Comparison of provocative tests for unexplained syncope: isoprenaline and glyceryl trinitrate for diagnosing vasovagal syncope.

Abstract

To compare the sensitivity, specificity and adverse event profile of glyceryl trinitrate head-up tilt with isoprenaline head-up tilt in the diagnosis of vasovagal syncope in patients with unexplained syncope and healthy controls. Forty-eight patients with unexplained syncope and negative passive head-up tilt at 70 degrees for 40 min, and 14 healthy controls underwent glyceryl trinitrate head-up tilt and isoprenaline head-up tilt (maximum dose 5 microg x min(-1)) one week apart in random order. Outcome measures were production of symptoms (syncope, pre-syncope) with development of hypotension. In those with negative passive head-up tilt, the sensitivity of glyceryl trinitrate for diagnosing vasovagal syncope was 48% and the specificity was 71%. Glyceryl trinitrate was well tolerated. Isoprenaline sensitivity was 21% with specificity 64%. Side-effects prevented completion of the test in 68%. Commonest adverse events were the development of hypertension or tachycardia and intolerable flushing or nausea. Glyceryl trinitrate head-up tilt is as effective as isoprenaline head-up tilt as a provocative agent for vasovagal syncope and has a lower incidence of adverse events.