Key result
Post-CABG patients with reduced left ventricular function exhibited lower heart rate variability during ambulation (e.g., STDRR 6.1 vs 8.9 ms) compared to those with normal function (p<0.05).
Why the study?
Does an exercise-based inpatient program evoke a different cardiac autonomic response in post-CABG patients with reduced left ventricular function compared to those with normal left ventricular function?
Observational (n=44)
Does an exercise-based inpatient program evoke a different cardiac autonomic response in post-CABG patients with reduced left ventricular function compared to those with normal left ventricular function?
Post-CABG patients with reduced left ventricular function exhibit a more pronounced cardiac autonomic response to an inpatient exercise program compared to those with normal function, suggesting exercise volume should be tailored to LVF.
Lower ambulatory HRV in reduced-LVF post-CABG patients suggests differential autonomic response to exercise; hypothesis-generating and should not yet alter rehabilitation protocols.
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.
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Mendes et al. (2013) conducted an observational in Post-coronary artery bypass graft (CABG) (n=44). Reduced left ventricular function (LVEF 35-54%) vs. Normal left ventricular function (LVEF ≥ 55%) was evaluated on Cardiac autonomic response assessed by indices of heart rate variability (HRV) at rest and during exercise (p=<0.05). Post-CABG patients with reduced left ventricular function exhibited lower heart rate variability during ambulation (e.g., STDRR 6.1 vs 8.9 ms) compared to those with normal function (p<0.05).
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