Europace Advance Access originally published online on August 31, 2007
Europace 2007 9(10):906-908; doi:10.1093/europace/eum178
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ABLATION
Tachyarrhythmias in Koch's triangle: to be burned out or to be cool?
1 Department of Cardiology, Medical Center Alkmaar, Alkmaar, The Netherlands; 2 Department of Clinical Electrophysiology, Erasmus Medical Center, Dr Molewaterplein 40, kamer Ba 577, Postbus 2040, 3000 CA Rotterdam, The Netherlands
* Corresponding author. Tel: +31 104633991. E-mail address: t.szilitorok{at}erasmusmc.nl
Radiofrequency (RF) ablation has proven to be highly effective in the treatment of tachyarrhythmias in Koch's triangle. Despite this successful approach, several disadvantages can be expected, such as patient discomfort, coagulum formation on the electrode, intralesional haemorrhage, endocardial disruption leading to thrombus formation, steam popping or perforation, some degree of tissue disruption with irreversible damage, and ragged edges, making it potentially arrhythmogenic. More importantly, there is an increased risk for right bundle branch block or inadvertent complete heart block. Therefore, alternative energy sources have been developed, of which cryo ablation seems to be very promising. This energy source has the ability to reversibly demonstrate loss of function with cooling to less negative temperatures (cryo mapping) so that prospective ablation sites can be investigated, before a definitive and irreversible lesion is created.1
This should lead to less applications and abolish the risk of permanent conduction disturbances. Progressive ice formation at the catheter tip causes adherence to the adjacent tissue, making ablation safe to perform during unstable catheter position or even during tachycardia, without the risk of dislodgement of the catheter at termination of the arrhythmia. The more precise delivery of therapy due to cryo mapping and the creation of smaller lesions both in area and volume, together with the formation of a homogenous fibrosis with a proven preservation of the extracellular matrix and a well demarcated border, makes it potentially less thrombogenic and proarrhythmic. In atrioventricular nodal reentrant tachycardia (AVNRT), it is the only method to target the slow pathway on EP basis, as during cryo mapping programmed atrial stimulation can be performed to determine if the AH jump has disappeared and/or AVNRT is no longer inducible without carrying the risk of dislodgement of the catheter.2 Of course, extensive clinical investigation is needed to evaluate these theoretical advantages. In this context, four articles have recently been published in this journal concerning cryo ablation in patients with AVNRT.3–6.
Acute success and recurrence rate
In a retrospective matched case–control study design Gupta et al.3 compared the acute and follow-up results of cryo ablation and RF for the treatment of AVNRT in 71 patients each. They concluded that in this patient, population cryo ablation was accompanied by a much higher acute failure rate and recurrence rate in comparison with RF. De Sisti et al.4 found in their single center study, in which 69 consecutive patients with AVNRT were treated with cryo energy, a comparable success rate as with RF, especially if a 6-mm tip catheter was used, but a higher recurrence rate was also reported.
To put these findings into a right perspective, several remarks should be made. The reason why and at what time during the procedure Gupta et al.3 decided to start with cryo energy instead of RF remains unclear as they stated that this was at the discretion of the experienced operators. Therefore, it could be that there was an inclusion bias where the energy source was only determined after the diagnostic EP study and the more difficult patients, such as those with a smaller window between the compact AV node and the coronary sinus underwent cryo ablation, partly explaining both their lower primary success and a higher recurrence rate. Furthermore, in their study a questionable mapping technique was used to determine the right ablation position. Cryo mapping to –30°C was done for only 20 s, aiming to assess AV conduction prolongation. At this point, there was no atrial extrastimulus given to induce AVNRT or to check whether an AH jump was still present. This was only investigated after cooling to –70°C for 90 s, and this could have caused a false-positive ‘successful’ ablation spot, because of a cryo mapping phenomenon in the periphery. It is well known that temperature rises away from the centre, so this region is less likely to suffer irreversible damage.1 This certainly could have contributed to the high number of recurrences with cryo energy. The higher acute success rate comparable with RF found in the De Sisti paper indeed suggests that cryo mapping provides significant advantages for the outcome.4 One could argue that in this patient population mostly a 6-mm tip catheter was used, in comparison with a 4-mm tip in the Gupta group without better outcome. Remarkable is that in the De Sisti group, four out of their first eight patients treated with a 4-mm tip catheter were unsuccessful. They stated that the catheter handling was mostly done by less experienced physicians, and it is welI known that for every new technique a learning curve exists.
Thus, the question is how to increase the success rate of cryo ablation to be comparable with RF energy. Some techniques already exist and the experience with cryo energy is improving. One of the possible techniques is the so called double freezing cycle (or freezing–thawing–freezing) at the successful spot. It seems to be more efficient since it results in deeper myocardial lesions,7 although this was not confirmed in the study of De Sisti et al.4 We also advise to increase the application time to 6 or even to 8 min based on our unpublished experience. Finally, smaller well-defined lesion requires more accurate mapping. Therefore, we also perform cryo mapping during ongoing tachycardia and only at sites where tachycardia terminates during the cryo mapping we proceed with ablation. This technique significantly reduces procedure time and unnecessary ablation lesions are not delivered. This will actually leave the arrhythmia substrate intact during the mapping procedure. Finally, we would like to comment on the improvement of catheter technology. Actually, the transcatheter technology for delivering cryo energy was developed based on analogies with RF catheters. It seems that 4-mm tip catheters are simply not equivalent in this regard. To further improve ablation results with cryo energy without compromising, the safety of the procedures a 6-mm tip catheter seems to be a better solution in this region, as was also seen in the De Sisti group.4 The suggestion that it maybe possible to decrease the high recurrence rate by aiming to achieve complete slow pathway block and by increasing the number of cryolesions as proposed by Gupta et al.3 is not supported by us, as this leads to unnecessary long procedures and increases the risk for permanent AV conduction disturbances.
Nevertheless, the significantly higher recurrence rate in both studies, which is seen in more studies, included our prospective randomized trial, is a reason for concern.2,8,9 Certainly, an ablation procedure for such a benign arrhythmia, where RF energy is proven to be highly effective should offer non-inferiority in terms of acute and long-term success rate without significant lengthening of the intervention. The aforementioned improvements in both cryo mapping and ablation and a better catheter design should not only increase the acute success rate but also decrease the recurrence rate. It has to be said that to rely solely on clinical symptoms of palpitations has a potential risk of misleading results. This was clearly demonstrated using RF energy too.10 We have shown that up to 65% of patients with recognizable complaints after cryo ablation of AVNRT suffered from other arrhythmias and this could partly explain the high recurrence rate in the de Sisti group.11 Furthermore, it should always be clear which patients have a recurrence, the one with an unsuccessful ablation, which is not surprising, or the one after a successful procedure. Nevertheless, the above mentioned factors and different ablation and mapping approaches are probably responsible for the significant outcome differences between recently published data (Table 1). Interestingly enough, both prospective randomized trials showed non-inferiority as compared with RF energy.
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Safety issue: inadvertent conduction disturbances
On top of all this, cryo ablation should provide a well-defined advantage as well. This is clearly seen indeed in the current paediatric practice all around the world. It seems that for small children, primary procedures are mostly performed using cryo energy when lesions are needed in the Koch's triangle, despite the slightly higher recurrence rate.12 This clearly demonstrates that what cryo energy offers is indeed significantly improved safety. So far no inadvertent permanent AV block was reported using this energy source and this was also not seen in both studies, although in the De Sisti group 21% of the patients developed AV conduction disturbances during cryo ablation, which was not observed during cryo mapping.2–4,8,9 The explanation for this phenomenon is probably multi-factorial: the depth and not the area or volume of a cryolesion is dependent on colder temperatures. A cryo mapping phenomenon occurs in the periphery as already mentioned, and a re-warming effect with cellular swelling can lead to disruption of cellular membranes. If this is moderate in duration and temperature (0 – 10°), it can be fully reversible.1 At all events, it stresses the need for careful surveillance not only during cryo mapping and cryo ablation, but also directly after an uneventful cryo ablation as transient AV conduction disturbances can develop, as it is described in two cases by Gonzalez-Torrecilla et al.5
In conclusion, we feel that the disappointment suggested by Gupta et al. and De Sisti et al. is not completely understandable. With more sophisticated mapping and better energy delivery, acute success rates should reach the level of RF procedures. Certainly, long-term success remains a question and requires further well-designed prospective multi-centre evaluation.
Conflict of interest: none declared.
Footnotes
The opinions expressed in this article are not necessarily those of the Editors of Europace, the European Heart Rhythm Association or the European Society of Cardiology.
References
[1] Skanes AC, Yee R, Krahn D, Klein GJ. Cryo ablation of atrial arrhythmias. Card Electrophysiol Rev (2002) 6:383–8.[CrossRef][Medline]
[2] Kimman GP, Theuns DA, Szili-Torok T, Scholten MF, Res JC, Jordaens LJ. CRAVT: a prospective, randomised study comparing transvenous cryothermal and radiofrequency ablation in atrioventricular nodal re-entrant tachycardia. Eur Heart J (2004) 25:2232–7.
[3] Gupta D, Al-Lamee MJ, Kistler P, Harris SJ, Nathan AW, Sporton SC, Schilling RJ. Cryo ablation compared with radiofrequency ablation for atrioventricular nodal re-entrant tachycardia: analysis of factors contributing to acute and follow-up outcome. Europace (2006) 8:1022–6.
[4] De Sisti A, Tonet J, Lacotte J, Barakett N, Leclercq J-F, Frank R. Transvenous cryo ablation of the slow pathway for the treatment of atrioventricular nodal re-entrant tachycardia: a single center initial experience study. Europace (2007) 9:401–6.
[5] Gonzalez-Torrecilla E, Arenal A, Atienza F, Almendral J. Transient atrioventricular block shortly after uneventful cryo ablation of atrioventricular nodal reentrant tachycardias: report of two cases. Europace (2007) doi:10.1093/europace/eum127.
[6] Khairy P, Novak PG, Guerra PG, Greiss I, Macle L, Roy D, et al. Cryothermal slow pathway modification for AV nodal re-entrant tachycardia. Europace (2007) doi:10.1093/europace/eum145.
[7] Bredikis A, Sidhu J. Critical nitrogen cryo ablation: transmurality and effects of double freezing cycle in chronic experiment. Poster at Heart Rhythm (2007).
[8] Zrenner B, Dong J, Schreieck J, Deisenhofer I, Estner H, Luani B, et al. Transvenous cryo ablation versus radiofrequency ablation of the slow pathway for the treatment of atrioventricular nodal re-entrant tachycardia: a prospective randomized pilot study. Eur Heart J (2004) 25:2226–31.
[9] Friedman PL, Dubuc M, Green MS, Jackman WM, Keane DT, Marinchak RA, et al. Catheter cryo ablation of supraventricular tachycardia: results of the multicenter prospective "Frosty" trial. Heart Rhythm (2004) 1:129–38.[CrossRef][Web of Science][Medline]
[10] Jordaens L, Vertongen P, Verstraeten T. Prolonged monitoring for detection of symptomatic arrhythmias after slow pathway ablation in AV-nodal tachycardia. Int J Cardiol (1994) 44:57–63.[CrossRef][Web of Science][Medline]
[11] Kimman GJ, Theuns DAMJ, Janse PA, Rivero-Ayerza M, Scholten MF, Szili-Torok T, et al. One-year follow-up in a prospective, randomized study comparing radiofrequency and cryo ablation of arrhythmias in Koch's triangle. Clinical symptoms and event recording. Eurpace (2006) 8:592–5.[CrossRef]
[12] Kriebel T, Broistedt C, Kroll M, Sigler M, Paul T. Efficacy and safety of cryo energy in the ablation of atrioventricular reentrant tachycardia substrates in children and adolescents. J Cardiovasc Electrophysiol (2005) 16:960–6.[CrossRef][Web of Science][Medline]
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