Is applying the same exercise-based inpatient program to normal and reduced left ventricular function patients the best strategy after coronary surgery? A focus on autonomic cardiac response

Abstract

Purpose: To assess whether the same exercise-based inpatient program applied to patients with normal and reduced left ventricular function (LVF) evokes a similar cardiac autonomic response after coronary artery bypass graft (CABG). Method: Forty-four patients post-CABG, subgrouped according to normal LVF [LVFN: n = 23; left ventricular ejection fraction (LVEF) ≥ 55%] and reduced LVF (LVFR: n = 21; LVEF 35–54%), were included. All initiated the exercise protocol on post-operative day 1 (PO1), following a whole progressive program until discharge. Cardiac autonomic response was assessed by the indices of heart rate variability (HRV) at rest and during exercise (extremity range of motion and ambulation). Results: During ambulation, lower values of HRV indices were found in the LVFR group compared with the LVFN group [standard deviation of all RR (STDRR; 6.1 ± 2.7 versus 8.9 ± 4.7 ms), baseline width of the RR histogram (TINN; 30.6 ± 14.8 versus 45.8 ± 24.9 ms), SD2 (14.8 ± 8.0 versus 21.3 ± 9.0 ms), Shannon entropy (3.6 ± 0.5 versus 3.9 ± 0.4) and correlation dimension (0.08 ± 0.2 versus 0.2 ± 0.2)]. Also, when comparing the ambulation to rest change, lower values were observed in the LVFR group for linear (STDRR, TINN, RR TRI, rMSSD) and non-linear (SD2 and correlation dimension) HRV indices (p < 0.05). On PO1, we observed only intra-group differences between rest and exercise (extremity range of motion), for mean intervals between heart beats and heart rate. Conclusion: For patients with LVFN, the same inpatient exercise protocol triggered a more attenuated autonomic response compared with patients with LVFR. These findings have implications as to how exercise should be prescribed according to LVF in the early stages following recovery from CABG.

Implications for Rehabilitation

• Exercise-based inpatient program, performed by post-CABG patients who have normal left ventricular function, triggered a more attenuated cardiac autonomic response compared with patients with reduced left ventricular function.

• Volume of the inpatient exercises should be prescribed according to the left ventricular function in the early stages following recovery from CABG.

• Autonomic nervous system
• coronary artery bypass graft
• myocardial function
• physical therapy

Acknowledgements

The authors are grateful to the UFSCar Cardiopulmonary Laboratory and Santa Casa of Araraquara Hospital staff for their enthusiastic help. The authors also extend their special thanks to the subjects for their participation. This study was supported by the Sao Paulo Foundation for Research Support (FAPESP, process 05/59427-7 and 09/54194-5) and by the Brazilian National Council for Scientific and Technological Development (CNPq).