Transient complete atrioventricular block following transvenous electrical cardioversion of atrial fibrillation in a horse.

This research examined a case where a horse with a heart disorder called atrial fibrillation, which was not responsive to drugs, underwent an electrical treatment. After the treatment, the horse showed signs of temporary heart block, which were then corrected with artificial pacing. The study suggests having an artificial heart pacemaker available during such procedures on horses.

Method and Procedure

• The horse was suffering from a condition known as atrial fibrillation, which previous drug treatments had failed to correct.
• To treat this, an approach called transvenous electrical cardioversion was attempted.
• A temporary pacing catheter and two defibrillation catheters were inserted into the horse’s heart via veins. These devices are used to deliver electric shocks.
• The horse was placed under general anaesthesia for the procedure.
• Electric shocks of varying intensities were delivered between the defibrillation catheters. Despite these efforts, the horse’s regular heart rhythm was not restored.

Findings and Observations

• Immediately after the shocks of 200, 300 and 360 joules, the horse experienced a temporary third-degree atrioventricular block that lasted 15, 40, and 55 seconds respectively.
• Third-degree atrioventricular block is a severe type of heart block where the signals from the atria to the ventricles are completely interrupted.
• Durning these periods, the horse’s heart rate dropped significantly (profound bradycardia).
• This was corrected by using the temporary right ventricular pacemaker until the horse’s own heart conduction resumed.

Conclusions and Recommendations

• The study concluded that right ventricular pacing should be available during electrical cardioversion for atrial fibrillation in horses.
• This is because electrical cardioversion can potentially induce periods of profound bradycardia or atrioventricular block, which can be managed effectively with temporary right ventricular pacing.
• Therefore, being prepared with the option of pacing can help to manage any complications during the procedure, ensuring the safety and health of the horse.