Beta-blocking agents may improve the survival rate for people at risk for sudden cardiac death, according to an article in the October 29th rapid access issue of Circulation.

The protective mechanism is unclear, said lead author Kristin E. Ellison, M.D., but it is likely to be due to the combined effects of beta-blocking drugs in improving blood flow and reducing blood pressure, heart rate, and frequency of arrhythmias. Sudden cardiac death kills about 250,000 Americans every year. Most cardiac arrests that lead to sudden death are associated with ventricular tachycardia or ventricular fibrillation.

Previously, beta blockers have been shown to reduce the risk of death by 25 to 40 percent in patients who have had a recent myocardial infarction and to reduce sudden cardiac death by as much as 50 percent in patients with a recent myocardial infarction. However, until the current study researchers had not known if beta blockers would have a similar positive effect on patients three or more years after their myocardial infarction or on patients at high risk for sudden death due to arrhythmias.

The American researchers, who were part of the Multicenter UnSustained Tachycardia Trial, analyzed trial data to evaluate the impact of beta blockers on the overall death rate, on death from arrhythmias, and on the need for resuscitation from cardiac arrest.

The prospective trial had tested the effectiveness of electrophysiologic studies. All subjects had a prior myocardial infarction, an ejection fraction less than or equal to 40 percent, and nonsustained ventricular tachycardia during electrophysiologic testing. On average, participants were enrolled 39 weeks after their most recent infarction.

Participants were divided into those with sustained tachycardia and those without it. The first group was randomized to antiarrhythmic therapy or no therapy; a small number received implantable cardioverter defibrillators if they did not respond to antiarrhythmic drugs. The group without sustained tachycardia received no antiarrhythmic therapy and was recorded in a registry.

The analysis on which the current study is based involved review of data on 2,096 patients (702 randomized and 1,394 registry patients) enrolled between November 1990 and October 1996. Of them, 799 patients received beta-blocking drugs---314 in the randomized group and 485 in the registry group. Of patients who did not receive a beta blocker, 388 were in the randomized group and 909 were in the registry.

The authors found that overall death rates for patients treated with beta-blocking drugs were 16 percent at two years and 34 percent at five years, figures significantly lower than the death rates of 27 percent at two years and 50 percent at five years for patients who did not receive beta-blocking drugs.

The life-saving properties of treatment with beta-blocking agents were consistent across the spectrum of study patients, including patients with and without inducible tachycardia. The sole exception was the group of patients with implantable cardioverter defibrillators.

In contrast to the positive effect of treatment with beta-blocking drugs on the overall death rate, treatment did not significantly reduce the incidence of arrhythmic death or cardiac arrest, the study’s primary end points. However, the authors note, “there was a trend toward fewer arrhythmic events and improved survival in those treated with antiarrhythmic drugs in combination with beta blocker therapy compared with antiarrhythmic therapy alone.”

This trend was not seen in patients with implantable cardioverter defibrillators, likely reflecting the “significant impact of [device] therapy on sudden cardiac death and the difficulty in further decreasing event rates,” they added.

The authors noted that patients treated with beta-blocking agents were younger, had higher ejection fractions, higher rates of recent angina, and more recent infarctions. One study limitation was the inability to randomize use of beta-blocking agents because therapy was left to the discretion of individual physicians. Another drawback was that the effects of beta-blocking agents in patients who received antiarrhythmic drugs may be obscured because several of those drugs possess some beta-blocking activity.

Even so, the significant decrease in the overall death rate of the high-risk patients taking beta-blocking drugs and who had not had a recent myocardial infarction combined with previous similar evidence led the authors to conclude “it is appropriate to prescribe these drugs in patients with the characteristics of those enrolled in the [MUSTT] trial.”