Prevalence and risk factors for atrial fibrillation in dogs with myxomatous mitral valve disease

Background: Atrial fibrillation (AF) is a common supraventricular arrhythmia more frequently observed in large breed dogs. Objectives: Estimate the prevalence of AF in dogs with myxomatous mitral valve disease (MMVD) and identify risk factors for developing AF. Animals: A total of 2194 client-owned dogs with MMVD, including 1280, 588, 290, and 36 dogs in ACVIM stages B1, B2, C, and D, respectively. Methods: Retrospective, cross-sectional study. The medical databases of 3 veterinary teaching hospitals were reviewed. Inclusion criteria were a diagnosis of MMVD after complete cardiovascular evaluation and cardiac rhythm assessment using routine 2-minute ECG or good quality ECG tracing during echocardiographic examination. Results: Atrial fibrillation was diagnosed in 59 dogs with a prevalence of 2.7%. Univariate analysis showed that mixed breed, male sex, advanced ACVIM stage, left atrial and ventricular enlargement, fractional shortening (FS), and presence of pulmonary hypertension were significantly associated with development of AF. According to 2 multivariable models, the left atrium (LA)-to-aorta ratio (odds ratio [OR] = 14.011, 7.463-26.304), early trans-mitral velocity (OR = 2.204, 1.192-4.076), body weight (OR = 1.094, 1.058-1.130), and FS (OR = 0.899, 0.865-0.934) and LA (OR = 5.28, 3.377-8.092), advanced ACVIM stage (OR = 4.922, 1.481-16.353), and FS (OR = 0.919, 0.881-0.959) were significant predictors of AF for models 1 and 2, respectively. Conclusions and Clinical Importance: Atrial fibrillation is an uncommon complication of MMVD and is significantly associated with the more advanced stage of the disease, increased LA dimension and body weight, and decreased FS.