Background: Up to one half of sudden deaths in the first weeks after myocardial infarction (MI) are caused by ventricular tachyarrhythmias, but antiarrhythmic drugs (except for beta blockers) have not been shown to reduce this risk. Several trials have demonstrated that implantable cardioverter-defibrillators (ICDs) can reduce mortality in patients with sustained ventricular tachyarrhythmias or depressed left ventricular ejection fraction (LVEF) without an arrhythmia. However, current guidelines recommend that an ICD not be implanted for a minimum of 40 days after an acute MI if it will be used primarily to prevent sudden death. Steinbeck and colleagues used the Immediate Risk Stratification Improves Survival trial to examine whether early ICD implantation would improve survival in patients with recent MI when compared with optimal medical therapy.
The Study: Patients were recruited within 31 days of an acute MI, and met at least one of two inclusion criteria: a heart rate of at least 90 beats per minute on the first electrocardiograph after the MI was diagnosed, or an LVEF of 40 percent or less; or nonsustained ventricular tachycardia with a heart rate of at least 150 beats per minute within the first month after the MI. Exclusion criteria included preexisting ventricular arrhythmias or severe heart failure (New York Heart Association class IV).
Patients were randomized to receive an ICD with optimal medical therapy, or optimal medical therapy alone, and were reassessed periodically thereafter. The primary end point was overall mortality between groups, with secondary end points of sudden cardiac death, nonsudden cardiac death, and noncardiac death.
Results: A total of 898 patients were followed for approximately 37 months after MI. Baseline demographics (including discharge medications) were similar between groups, although diabetes and left bundle branch block were slightly more common in the ICD group. No differences in mortality rates were noted between groups at any point during the follow-up period. The ICD group experienced fewer sudden cardiac deaths (hazard ratio [HR] = 0.55), but this was paralleled by an increase in nonsudden cardiac death (HR = 1.92). These findings were similar in patients who met one or both of the inclusion criteria.
Conclusion: Early ICD implantation does not confer a survival benefit over optimal medical therapy in patients who have an acute MI with clinical features placing them at an increased risk of death.