ALTERATIONS IN TEMPORAL PATTERNS OF HEART-RATE-VARIABILITY AFTER CORONARY-ARTERY BYPASS GRAFT-SURGERY

Background: Preliminary studies have indicated that autonomic nervous system dysfunction may be present in patients after cardiac surgery. T he purpose of this study was to evaluate cardiac autonomic nervous sys tem function, as assessed by analysis of heart rate variability (HRV), in adult patients undergoing uncomplicated coronary artery bypass gra ft surgery. Methods: Longitudinal changes in HRV were determined perio peratively by continuous electrocardiographic monitoring in 40 adult p atients undergoing elective coronary artery bypass graft surgery and w ere compared with HRV in two groups of control subjects: 15 patients u ndergoing nonthoracic major vascular surgery and 19 healthy volunteers . Exclusion criteria were diabetes, renal failure, recent or periopera tive myocardial infarction, or use in inotropic drugs. HRV data during electrocardiographically documented episodes of myocardial ischemia w ere omitted. Results: There were no differences in any measurement of preoperative HRV between groups during the day, but HRV was greater at nigh (12:00 AM to 5:00 AM) in volunteers than in patients in either s urgical group. In the hour after induction of anesthesia (before cardi opulmonary bypass), the components of HRV were decreased compared with those in the preoperative daytime but were similar in two surgical gr oups. After surgery, HRV in the group undergoing nonthoracic vascular surgery remained at about the same level as that observed after induct ion of anesthesia, whereas in the group undergoing coronary artery byp ass graft surgery, HRV was further reduced and was approximately 40-50 % less than that in the vascular surgery group (P < 0.05). In the coro nary artery bypass group, the reduction in HRV compared with the preop erative daytime measurements persisted on postoperative day 5. Conclus ions: HRV is reduced after uncomplicated coronary artery bypass graft surgery. Although we cannot exclude the effects of uncontrolled variab les in this reduction of postoperative HRV, the observed changes in HR V did not appear to result from general anesthesia, perioperative stre ss responses, and other factors associated with the early postoperativ e period. These data are consistent with the supposition that cardiac autonomic nervous system function is impaired after cardiac surgery.