ECHOCARDIOGRAPHIC ASSESSMENT AFTER INTRAVENOUS AMITRAZ OR XYLAZINE INJECTION IN CATS

Amitraz acts on a2-adrenergic receptors in a competitive and reversible way, leading to some xylazine-like effects. To evaluate the left ventricular function index after amitraz or xylazine administration, eight mongrel cats were submitted to intravenous injection: group X (xylazine), group A (amitraz) or group D (diluent). The same cats were used in all groups, after a 15-day interval. Heart rate (HR) and rhythm, shortening fraction (%SF), ejection fraction (%EF) and cardiac index (CI) were measured by echocardiography immediately before and during 60 minutes after drug injection. Amitraz and xylazine induced first-degree atrioventricular block (1st AVB) and decreases in HR, %SF, %EF and CI. The mean values of HR and all echocardiographic parameters of group X were significantly lower comparing to group A. It was concluded that both a2-agonists produce bradycardia and 1st AVB, but xylazine causes greater depression of the cardiac contractility.