CORRESPONDENCE: LETTER TO THE EDITOR
Reply
Luigi Di Biase, MD,
J. David Burkhardt, MD,
Robert A. Schweikert, MD,
Walid I. Saliba, MD and
Andrea Natale, MD*
* Division of Cardiology, Stanford University, Palo Alto, California 94305 (Email: nataleam{at}roadrunner.com).
We thank Drs. Pappone and Santinelli for their interest in our paper (1).
Overall, our study (1) demonstrated that remote magnetic navigation is feasible and safe for mapping in the left atrium. Our major concern was limited to the use of the 4-mm catheter tip (the only one available at the time of the study) which, in our experience, was unable to create effective lesions to achieve complete electrical isolation of the pulmonary vein antrum; in addition, ablation with this catheter was associated with charring in a large number of patients (1).
Regarding the specific questions contained in their letter, our reply follows.
In the first 48 cases (considered the learning curve), we did not perform ablation. These cases were used to practice mapping and navigation in the left atrium and no radiofrequency energy was delivered.
Two of the 20 authors performed all the procedures in the learning curve group and subsequently performed the ablation procedures in the 45 patients who were the object of the study.
As far as the alignment of the catheter tip and the abatement of the atrial potentials are concerned, it is well established (2) that reduction of local electrograms does not necessarily reflect the transmurality of the lesions. In addition, in our experience, the soft tip did not appear to increase the ability to position the catheter parallel to the tissue plane. However, regardless of the catheter orientation, lesion formation should follow the same biophysical principles. Indeed, previous experimental data show that the time to steady-state tissue temperature during radiofrequency catheter ablation is approximately 60 to 90 s (3,4).
In the patients undergoing ablation, the duration and maximum power were reduced from 60 to 45 s and from 50 to 40 W once charring was observed. This did not abolish charring, which was observed even after a few seconds of energy delivery.
The setting parameters during catheter ablation were clearly reported in the Methods section. Similarly, we mentioned that to prevent charring, we tried to reduce lesions duration and maximum power, and realized, by monitoring with intracardiac echo, which was not used in the Pappone et al. (5) study, that charring can form within a few seconds and most of the time it is not associated with any change in impedance. On average, there was no difference in delivery settings between lesions with and without charring. Besides direct visualization of the charring with intracardiac echo, the only indirect clue observed at times was a sudden drop of the delivered power.
Our results were shared and endorsed in the editorial of Lindsay (6), who appeared to have experienced similar problems. In this respect, even ablation of left side pathways has been associated with a wide range of success (from 67% to 92%) based on the catheter design (7).
We do not share the conclusions of Drs. Pappone and Santinelli that our study "limits the enthusiasm of preliminary encouraging results of joystick ablation" with magnetic navigation. We are enthusiastic about remote catheter ablation. We are currently using the new 8-mm catheter tip and are waiting for the development of the irrigated cool tip catheter, because we are sure that it will improve the results.
On the other hand, we do not understand why Drs. Pappone and Santinelli are so eager to use the new cool tip catheter considering that they had no problems with the standard 4-mm catheter tip. It is ironic that they consider the irrigated tip catheter important in moving this technology forward.
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References
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1. Di Biase L, Fahmy TS, Patel D, et al. Remote magnetic navigation: human experience in pulmonary vein ablation J Am Coll Cardiol 2007;50:868-874.[Abstract/Free Full Text]2. Hocini M, Sanders P, Jais P, et al. Prevalence of pulmonary vein disconnection after anatomical ablation for atrial fibrillation; consequences of wide atrial encircling of the pulmonary veins. Eur Heart J 1005;26:696–704. 3. Haines D. The biophysics and pathophysiology of lesion formation during radiofrequency catheter ablationIn: Zipes DP, editor. Cardiac Electrophysiology: From Cell to Bedside. 4th edition. New York, NY: WB Saunders; 2006. pp. 1018-1027. 4. Calkins H, Brugada J, Packer DL, et al. HRS/EHRA/ECAS expert consensus statement on catheter and surgical ablation of atrial fibrillation: recommendations for personnel, policy, procedures and follow-up. A report of the Heart Rhythm Society (HRS) Task Force on Catheter and Surgical Ablation of Atrial Fibrillation. Heart Rhythm 2007;4:816-861.[CrossRef][Web of Science][Medline] 5. Pappone C, Vicedomini G, Manguso F, et al. Robotic magnetic navigation for atrial fibrillation ablation J Am Coll Cardiol 2006;47:1390-1400.[Abstract/Free Full Text] 6. Lindsay BD. Is pulmonary vein antrum isolation a critical determinant of recurrent arrhythmias after ablation of atrial fibrillation? J Am Coll Cardiol 2007;50:875-876.[Free Full Text] 7. Chun JKR, Ernst S, Matthews S, et al. Remote-controlled catheter ablation of accessory pathways: results from the magnetic laboratory Eur Heart J 2007;28:190-195.[Abstract/Free Full Text]
Related Article
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Safety and Efficacy of Remote Magnetic Ablation for Atrial Fibrillation
- Carlo Pappone and Vincenzo Santinelli
J. Am. Coll. Cardiol. 2008 51: 1614-1615.
[Full Text]
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