Heart rate variability in acute myocardial infarction and its association with infarct site and clinical course

Abstract

Heart rate (HR) variability is now recognized as an important independent prognostic factor after an acute myocardial infarction, in addition to other traditional measures (e.g., left ventricular dysfunction, positive exercise test results and ventricular arrhythmias). Wolf et al 1 were the first to observe that lack of respiratory sinus arrhythmia in the Coronary Care Unit carried a poor prognosis even in patients matched for other variables such as size of infarct or presence of heart failure. Survivors of acute myocardial infarction with low HR variability at the time of discharge have a higher mortality rate than patients with high HR variability. 2 HR variability may be quantified by power spectral analysis 3 and standard deviation (SD) of RR intervals, 2 or by the mean of differences between consecutive RR intervals. 4 HR variability is influenced by the balance between sympathetic and parasympathetic tone 3; differences in parasympathetic activity between night and daytime in patients with high or low 24-hour HR variability 5 and between anterior and inferior infarcts during the early phase of infarction 6,7 have been described. However, other studies 3 found no influence of the infarct site on HR variability. In this study we compared the night and daytime HR variability in patients with anterior and inferior wall acute myocardial infarction during the first day of admission to hospital.