SUBJECTS AND METHODS: Two hundred patients, undergoing baseline HUT (60 degrees for 20 minutes) for suspected vasovagal syncope or presyncope and unexplained dizziness, were enrolled. If the baseline HUT was negative, isosorbide dinitrate (2.5 mg) spray was applied sublingually (group I, n=93), or isoproterenol (3 microgram/min) infused (group II, n=93), in a randomized fashion. The values of isosorbide dinitrate and isoproterenol were compared in those patients that developed a positive vasovagal response or who completed the drug-provocative HUT.

RESULTS: Syncope was similarly reproduced in both groups (47.7 vs. 41.9%, p>0.05). Type I responses were most common in both groups, and types I and II responses were more common in group I than group II (78.0 vs. 55.6% and 12.2 vs. 5.6%, p<0.05, respectively). The average time to a positive response was longer in group I than group II (8.5±3.4 vs. 6.1±3.6 minutes, p<0.01). The sensitivity and specificity of the drug-provocative HUT were significantly higher in group I than group II (73.5 and 87.5% vs. 58.5 and 71.1%; respectively, p<0.01). The incidence of minor adverse effects were similar in both groups, but serious cardiac side effects were significantly more common in group II than group I (4.3 vs. 0%, p<0.05).

CONCLUSION: Sublingual isosorbide dinitrate spray may be used as a simple, effective and well tolerated provocative drug during HUT.