Predicting mortality after myocardial infarction from the response of RR variability to antiarrhythmic drug therapy

OBJECTIVES: This study was designed to test the hypothesis that antiarrhythmic drugs that decrease RR variability will predict all-cause mortality during follow-up after myocardial infarction. BACKGROUND: RR variability, a noninvasive indicator of autonomic nervous system activity, predicts death after acute myocardial infarction independently of other risk predictors and changes substantially in response to some drugs. A previous study in patients with chronic heart disease and frequent ventricular premature complexes reported that flecainide decreased vagal modulation of RR intervals but amiodarone did not. The investigators of that study speculated that changes in RR variability during antiarrhythmic drug therapy predict an increased mortality rate during long-term drug treatment. To explore this hypothesis further, we compared the effects of encainide and flecainide, which increase long-term mortality substantially, on RR variability with the effects of placebo and moricizine, which have no significant effect on mortality during long-term treatment of unsustained ventricular arrhythmias after myocardial infarction. METHODS: The 24-h power spectral density was computed from the baseline electrocardiographic recordings and drug evaluation tapes, and six frequency domain measures of RR variability were calculated: ultra-low frequency ( 2.0, adjusted p < 0.05). The antiarrhythmic drug-induced change in measures of RR variability was not a significant predictor of all-cause mortality during a year of follow-up after myocardial infarction. CONCLUSIONS: Encainide, flecainide and moricizine all caused a decrease in RR variability in patients studied approximately 1 month after acute myocardial infarction. Encainide and flecainide caused a significant increase in mortality rates; placebo and moricizine did not. Baseline measurements of RR variability also predicted all-cause mortality after myocardial infarction. The decrease in RR variability produced by the three antiarrhythmic drugs did not predict mortality during follow-up.