Effect of coronary artery bypass grafting on cardiac parasympathetic nervous function.

Low heart rate variability (HRV) is a predictor of a poor outcome after myocardial infarction. To determine whether coronary artery bypass grafting (CABG) has any effect on HRV, the power spectrum components of HRV were measured in 35 patients before, and 1 week after, CABG. Significant attenuation of all spectral components of HRV were found after CABG (P less than 0.001). High frequency (HF) power decreased to one third of the preoperative level, mid-frequency (MF) power to as little as one fifteenth and low frequency (LF) power to one seventh of the preoperative level. No significant restoration in MF or HF powers occurred during the 6-week follow-up period. The results suggest that CABG causes a marked attenuation of HRV. The prognostic significance of this attenuation is not known.