Risk factors for recurrence of atrial fibrillation in horses after cardioversion to sinus rhythm.

Background: Although atrial fibrillation (AF) can be successfully treated in horses, recurrence occurs frequently. In humans, atrial function after cardioversion can predict recurrence.

Objectives: To examine the prognostic value of atrial mechanical function at 24 hours after cardioversion and other potential predictor variables for AF recurrence in horses.

Animals: 117 horses treated for AF at 4 referral centers.

Methods: Retrospective study. Inclusion criteria were successful cardioversion, echocardiography at 24 hours after cardioversion and ≥4 months follow-up. To determine factors associated with AF recurrence, a multivariable survival model was built.

Results: 133 AF episodes in 117 horses were included. AF recurred in 36/100 horses with a first AF episode and in 57/133 AF episodes overall. Factors associated with recurrence in horses with a first episode were previous unsuccessful treatment attempt (hazard ratio HR 2.36, 95% confidence interval CI 1.11-4.99, P = .025) and mild or moderate mitral regurgitation (HR 2.70, 95% CI 1.23-5.91, P = .013). When the last AF episode of all horses was included, previous AF (HR 2.53, 1.33-4.82, P = .005) and active left atrial fractional area change ≤9.6% (HR 3.43, 1.22-9.67, P = .020) were significant predictors.

Conclusions And Clinical Importance: The only echocardiographic variable of left atrial function with significant prognostic value for recurrence was low active left atrial fractional area change. Further research is necessary to evaluate whether echocardiography at a later timepoint could provide more prognostic information.