Fractal correlation properties of R-R interval dynamics and mortality in patients with depressed left ventricular function after an acute myocardial infarction

Background-Preliminary data suggest that the analysis of R-R interval varia bility by fractal analysis methods may provide clinically useful informatio n on patients with heart failure. The purpose of this study was to compare the prognostic power of new fractal and traditional measures of R-R interva l variability as predictors of death after acute myocardial infarction. Methods and Results-Time and frequency domain heart rate (HR) variability m easures, along with short- and long-term correlation (fractal) properties o f R-R intervals (exponents alpha(1) and alpha(2)) and power-law scaling of the power spectra (exponent beta), were assessed from 24-hour Holter record ings in 446 survivors of acute myocardial infarction with a depressed left ventricular function (ejection fraction less than or equal to 35%). During a mean+/-SD follow-up period of 685+/-360 days, 114 patients died (25.6%), with 75 deaths classified as arrhythmic (17.0%) and 28 as nonarrhythmic (6. 3%) cardiac deaths. Several traditional and fractal measures of R-R interva l variability were significant univariate predictors of all-cause mortality . Reduced short-term scaling exponent alpha(1), was the most powerful R-R i nterval variability measure as a predictor of all-cause mortality (alpha(1) <0.75, relative risk 3.0, 95% confidence interval 2.5 to 4.2, P<0.001). It remained an independent predictor of death (P<0.001) after adjustment for other postinfarction risk markers, such as age, ejection fraction, NYHA cla ss, and medication, Reduced alpha(1) predicted both arrhythmic death (P<0.0 01) and nonarrhythmic cardiac death (P<0.001). Conclusions-Analysis of the fractal characteristics of short-term R-R inter val dynamics yields more powerful prognostic information than the tradition al measures of HR variability among patients with depressed left ventricula r function after an acute myocardial infarction.