Latest Treatments in Atrial Fibrillation

Atrial fibrillation (AF) is the most common atrial arrhythmia associated with poor performance in horses (Bonagura et al.2010). The majority of horses with sustained AF have no evidence of significant structural heart disease, but ultrastructural and functional myocardial pathology, including AF-induced atrial remodelling, may still be present, predisposing to AF (Schwarzwald et al. 2007a; De Clercq et al. 2008a). Early recognition and prompt treatment of AF are thought to be important to prevent irreversible AF-induced atrial remodelling.

The most common treatment for AF involves conversion to normal sinus rhythm (NSR), unless there is concurrent congestive heart failure or the horse is aged and therapy is deemed of little benefit. Conversion of AF to sinus rhythm can be accomplished using a number of drugs or through transvenous electrical cardioversion (TVEC).

Quinidine sulphate (with or without the addition of digoxin) has been used for the longest period of time and still represents the standard treatment for AF in horses, despite the fact that treatment can be complicated by a variety of severe adverse reactions (Reef 2003; Bonagura et al. 2010). An excellent prognosis for quinidine conversion (>95% conversion rate) may be given for horses with short-lasting AF (<4 months) without underlying structural heart disease (Reef et al. 1988, 1995). Recurrences affect approximately 25% of these horses. Acceleration of AV nodal conduction is common during quinidine treatment, resulting in rapid supraventricular tachycardia. Affected horses are usually treated with digoxin to slow the ventricular rate. However, digoxin has a delayed onset of action, a low toxic-to-therapeutic ratio and may fail to effectively control heart rate. Based on recent studies (Schwarzwald et al. 2005, 2007a), diltiazem is likely to be safe and might be more effective than digoxin for ventricular rate control during quinidine treatment, provided that blood pressures can be closely monitored (Bonagura et al. 2010). Clinical experience with the use of diltiazem is limited and doses should be carefully titrated to effect. [...]