Longitudinal analysis of echocardiographic and cardiac biomarker variables in dogs with atrial fibrillation: The optimal rate control in dogs with atrial fibrillation II study.

Background: Rate control (RC; meanHR ≤ 125 bpm) increases survival in dogs with atrial fibrillation (AF). The mechanisms remain unclear.

Hypothesis/objectives: Investigate echocardiographic and biomarker differences between RC and non-RC (NRC) dogs. Determine if changes post-anti-arrhythmic drugs (AAD) predict successful RC in subsequent Holter monitoring. Evaluate if early vs late RC affects survival.

Animals: Fifty-two dogs with AF.

Methods: Holter-derived mean heart rate, echocardiographic and biomarker variables from dogs receiving AAD were analyzed prospectively at each re-evaluation and grouped into RC or NRC. The primary endpoint was successful RC. Between group comparisons of absolute values, magnitude of change from admission to re-evaluations and end of study were performed using Mann-Whitney tests or unpaired t-tests. Logistic regression explored variables associated with inability to achieve RC at subsequent visits. Kaplan-Meier survival analysis was used to compare survival time of early vs late RC.

Results: At visit 2, 11/52 dogs were RC; at visit 3, 14/52 were RC; and at visit 4, 4/52 were RC. At the end of study, 25/52 remained NRC. At visit 2, both groups had increased cardiac dimensions, but NRC dogs had larger dimensions; biomarkers did not differ. At the end of study, RC showed decreased cardiac dimensions and end-terminal pro-brain natriuretic peptide (NT-proBNP) compared with NRC. No variables were useful at predicting RC success in subsequent visits. Survival analysis found no differences between early vs late RC.

Conclusions And Clinical Importance: The RC dogs had decreased cardiac dimensions and NT-proBNP, suggesting HR-mediated reverse-remodeling might benefit survival, even with delayed RC achievement. Pursuit of RC is crucial despite initial failures.