Role of heart rate variability in patients at high risk of arrhythmic events after acute myocardial infarction

In the present study we evaluated a possible combined use of HR variability and other recognised risk variables for assessing the arrhythmic propensity in a group of patients surviving an AMI. Among 243 consecutive patients admitted to our Institute for cardiac rehabilitation from September 1989 to September 1991, 53 patients were eligible for the present study because of the presence of at least 2 of the following risk variables: left ventricular ejection fraction <0.40 on 2D echocardiogram, ventricular late potentials on signal-averaged ECG and Lown 4A-4B ventricular ectopic beats on 48 h Holter monitoring. Among these patients with an higher risk of late arrhythmic events, HR variability, expressed as SDRR, and the average RR interval of normal cycles were analysed in 46 patients (mean age 58 +/- 8 years) in the first 24 h of every Holter recording; 7 patients were excluded from the study because of diabetes or bad quality recording. At a mean follow-up of 16 +/- 8 months from AMI, 12/46 patients (26%) showed a late arrhythmic event. Low left ventricular ejection fraction (<0.40) (12/12 vs 19/34; p <.05), left ventricular dyskinesia (9/12 vs 9/34; p <.01), SDRR (80 +/- 25 vs 107 +/- 30 ms; p <.01), SDRR <100 ms (11/12 vs 13/34; p <.01) and the average RR interval of normal cycles (828 +/- 67 vs 896 +/- 109 ms; p <.05) were significantly related to late arrhythmic events. The relative risk for late arrhythmic events of SDRR <100 ms was 17.8; sensitivity, specificity, positive and negative predictive value were 92%, 62%, 46% and 95% respectively. The stepwise logistic-regression analysis showed SDRR (p <.01), left ventricular dyskinesia (p <.05) and low left ventricular ejection fraction (p <.05) as independent predictors of late arrhythmic events. In conclusion an altered autonomic balance could play a very important role in triggering malignant ventricular arrhythmias after AMI. Measurement of HR variability in time domain is a simple and useful tool for assessing the arrhythmic propensity of patients with an arrhythmogenic substrate and an higher risk of events.