Use of Isoproterenol during anaesthesia in a dog with sick sinus syndrome (SSS)

A West Highland white terrier with clinically asymptomatic sick sinus syndrome (SSS) underwent 2 general anaesthesias. During the first anaesthesia severe bradycardia was obvious (19 - 40 beats per minute). Incremental doses of atropine up to a total dose of 0.12 mg/kg were given without any increase in heart rate. To increase HR during the second anaesthesia isoproterenol, a specific (3 sympathomimetic was used. With a continuous rate infusion (CRI) of isoproterenol (0.03 - 0.04 mu g/kg/min) heart rate was stable (100-120 bpm). Isoproterenol administration resulted in a moderate drop in blood pressure, especially of diastolic and mean blood pressure. Hypotension was nonresponsive to dopamine. The relevance of SSS for the anaesthetic protocol is discussed and the effects and side effects of isoproterenol are compared.