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

Background: Transvenous electrical cardioversion (TVEC) is one 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. Objectives: To determine the factors affecting success, difficulty of TVEC and recurrence in a mainly Warmblood population. Study Design: Retrospective study. Methods: TVEC records of patients admitted for AF without severe echocardiographic abnormalities were studied. Patient and procedural factors for success rate and cumulative amount of energy (≤600J versus >600J) were determined using multiple logistic regression. A survival analysis was performed to determine risk factors for recurrence within one year after a first AF episode. Results: 231 TVEC procedures were included, with a 94.4% success rate and 34.3% recurrence rate. The depth of pulmonary artery catheter insertion was the only independent predictor for success (OR 1.143, 95%CI [1.005-1.300], P=0.041). Catheter type (OR 0.257, 95%CI [0.109-0.606], P=0.002), height at the withers (OR 1.087, 95%CI [1.021-1.157], P=0.009) and previous AF episode (OR 2.909, 95%CI [1.043-8.112], P=0.041) were significantly correlated with cumulative amount of energy. Significant risk factors for recurrence were male sex (HR 6.648, 95%CI [2.591-17.060], P<0.001), immediate AF recurrence during TVEC (HR 6.232, 95%CI [1.627-23.877], P=0.007), AF duration (HR 1.002, 95%CI [1.0003-1.003], P=0.017) and need for ventricular pacing (HR 3.455, 95%CI [1.005-11.879], P=0.049). Main Limitations: The retrospective nature of the study resulted in missing values. Conclusion: TVEC success and difficulty depend both on patient factors and procedural factors such as catheter insertion depth and catheter type.