without ventricular electrical instability after MI have a low risk of instantaneous death within 1 year; prospective studies of antiarrhythmic therapy and measures to prevent reinfarction and optimize left ventricular performance are required to determine whether instantaneous death can be prevented in unstable patients; and therapy to prevent reinfarction and optimize left ventricular performance may offer the best chance to improve prognosis in stable patients.