CHANGES IN PLASMA EPINEPHRINE CONCENTRATION AND IN HEART-RATE DURING HEAD-UP TILT TESTING IN PATIENTS WITH NEUROCARDIOGENIC SYNCOPE - CORRELATION WITH SUCCESSFUL THERAPY WITH BETA-RECEPTOR-ANTAGONISTS

Introduction: Tilt table testing is widely used in the management of p atients with neurocardiogenic syncope, However, the exact pathophysiol ogic mechanism of this disorder is still under debate, Likewise, thera py of these patients continues to represent a challenge in many cases, Therefore, the present study aimed to gain further insight into the p athophysiology of this syndrome and to examine easily accessible clini cal parameters that can improve therapy selection. Methods and Results : In 16 patients with neurocardiogenic syncope, changes in endogenous catecholamine concentrations were determined during repeated tilt tabl e testing before and during treatment with metoprolol, Tachycardia pre ceded syncope in 8 of 10 responders compared to only 1 of 6 nonrespond ers (P < 0.05), In responders, the relative increase in epinephrine le vels averaged 197% +/- 51% during drug-free tilting and 75% +/- 33% du ring repeated testing while on beta-blocker therapy (P < 0.05), In non responders, there was a smaller relative increase in epinephrine avera ging 137% +/- 35% at baseline tilt, During repeated tilt testing, a si milar increase was observed in these patients with recurrent syncope ( 156% +/- 104%; P = NS compared to baseline). Conclusion: In patients w ith neurocardiogenic syncope who show both an increase in epinephrine concentration during tilt test and sinus tachycardia prior to the onse t of symptoms, beta-blocker treatment is very effective, These finding s confirm the major role of sympathetic activation as a trigger of syn cope, Particularly, heart rate changes at the onset of syncope may all ow early identification of patients responding to antiadrenergic thera py.