Treatment of recent-onset atrial fibrillation with quinidine and flecainide in Thoroughbred racehorses: 107 cases (1987-2014).

The research focused on comparing the effectiveness of quinidine and flecainide in treating onset atrial fibrillation (AF) in racehorses. It found that quinidine was generally more effective, although rates of complications did not differ significantly between treatments.

Study Overview

• The study assessed the efficacy of quinidine and flecainide in treating recent onset of atrial fibrillation (AF), a heart condition, in Thoroughbred racehorses. AF is a condition that affects the heart’s rhythm and can lead to severe health complications if left untreated.
• The research was a retrospective case series, meaning it looked back at medical records from 1987 to 2014. The horses included had AF and were treated either with quinidine or flecainide.

Methodology

• The researchers divided the horses treated for AF into two groups based on the initial treatment they received: those treated with quinidine (group 1) and those treated with flecainide (group 2).
• If a horse in group 2 did not convert to normal sinus rhythm with flecainide, it was then given quinidine (this constitutes group 3).
• The complications, total quinidine dose, treatment duration, and conversion rates of the horses treated with either drug were compared.

Findings

• The overall rate of conversion back to normal heart rhythm (sinus rhythm) was 91% (97 out of 107 horses).
• The rate of conversion was significantly higher for horses treated initially with quinidine (91% – 71 of 78 horses) compared to those treated initially with flecainide (41% – 12 of 29 horses).
• In group 3, where horses initially treated with flecainide were administered quinidine due to failure of conversion, the conversion rate was 82% (14 of 17 horses).
• Neither the total quinidine dose nor the duration of treatment differed significantly between groups 1 and 3.

Conclusions and Clinical Relevance

• Overall, the cardioversion rate (return to normal heart rhythm) for Thoroughbred racehorses with AF was consistent with prior research.
• Flecainide treatment was less effective than quinidine, but the rate of complications was not different between either medication.
• The authors suggest further research to explore the effectiveness of flecainide in treating AF in athletic horses.