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The use of phenytoin in two horses following conversion from atrial fibrillation

Authors: Dicken M, Gordon SJG, Mayhew IG
Publication: New Zealand Veterinary Journal, Volume 60, Issue 3, pp 210-210, May 2012
Publisher: Taylor and Francis

Animal type: Horse, Livestock
Subject Terms: Cardiology, Disease/defect, Pharmacology, Treatment/therapy
Article class: Correspondence

Abstract:

Atrial fibrillation is the most commonly diagnosed arrhythmia with the potential to affect performance in horses (Reef et al.1988, 1995). It can be treated medically or with electroconversion. Medical treatments using oral quinidine sulphate have a success rate of approximately 88% in converting atrial fibrillation to normal rhythm (Reef et al.1988, 1995), although side effects are frequently encountered. These side effects include flatulence, diarrhoea, colic, upper respiratory tract stridor, ataxia, hypotension, tachycardia, and sudden death (Reef et al.1995), resulting in medication being stopped as soon as conversion takes place. Other medical treatments that have been trialled include I/V amiodarone (De Clercq et al.2006) and flecainide (van Loon et al.2004). Electroconversion is a new method that necessitates general anaesthesia and specialised equipment but was shown to have a success rate of 98% in one study (McGurrin et al.2008). Electroconversion is not universally available due to the need for specialised equipment and the requirement for a general anaesthetic, which may be contra-indicated in some cases. This means that medical conversion is still widely used. Both medical treatment and electroconversion can result in conversion followed by relapse into atrial fibrillation. Such relapses may be more likely with medical cases that have had a duration of atrial fibrillation of more than, compared with less than, 4 months (Reef et al.1988).

This paper describes the use of phenytoin after successful quinidine conversion of atrial fibrillation in two horses with the aim of maintaining sinus rhythm.

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