Transcristal Conduction During Isthmus Ablation of Typical Atrial Flutter:

The crista terminalis (CT) has been recognized as the anatomic structure responsible for the line of conduction block at the posterior right atrial wall during typical atrial flutter.1 It is now well established that this line of block is mainly functional.2-4 Transverse conduction across the CT can be observed at long pacing cycle length or during some atrial arrhythmias, such as lower loop reentrant tachycardia.5 During typical atrial flutter ablation, determination of complete clockwise isthmus block most often is based on the recording of a purely craniocaudal activation sequence at the anteroinferior right atrium (AIRA) while pacing the proximal coronary sinus (pCS).6,7 However, rapid transverse conduction across the CT can modify the activation sequence at the AIRA and masquerade as persistent residual clockwise isthmus conduction.4 The aims of this study were to evaluate (1) the incidence of transverse conduction across the CT, (2) the influence of transcristal conduction on AIRA activation sequence during pCS pacing after isthmus block,completion and (3) the effectiveness of a dynamic pacing technique (positional pacing) in discriminating anterior from posterior low right atrial conduction properties during typical atrial flutter ablation.