© 2005 The European Society of Cardiology. Published by Elsevier Ltd. All rights reserved.
EDITORIAL
Atrial flutter: Watch and control?
Clinical Electrophysiology, Thoraxcentre Erasmus MC, Rotterdam, The Netherlands
Manuscript submitted 22 April 2005. *Corresponding author. Tel.: +31 10 463 3991; fax: +31 10 463 4420. E-mail address: a.thornton{at}erasmusmc.nl
Since the demonstration of the circuit of typical atrial flutter, and the recognition that an ablation line across the cavotricuspid isthmus could be a permanent cure for this arrhythmia [1,
2], electrophysiologists have been attempting to improve the success rates for this procedure. The clarification of an acceptable end-point with relatively low risk for recurrence [3,4] has now led to an attempt to optimise the acute success rates, and thus also long-term efficacy, of this procedure. The introduction to the article by Hillock et al. [5] in this issue highlights some of the frustrations experienced by electrophysiologists attempting to ablate this region. The isthmus can be irregular and thick, and anatomical structures such as the Eustachian valve can make ablation both difficult and long [6]. In experienced centres there are always attempts to improve success rates. Furthermore, the success rates in excess of 90% with minimal radiation and short procedure times described by high volume units are presumably not always repeated by operators in less experienced centres, prompting attempts safely to improve these rates. Thus, there is a background which encourages operators to try new techniques not only to improve success rates, but also to shorten procedure and radiation times. Numerous authors have compared different energy types, different catheter tip sizes and different energy settings [7–11], as well as the use of advanced cardiac mapping systems [12], but the search for improved techniques continues.
Clearly it is important to balance the effectiveness of the procedure with the risks associated with the use of alternate techniques. As Hillock et al. have shown, the use of "un-monitored" very high power settings (>100 W) is associated with a significant risk of "pops" and subsequently of perforation and tamponade. These added risks were apparently not seen in other studies using long tip catheters and up to 100 W [10,11].
In the ablation of the cavotricuspid isthmus a number of features could potentially lead to an improvement in the success rate, while at the same time also improving safety.
What is needed pre-, or during ablation, is an accurate picture of the isthmus itself. These images would demonstrate anatomical variations which may prove to be an impediment to ablation, such as a markedly irregular or very thick isthmus, or the presence of deep pits or a large Eustachian ridge or valve. Detailed knowledge of the anatomy would allow for the planning of the best line so as to avoid difficult areas and move to the easier areas. Although an electroanatomic mapping system can be used to delineate anatomy, potential anatomical problems and to tag a line [12], perhaps this visualisation could be done better by direct imaging. Whether this enhanced anatomical knowledge is best based on a pre-study CT scan or MRI, or is made on the basis of intraprocedure angiography [13,14] or echocardiography [15] will become clearer in the future. Present techniques need to be further improved, because the resolution now is not always optimal (or cost effective) to make detailed plans.
In addition the optimal delivery of energy to cause lesions is also important. It is clear that the use of 4 mm tip radiofrequency catheters has become antiquated and that at the very least 8 mm tip or irrigated tip catheters are the preferred tools of most electrophysiologists [16]. The place of cryotherapy has yet to be fully established especially with the availability of large tip cryocatheters. Our experience of 8 mm tip cryocatheters is that the acute success rate over the last year appears to be as good of that of 8 mm tip radiofrequency catheters, with less pain experienced by the patients. This is the subject of an ongoing prospective study at our institution. The use of "un-monitored" high power radiofrequency energy has been the subject of a limited number of studies. It would appear from the present study, however, that the un-monitored use of energy greater than 100 W should probably not be attempted. The question is really, what is the optimal catheter type or energy setting to use, and whether better monitoring of energy delivery would assist in the formation of optimal lines of block. Ablation for atrial fibrillation complicated by the highly publicised risk of oesophageal fistula formation has refocused our attention on optimal energy delivery and optimal monitoring [17]. From the limited knowledge available, it seems that power may not be a good indicator of tissue temperature especially with the use of irrigated tip catheters, and assessment of micro-bubble formation for instance may be useful both for assessment of target tissue temperature and to decrease complications [18]. The ability to see lesions acutely and assess their placement and especially their adequacy, for example by intracardiac contrast ultrasound, helping us to place and form lesions, might also be a tool in increasing safety and efficacy in atrial flutter ablation.
All in all, despite what some electrophysiologists might think, we do need further study to improve the outcome in ablation of atrial flutter while improving patient safety and the efficacy of this ablation technique.
References
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