Transvenous Electrical Cardioversion of Equine Atrial Fibrillation Technical Considerations

Abstract

Conventional treatment of equine atrial fibrillation (AF) involves administration of quinidine salts. Most uncomplicated cases respond to treatment, but pharmacologic cardioversion involves a range of adverse effects, and some horses are unable to tolerate medication. A study was undertaken to develop transvenous electrical cardioversion (TVEC) as an alternative treatment. Safety issues and catheter placement techniques with catheter-integrated cardioversion electrodes were investigated, and responses to shock application were evaluated. After the premortem catheterization of elective-euthanasia horses, no tissue abnormalities were detected at postmortem examination. To evaluate the response to the application of shocks and appropriate electrode positions, an electrical cardioversion of research horses in chronic AF was then attempted. After catheterization of the right atrium (RA) and pulmonary artery through the right jugular vein, horses were placed under general anesthesia. Biphasic, truncated exponential shock waves were delivered at incremental energies until cardioversion was achieved or until a maximum energy of 300 J was reached. Five treatment events were applied to 3 horses, with cardioversion achieved in one of the treatment events. No adverse effects of cardioversion attempts or general anesthesia were observed. The procedure was then applied to 8 client-owned horses, with cardioversion achieved in 7. No adverse responses to appropriately delivered shocks were observed. No antiarrhythmic medications were administered to any horse at any stage. Catheter design and placement technique evolved throughout the study, with combined ultrasonography and pressure guidance proving most effective in achieving appropriate electrode placement. Results suggest TVEC, as applied in the present study, is a safe, effective, and realistic therapeutic option for equine AF.Key words: Cardiac disease; Electrophysiology; Heart; Horse. Management of atrial fibrillation (AF) in horses has traditionally involved the administration, PO and, more recently, IV, of a quinidine salt.1-4 The treatment is effective in approximately 80% of horses but involves a range of dose-related and idiosyncratic toxic responses varying from mild and benign to fatal.1-4 Additional therapeutic modalities are required to avoid these adverse effects and to provide options for those horses that fail to respond to, or are intolerant of, quinidine salts.Electrical cardioversion involves the application of electrical shock (with a defibrillator) with the goal of depolarizing all or part of the atrial myocardium. Electrical cardioversion of AF is becoming routine in human medicine, because the efficacy of this modality is often higher than that of pharmacologic methods for the restoration of sinus rhythm.5 In humans, lower energy requirements and higher efficacy have been reported with internal electrical cardioversion with catheter-mounted electrodes (transvenous electrical cardioversion [TVEC]) than with external techniques with thoracic paddles, 5-7 ...

The diagnosis and management of atrial fibrillation in the horse

“…Efficacy may be influenced by case selection or by technique, including electrode design and positioning. 24 , 25 , 46 Breed, patient weight, and duration of AF were not shown to influence efficacy in two studies. 24 , 46 Horses with AF have been reported as good candidates for anesthesia, and the anesthetic risks for the procedure are reported as comparable to other elective anesthetic procedures.…”

“…Various configurations of catheter designs have been used with success in the horse. 19 , 23 – 25 An advantage to TVEC is that antiarrhythmic medications are not required; therefore, this option is a consideration for those animals in which these medications are not an option (did not work/adverse response). With TVEC, the electrodes are placed through a jugular vein and guided into the right atrium and left pulmonary artery.…”

“…Overall, the recurrence rates between horses treated with quinidine and TVEC are considered similar. 10 , 19 , 23 – 25 , 43 , 45 , 46 There appears to be a higher risk for recurrence in warm-blood horses and in horses that had AF for longer duration prior to treatment. 10 , 43 , 46 Slow return to exercise in the latter group may decrease risk of early recurrence due to AF-induced remodeling.…”

Paroxysmal Atrial Fibrillation in Horses: Pathophysiology, Diagnostics and Clinical Aspects

“…There are few treatment options for horses with pAF, but cardioversion is currently recommended if the episode lasts longer than 48 h [24,62]. Cardioversion can be achieved either pharmacologically with quinidine sulphate or by transvenous electrical cardioversion (TVEC), but these procedures are not within the scope of this review and are described in detail elsewhere [1,24,117,118]. Cardioversion of AF horses presenting with sudden reduced performance but without underlying diseases can return them to their previous level of performance [7,17,61].…”