Adenosine test in the diagnosis of unexplained syncope: marker of conducting tissue disease or neurally mediated syncope?

Adenosine test (supine administration of a 20 mg intravenous bolus with electrocardiographic and blood pressure monitoring) has been endorsed by the European Society of Cardiology guidelines on syncope management as an 'experimental' test in the diagnosis of unexplained syncope. The test is quick and cheap, but there is no consensus as to what condition, if any, the adenosine test is exposing, with conducting tissue disease and neurally mediated syncope proposed by various authors. In this article, we review the possible mechanisms underlying a positive adenosine test, its safety, and a comprehensive examination of the literature supporting each of the putative causal diagnoses.