Introduction:
Elevated muscle sympathetic nerve activity (MSNA) both at rest and during dynamic cycling relates inversely to peak oxygen uptake (VO
2peak
) in patients with heart failure due to a reduced ejection fraction (HFrEF). We observed a drop in MSNA both rest (-6±2 bursts/min) and mild exercise (-4±2) in HFrEF patients after 6 months of cardiac rehabilitation.
Hypothesis:
We hypothesized that after training those HFrEF patients with LOW VO2peak (less than median 74% of age predicted) would have a larger decrease in MSNA during dynamic exercise than those with HIGH VO2peak (over 74%).
Methods:
In 21 optimally treated HFrEF patients (5 Female) (13 HIGH: mean VO
2peak
=26 ml·kg/min; 98% of predicted; 8 LOW VO
2peak
=12; 50%) we assessed VO
2peak
(open-circuit spirometry), heart rate variability (HRV) and fibular MSNA (microneurography) at rest, during 1-leg cycling (2 min each of mild and moderate intensity upright 1-leg cycling, n=19) and recovery before and after 6 months of exercise training (45 min aerobic exercise, 5 days/ wk at 60-70 % of VO
2peak;
and resistance training 2 days/wk).
Results:
HIGH and LOW groups had similar age (63±3 vs 63±4 years) , LVEF (30±2 vs 28±3%), BMI, resting heart rate (HR), blood pressure and MSNA (52±3 vs 50±3 bursts/min). Training increased VO
2peak
in both groups (main effect P=0.009), with no group difference in HR response or ratings of perceived exertion. MSNA at rest tended to decrease after training in the HIGH but not LOW group (interaction P=0.08). MSNA during cycling increased in both HIGH (P=0.04) and LOW (P<0.001) groups but was blunted post-training in the HIGH group only (P=0.04 vs. 0.90 in LOW). Training-induced sympatho-inhibition during exercise recovery occurred in the HIGH but not LOW group (interaction P=0.01). In contrast, HRV was not improved by training in either group.
Conclusions:
Contrary to our hypothesis, the sympatho-inhibitory effect of 6 months of exercise-based cardiac rehabilitation favours HFrEF patients with an already normal VO
2peak
. This suggests that increasing initially low VO
2peak
may be insufficient to trigger beneficial exercise and recovery autonomic modulation and altered training paradigms may be required in such patients.
Funded by Canadian Institutes for Health Research (CIHR)
Ivabradine and endothelium: an update
