EP Lab Digest - February 2008 - (Page 28)

28 CRYOTHERAPY ROUNDTABLE Continued from page 26 UPDATE FEBRUARY 2008 if I’m going to use cryotherapy for an accessory pathway, for instance, the best success rate I’m going to get is 75%.” If you look at the way the trial was set up and what we do now with cryotherapy, using larger catheter tips, doing freezes, thawing in the same spot, refreezing in the same spot, and also getting an idea of what the signal should look like on the monitor for AV node reentry, the procedure times that are reported in previous trials as well as the success rates would potentially be different. GEORGE F.VAN HARE, MD: I just want to make the point that I find it interesting from this trial that even when they set out to attempt to cause heart block, they only succeeded two-thirds of the time. PETER J.WELLS, MD: It’s reassuring. RAJJIT ABROL, MD: If you look at one electrogram tracing courtesy of Dr. Friedman showing the cryo at 6.25mm per second speed, you see the cryotherapy comes off on somebody who developed a 2:1 heart block, and in a short period of time, the conduction comes back. You know, I can’t emphasize enough as a young electrophysiologist going into practice that cryotherapy has really made these procedures extremely comfortable for me. It took a lot of procedures during my fellowship — over 50 AV node reentry cases with cryotherapy — in order to learn exactly how to use the catheter. It also took a while for the entire lab staff to learn how to use it because it is distinct from RF. Knowing that if you do inadvertently get a fast pathway in a spot where you think you’re ‘safe’, using cryotherapy and seeing connections come back is extremely comforting to a young electrophysiologist.You don’t want to be known as the guy who is giving everybody heart block with ablations! Consenting with patients is also extremely important.When giving patients the alternative of RF versus cryotherapy, in which their chances of a repeat procedure or the possibility that they may end up with a pacemaker is higher, I think that the choice for cryotherapy for those patients becomes pretty easy for them. It’s not uncommon that a patient will ask me “Why would you even use radiofrequency?” I use cryo for almost all of my AVNRT cases. PETER J. WELLS, MD: This efficacy issue was a problem.There have been two randomized trials, both conducted in Europe, and this is one that was published by Zrenner where patients with AV node reentry were randomized to either RF or cryo, again with the 4mm catheter. The endpoint of this study, which I think raised some concern about efficacy, was a composite endpoint. The endpoint was either no acute procedural success, development of complete irreversible heart block, or recurrence of SVT.The interesting thing is that the acute procedural success was very similar between cryo and RF — although there was one case of AV block with RF and none with cryo — so what really drove this endpoint was recurrent SVT. The efficacy issue is germane — let’s address that. GEORGE F.VAN HARE, MD: If you notice, we are still seeing recurrences beyond 180 days.What the FROSTY trial defined as success was 180 days without recurrence. Here we’re still seeing them beyond a year, so if you are cautioning patients about the possibility for a recurrence, make sure that they know it could still happen beyond six months. PETER J.WELLS, MD: Excellent point. Okay, so just a summary about efficacy: the FROSTY trial in 2003 had a 91% acute procedural success. Then came the European trial, and finally, a single-site registry in Sweden where a 6mm catheter was used.2 The acute procedural success is now up to 99%, and the recurrence rate, although still maybe a bit more than we would expect with RF, is certainly better.This raises the question of best practices, also in pediatric patients. GEORGE F. VAN HARE, MD: It’s my turn to talk a little bit about pediatrics. We really jumped at the opportunity to use this technology when it first became available. However, it is important to remember that when we talk to our patients, we’re also talking to our patients’ families. It’s much more difficult for a parent to give permission for a procedure for their child than it is for them to give permission for a procedure on themselves.The possibility of heart block, I think, loomed very large in the parents of our patients, and so being able to offer them a procedure that perhaps would have a higher recurrence risk but would clearly have a lower risk of heart block was a major advantage. To date, in about 189 procedures at our center, our overall success rate is 93%, which is pretty good. The recurrence risk is about 9%, which is a little disappointing and certainly higher than is reported for the RF ablation registry that we did over approximately 15 years. Also importantly, there was not a single case of persistent AV block in any of these patients. We do worry about the coronary arteries in children using RF, but there are no incidences of coronary injury using cryoablation in this series. RAJJIT ABROL, MD: George, in terms of recurrence rates, do you know the mix between the 4mm and 6mm catheters? GEORGE F. VAN HARE, MD: Yes, most of the recurrences were with the 4mm catheters. PETER J.WELLS, MD: So how can we maximize cryo? We’ve had decades to maximize RF, and hopefully that process is still ongoing, but how can we maximize the use of cryo? That involves what we call cryo best practices. The first thing is that cryoablation, just like RF ablation, is a contact-dependent energy source. If you look at making lesions, the more contact force you have with the catheter in general, the larger lesion you have — not only that, but the larger electrode you have, the larger lesion you make, similar to RF. There are 4mm, 6mm, and 8mm electrode catheters; as you get a larger electrode, in general you will get a larger lesion. Also, the electrode orientation is important. If we’re orienting the electrode perpendicular to the endocardium, we get a lesion of a certain depth. If we orient it parallel to the endocardium, we get the same lesion depth but typically more diameter, and therefore a larger lesion size, so in general we try to orient the electrode parallel to the endocardium rather than perpendicular. Also, the increased duration of the freeze affects the lesion size, and this is dependent on both the time that the catheter is on and how big the catheter is, but in general, the longer you freeze — in some animal studies as long as eight minutes — the bigger the lesion does tend to get.Therefore, we want to try to freeze for a long period of time. Also very important is that the refreeze after thaw increases lesion size.We’re not exactly sure why this is, but it may have to do with interruption of the microcirculation such that the second lesion is met with less resistance from conductive heat because the capillary network has been destroyed. Thus, it’s very important to consider those if we’re going to maximize effectiveness. We should also discuss how the lesion sizes vary with 4mm, 6mm, and 8mm catheters.There are no dimensions on this, but I think all of us

Table of Contents Feed for the Digital Edition of EP Lab Digest - February 2008

EP Lab Digest - February 2008 Creating the U-M Center for Arrhythmia Research: Interview with José Jalife, MD Texas Cardiac Arrhythmia Institute and St. David’s Medical Center Launch State-of-the-Art Training Center Contents Letter from the Editor Spotlight Interview: Caritas St. Elizabeth’s Medical Center 10-Minute Interview: Sue Deck, BS, RN, RCES Keeping Pace With a Blog Roundtable Discussion on Cryoablation Procedures Email Discussion Group: February 2008 Events Calendar Industry News and Products Classifieds Advertisers Index

EP Lab Digest - February 2008

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