Sick sinus syndrome in nine West Highland white terriers

Sick sinus syndrome is a clinical term used to describe flee clinical signs of sinus node dysfunction. This paper describes the clinical data from nin e West Highland white terriers, eight females and one male, in which a diag nosis of sick sinus syndrome was made. The most common clinical signs were episodic weakness and presyncope. Electrocardiographic findings included si nus bradycardia, sinus arrest with or without escape complexes, disturbance s of atrioventricular conduction, paroxysmal supraventricular tachycardia, or some combination of these dysrhythmias. The main radiographic changes we re mild right-sided cardiomegaly in five cases, and a slight increase in br onchial and interstitial markings in four, but there was no evidence of con gestive heart failure in any of the dogs. Echocardiography revealed mild to moderate mitral endocardiosis in three cases with no other significant abn ormalities. The dogs' responses to parenteral atropine were variable and we re not necessarily related to their response to oral anticholinergic agents . Five of the dogs were initially treated with propantheline bromide, but i n only two of them were the clinical signs controlled in the long term. Six of the dogs were successfully treated by the implantation of a transvenous pacemaker.