S88 Comparison of Sequential Changes in Heart Rate Variability After On-Pump and Off-Pump Coronary Artery Bypass Grafting (#2001-6850 … June 27, 2001) Jurij-Matija Kalisnik 1 , Viktor Avbelj 2 , Roman Trobec 2 , Borut Gersak 1 1 Department of Cardiovascular Surgery, University Medical Center, Zaloska 7, SI-1000 Ljubljana, Slovenia 2 Department of Communications and Computer Networks, Jozef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia Presented at the Fourth Annual Scientific Meeting of the International Society for Minimally Invasive Cardiac Surgery, June 27-30, 2001, Munich, Germany. Address correspondence and reprint requests to: Jurij-Matija Kalisnik, MD, MSc, Department of Cardiovascular surgery, Medical Center, 1000 Ljubljana, Slovenia, Phone & fax: +386 1 433 4162, Email: jurij-matija.kalisnik@mf.uni-lj.si ABSTRACT Background: Cardiac vagal modulation is reduced in patients with coronary artery disease or previous myocardial infarction. The propensity to lethal arrhythmias and oxygen consumption is thus increased. The objective of the present study was to assess the effect of different techniques used in coronary artery bypass grafting (CABG), namely on-pump versus off-pump, on the level of vagal modulation in the immediate postoperative period. Methods: Thirty-three patients, aged 34–76 years were enrolled in the study. Six patients undergone off-pump CABG; the rest were operated on-pump. The electrocardiograms (ECG) and respiratory waveform signals were recorded in the afternoons in supine position. Power spectra of the heart rate variability (HRV) were computed using Fast Fourier Transform analysis (FFT). The following HRV indexes were calculated: total power (TP) of spectra was defined in the range of 0.01-0.40 Hz, high frequency (HF) power within 0.15- 0.40 Hz, low frequency (LF) power within 0.04-0.15 Hz. Normalized power (n) was defined as the ratio of power in each band / total power. The nHF power indicated cardiac vagal modulation; nLF power indexed sympathetic baroreflex modulated activity. The LF/HF ratio represented sympathovagal balance. Kolmogorov-Smirnov test, paired t-test or Wilcoxon signed rank and Mann-Whitney U test have been applied in statistical analysis, a value of p<0.05 was considered significant. Results: The HRV indexes were diminished markedly after CABG regardless of the technique applied. TP, HF, LF, LF/HF ratio changed by 40 – 70%, the differences were significant on fourth and seventh postoperative day. Comparing off-pump versus on-pump group, the HF power was significantly higher by factor 2 in off-pump patients on the fourth and seventh day after CABG. Conclusions: The results indicate marked attenuation of HRV indexes with no signs of restoration after one week regardless of the technique applied. However, a tendency to higher vagal modulation has been observed in beating heart patients may indicate tendency toward better preserved cardiac vagal autonomous regulation in off-pump patients.