Changes in Plasma Epinephrine Concentration and in Heart Rate During Head‐Up Tilt Testing in Patients with Neurocardiogenic Syncope:

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Abstract
Tilt table testing is widely used in the management of patients with neurocardiogenic syncope. However, the exact pathophysiologic mechanism of this disorder is still under debate. Likewise, therapy of these patients continues to represent a challenge in many cases. Therefore, the present study aimed to gain further insight into the pathophysiology of this syndrome and to examine easily accessible clinical parameters that can improve therapy selection. In 16 patients with neurocardiogenic syncope, changes in endogenous catecholamine concentrations were determined during repeated tilt table testing before and during treatment with metoprolol. Tachycardia preceded syncope in 8 of 10 responders compared to only 1 of 6 nonresponders (P < 0.05). In responders, the relative increase in epinephrine levels averaged 197% +/- 51% during drug-free tilting and 75% +/- 33% during repeated testing while on beta-blocker therapy (P < 0.05). In nonresponders, there was a smaller relative increase in epinephrine averaging 137% +/- 35% at baseline tilt. During repeated tilt testing, a similar increase was observed in these patients with recurrent syncope (156% +/- 104%; P = NS compared to baseline). In patients with neurocardiogenic syncope who show both an increase in epinephrine concentration during tilt test and sinus tachycardia prior to the onset of symptoms, beta-blocker treatment is very effective. These findings confirm the major role of sympathetic activation as a trigger of syncope. Particularly, heart rate changes at the onset of syncope may allow early identification of patients responding to antiadrenergic therapy.