Abstract

Several studies have shown that altered cardiovascular autonomic regulation is associated with hypertension, diabetes, aging, angiographic severity of coronary artery disease (CAD), and increased mortality after acute myocardial infarction (AMI). The purpose of this study was to assess the temporal changes and prognostic significance of various measures of heart rate (HR) behaviour and their possible associations to coronary risk variables, and the progression of CAD in different populations.

This study comprised five patient populations. The first consisted of 305 patients with recent coronary artery bypass graft surgery (CABG) and lipid abnormalities, the second of 109 male patients with recent CABG, the third of 53 type II diabetic patients with CAD, the fourth of 600 patients with recent AMI, and the fifth of 41 elderly subjects. HR variability and non-linear measures of HR dynamics were analysed.

Among the patients with prior CABG, a significant correlation existed between the baseline HR variability (standard deviation of N-N intervals, SDNN) and the progression of CAD (r = 0.26, p < 0.001)). In the longitudinal study of patients with prior CABG, only the fractal indexes of HR dynamics, such as the power law slope (β) and the short-term fractal exponent (α₁), decreased significantly. In diabetic patients, SDNN decreased significantly (p < 0.001) during the three-year period. The reduction of SDNN was related to cholesterol, triglyceride, and glucose levels, and also to progression of CAD (r = 0.36, p < 0.01). In the longitudinal follow-up study of patients with recent AMI, reduced fractal indices (α₁ and β), and reduced HR turbulence predicted cardiac death when measured at the convalescent phase after AMI. Reduced β and turbulence slope predicted cardiac death when measured at 12 months after AMI. In the elderly population, β (p < 0.001) and α₁ (p < 0.01) reduced significantly. Low-frequency power spectra were the only traditional measure of HR variability that decreased significantly during the 16-year period.

HR variability is associated with many risk factors of atherosclerosis and with progression of CAD among patients with ischemic heart disease. Fractal HR dynamics are more sensitively able to detect age-related changes in cardiovascular autonomic regulation. Altered fractal HR dynamics and HR turbulence are associated with increased mortality after AMI.