Lower exercise capacity correlates with slower heart rate recovery in post-coronary artery bypass surgery patients

Funding Acknowledgements Type of funding sources: None. Background Heart rate recovery (HRR) describes the ability of the autonomic nervous system changes from the sympathetic to the parasympathetic nervous system. The slower heart rate recovery means there is an autonomic dysfunction of the nervous system. Heart rate recovery has been known to be a predictor of mortality in patients undergoing exercise stress test. Patients with slow heart rate recovery have a higher risk of cardiovascular death. Decreased exercise capacity is also known to increase the risk of cardiovascular death. Purpose This study aims to determine the relationship between low exercise capacity and slow heart rate recovery. Methods Patients who underwent post-coronary artery bypass (CABG) surgery cardiovascular rehabilitation program at our national cardiovascular center in 2022 were enrolled in this study. We assessed heart rate recovery during the maximal exercise stress test, by subtracting from maximal heart rate during the exercise stress test with heart rate at the first and second minute after exercise stress test. We used predicted METs from Bruce protocols treadmill test time to determine each patient’s exercise capacity. Results There were 238 patients (age 58±7 years old, 89.9% male). The mean exercise capacity was 6.42±2.21 METs and the mean first and second-minute heart rate recovery was 14±11 and 26±15 beats per minute. Predicted exercise capacity had a significant positive weak correlation with first-minute heart rate recovery/HRR1 (r=0.279; p=0.000) and a significant positive moderate correlation with second-minute heart rate recovery/HRR2 (r=0.409; p=0.000) in post-CABG patients. We performed receiver operating characteristic analysis that showed the area under the curve for exercise capacity was 0.69 for HRR1 and 0.71 for HRR2, and found the exercise capacity cut-off was 5.5 METs . Patients with exercise capacity less than 5.5 METs were likely to have slower HRR1 (OR=4.4 (95% CI, 2.7 – 7.2) p=0.000) and slower HRR2 (OR=3.8 (95% CI, 2.4 – 6.0) p=0.000). Conclusions There is a correlation between low exercise capacity and slow heart rate recovery. Patients with lower exercise capacity were likely to have slower heart rate recovery in post-CABG patients.