Intravenous nitrates for pharmacological stimulation during head-up tilt testing in patients with suspected vasovagal syncope and healthy controls

Nitrates may be used for pharmacological stimulation during tilt testing fo r the diagnosis of vasovagal syncope. In this study we assessed the diagnos tic value of intravenous nitrates during tilt testing in patients with a ty pical history of vasovagal syncope. Twenty patients and 23 controls were ti lted at 70 degrees for a maxim um duration of 30 minutes. After a 10-minute baseline supine phase, the test started with a continuous nitrate infusion at 1 mu g/kg/min and increased every 5 minutes by 1 mu g/kg/min, to a maxi mum of 6 mu g/kg/min at the end of the test. The test was ended if the subj ects developed a positive response (syncope or presyncope). Nineteen patien ts (95 %) and 17 (74 %) of the controls had a positive response. At test en d sensitivity was 95 %, but specificity was 26 % and accuracy was 58 %. Rec eiver operator characteristics (ROC) analysis revealed a maximum accuracy o f 79 % at 18 minutes, with a sensitivity of 80 % and a specificity of 78 %. Intravenous nitrates during tilt testing in patients with typical clinical criteria of vasovagal syncope is highly effective in provoking vasovagal s yncope. Based on the ROC analysis, a maximum accuracy of 79 % was attained at 18 minutes (at a dose of 4 mu g/kg/min), suggesting a good diagnostic pe rformance when tilt duration is limited to this point. A positive result re quiring more than 28 minutes of stimulated tilting should be interpreted wi th caution, due to the accompanying considerable decrease of specificity.