A simplified differential pacing technique for the evaluation of bidirectional cavo-tricuspid isthmus block during ablation of typical atrial flutter

Purpose Bidirectional block of the cavo-tricuspid isthmus (CTI) is an established endpoint of CTI-dependent atrial flutter (AFl) ablation. Differential pacing has been used to evaluate the CTI block. The purpose of this study is to describe a modified differential pacing technique to evaluate the CTI block. Methods Sixty-two patients underwent radiofrequency (RF) ablation of CTI-dependent AFl. The acute endpoints were non-inducibility of the AFl, and verification of the bidirectional CTI block by our methodology. Pacing was performed in the CS with an ablation catheter positioned immediately lateral to the CTI ablation line, and then 1–2 cm more laterally. The stimulus-to-ablation catheter atrial electrogram intervals were measured at these sites (Stim CS -Abl 1 and Stim CS -Abl 2 , respectively). Pacing with the ablation catheter also was performed at these 2 sites, and the stimulus-to-CS electrogram intervals (Stim ABL1 -CS and Stim ABL2 -CS) were measured. The criteria for the bidirectional block were Stim CS -Abl 1 > Stim CS -Abl 2 , and Stim ABL1 -CS > Stim ABL2 -CS. Clinical efficacy was defined as freedom from recurrent AFl during follow-up. Results Following 12.2 ± 3.7 min of RF delivery across the CTI, intervals were Stim CS -Abl 1 = 181.2 ± 22.7 ms and Stim ABL1 -CS = 181.0 ± 23.6 ms, and Stim CS -Abl 2 = 152.2 ± 26.5 ms and Stim ABL2 -CS = 151.2 ± 22.7 ( P < 0.001). Atrial flutter was rendered not inducible in all patients, and no procedural complications were encountered. During the next 15.9 ± 0.7 months, two patients were lost to follow-up, and among the 62 other patients, one (1.7%) had flutter recurrence. Conclusions The bidirectional CTI block can be assessed quickly and easily using only the ablation and CS catheters for differential pacing.