Biphasic response of the SA node of the dog heart in vivo to selective administration of ketamine.

Effect of ketamine on the SA node of the dog heart was studied in vivo using a selective perfusion technique of the SA node artery. Injections of ketamine in doses from 100 microgram to 3 mg into the artery produced a depression of the SA nodal activity by a direct action. This depression was followed by the sudden appearance of a stimulatory phase. Bilateral vagotomy and sympathectomy or prior administration of a ganglion blocker failed to inhibit the occurrence of the ketamine-induced tachycardia, while it was completely abolished in the reserpinized dogs or by a prior injection of a beta-blocking agent into the SA node artery. This may indicate that an activation of the peripheral adrenergic mechanism plays an important role in the induction of the excitatory effect of ketamine injected in the SA node artery.