Treatment of atrial fibrillation in horses: new perspectives.

The research study focuses on the treatment of atrial fibrillation (AF) in horses using a specific dosage of quinidine sulfate and managing potential side effects using digoxin. The researchers assessed the effectiveness of the treatment and evaluated the relationship between adverse effects and plasma quinidine concentrations.

Study Design

• The study involved the treatment of forty-one horses that were suffering from atrial fibrillation.
• A dosage of 22 mg/kg of quinidine sulfate was administered via a nasogastric tube in 2-hour intervals until the horse converted to sinus rhythm, or had reached a total dose of between 88 and 132 mg/kg, or showed any adverse or toxic reactions to the drug.
• If conversion to sinus rhythm did not occur after the initial treatment, the dosage intervals were extended to every six hours.

The Role of Digoxin

• The use of digoxin was tested in specific cases. These included horses with a fractional shortening of 27% or less, prone to tachycardia with a resting heart rate above 60 beats per minute, or a history of sustained tachycardia over 100 beats per minute during prior treatment.
• Digoxin was also administered if the horse developed sustained tachycardia during the first day of the quinidine treatment, or on the second day if the conversion to sinus rhythm had not occurred.

Findings and Observations

• Plasma quinidine concentrations within the first hour of AF conversion to sinus rhythm ranged from 1.7 to 7.5 micrograms/mL, and 1.7 to 4.7 micrograms/mL in 97% of the horses.
• Adverse or toxic effects of quinidine were observed in 92% of the horses that exhibited plasma quinidine concentrations exceeding 5 micrograms/mL.
• No statistical association was found between plasma quinidine concentrations and sustained tachycardia, diarrhea, or colic. However, strong connections were observed with ataxia and upper respiratory tract stridor.
• In 98% of cases, the conversion did not occur if toxic or adverse effects of the drug were present or when plasma quinidine concentrations exceeded 5 micrograms/mL.