VASOVAGAL SYNCOPE AFTER INFUSION OF A VASODILATOR IN A HEART-TRANSPLANT RECIPIENT

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. © 1990, Massachusetts Medical Society. All rights reserved.