Effects of amiodarone on cardiac performance in arrhythmic dogs

Abstract

Arrhythmia is one of a serious cardiovascular problem that can lead to sudden cardiac death. In veterinary medicine, there are a few effective and safe anti-arrhythmic agents clinically available. Amiodarone is a class III potassium channel blocking agent that has prescribed more than 50 years in humans; however, there are few reports in the veterinary medicine. The drug also acts as beta-adrenergic and calcium channel antagonist which may produce adverse effects on cardiac contractility, relaxation, and thyroid functions. This study aimed to investigate the effects of amiodarone on arrhythmic control, cardiac performance, and thyroid hormone levels in dogs. Eight client-owned dogs with heart diseases were recruited from the cardiology unit, small animal teaching hospital, Chulalongkorn University. All dogs were had dilated Hearts and confirmed types of arrhythmia by Lead II ECGs and 24-hour Holter monitoring. Amiodarone were administrated at a loading dose of 10 mg/kg twice a day for 7 days, and followed by a maintenance dose of 5 mg/kg once a day. After treatment with amiodarone for 15 days, the results showed significant decreases in heart rate and total arrhythmic count (p < 0.05). Proarrhythmic assessment were found insignificantly changes both transmural dispersion of ventricle repolarization and beat-to-beat variability while QT interval was tended to lengthen (p = 0.06). Echocardiograms were displayed significantly prolongation of the pre - ejection period and isovolumic contraction time (p < 0.05). Moreover, Tei index tended to increase (p = 0.07). After 60 days of amiodarone treatment, both total plasma tri-iodothyronine (T3) and tetra-iodothyronine (T4) showed insignificant changes when compared with the baseline (p = 0.44 and 0.37, respectively). We conclude that the dosage of amiodarone treated in this study is effective, low risk of proarrhythmia, less negative inotropy, and fewer side effects which do not have any impact on clinical conditions. Therefore, amiodarone is safe for treated cardiac arrhythmias in dogs with organic heart diseases.