Transvenous electrical cardioversion of equine atrial fibrillation: Patient factors and clinical results in 72 treatment episodes

Background: Transvenous electrical cardioversion (TVEC) has been developed for treatment of atrial fibrillation (AF) in horses. The relationship among patient variables, treatment response, and outcome in a typical referral population has not been evaluated. Hypothesis: Patient variables such as age, sex, weight, and duration of arrhythmia affect prognosis for response to treatment and the energy level at which cardioversion occurs. Animals: TVEC was applied to 72 episodes of lone AF in 63 client-owned performance horses, with the majority (54) being Standardbred racehorses. Methods: Catheterization of the right atrium (RA) and pulmonary artery (PA) through the jugular vein was used for electrode placement before horses were placed under general anesthesia. Biphasic, truncated exponential shock waves were delivered at incremental energy levels until cardioversion was achieved or a maximum single-energy level of 300 J was reached (cumulative energy 50-1,960 J). A multivariate model was constructed to evaluate influence of patient factors on cardioversion energy. Results: Cardioversion was achieved in 71 of 72 episodes (62 of 63 horses) at a mean energy of 165.43 +/- 8.75 J. Cardioversion energy was higher for females than for males, and for interaction terms, weight was negatively related to energy in females and positively related in males. Age was positively related to cardioversion energy in females. No relationship was identified between duration of arrhythmia before treatment and prognosis for response or cardioversion energy. Conclusions and Clinical Importance: TVEC is highly effective in the treatment of lone AF in horses. Although age and sex influence cardioversion energy level, duration of arrhythmia does not.