Clinical characteristics of unexplained syncope and their relationship to tilt table test outcomes

To describe the clinical characteristics of patients presenting to a tertiary referral centre undergoing tilt table testing (HUT), comparing those who have vasovagal syncope (VVS) confirmed as a cause of symptoms and those with unexplained syncope after HUT.

Prospective study of consecutive patients presenting to a regional tertiary referral centre, with more than two episodes of unexplained syncope in the past year. Detailed semi-structured questionnaires were completed regarding presenting symptoms, prodromal features and precipitating factors.

Eighty-seven patients were studied, 31 had positive passive head up tilt (HUT), 31 positive provocative HUT (either sublingual glyceryl trinitrate or intravenous isoprenaline) and in 25 patients, syncope remained unexplained at the end of tilt testing. Characteristics of patients with positive passive HUT did not differ significantly from those requiring pharmacological provocation, although passive HUT patients were more likely to have classical prodrome and precipitants. The clinical characteristics of those whose syncope remained unexplained differed from those who had VVS confirmed by tilt table testing, in particular symptoms after syncope were less common and clustering of episodes was unlikely. Prodrome was absent in over 80 % of the "unexplained" group.

Clinical characteristics of patients with unexplained syncope and negative tilt tests differ from those with positive tilt studies. Further cardiovascular testing should be undertaken in this group to determine other causes of syncope.