RR INTERVAL DYNAMICS BEFORE ATRIAL-FIBRILLATION IN PATIENTS AFTER CORONARY-ARTERY BYPASS GRAFT-SURGERY

Background-Atrial fibrillation/flutter (AF) is a frequent complication of coronary artery bypass graft surgery (CABG) that leads to increase d costs and morbidity. We hypothesized that heart rate variability (HR V), an indicator of cardiac sympathovagal balance, is altered before t he onset of postoperative AF. Because nonlinear methods of HRV analysi s provide information about heart rate dynamics not evident from usual HRV measures, we also hypothesized that approximate entropy (ApEn), a nonlinear measure of HRV, might have predictive value. Methods and Re sults-Analysis of HRV was performed in 3 sequential 20-minute interval s preceding the onset of postoperative AF (24 episodes in 18 patients) . These data were compared with corresponding intervals in 18 sex- and age-matched postoperative control subjects who did not develop AF. Pa tients had left ventricular ejection fractions >45% before surgery and were not receiving P-blockers during ambulatory ECG monitoring after surgery. Logistic regression demonstrated that on the basis of average d values for the three 20-minute intervals, increased heart rate and d ecreased ApEn were independently associated with AF, Heart rate dynami cs before AF was associated with either lower (n=19) or higher (n=5) R R interval variation by traditional measures of HRV or quantitative Po incare analysis, suggesting the possibility of divergent autonomic con ditions before AF onset. Conclusions-In the hour before AF after CABG surgery, higher heart rate and lower heart rate complexity compared wi th values in control patients were independent predictors of AF. Decre ased ApEn occurs in patients with either increased or decreased HRV by traditional measures and may provide a useful tool for risk stratific ation or investigation of mechanisms.