Autonomic influence on atrial fibrillatory process: head‐up and head‐down tilting

Background Changes in the autonomic nervous system ( ANS ) tone are present before, during, and after episodes of atrial fibrillation ( AF ). Atrial fibrillatory rate ( AFR , the inverse of the atrial cycle length) has been used as a surrogate marker for local refractoriness and is a key characteristic of the fibrillatory process in patients with AF . Aim of this study is to assess changes in AFR , as an effect of autonomic balance change. Methods Forty patients undergoing cardiac cardioversion for symptomatic persistent AF were included in the study. Surface ECG was recorded during rest, head‐down ( HDT , −30°), and head‐up tilt ( HUT , +60°). A median value of AFR was computed in each phase of the protocol. Results AFR decreased during HDT compared to the baseline (B) condition in all patients but three (median AFR _B = 391 fpm vs. AFR _ HDT  = 377 fpm, p  < .0001). HUT increased AFR , making it significantly higher than HDT and baseline conditions (median AFR _ HUT  = 396 fpm, p  < .0001 vs. B and HDT ). Heart rate ( HR ) increased during HUT , but had a heterogeneous behavior in the population during HDT : about one third of the patients had an HR lower during HDT than during baseline, whereas the remaining two third had an increase in HR during HDT . Conclusions Dominant sympathetic/vagal tone during HUT / HDT significantly affects AFR , increasing/decreasing in respect to baseline. It may be worth exploring the possibility that patients with AF of shorter duration can convert to sinus rhythm during HDT .