Atrial fibrillation in horses Part 2: Diagnosis, treatment and prognosis.

This research article concentrates on diagnosing, treating, and the prognosis of Atrial Fibrillation (AF) in horses, detailing methods like electrocardiography and heart rate monitoring and treatments like cardioversion and use of various therapeutic drugs. The study notes that after treatment, most horses can return to previous performance levels, but recurrence can happen with many associated risk factors.

Diagnosing Atrial Fibrillation

• The researchers identify initial signs of AF through the irregular rhythm of a horse’s heart rate during a resting phase. This is further confirmed by using electrocardiography.
• Heart rate monitoring, especially during exercise when the heart rate disproportionally increases or heart rate variability increases, is found useful in detecting AF.
• Echocardiography and laboratory analysis come into play when there is a need to identify an underlying cardiac disease that may be contributing to AF.

Treatment of Atrial Fibrillation

• The researchers discourage subjecting horses with severe cardiac disease to cardioversion due to the apparent risk of AF recurrence.
• Cardioversion is recommended for horses showing average maximum heart rates exceeding 220 beats per minute or abnormal ventricular complexes during exercise or stress. These horses are typically high-performance horses.
• The paper talks about a pharmacological cardioversion method where quinidine sulphate is administered orally. This method has an 80% success rate as per reported cases.
• Other therapeutic drugs that have been experimented with include flecainide, amiodarone, and novel atrial-specific compounds.
• A highly successful method of cardioversion is Transvenous Electrical Cardioversion (TVEC), where a shock is delivered between two cardioversion catheters positioned in the left pulmonary artery and right atrium. This method has a success rate exceeding 95%.

Prognosis and Recurrence

• The researchers noted recurrence rates of up to 39% following either pharmacological or electrical cardioversion treatments.
• Previous unsuccessful treatment attempts, the presence of atrial premature depolarisations, low atrial contractile function after cardioversion, and valvular regurgitation have all been linked to recurrence.
• Risk factors for recurrence are also thought to include a large atrial size and long periods of AF.
• Lastly, the paper mentions the administration of sotalol as a possible method for preventing recurrence. However, it also notes that large clinical studies confirming its effectiveness haven’t been published yet.