[The adenosine-5'-triphosphate (ATP) test: a diagnostic tool in the management of syncope of unknown origin. Basic and clinical aspects].
The prevalence of syncope increases in elderly population. An inappropriate reflex reaction of the autonomous nervous system in specific circumstances is responsible for symptoms in more than 50% of cases. These neurocardiogenic or vasovagal syncopes are due to a vasoplegia or to a cardio-inhibitory reflex or to the association of both mechanisms. Reproducing the symptoms may contribute to identify the responsible mechanism of syncope; this objective is partly reached by the head-up tilt test--a provocative test--which reproduces symptoms in about half of the cases, mainly by provoking a severe vasodilation with fall of blood pressure. On the opposite, the ATP test (20 mg i.v. bolus)--a descriptive test--provokes a strong cardio-inhibitory reflex independent from external factors like body position but it must be undertaken in a calm environment for preventing any anticipative sympathetic reaction. The test is considered positive if ATP produces a cardiac pause longer than 10 seconds and related symptoms are not taken into account for assessing the final result. ATP test positivity increases with age and with the presence of cardiac diseases. Permanent dual chamber pacing at 70 bpm has been shown to reduce significantly the syncope recurrences in patients with positive ATP test and to have no influence on patients with a negative test. The use of ATP test should be extended to all syncope screening. Its positivity identifies a group of patients in whom the mechanism of the syncope is susceptible to be improved by a permanent dual chamber pacing.