Retrospective Evaluation of the Effect of Heart Rate on Survival in Dogs with Atrial Fibrillation

Background Atrial fibrillation ( AF ) usually is associated with a rapid ventricular rate. The optimal heart rate ( HR ) during AF is unknown. Hypothesis/Objectives Heart rate affects survival in dogs with chronic AF . Animals Forty‐six dogs with AF and 24‐hour ambulatory recordings were evaluated. Methods Retrospective study. Holter‐derived HR variables were analyzed as follows: mean HR (mean HR , 24‐hour average), minimum HR (min HR , 1‐minute average), maximum HR (max HR , 1‐minute average). Survival times were recorded from the time of presumed adequate rate control. The primary endpoint was all‐cause mortality. Cox proportional hazards analysis identified variables independently associated with survival; Kaplan‐Meier survival analysis estimated the median survival time of dogs with mean HR <125 bpm versus ≥125 bpm. Results All 46 dogs had structural heart disease; 31 of 46 had congestive heart failure (CHF), 44 of 46 received antiarrhythmic drugs. Of 15 dogs with cardiac death, 14 had CHF . Median time to all‐cause death was 524 days (Interquartile range (IQR), 76–1,037 days). Mean HR was 125 bpm (range, 62–203 bpm), min HR was 82 bpm (range, 37–163 bpm), max HR was 217 bpm (range, 126–307 bpm). These were significantly correlated with all‐cause and cardiac‐related mortality. For every 10 bpm increase in mean HR , the risk of all‐cause mortality increased by 35% (hazard ratio, 1.35; 95% CI , 1.17–1.55; P < 0.001). Median survival time of dogs with mean HR <125 bpm (n = 23) was significantly longer (1,037 days; range, 524‐open) than mean HR ≥125 bpm (n = 23; 105 days; range, 67–267 days; P = 0.0012). Mean HR was independently associated with all‐cause and cardiovascular mortality ( P < 0.003). Conclusions and Clinical Importance Holter‐derived mean HR affects survival in dogs with AF . Dogs with mean HR <125 bpm lived longer than those with mean HR ≥ 125 bpm.