Exercise metaboreflex activation and endothelial function impairment in atrial fibrillation

Area of Science:

• Cardiovascular Physiology
• Respiratory Regulation
• Endothelial Function

Background:

• Exercising muscle hypoperfusion stimulates ventilation regulation via metaboreceptors.
• Atrial fibrillation (AF), particularly with endothelial (ED) dysfunction from hypertension (HP) or diabetes mellitus (DM), impairs ED activity and heightens exercise hyperventilation.
• The interplay between AF, ED function, and metaboreflex activity remains unexplored.

Purpose of the Study:

• To investigate the relationship between endothelial function and metaboreflex activity in patients with atrial fibrillation.
• To explore the effects of vitamin C and cardioversion on these parameters in lone AF, AF with HP, and AF with DM.

Main Methods:

• Evaluated brachial artery flow-mediated dilatation (ED function) and ventilation during handgrip exercise recovery (metaboreflex) in 36 subjects (lone AF, AF+HP, AF+DM).
• Utilized a double-blind crossover design with placebo or vitamin C, before and after cardioversion (CV) to sinus rhythm.
• Assessed oxidative injury and its relationship with ED dysfunction and metaboreflex activity.

Main Results:

• Baseline ED impairment and metaboreflex activity were most severe in AF+HP and AF+DM groups compared to lone AF.
• Vitamin C and CV improved ED function and metaboreflex activity in lone AF and AF+HP, with no additive effect post-CV.
• In AF+DM, neither vitamin C nor CV showed significant improvement, suggesting refractory oxidative injury or extensive baseline damage.

Conclusions:

• Atrial fibrillation induces oxidative injury, exacerbated by hypertension.
• A direct link exists between endothelial dysfunction and metaboreflex activity in AF.
• The benefits of cardioversion for ventilation are inversely proportional to the severity of endothelial oxidative impairment.