European Heart Journal Advance Access originally published online on September 1, 2008
European Heart Journal 2008 29(19):2321-2322; doi:10.1093/eurheartj/ehn390
Rhythm-‘a-line-ment’ during catheter ablation of chronic atrial fibrillation: the role of left atrial linear lesions
University Hospital Eppendorf, Heart Center, Department of Electrophysiology, D-20246 Hamburg, Germany
* Corresponding author. Tel: +49 40 428034120, Fax: +49 40 428034125, Email: willems{at}uke.uni-hamburg.de
This editorial refers to ‘Left atrial linear lesions are required for successful treatment of persistent atrial fibrillation’
by S. Knecht et al., on page 2359
Footnotes
The opinions expressed in this article are not necessarily those of the Editors of the European Heart Journal or of the European Society of Cardiology.
Although recommended by the current guidelines for the treatment of atrial fibrillation (AF),1,2 catheter ablation of long-standing persistent AF (herein referred to as chronic AF) still remains a challenge for the interventional electrophysiologist. Initial attempts at a successful treatment of chronic AF have concentrated on different lesion sets. In the past, we have learned that pulmonary vein (PV) isolation alone, irrespective of its extension in terms of isolated atrial tissue around the PVs, is not sufficient to achieve a considerable success rate and, therefore, is restricted to a very selected cohort of chronic AF patients.3,4 Thus, additional arrhythmogenic processes beyond the PVs have become evident in the pathophysiology of chronic AF. Based on the concept of the ‘multiple wavelet’ hypothesis and in an effort to replicate the results of the surgical treatment of AF, linear lesions were applied to the left atrium, alone or in addition to PV isolation. However, with bidirectionally blocked lines at the left atrial roof and the mitral isthmus,4 or even with complete electrical isolation of the posterior left atrium including the PVs,5 the success rates range between 60 and 70%. Since a significant number of patients did not benefit from a standardized lesion set, the new concept rather to tailor the ablation approach to the patients' individual chronic AF processes has been implemented by Haissaguerre and co-workers.6 This concept was based on the observation that chronic AF could occasionally be terminated by ablation. Thus, using the combination of different strategies, i.e. PV isolation, ablation of complex fractionated atrial electrograms, and, as a final step, left atrial linear ablation, termination of chronic AF was used as the desired procedural end-point for the first time. Interestingly, AF termination did not require the application of linear lesions in a considerable number of patients. This observation, along with the complexity of linear ablation, has resulted in the trend to exclude left atrial lines from the routine ablation approach and therefore led to a putatively limited role in chronic AF ablation.
In a series of 180 chronic AF patients undergoing the stepwise ablation approach, Knecht et al.7 consequentially investigated the role of left atrial linear lesions in long-term freedom from arrhythmias. The study compared subsequent as well as recurrent arrhythmias and the outcome of patients who did not require linear ablation for AF termination (55%) vs those patients who have had undergone ablation of two left atrial lines (i.e. the roof-line and mitral isthmus line) prior to termination of AF. While only a minority of the latter patient group demonstrated left atrial macrore-entrant tachycardias (presumably on the basis of electrically incomplete lines as they have been applied during AF), almost two-thirds of the patients who terminated without linear ablation subsequently developed macrore-entrant tachycardias after AF termination. Thus, on the way to finally achieve sinus rhythm, 95% of patients required a roof-line and 77% ablation of the mitral isthmus during the index procedure. Even though a relatively high proportion of patients of the entire study population have had linear ablation during the index procedure, almost half of the patients with AF termination experienced atrial tachycardia recurrences (43%) with half of them resulting from macrore-entry. Remarkably, macrore-entry occurred much more often in patients without conduction block of the lines during the index procedure than in patients with electrically complete lines. During the follow-up period of >2 years, >95% of patients required left atrial linear ablation to remain free of arrhythmia recurrences.
The presented study from the Bordeaux group adds important information on the mechanisms of recurrences following the stepwise ablation approach and the role of left atrial linear lesions in the treatment of both chronic AF and subsequent atrial tachycardias. Furthermore, it is an important additional result of the study that only 6% of patients with AF termination during the index procedure demonstrated AF recurrences during follow-up, again revealing AF termination by ablation as the key to freedom from AF. However, (macrore-entrant) atrial tachycardias are a frequent observation during both the index procedure and the post-interventional period. Thus, the presented data force the interventional electrophysiologist into the dilemma of returning the focus in chronic AF ablation (at least in part) to left atrial linear ablation. To date, left atrial lines still remain an inconvenient part of the procedure because only complete lines are good lines. It has been demonstrated that patients with electrically complete left atrial linear lesions have a lower number both of AF recurrences and of occurrences of atrial tachycardia.4,8 It is, conversely, difficult to achieve complete electrical block of left atrial lines, particularly at the mitral isthmus. Even highly experienced centres fail in 
15% of cases to achieve bidirectional mitral isthmus block,7 and the overall success rate in other, less experienced centres in terms of left atrial linear ablation can be assumed to be even lower. Another important aspect of left atrial linear ablation is that, even when the lines could be blocked initially, conduction recurrences with subsequent macrore-entrant tachycardias are more frequent, as is the case in cavotricuspid isthmus ablation9, the ‘prototype’ of linear ablation. Finally, many investigators report that cardiac perforation during AF ablation occurred particularly during mitral isthmus ablation, usually accompanied by an audible pop phenomenon as a hint of catheter entrapment in an atrial crevice resulting in sudden catheter tip overheating.
Knecht and colleagues also reported that in 84% of patients, AF converted to atrial tachycardia(s) before termination to sinus rhythm. This common observation, along with the frequent occurrence of atrial tachycardias following the stepwise ablation of chronic AF, has stimulated the ongoing discussion on the mechanisms of those subsequent arrhythmias. Given the fact that a high amount of radiofrequency delivery is usually required to terminate chronic AF6,7 and considering that ablation of complex fractionated atrial electrograms potentially targets areas not actively involved in the AF process,10 one might argue that subsequent regular arrhythmias are a proarrhythmogenic consequence of the ablation itself. On the other hand, it is well recognized that diminishing the fibrillatory process by antiarrhythmic drugs commonly results in organization of the arrhythmia with conversion to common type right atrial flutter (without any previous ablation). Therefore, a potentially important role of subsequent tachycardias as contributors to the AF process may also be hypothesized. It can be assumed that the complex chronic AF process is a result of different arrhythmogenic drivers, including focal sources, microre-entrant activity, and the macrore-entrant excitation path, whose interactions perpetuate each other and apparently give the pattern of high frequency and chaotic fibrillatory activity of the atria. While gradually eliminating these AF contributors using the stepwise ablation approach, the AF cycle length progressively increases before finally resulting in termination of AF and conversion to a regular atrial tachycardia. Interestingly, in patients with multiple subsequent tachycardias, the overall cycle length still increases with the elimination of each atrial tachycardia. Thus, one may also argue that those tachycardias have had an important contributing role in the chronic AF process rather than representing a proarrhythmogenic consequence of the ablation procedure itself.
To date, it remains an essential issue of further investigations to elucidate the nature of atrial tachycardias occurring during and late after stepwise ablation of chronic AF aiming arrhythmia termination. However, considering the presented data of the Bordeaux group, it has become clearer that left atrial linear ablation remains an imperative step on the road to sinus rhythm in patients with chronic AF.
Conflict of interest: none declared.
Footnotes
The opinions expressed in this article are not necessarily those of the Editors of the European Heart Journal or of the European Society of Cardiology.
doi:10.1093/eurheartj/ehn302 
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