Components of clinical trials for vasovagal syncope.

The time is ripe for adequately powered, randomized, placebo-controlled clinical trials in vasovagal syncope. Vasovagal syncope is a common syndrome, the symptoms of which can be troublesomely frequent. It is usually diagnosed by tilt-table testing, although this has persistent problems with both sensitivity and specificity. Patients with syncope and positive tilt tests have been the subjects of numerous studies of natural history, risk stratification, and treatment. This paper discusses studies of treatments for vasovagal syncope in the context of a classification of the levels of evidence that can be gleaned from clinical studies. The reasons for placebo-controlled trials are reviewed, as is the evidence for various methods of risk stratification. Data for power calculations are presented for the primary outcome, the time to the first syncope recurrence. Strengths and weakness of the four main types of outcomes for clinical trials are compared.