INTRODUCTION
Ablation of the cavo-tricuspid isthmus (CTI) to produce persistent bidirectional block is the treatment of choice for typical atrial flutter,1 making it one of the most common procedures in cardiology. Because the conduction block produced by radiofrequency (RF) energy can be reversible, it is usual to wait for a period of 20-30 minutes after the achievement of CTI block before the procedure is concluded.2 This waiting period adds to the duration of the procedure, and therefore to its cost.
Administration of adenosine or of adenosine triphosphate (ATP), originally used to demonstrate residual accessory pathway conduction by blocking atrioventricular nodal conduction,3 was subsequently noticed to reawaken conduction in some pathways blocked by RF delivery.4 This transient recurrence was predictive of a subsequent persistent recurrence of conduction. Similar resurrection of dormant conduction has been shown for block between pulmonary veins and the atrium after RF isolation,5and between an isolated superior vena cava and the adjacent right atrium.6 The effect is believed to derive from adenosine induced resting-potential hyperpolarization which reverses the depolarisation that characterises RF-induced injury.7The same phenomenon occurs after CTI block,8 so adenosine testing has been proposed as a substitute for the traditional waiting period.9