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Eur J Cardiothorac Surg 2005;28:109-113
© 2005 Elsevier Science NL

Nonlinear heart rate variability in CABG patients and the preconditioning effect

^a Department of Cardiac Surgery, Affiliated 1st Hospital, Sun Yat-sen University, GuangZhou, China
^b Department of Cardiac Surgery, Cardiac Center, Tampere University Hospital, Tampere, Finland
^c Department of Cardiology, Cardiac Center, Tampere University Hospital, Tampere, Finland
^d Department of Clinical Physiology, Tampere University Hospital, Tampere, Finland
^e Division of Cardiology, Department of Medicine, University of Oulu, Oulu, Finland

Received 16 January 2005; received in revised form 10 March 2005; accepted 11 March 2005.

^* Corresponding authors. Address: Clinic of Cardiac Surgery, Tampere University Hospital, 33521 Tampere, Finland. Tel./fax: +358 3 247 5756. (Email: lozhwu{at}uta.fi; Matti.Tarkka{at}pshp.fi).

Objective: Heart rate variability (HRV) is the most frequently used noninvasive diagnostic method in the assessment of cardiac autonomic control. The clinical relevance of HRV, especially nonlinear HRV in CPB patients has not been well studied. Short brief myocardial ischemia has been reported to influence HRV. We therefore hypothesis that the protective mechanism of ischemic preconditioning (IP) may involve in cardiac autonomic regulation. Methods: Eighty-six CABG patients were randomized into a control and an IP group. The IP patients received two periods of 2-min ischemia followed by 3-min reperfusion by aortic cross-clamped. Holter data were collected in 86 CABG patients before and after surgery. Arrhythmias, linear and nonlinear HRV measures were analyzed. Results: All time and frequency domain HRV variables as well as nonlinear indexes of HRV, the short-term (4–11 beats) scaling exponent ₁, were suppressed significantly after surgery in both study groups. The lower pre- and postoperative exponent ₁ predict the higher incidence of postoperative AF and worse postoperative outcome. The suppressed exponent ₁ was attenuated in the IP group as compared to controls (P=0.008). No other differences were observed in the changes in linear HRV measures between the groups. IP significantly reduced the incidence of postoperative arrhythmias and improved postoperative outcome. Conclusions: The present findings show that cardiac autonomic regulation is impaired after CABG. Nonlinear HRV exponent ₁ is a more sensitive measure to predict the postoperative outcome in CABG patients. IP alleviates the extreme autonomic reactions after surgery, suggesting that cardiac autonomic regulation is involved in the IP protective mechanism.

Key Words: Autonomic nervous system • Preconditioning • Cardiopulmonary bypass • Ischemia/reperfusion • Myocardial injury

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