Prognostic role of heart rate variability in patients with a recent acute myocardial infarction

A low heart rate variability (HRV) has been shown to be a powerful predicto r of cardiac events in patients surviving an acute myocardial infarction (M I), but it is not clear yet which among the HRV parameters has the best pre dictive value. Time domain and frequency domain HRV was assessed on 24-hour predischarge Halter recording of 239 patients with a recent MI. Patients w ere followed up for 6 to 54 months (median 28), during which 26 deaths (11% ) occurred, 19 of which were cardiac in origin and 12 were sudden. Most HRV s did not show any difference between patients with or without mortality en d points, but the average low-frequency and low-frequency/high-frequency ra tio was lower in patients with events. However, when dichotomized according to cut points that maximized the risk of sudden death, several HRVs were s ignificantly predictive of clinical end points. Overall, the mean of the st andard deviations of all RR intervals for all 5-minute segments and the sta ndard deviation of the mean RR intervals for all 5-minute segments were the rime domain variables most significantly associated with mortality endpoin ts, whereas very low frequency was the most predictive frequency domain var iable. Compared with the best time domain variables, very low frequency sho wed a better sensitivity (0.27 to 0.42 vs 0.19 to 0.33) for end paints with only a small loss in specificity (0.92 vs 0.96). On multivariate Cox propo rtional analysis, a left ventricular ejection fraction <40% and a number of ventricular premature beats greater than or equal to 10/hour were the most powerful independent predictors for all end points, whereas no HRV was ind ependently associated with the events. A low frequency/high frequency ratio <1.05 only had a borderline association with sudden death (RR = 2.86, p = 0.076) Our data show a strong association between HRV and mortality in pati ents surviving a recent MI, with a slight better sensitivity;of frequency d omain analysis. In our study, however, HRV did not add independent prognost ic information to more classic prognostic variables (e.g., left ventricular function and ventricular arrhythmias). (C) 1998 by Excerpta Medica, Inc.