Relation of heart rate dynamics to the occurrence of myocardial ischemia after coronary artery bypass grafting.

Postoperative myocardial ischemia is a common finding after coronary artery bypass grafting (CABG) and is associated with an adverse short-term clinical outcome. The reasons and pathophysiologic background for the occurrence of ischemia after CABG are not well established. We tested the hypothesis that altered heart rate (HR) behavior precedes the onset of myocardial ischemic episodes in patients after CABG. Time-domain HR variability measurements, along with analysis of Poincaré plots and fractal scaling analysis were assessed in 40 CABG patients from 48-hour postoperative Holter recordings. Twenty patients experienced 195 ischemic episodes during the postoperative course. In the univariate analysis of HR variability measurements of the first postoperative day (POD), the increased ratio between the short-term (SD1) and long-term (SD2) HR variability analyzed from the Poincaré plot and the decreased short- and intermediate-term fractal scaling exponents alpha(1) and alpha(2) were significantly associated with ischemia during the study period (p <0.01, p <0.05, and p <0.05, respectively). In the multivariate model, the increased SD1/SD2 ratio of the first POD was the most powerful independent predictor of all possible confounding variables for the occurrence of postoperative ischemia (corresponding to a change of 0.15 U; odds ratio 2.2 and 95% confidence interval 1.2 to 5.7; p <0.01). Altered HR dynamics have been associated with myocardial ischemic episodes in patients after CABG, suggesting that the autonomic nervous system has an important role in the pathogenesis of myocardial ischemia in the postoperative phase of CABG.