Neosynephrine restores the normal sinus rhythm within thirty-five to seventy seconds after rapid intravenous injection in most cases of paroxysmal supraventricular tachycardia. The reversion of the supraventricular tachycardia is attributable to reflex cardiac inhibition elicited by the rapid rise in pressure in the carotid sinuses and aortic arch. The rise in pressure occurs as a result of the vasoconstriction produced by Neosynephrine. Presumably, any vasoconstrictor compound which acts quickly and briefly, and which has little or no direct stimulating action on the cardiac conducting system, would revert paroxysmal supraventricular tachycardia. Neosynephrine reverted paroxysmal supraventricular tachycardia in most cases when the systolic pressure reached a level of 160 mm. Hg or less. Some of the attacks which were terminated were refractory to treatment by mechanical methods and by various drugs. In occasional cases reversion was produced with Neosynephrine only when the systolic pressure was elevated to levels which might be considered too high for safety. In the typical case the rise in systolic blood pressure is proportional to the dose of Neosynephrine, and the maximum dose to be used is determined by the maximum rise in pressure which is considered safe for the individual patient. The initial dose should not exceed 0.5 mg., and any subsequent dose is selected on the basis of the pressor response to the initial dose. Most attacks were reverted by 1.0 mg. or less. These studies suggest that intravenous injection of Neosynephrine, or some other rapid-acting vasopressor substance, will prove to be the treatment of choice in selected cases of paroxysmal supraventricular tachycardia. © 1949.
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