Introduction: Modifications of autonomic nervous activation, notably during mental or physical stress, could represent a potential risk of sudden death or ventricular fibrillation in cardiac patients. Heart rate (HR) and heart rate variability (HRV) have been used to investigate these adaptations mediated by the autonomic nervous system. Effects of exercise training on HR and HRV are well known at rest, but have been less investigated during stress. This study hypothesizes that physical and mental stress and their association could represent a potential risk in cardiac patients, by a concomitant increase of HR and sympathetic activation, and that endurance exercise training could decrease it.

Methods: Twenty-four male patients (mean age = 51.6+/-6.5 years) suffering from coronary artery disease (n = 12) or heart failure patients (n = 12) participated to the study. They completed 2 experimental sessions, before and after 4-week rehabilitation program training. During each session, a Holter ECG recording was realized during a mental stress using cognitive exercises, an acute exercise at 30% of maximal power, and their association.

Results: Both stresses and their association increased HR but had no significant effect on HRV parameters. There was a potentiation of HR increase during the association of both stresses. Exercise training had no effect on HR and HRV at rest, during mental stress and during acute exercise at the same relative intensity. Considering absolute power of exercise, which is an important factor of sympathetic activation, there is an improvement of HR response to exercise after training.

Conclusion: Both stresses could represent a cardiac risk, which is well identified by HR increase than HRV in cardiac population. The association of both stresses potentiates this risk. Cardiac rehabilitation programs have a beneficial effect on this potential risk during acute exercise but not during mental stress. Neural mechanisms of these adaptations should be investigated in future studies.