Heart rate variability after coronary artery bypass grafting

Forty-nine CABG patients, aged from 38 to 77 years, were examined by 24-h ambulatory ECG monitoring before and 4 weeks after surgery. HRV spectral components were obtained by MEM analysis and the 24-h averages of time and frequency domain measures were obtained. Comparison of groups was done by the paired t-test and p<0.05 was defined as statistical significance. The average HR for a 24-h period increased significantly after CABG (P<0.0001). VLF and LF components showed a decrease after surgery (1225.0 vs. 572.3, p<0.0001, and 260.3 vs. 125.9, p<0.002) but the HF spectral power did not show a significant change (98.7 vs. 125.9, N.S.). Analysis of the normalized units revealed a significant increase of ULF/TF from 0.6496±0.0931 to 0.7003±0.1338 (p<0.0001), and a significant decrease of the VLF/TF and LF/TF from 0.2671±0.0689 to 0.2040±0.0832 (p<0.0001) and from 0.0568±0.0290 to 0.0429±0.0232 (p=0.00888), respectively. There was no significant alteration of HF/TF. These results suggest that CABG improves cardiovascular function in CAD patients with increased sympathetic activity. These observations might be explained by prolonged recovery of the myocardium after normalization of myocardial perfusion