Heart rate variability in ischemic heart disease

Major untoward events, such as life-threatening arrhythmias and acute coron ary events, have been suggested to be triggered by the activation of the au tonomic nervous system in patients with coronary artery disease. Analysis o f heart rate variability by conventional time and frequency domain methods, as well as by newer methods derived from nonlinear system theory, has offe red a novel approach for studying the abnormalities in cardiovascular neura l regulation in ischemic heart disease. Heart rate variability has been sho wn to be altered among patients with ischemic heart disease as compared to their age-matched controls without the evidence of ischemic heart disease. There are also obvious differences in various measures of heart rate variab ility between patients with uncomplicated coronary artery disease and these with coronary artery disease with complicated myocardial infarction. Impai red high-frequency oscillations of heart rate is the most prominent feature in patients with uncomplicated coronary artery disease, suggesting mainly an impairment in vagal autonomic regulation. Patients with prior myocardial infarction have a reduced overall heart rate variability, and a specific s pectral pattern with a reduced low-frequency spectral component has been ob served in patients with prior myocardial infarction and impaired left ventr icular function. Recent studies have shown that the new nonlinear measures, particularly fractal analysis methods of heart rate dynamics, can detect s ubtle changes in heart rate behavior that are not easily detected by tradit ional analysis methods from ambulatory recordings. Patients with prior myoc ardial infarction have steeper power-law slope analyzed from the ultra and very low-frequency spectral bands, and they also have more random short-ter m heart rate dynamics analyzed by the detrended fluctuation method. A large body of data indicate that reduced overall heart rate variability is assoc iated with an increased risk of mortality and nonfatal cardiac events in pa tient with ischemic heart disease. Of particular note, recent studies indic ate that fractal analysis methods perform even better than the traditional analysis methods of heart rate variability as predictors of death and the o nset of life-threatening arrhythmic events in post-infarction populations. These findings support the notion that heart rate variability analysis meth ods, such as fractal and complexity measures as well as conventional techni ques, give valuable clinical information among patients with ischemic heart disease. (C) 2001 Elsevier Science B.V. All rights reserved.