Early assessment of heart rate variability is predictive of in-hospital death and major complications after acute myocardial infarction

Background: Depressed heart rate variability at acute myocardial infarction discharge is associated with poor long-term prognosis. However, its early (<48 h) predictive value has not been extensively investigated. Aim of this Multicenter Italian Study was to investigate, during acute myocardial infarction, in-hospital prognostic value of heart rate variability and its short-term evolution. Methods: Twenty-four hour ECG monitoring was prospectively obtained on admission in 413 patients with new-onset acute myocardial infarction and repeated in 349 at discharge. Heart rate variability statistical and frequency domain indices, peak creatine kinase, echocardiographic wall motion score index and risk factors were obtained. The occurrence of cardiac death and resuscitated ventricular fibrillation were the primary end-points; cardiogenic shock, ventricular tachycardia, post-infarction angina and heart failure the secondary end-points. Results: At admission, a marked reduction in heart rate variability indices was evident. Nine patients died during hospitalization and 13 were resuscitated from ventricular fibrillation. Secondary endpoints occurred in other 91 patients. At univariate analysis, low frequencies (LF), mean time interval between consecutive heart beats (RR), wall motion score index and family history of ischemic heart disease were predictive of combined primary and secondary end-points. At multivariate analysis, only LF and family history were predictive with a relative risk of 2.01 and 1.84, respectively (P<0.003). In survivors, heart rate variability indices significantly increased during hospitalization, still remaining below reference values. Conclusions: A depressed heart rate variability was present in the early phase of infarction and improved at discharge. LF power was an independent predictor of the combined unfavorable short-term events.