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