Failing Hearts Are More Vulnerable to Sympathetic, but Not Vagal Stimulation-Induced, Atrial Fibrillation-Ameliorated with Dantrolene Treatment

Background: Both vagal (VS) and sympathetic (SS) stimulations can increase atrial fibrillation (AF) inducibility, with VS being known as more arrhythmogenic in normal hearts. Heart failure (HF) results in autonomic dysfunction (characterized by sympathetic activation and vagal withdrawal) and is associated with an increased AF incidence. This study investigated whether failing hearts, compared with normal control hearts, respond differently to autonomic stimulation induced AF arrhythmogenesis and the effect of dantrolene on SS-enhanced AF in HF. Methods and Results: A rat myocardial infarction (MI) HF model was used. In experiment 1, AF inducibility was compared in 9 MI-HF rats versus 10 sham-control animals at baseline, during VS, and during SS with isoproterenol infusion. In experiment 2, dantrolene treatment (n = 8) was compared with placebo -control (n = 9) on SS-induced AF inducibility in HF. Compared with the sham -control, baseline AF inducibility was higher in the MI-HF group. AF inducibility was augmented in both groups by autonomic stimulation. However, under VS the increased magnitude was less in the MI-HF group (49% +/- 11% vs 80% +/- 10%; P = .029), but under SS was significantly more (53% +/- 8% vs 6% +/- 7%; P < .001), compared with sham -control. Dantrolene significantly attenuated SS-enhanced AF in HF (69% +/- 6% vs 29% +/- 9%; P = .006). Conclusions: Failing hearts are less sensitive to VS, but more vulnerable to SS-induced AF compared with normal-control hearts. Dantrolene can significantly attenuate SS-enhanced AF in HF, indicating that cardiac ryanodine receptor dysfunction may play a critical role in SS-enhanced AF in HF, and stabilizing leaky ryanodine receptor with the use of dantrolene may be a new treatment option in this condition.