A simple and definite proof of complete cavotricuspid isthmus block

This editorial refers to ‘A simple pacing method to diagnose postero-anterior (clockwise) cavo-tricuspid isthmus block after radiofrequency ablation’ by A. Pastor et al. , on page 1290 Deep understanding of typical atrial flutter and its ablative treatment covers huge areas of our subspeciality. Until the rise of ablation of atrial fibrillation, typical atrial flutter ablation was the most frequently performed catheter ablation procedure. It still is the first ablative technique to be performed by any fellow. The paper of Pastor et al.1 is a proof for the fact that atrial flutter ablation, 23 years after its first catheter-based treatment description, 2 is still subject for research. Complete bidirectional block of the cavotricuspid isthmus (CTI) after radiofrequency ablation of typical atrial flutter is an established endpoint. Methods to determine completeness of block are subject to debate, 3–6 since the ultimate electrophysiological proof does not seem to exist. Additionally, because of increasing economic constraints, the number of usable catheters and poles may become limited. The criterion for clockwise (CW) CTI block based on the anterior right atrium (RA) activation sequence during septal CTI pacing has been proposed to overcome the limitations of other criteria. 7 Pastor et al. elegantly and meticulously evaluate the clinical significance of this method, validating it as a powerful predictor of a freedom of recurrence after more than 3 years. Several issues are to be raised. First, in this retrospective series, three types of ablation catheters have been used which may partially affect the conclusion that can be drawn from this study: a solid 4 mm-tip catheter, a solid 8 mm-tip catheter, and an open-irrigation 4 mm-tip catheter. It seems that the solid 4 mm-tip catheter was the least effective and accounted for the majority of recurrences. Secondly, the importance of obtaining non-ambiguous evidence of complete bidirectional CTI block is stressed again. Atrial flutter recurrence rate was only 3% in the presence of bidirectional block vs. 22% in the case of unidirectional block and 67% in the absence of block ( P < 0.001 vs. bidirectional block). This is not a new observation but interestingly and, in our opinion, of major importance, CW CTI block, as demonstrated by completely descending anterior RA activation sequence during septal CTI pacing, was simultaneously proven by differential pacing in only 64% of these cases. The limited sensitivity of septal differential pacing was attributed to the unclear local CTI electrogram interpretation (due to the low voltage and fragmented potentials) and was observed in 36% of cases, which is similar to our experience. 5 Moreover, CTI anfractuous anatomy 8 , 9 makes detailed assessment of the ablation line difficult. We still think that accurate activation mapping of the anterior RA activation sequence during septal CTI pacing is of prime importance to clearly identify complete CTI block. The usefulness of a multipolar catheter is stressed out once more in this paper, with its distal poles placed along the antero-inferior RA wall but in the most immediate vicinity of the ablation line. Many cases of localized slow (yet persistent) conduction are then easily ruled out. Moreover, the use of this type of catheter also helps to identify transcristal conduction while pacing immediately septal to the ablation line. Transcristal conduction is particularly confusing while evaluating CW block by differential septal pacing 10 and may require more laborious pacing maneuvers. 11 At last and particularly important, a new finding is underlined in this study. All patients with CW block also had counterclockwise (CCW) block, whereas unidirectional block concerned only the CCW direction (nine patients); they had persistent CW conduction, a higher recurrence rate than patients with CW block (22 vs. 3%, p < 0.001). None of the patients had unidirectional CW block. In addition to a very low long-term recurrence rate of atrial flutter in CW block patients, which translates into persistent CCW block, one might assume that CW block, as assessed by the descending anterior RA activation sequence during septal CTI pacing, is predictive of long-term CCW block. Proving the completeness of block of an ablation line is an everyday challenge for the electrophysiologist. The authors are to be congratulated for their important and elegant work which brings a clinical validation of a powerful block criterion. They remind us of a basic electrophysiological principle such as the importance of detailed mapping of one side of a line of block while pacing closely the other side of the line. Even though not perfect, these principles rule out many ‘pseudo-block’ cases due to slow conduction and should be, in our opinion, systematically used in clinical practice. Conflict of interest: none declared.