Prevention of atrial fibrillation by bucindolol is dependent on the beta₁389 Arg/Gly adrenergic receptor polymorphism

Objectives: This study assessed the impact of bucindolol, a beta-blocker/sympatholytic agent, on the development of atrial fibrillation (AF) in advanced chronic heart failure with reduced left ventricular ejection fraction (HFREF) patients enrolled in the BEST (Beta-Blocker Evaluation of Survival Trial). Background: β-blockers have modest efficacy for AF prevention in HFREF patients. Bucindolol's effects on HF and ventricular arrhythmic endpoints are genetically modulated by β₁- and α_2c-adrenergic receptor (AR) polymorphisms that can be used to subdivide HFREF populations into those with bucindolol effectiveness levels that are enhanced, unchanged, or lost. Methods: BEST enrolled 2,708 New York Heart Association (NYHA) class III to IV HFREF patients. A substudy in which 1,040 patients' DNA was genotyped for the β₁-AR position 389 Arg/Gly and the α_2c322-325 wild type (Wt)/deletion (Del) polymorphisms, and new-onset AF was assessed from adverse event case report forms or electrocardiograms at baseline and at 3 and 12 months. Results: In the entire cohort, bucindolol reduced the rate of new-onset AF compared to placebo by 41% (hazard ratio [HR]:0.59[95% confidence interval (CI): 0.44 to 0.79], p= 0.0004). In the 493 β₁389 arginine homozygotes (Arg/Arg) in the DNA substudy, bucindolol reduced new-onset AF by 74% (HR: 0.26 [95% CI: 0.12 to 0.57]), with no effect in β₁389 Gly carriers (HR: 1.01 [95% CI: 0.56 to 1.84], interaction test= 0.008). When β₁389 Gly carriers were subdivided by α_2c Wt homozygotes (n=413, HR: 0.94 [95% CI: 0.48 to 1.82], p= 0.84) or Del variant carriers (n= 134, HR: 1.33 [95% CI: 0.32 to 5.64], p=0.70), there was a positive interaction test (p= 0.016) when analyzed with β₁389 Arg homozygotes. Conclusions: Bucindolol prevented new-onset AF; β₁ and α_2c polymorphisms predicted therapeutic response; and the 47% of patients who were β₁389 Arg homozygotes had an enhanced effect size of 74%. (Beta-Blocker Evaluation in Survival Trial [BEST]; NCT00000560).