Exercise metaboreflex activation and endothelial function impairment in atrial fibrillation

Exercising muscle hypoperfusion stimulates afferents (metaboreceptors) involved in the regulation of ventilation. Atrial fibrillation (AF), particularly when combined with diseases causing endothelial (ED) impairment, such as hypertension (HP) and diabetes mellitus (DM), depresses the ED activity and enhances exercise hyperventilation. The relationship between these two functions and the underlying mechanisms have not been explored previously. In lone AF or AF associated with HP or DM (12 subjects in each cohort), we investigated the brachial artery flow-mediated dilatation (ED function) and ventilation during the recovery phase of handgrip (metaboreflex) exercise for subjects receiving placebo or oral vitamin C (double-blind crossover), both before and after cardioversion (CV) to sinus rhythm. Baseline ED impairment was increasingly more severe and the ergoreflex activity more pronounced in AF + HP and AF + DM compared with lone AF. Vitamin C and CV significantly improved both flow-mediated dilatation and metaboreflex activity in lone AF and AF + HP, and vitamin C did not produce any additive effect when administered after CV. In AF + DM, neither vitamin C nor CV was effective. This study provides the following information: AF generates oxidative injury, which is less when the arrhythmia is lone AF and greater when the arrhythmia is associated with HP. In DM, the oxidative injury generated by AF is refractory to a rather weak antioxidant, like vitamin C, or the baseline damage is such as to prevent any additive influence of AF. In AF, a cause-effect link exists between ED dysfunction and metaboreflex activity. Ventilatory advantages of CV seem to be inversely related with the extension of the underlying ED oxidative impairment.