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.