Isoproterenol induced cerebral hypoperfusion in a heart transplant recipient

To determine the effect of tilt isoproterenol provocation on cerebral perfusion in a patient with denervated heart, transcranial Doppler sonography was used to assess changes in cerebral blood flow velocity during upright tilt test. A 51-year-old man with history of syncopal spells after heart transplantation was evaluated by using upright tilt test with and without isoproterenol for 30 minutes, respectively, at 80 degrees inclined. Mean cerebral blood flow was measured in the main stem of the right middle cerebral artery. Blood pressure and heart rate were noninvasively monitored. Tilt isoproterenol provocation but not tilt alone induced a significant reduction in cerebral blood flow velocity, without remarkable hypotension. There was no change in respiratory activity. This may indicate that vagal reflexes are not implicated in the mechanism of isoproterenol to induce cerebral hypoperfusion and hence neurally mediated syncope.