Atrial Fibrillation as a Prognostic Indicator in Medium to Large‐Sized Dogs with Myxomatous Mitral Valvular Degeneration and Congestive Heart Failure

BACKGROUND: The prevalence and prognostic importance of atrial fibrillation (AF) on survival in nonsmall breed dogs with myxomatous mitral valvular disease (MMVD) and congestive heart failure (CHF) remain unknown. AIM: To identify the prevalence of AF in nonsmall breed dogs with CHF because of MMVD and to characterize the impact of AF on survival outcome. ANIMAL: Sixty‐four client‐owned dogs (>15 kg) with MMVD and CHF. METHODS: Retrospective review of medical records for dogs weighing >15 kg with MMVD treated for CHF. RESULTS: Thirty‐three dogs presented with AF or developed AF during follow‐up examinations, and 31 dogs were free of AF until cardiac‐related death. For dogs with AF, median survival time (MST) was 142 days (range: 9–478) while dogs without AF lived 234 days (range: 13–879 days). AF increased risk of cardiac‐related death (HR = 2.544; 95% CI = 1.41–4.59; P = .0019) when compared to dogs without AF. MST was significantly prolonged for dogs with AF whose rates were adequately controlled (<160 bpm; 171 days; n = 13) when compared to dogs that failed to respond to negative chronotropic agents (61 days; n = 20; P = .032). The administration of combination treatment (diltiazem and digoxin) significantly decreased median HR to 144 bpm (range: 84–218 bpm) in dogs with AF and significantly prolonged MST (diltiazem+digoxin: 130 days versus diltiazem: 35 days, P = .0241) when compared to diltiazem alone. CONCLUSIONS AND CLINICAL IMPORTANCE: Inadequately controlled AF is associated with a higher rate of mortality. Optimization of therapeutic strategies for the rate control of AF remains determined.