Tilt-table testing: transient loss of consciousness discriminator or epiphenomenon?

Syncope accounts for 1–1.5% of emergency room visits and up to 6% of general hospital admissions. Patients with syncope present with a blackout, or transient loss of consciousness (T-LOC), and may present in family practice, cardiology, general medicine, accident and emergency, neurology, geriatric medicine, and psychiatry. Generally, a patient with T-LOC can only give limited details of the event, covering premonition and aftereffects. An eyewitness account is essential for filling in details during T-LOC. However, there are important causes of T-LOC other than syncope, e.g. generalized epilepsy and psychogenic blackouts. When patients present having had T-LOC, clinicians seek a test that will discriminate between these important causes. Is tilt-table testing such a test? Tilt testing is a simple, non-invasive test with a low risk of complications. The physiological and pathophysiological effects of orthostatic stress by tilt testing have been known for 60 years. In 1986, Kenny et al. observed a high rate of tilt-induced syncope, with hypotension and bradycardia, in patients with syncope of previously unknown origin when compared with controls. Subsequently, many reports profiled the use of the test, and guidelines and recommendations emerged. However, clinical practice featured a very variable yield from a wide range of protocols, varying in duration and angle of tilt, the use of drug provocation to increase yield, and most importantly, the type of patients studied. Such factors presumably underlie the variable yield of tilt-table testing, which is from 26 to 87%. The overall reproducibility of a negative response (85–94%) is higher than that of an initial positive response (31–92%). The impact of these variations in protocol and patient clinical types, and their effect on the interpretation of a test result for T-LOC discrimination, is considered below. What types of patients were studied?