| Conventional treatment for atrial fibrillation (AF) in the horse involves administration, orally or intravenously, of quinidine salts. The majority of uncomplicated cases respond to treatment, but a proportion do not. In many cases, achieving therapeutic response can involve a range of side-effects, and some horses are unable to tolerate medication. Proarrhythmia and sudden death are potential, albeit rare, complications. The purpose of the present investigation was to develop and evaluate transvenous electrical cardioversion as an alternative therapeutic modality. Preliminary studies involved investigation of catheter placement techniques and catheterisation safety issues using catheter-integrated cardioversion electrodes. Electrical cardioversion of research horses in chronic AF under general anaesthesia was then attempted to evaluate the safety of, and response to, application of cardioversion shocks, and to determine appropriate cardioversion electrode positions. No antiarrhythmic medications were administered. Catheterisation of the RA and PA through the right jugular vein was used for electrode placement, and horses were then placed under general anaesthesia before biphasic, truncated, exponential shock waves were delivered at incremental energy levels until cardioversion was achieved or a maximum energy level of 300J was reached. Five treatment events were applied to three horses with chronic AF. Treated horses were observed for seven days post-treatment by physical examination, electrocardiography, analysis of serum biochemistry profiles and analysis of troponin 1. No adverse effects of cardioversion attempts or of general anaesthesia were observed, Cardioversion was achieved in one treatment event in a horse with a 3,5 year history of AF. This horse remained in sinus rhythm with no ongoing therapy. The procedure was then applied to eight client-owned horses, seven of which were successfully cardioverted using the technique. Duration of AF before treatment in these horses ranged from 3 weeks to at least 4 months. Cardioversion was achieved at energy levels ranging from 100--300J. Four of these horses had been previously treated with quinidine sulphate or gluconate. The client-owned horses have successfully returned to training. All horses have remained in sinus rhythm (7--21 months since treatment). Results suggest transvenous electrical cardioversion is a realistic therapeutic option for AF, whether of recent onset, chronic, or drug-resistant in nature. |
