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

Abstract Background Rate control (RC; meanHRHolter ≤ 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.