Carlo Menozzi, Michele Brignole,
Germano Gaggioli, Lorella Gianfranchi, Angelo Bartoletti, Nicola Bottoni, Gino Lolli,
Daniele Oddone, Attilio Del Rosso, Giuseppe Pellinghelli.
Sections of Arrhythmology, Ospedale S. Maria Nuova, Reggio Emilia, Ospedali Riuniti,
Lavagna, Italy
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Adenosine 5' triphosphate (ATP) and its related
nucleoside, adenosine, are ubiquitous biological compounds which exert a potent depressant
activity on the AV node; this can result in transient atrioventricular block (AVB). ATP
and adenosine are released from myocardial cells under physiological and pathological
conditions (for example in the case of myocardial oxygen supply-demand imbalance) and have
similar effects. The negative dromotropic action of ATP is due to its rapid catabolism to
adenosine and the subsequent action of adenosine at purinoceptor sites1-4.
Inadvertent AVB has sometimes been observed after exogenous ATP or adenosine infusion in
patients undergoing electrophysiological studies4, in
patients with paroxysmal supraventricular tachycardia5,
and in patients undergoing adenosine stress testing for the diagnosis of coronary artery
disease6,7. At higher doses, an intravenous bolus of
ATP or adenosine has been seen to cause transient AVB in many patients with
neurally-mediated syncope, or sick sinus syndrome and in controls; the AVB has sometimes
been associated with a prolonged asystolic ventricular pause8-10.
Therefore, because of its powerful negative effect on AV conduction, we hypothesized
that an increased susceptibility of the AV node to adenosine may play a role in the
genesis of some cases of unexplained syncope. The aims of the present study were to
evaluate: the normal range of responses to an intravenous bolus of ATP (ATP test) in
control subjects without syncope; and the diagnostic value of ATP testing in patients with
syncope of unexplained origin (SUO).
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