Effects ofAdenosine on Atrial Tachycardia

Background Recent reports suggest thatadenosine, inaddition toterminating supraventricular tachycardia involving theatrioventricular (AV)node,mayhaveantiarrhythmic effects onatrial tachycardia. Theelectrophysiological effects of adenosine onsupraventricular tissue include shortening of action potential duration inatrial myocytes mediated bythe potassium current, IKAChAdO; shortening ofaction potential duration andhyperpolarization insinus nodecells; andantiadrenergic electrophysiological effects resulting frominhibition ofadenylyl cyclase. We therefore hypothesized thatthe response ofatrial tachycardia toadenosine wouldbemechanismspecific, withtermination ofatrial tachycardia dueto sinus nodereentry orcAMP-mediated triggered activity, transient suppression ofautomatic atrial tachycardia, andan absence ofantiarrhythmic effect ontachycardia duetointraatrial reentry. A denosine's antiarrhythmic effects onsupraventriculartachycardia wereoriginally thought tobe confined totachycardias involving theatrioventricular (AV)nodesuchasAV nodalreentrant tachycardia andreciprocating tachycardia using anaccessory AV pathway.1"2 Mostother formsofatrial tachycardia areconsidered tobeinsensitive toadenosine,34 asare mostforms ofventricular tachycardia.5'6 Although earlier studies showed that(with rareexceptions) adenosinefailed toterminate atrial fibrillation,7 atrial flutter, 38 intra-atrial reentry,4'7 andautomatic atrial rhythms,9-1" thepresent role ofadenosine inidentifying themechanism oftachycardia inpatients presenting withnarrowcomplex tachycardia isunclear because recent reports suggest that adenosine mayterminate as manyas80%ofthese arrhythmias.12"13 Theantiarrhythmic effects ofadenosine relate toits site-specific cellular electrophysiological effects. Activa