ABSTRACT
AIMS: Bidirectional block of the cavo-tricuspid isthmus (CTI) is a widely accepted endpoint for typical atrial flutter ablation, but its evaluation may be difficult, especially in the postero-anterior (clockwise) direction. The main goal was to evaluate pacing at the septal edge of the ablation line as an indicator of clockwise CTI block and as a predictor for flutter recurrence. METHODS AND RESULTS: In 94 patients undergoing flutter ablation, CTI block in the antero-posterior (counterclockwise) direction was determined by differential pacing from several levels of the anterior right atrial (RA). CTI block in the clockwise direction was evaluated by analysing electrograms (EGM) at the ablation line during differential pacing of the septal RA (differential septal pacing) or by anterior sequence of RA during pacing septal isthmus, next to the ablation line (septal CTI pacing). Ablation produced bidirectional block in 78% of the patients, unidirectional counterclockwise block in 9% and bidirectional conduction persisted in 13%. After follow-up (37 +/- 23 months), flutter recurrence occurred in 13% (48% if persistent conduction vs. 3% if bidirectional block, P < 0.001). During differential septal pacing, EGMs were difficult to interpret in 36% of the patients; in these cases, the diagnosis of CTI block or conduction in the clockwise direction was clearly established by using septal CTI pacing. CONCLUSION: Activation sequence of anterior RA during septal CTI pacing, next to the ablation line, is a reliable and simple method to diagnose clockwise CTI block and is associated with a low flutter recurrence.
