LIMITATIONS OF ADENOSINE IN ASSESSING THE EFFICACY OF RADIOFREQUENCY CATHETER ABLATION OF ACCESSORY PATHWAYS

Adenosine has been shown to reliably confirm the success of accessory pathway catheter ablation by producing transient atrioventricular (AV) block during atrial and ventricular pacing. This is due to the insens itivity of accessory pathway conduction to adenosine (with the rare ex ception of accessory pathways with decremental conduction properties). However, 4 of 204 consecutive patients who underwent successful acces sory pathway ablation (as shown by adenosine-induced transient AV bloc k) had recurrent AV reciprocating tachycardia involving a second, prev iously nonmanifest accessory pathway. In each case, the second accesso ry pathway was localized to a site disparate from the original pathway . No pathway showed decremental anterograde or retrograde conduction p roperties. In 2 patients, adenosine initially did not show the presenc e of the second concealed accessory pathway, because the refractory pe riod of the accessory pathway was longer than the pacing cycle length used to assess ventriculoatrial conduction. Only when the refractory p eriod of this second accessory pathway was shortened by infusion of is oproterenol did adenosine reveal the presence of the pathway during fo llow-up electrophysiologic study. In another patient, a nondecremental accessory pathway was shown to be sensitive to adenosine. In the rema ining patient, the second accessory pathway may have been transiently injured during the initial study, thereby simulating adenosine sensiti vity. Therefore, it is concluded that (1) adenosine is a highly, but n ot completely, effective method for immediately assessing the efficacy of accessory pathway catheter ablation; (2) concomitant infusion of i soproterenol during adenosine administration is necessary to recognize the presence of accessory pathways with prolonged refractory periods; and (3) assessment of the presence of accessory pathway conduction wi th adenosine after ablation should preferably be performed at the long est possible, paced cycle length.