Adenosine-Induced Paroxysmal Atrioventricular Block: a New Possible Cause of Unexplained Syncope?
Adenosine 5’ triphosphate (ATP) and its related nucleoside, adenosine, are ubiquitous biological compounds which exert a potent depressant activity on the atrioventricular (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 sites [1–4]. Inadvertent AVB has sometimes been observed after exogenous ATP or adenosine infusion in patients undergoing electrophysiological studies , in patients with paroxysmal supraventricular tachycardia , and in patients undergoing adenosine stress testing for the diagnosis of coronary artery disease [6, 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 pause [8–10].
KeywordsAtrioventricular Block Sick Sinus Syndrome Unexplained Syncope Carotid Sinus Massage Rapid Catabolism
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