Head up tilt test: is a single dose of nitroglycerine good for all?

Introduction: Head Up Tilt Test (HUTT) is the arguable gold standard for diagnosing neurocardiogenic syncope (NCS) with a diagnostic specificity of 80 to 100% and a sensitivity of 40 to 70%. Nitroglycerine (NTG) provocation elicits susceptibility to NCS. Aim: To test a new provocation protocol in patients with high pretest probability of NCS. Methods: All patients referred for HUTT for recurrent syncope. A history before the test established an index of suspicion for NCS. The patients consented for the test and were tilted at 60 degrees for 20 minutes then a first dose of sublingual NTG 500 mcg (20 minutes tilt) and then another 500 mcg (20 minutes tilt). Results: Nine subjects including one healthy volunteer (male, 28 years), 50% were males, mean age 55 years (range 28 to 81). HUTT was positive in 6 patients (75%). The control HUTT was negative. For positive tests the baseline pulse was 76.5 bpm (range 53 – 105 bpm), BP 141 mm Hg (range 100 – 190 mmHg) and for the negative tests the baseline pulse was 62.5 bpm (range 55 – 70 bpm), BP 155.5 mm Hg (range 150 – 161 mmHg). Of the 2 negative patients one had sinus node dysfunction and isorhythmic AV dissociation, the 2nd an 81 year old remained undiagnosed. The mean time to positive was 8.8 seconds (range 4 to 20 minutes). Heart rate drop for was 64.5 bpm (range 23 – 145 bpm), mean BP drop 58 mmHg (range 20 – 90 mmHg); in 2 cases BP was un-recordable. The ECG showed sinus bradycardia 4, sinus pause 1 and asystole 1. All positive cases and none of the negative tests showed paradoxical bradycardia despite drop in BP as a nitrate effect. Conclusion: A serial double dose nitrate provocation test improves the diagnostic yield. Keywords: HUTT, nitrate provocation, neurocardiogenic syncope, vagal syncop