Adenosine's effectiveness in long RP' re-entrant tachycardia: additional evidence of the decremental qualities of the retrograde limb. 
Adenosine's ability to terminate atrioventricular (AV) re-entrant supraventricular tachycardia is well documented.  Typically, termination occurs as a consequence of transient conduction block in the atrioventricular node, a tissue with decremental qualities.  However, the atrioventricular node is not always the site of action when adenosine is used on the re-entrant types of long RP' tachycardias.  These tachycardias are, in part, characterized by the decremental qualities of the retrograde limb of the tachycardia circuit, which, in turn, are typically exemplified by retrograde Wenckebach during ventricular (VVI) pacing during intracardiac electrophysiology studies.  This case report involves adenosine's ability to block conduction in the retrograde limb of the permanent form of junctional reciprocating tachycardia to provide further evidence as to the AV "nodelike" decremental qualities of this limb.