Optimal rate control in dogs with atrial fibrillation—ORCA study—Multicenter prospective observational study: Prognostic impact and predictors of rate control

BACKGROUND: The optimal heart rate (HR) in dogs with atrial fibrillation (AF) is unknown. Impact of HR on survival needs elucidation. HYPOTHESIS/OBJECTIVES: Dogs with a 24 hours Holter‐derived meanHR ≤125 beats per minute (bpm; rate controlled) survive longer than dogs with higher meanHR. We further aimed to determine which variables predict ability to achieving rate control. ANIMALS: Sixty dogs with AF. METHODS: Holter‐derived meanHR, clinical, echocardiographic, and biomarker variables were analyzed prospectively. Survival was recorded from time of rate control, with all‐cause mortality as primary endpoint. Cox proportional hazards analysis identified variables independently associated with survival; Kaplan‐Meier survival analysis estimated the median survival time of dogs with meanHR ≤125 bpm vs >125 bpm. Logistic regression explored baseline variables associated with inability to achieve rate control. RESULTS: Structural heart disease was present in 56/60 dogs, 50/60 had congestive heart failure, and 45/60 died. Median time to all‐cause death was 160 days (range, 88‐303 days), dogs with meanHR >125 bpm (n = 27) lived 33 days (95% confidence interval [CI], 15‐141 days), dogs with meanHR ≤125 bpm (n = 33) lived 608 days (95% CI, 155‐880 days; P < .0001). Congenital heart disease and N‐terminal pro‐B‐type natriuretic peptide were independently associated with higher risk of death (P < .01 and <.0001, respectively) whereas meanHR ≤125 bpm decreased the risk of death (P < .001). Increased left atrial size, increased C‐reactive protein concentration and lower blood pressure at admission were associated with failure to achieve rate control. CONCLUSIONS AND CLINICAL IMPORTANCE: Rate control affects survival; an optimal target meanHR <125 bpm should be sought in dogs with AF. Baseline patient variables can help predict if rate control is achievable.