Effect of pilocarpin upon the cardiac mechanism in circus rhythm with ventricular tachycardia.

Abstract

Pilocarpine is known to stimulate the cardiac fibers of the vagus. The site of its action is in the neighborhood of the myoneural junction. Since vagus stimulation tends to increase the rate of the circus rhythm in auricular flutter and fibrillation and also to reduce the ventricular rate, pilocarpin might be expected to produce these effects.

We have given pilocarpin hydrochloride intravenously, in doses of one-sixteenth to one-eighth grain, to a number of patients with auricular fibrillation or flutter. In the majority of cases no definite effect was produced either upon the ventricular rate or upon the auricular mechanism. In one instance short attacks of auricular flutter were immediately abolished. In two cases of extreme ventricular tachycardia which followed the administration of quinidin, pilocarpin produced a sudden and abrupt fall of ventricular rate. In one of these cases, in which the auricles were fluttering, this was associated with a slight rise in the rate of the circus rhythm.

The action of pilocarpin, upon the vagus, in the dosage referred to, is very feeble. Nevertheless, the drug may occasionally prove useful in the suppression of post-quinidin tachycardia. The tachycardia which follows the administration of quinidin in cases of auricular fibrillation and auricular flutter is due to a depression of the rate of the circus rhythm, combined with partial vagus paralysis. It may be extreme and may cause the patient serious discomfort. The action of pilocarpin is peripheral to that of quinidin, and although its action is feeble it may increase vagal tone sufficiently to greatly reduce the ventricular rate.