Spontaneous vs nitroglycerin-induced vasovagal reflex on head-up tilt: Are there neuroendocrine differences?

Patients with spontaneous VVS on HUT reported more syncopal events than those with drug-potentiated positive HUT, but both groups shared similar supine neuroendocrine profiles. However, spontaneous VVS during HUT is characterized by lower blood pressure, pronounced increases in epinephrine and vasopressin during early HUT phase, and higher frequency of reflex asystole.