Abstract 12556: Prospective Association of Incident Atrial Fibrillation With Resting Heart Rate: The Henry Ford Hospital Exercise Testing (FIT) project

Abstract

Objective: Autonomic nervous system dysfunction plays an important role in atrial fibrillation (AF) initiation. Research suggests that vagal tone may mediate paroxysmal AF, such that a low resting heart rate (RHR) is associated with incident AF. However, conflicting reports also suggest that elevated RHR identifies risk for AF. Thus, we sought to further clarify the link between RHR and AF, independent of cardiorespiratory fitness (CRF). Methods: We analyzed 51,451 individuals without a history of AF who underwent a clinically-indicated exercise stress test between January 1991 and May 2009. Persons on nodal blocking medications were excluded. Adjusted hazard ratios (HRs) for AF were estimated using Cox models with baseline RHR categorized by <70, 70-85 (reference) and >85 beats-per-minute (bpm) (sensitivity analyses used quartile of RHR). Incident AF was defined by coding for new AF on claims files on ≥three subsequent encounters. We tested for effect modification by age (<60 vs. ≥60 years) and CRF (determined metabolic equivalents [METs] achieved on stress testing). Results: Mean age was 53 ± 13 years, 53% were men and 28% were black. Subjects in the lowest RHR category (<70 bpm) were older, more likely to be male diabetic and hypertensive, but had higher CRF. Compared to RHR 70-85, those with RHR <70 were at increased risk of AF [HR (95% CI), 1.15 (1.06-1.25)] (Table). While there was a trend for higher risk with RHR >85, this was non-significant after full adjustment. The association between low RHR and AF was independent of CRF and, in the sensitivity analysis using RHR quartile, appeared to be driven by excess risk in persons with RHR <64 bpm. There was no interaction by age or CRF level. Conclusion: We found that low RHR had a robust association with incident AF. Persons with low RHR, particularly in the presence of other AF risk factors, may benefit from AF screening and heart rhythm surveillance.