Transvenous electrical cardioversion of atrial fibrillation in horses: Horse and procedural factors correlated with success and recurrence.

Background: Transvenous electrical cardioversion (TVEC) is 1 of the main treatment options for atrial fibrillation (AF) in horses. Large-scale studies on factors affecting success and prognosis have primarily been performed in Standardbred populations.

Hypothesis/objectives: To determine factors affecting cardioversion success, cardioversion difficulty and recurrence in a predominant Warmblood study sample.

Animals: TVEC records of 199 horses.

Methods: Retrospective study of TVEC procedures of horses admitted for AF without severe echocardiographic abnormalities. Horse and procedural factors for success and cumulative amount of energy (≤ 600 J vs > 600 J) were determined using multivariable logistic regression. A survival analysis was performed to determine risk factors for recurrence.

Results: Two hundred and thirty-one TVEC procedures were included, with a 94.4% success rate and 31.9% recurrence rate (51/160). Mitral regurgitation (OR 0.151, 95% CI 0.032-0.715, P = .02) and AF cycle length (OR 1.05, 95% CI 1.01-1.09, P = .02) were independent determinants for success. Catheter type (OR 0.154, 95% CI 0.074-0.322, P < .001), previous AF episode (OR 3.10, 95% CI 1.20-8.01, P = .02), tricuspid regurgitation (OR 2.54, 95% CI 1.25-5.13, P = .01), and body weight (OR 1.009, 95% CI 1.003-1.015, P = .004) were significantly correlated with cumulative amount of energy delivered. Significant risk factors for recurrence after a first AF episode were sex (stallion; HR 3.05, 95% CI 1.34-6.95, P = .008), mitral regurgitation (HR 1.91, 95% CI 1.08-3.38, P = .03), and AF duration (HR 1.001, 95% CI 1.0001-1.0026, P = .04).

Conclusions And Clinical Importance: Both horse and procedural factors should be considered when assessing treatment options and prognosis in horses with AF.