The aim of our present study was to assess the value of
nitroglycerin infusion during upright posture as a new provocative test for diagnosis of
vasovagal syncope. To this purpose 40 patients with unexplained
syncope (17 men and 23 women, mean age 47 years) and 25 asymptomatic control subjects with negative baseline head-up tilt underwent two other tilting tests, one during
nitroglycerin infusion and one during
isoproterenol infusion. The protocol of the
nitroglycerin test consisted of a maximum of five successive stages of 5 minutes in the supine position plus 10 minutes 80-degree upright tilt at progressively increasing infusion rates (increments of 0.86 microgram/kg/hr every stage). During the
nitroglycerin test a positive response (
syncope in association with sudden
hypotension and
bradycardia) occurred in 21 (53%) patients with unexplained
syncope, an exaggerated response (minor symptoms in association with slowly increasing
hypotension alone) occurred in 10 (25%), a negative response in 9 (22%), and
drug intolerance in 0. During the
isoproterenol test these percentages were 25%, 25%, 32%, and 18%, respectively. Only 2 (8%) control subjects had a positive response to
nitroglycerin test and 2 (8%) to
isoproterenol test. Thus the
nitroglycerin test seems to be a useful alternative tool for diagnosis of
vasovagal syncope; it is equally specific but more sensitive and feasible than the
isoproterenol test.