Vasovagal Syncope after Infusion of a Vasodilator in a Heart-Transplant Recipient

Abstract

HYPOTENSIVE states are well known to activate the sympathetic nervous system, leading to reflex vasoconstriction and tachycardia.¹ Hypovolemic hypotension, however, can be accompanied by paradoxical withdrawal of sympathetic drive, leading to vasodilation and bradycardia — responses that, in turn, exacerbate the decrease in blood pressure.^{2 3 4 5} In humans, hypotension with an inappropriately normal or frankly decreased heart rate has been observed during hemorrhagic shock,⁶ after the infusion of vasodilators,⁷ and most recently, in response to the infusion of isoproterenol during the upright-tilt test, which is used to provoke syncope.^{8 , 9} The current belief is that this type of vasodepressor reaction is a . . .