Patients with depressed ejection fractions after myocardial infarction are at increased risk for congestive heart failure and ventricular arrhythmia–related sudden death. It has been reported that implanted defibrillators have reduced mortality rates in patients with previous episodes of malignant ventricular arrhythmias. Moss and associates conducted a large, randomized trial that examined the prophylactic use of defibrillators to prevent ventricular arrhythmias and death in patients with myocardial infarction who had ejection fractions below 30 percent.
The study investigators followed 1,232 patients with a previous myocardial infarction from 76 different hospital centers for an average follow-up length of 20 months. Patients were randomly assigned in a 3:2 ratio to receive either defibrillator implantation (742 patients) or conventional medical therapy (490 patients). The large majority of patients had ventricular ectopic beats on screening electrocardiograms. Patients were not required to undergo electrophysiologic screening for inducible arrhythmias before surgery. Of the patients randomized to medical therapy, 4.5 percent later received a defibrillator; the majority of these patients required a defibrillator because of documented malignant ventricular arrhythmia.
The overall death rate was 19.8 percent among patients in the conventional therapy group compared with 14.2 percent among patients who received defibrillators during the study follow-up period. The protection provided by defibrillator placement was similar by age, sex, and severity of depressed ejection fraction. Patients with defibrillators did have an increased incidence of hospitalization for exacerbations of congestive heart failure (19.9 percent versus 14.9 percent in patients receiving conventional therapy). Additional surgical intervention was required in 2.5 percent of defibrillator recipients because of subsequent electrical lead problems or infection.
The authors concluded that prophylactic use of implanted defibrillators in patients with myocardial infarction and depressed ejection fractions was associated with improved mortality rates.
editor's note: The lower mortality rate among patients with implanted defibrillators could be touted as a “30 percent improvement” in relative mortality rates, but the more clinically appropriate statistic is the modest 5.6 percent absolute mortality rate difference. These numbers translate to a “number needed to treat” of about 18. Whether society can afford, or patients would accept, implantation of 18 defibrillators to prevent one death is a question that requires debate beyond the realm of just medical statistics. Identification of patients who are at high risk (e.g., when inducible arrhythmias are demonstrated on electrophysiologic screening) might help target this invasive and costly option to the patients most likely to benefit.—b.z.