Correlation properties and complexity of perioperative RR-interval dynamics in coronary artery bypass surgery patients

Background: Dynamic measures of heart rate variability (HRV) may uncover ab normalities that are not easily detectable with traditional time and freque ncy domain measures. The purpose of this study was to characterize changes in RR-interval dynamics in the immediate postoperative phase of coronary ar tery bypass graft (CABG) surgery using traditional and selected newer dynam ic measures of HRV. Methods: Continuous 24-h electrocardiograph recordings were performed in 40 elective CABG surgery patients up to 72 h postoperatively, In one half of the patients, Holter recordings were initiated 12-40 h before the surgery. Time and frequency domain measures of HRV were assessed. The dynamic measur es included a quantitative and visual analysis of Poincare plots, measureme nt of short- and intermediate-term fractal-like scaling exponents (alpha(1) and alpha(2)), the slope (beta) of the power-law regression line of RR-int erval dynamics, and approximate entropy. Results: The SD of RR intervals (P < 0.001) and the ultra-low-, very-low-, low-, and high-frequency power (P < 0.01,P < 0.001, P < 0.001, P < 0.01, re spectively) measures in the first postoperative 24 h decreased from the pre operative values. Analysis of Poincare plots revealed increased randomness in beat-to-beat heart rate behavior demonstrated by an increase in the rati o bem een short-term and long-term HRV(P < 0.001) after CABG. Average scali ng exponent alpha(1) of the 3 postoperative days decreased significantly af ter CABG (from 1.22 +/- 0.15 to 0.85 +/- 0.20, P < 0.001), indicating incre ased randomness of short-term heart rate dynamics (i.e., loss of fractal-li ke heart rate dynamics). Reduced scaling exponent alpha(1) of the first pos toperative 24 h was the best HRV measure in differentiating between the pat ients that had normal (less than or equal to 48 h, n = 33) or prolonged (>4 8 h, n = 7) intensive care unit stay (0.85 +/- 0.17 us. 0.68 +/- 0.18; P < 0.05), In stepwise multivariate logistic regression analysis including typi cal clinical predictors, alpha(1) was the most significant independent pred ictor (P < 0.05) of long intensive care unit stay. None of the preoperative HRV measures were able to predict prolonged intensive care unit stays. Conclusions: In the selected group of patients studied, a decrease in overa ll HRV was associated with altered nonlinear heart rate dynamics after CABG surgery, Current results suggest that a more random short-term heart rate behavior may be associated with a complicated clinical course. Analysis of fractal-like dynamics of heart rate map provide new perspectives in detecti ng abnormal cardiovascular function after CABG.