Value of Head-Up Tilt Testing Potentiated With Sublingual Nitro lycerm to Assess the Origin of Unexp ained 1 Syncope

This study was undertaken to assess the value of sublingual nitroglycerin administration during u as a simple practical test for the diagnosis o P right tilt vasovagal syncope. To this purpose, 235 patients with syncope of unknown origin and no evidence of organic heart disease (110 men, mean age 52 f 20 years) and 35 asymptomatic control subjects underwent head-up tilt testing with nitroglycerin challenge. Patients and subjects were tilted at 60” for 45 + 20 minutes; the initial 45 minutes were without medication and the final 20 minutes after 300 pg of sublingual nitroglycerin. During the drug-free phase of the test, 59 patients (25%) and no controls had a positive response. After drug administration, a positive response (syncope in associa-