Reflex versus tonic vagal activity as a prognostic parameter in patients with sustained ventricular tachycardia or ventricular fibrillation.

Abstract

BACKGROUND The autonomic nervous system has been demonstrated to play a decisive role in the genesis of sudden cardiac death. The loss of protective vagal reflexes, in particular, appears to be associated with an increased incidence of malignant ventricular tachyarrhythmias. Two clinically applicable methods for assessment of cardiac autonomic control have been developed: determination of heart rate variability and evaluation of baroreflex sensitivity. METHODS AND RESULTS To compare the potential predictive value of both methods, two groups of patients were studied. Group 1 comprised 14 postinfarction patients who had experienced at least one episode of ventricular fibrillation or sustained ventricular tachycardia and who were studied after this event. Group 2 consisted of 14 postinfarction patients without tachyarrhythmic events after their infarct. Both groups were carefully matched with respect to age, sex, infarct location, extent of coronary artery disease, left ventricular ejection fraction, blood pressure, and heart rate at rest. Heart rate variability was assessed from 24-hour Holter recordings, and baroreflex sensitivity was determined by means of the phenylephrine method. Indices of heart rate variability were not significantly different between the two groups (SD of the mean RR interval, 84 +/- 30 milliseconds versus 103 +/- 20 milliseconds; proportion of adjacent RR intervals > 50 milliseconds different, 2.8 +/- 3.2% versus 5.0 +/- 4.1% in group 1 versus 2). Baroreflex sensitivity, however, showed a striking difference: Group 1 patients had a mean value of 1.75 +/- 1.63 ms/mm Hg compared with 9.17 +/- 5.40 ms/mm Hg in group 2 (P = .0002). Eleven of 14 group 1 patients had a baroreflex sensitivity < or = 3.0 ms/mm Hg. By contrast, only 1 of 14 group 2 patients had such a depressed value. CONCLUSIONS The results of this study indicate that postmyocardial infarction patients who develop life-threatening ventricular tachyarrhythmias, compared with carefully matched postinfarction patients without major arrhythmic episodes, differ strikingly in terms of baroreflex sensitivity but not in terms of heart rate variability. This finding may have implications for the risk stratification of postinfarction patients and may lead to a differential therapeutic strategy based on autonomic testing.