EP Lab Digest - February 2008 - (Page 26)

CRYOTHERAPY ROUNDTABLE Continued from page 24 UPDATE FEBRUARY homogeneous. An RF lesion is not as homogeneous and dense a lesion as with cryo. Secondly, and this is very important, particularly for ablation on the left side of the heart, the endocardium on a cryolesion is very thin, it stains blue, and there is just a slight amount of thrombus there. However, the endocardium is largely intact, which minimizes the risk of thrombus. On an RF lesion there is fibrinoid necrosis of the endocardium and quite a bit of adherent thrombus, and so this is another advantage of cryo — being relatively sparing of the endocardium.Thirdly, cryolesions tend to be less arrhythmogenic; this is predominantly related to the border of the lesion. If you were to analyze the border of these two lesions, you would see that the border of the cryo lesion is very sharply demarcated, whereas there is a relatively non-homogeneous border to the RF lesion.This is an important factor. It was found early on that this density and homogeneity tended to be non-arrhythmogenic, whereas if there were surviving strands of heart muscle and fibrotic tissue, arrhythmias (particularly late arrhythmias) could occur. RAJJIT ABROL, MD: If you think about arrhythmogenesis when we talk about cryo and the different arrhythmias that you’re going to use it for (e.g., AV node reentry, atrial fibrillation, atrial tachycardia), as well as the nonarrhythmogenic factor, you need to look at previous studies that describe late recurrence of arrhythmias. A lot of times if you treat one arrhythmia with RF, there is not an inconsequential number of different arrhythmias that come about later on. Therefore, I believe the nonarrhythmogenic factor is hard to see in the short term when you are following up the patient, but when you follow up with patients five to ten years later, especially those patients with AV node reentry, it is possible that those sites that end up giving you atrial tachycardias and other dysrhythmias, that cryo would potentially give you less of that. PETER J. WELLS, MD: Lastly, preservation of myocardial tissue strength is very important. If you compare the two lesions, the structural proteins such as collagen and the cytoskeleton of the cell are denatured with RF ablation. Therefore, if you have just made an RF lesion and are continuing to push, for example, on the left atrium with the catheter, you actually have weakened it structurally, and so potentially the risk of cardiac perforation is higher. However, with cryo, the structural proteins are preserved, therefore the risk of perforation would potentially be less.What does that mean as far as clinical benefits? First of all, you can look for reversibility of the effect that you want. We’ll allude to this more later and show you some examples where one can observe for both the therapeutic as well as the adverse effect before either are permanent. If you like what you see, it can be converted to a lesion; if not, you can come off. We are not afforded this luxury when we perform cases with RF. Secondly, as George alluded to a moment ago, once the cryocatheter electrode temperature reaches about -30 degrees, it becomes adherent to the endocardium so catheter stability tends to be better, particularly with right-sided accessory pathways where the tricuspid annulus is being tugged quite a bit. Next, we’ve referred to the welldemarcated homogeneous lesion, and Raj made the point about late arrhythmia recurrence, which certainly is a concern with as many as 30% of people at 10 years experiencing either late heart block after ablation for AV node reentry or some new arrhythmia. Also, there is reduced patient discomfort during the procedure. We all ablate in sites that are very tender to the patient — such as the area around the mouth of the coronary sinus, the isthmus, or the area around the sinus node — so if patients are not fully anesthetized, they can experience significant discomfort with RF; however, this is not the case with cryo. The connective tissue matrix we referred to a moment ago is left intact and therefore we do not get burning, charring, or steam pops that can predispose to perforation. The other advantage to cryo is that there is a very precise ablative effect. I think many of us have learned over the years that the RF catheter tends to paint the endocardium during an ablation, meaning it tends to move. To some extent, that actually generates a bigger lesion, and so that may be a good thing, but on the other hand, it gives you a little bit less precise of an ablative effect.What are the implications? Obviously there is less risk of inadvertent AV block if you are working near the AV node, either with slow pathway ablation or ablation of an accessory pathway that is near the AV node. You can predict a successful ablation by the results of cryomapping: the catheter stability is better, there are probably going to be less late arrhythmias, and there is a reduced risk of embolization of thrombotic material. In addition, since it is more comfortable, you need less sedation, which can be important for COPD patients or patients that don’t want to be put under. There is also potentially less risk of perforation, Knowing that if you do inadvertantly 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. and there has never been, as far as I’m aware, a single case of pulmonary vein stenosis with cryo. RAJJIT ABROL, MD: Clinically significant pulmonary stenosis. PETER J. WELLS, MD: Correct — clinically significant pulmonary vein stenosis is another potential advantage if we are ablating in the left atrium, near the ostium of pulmonary veins.Those are all either advantages or potential advantages, but there are some concerns as well. One concern is that the efficacy of cryoablation potentially is not as great as with RF ablation. That is a concern, and we’ll discuss that later and talk about what sorts of things can be done to maximize the efficacy of cryoablation. GEORGE F.VAN HARE, MD: I just want to make one point about the sedation issue.When you do a procedure that causes pain, I think the patient’s autonomic state becomes a moving target. We’ve all seen situations where a patient wakes up and experiences sinus tachycardia, and if you’re addressing an arrhythmia that is very dependent on autonomic activity, like AV node reentry, your baseline state is no longer present. Therefore, by using something that doesn’t cause pain, you get a much more steady situation autonomically. RAJJIT ABROL, MD: We’ve listed a number of advantages to cryotherapy, but being a recent fellow myself, it’s very often that I also talk to patients about what the risks or disadvantages of a therapy are compared to the advantages. If we can list a number of things that potentially give us the advantage of using cryotherapy, ultimately patients will say, “We can’t have heart block, and maybe you can’t have these other tissuerelated phenomenon, so what’s the downside?” The downside so far that we’ve seen is the efficacy, meaning, whether or not the person will have to go through a repeat procedure. The second thing that we’ll address is the actual time of the procedure, with fourminute lesions as opposed to shorter lesions with radiofrequency. However, looking at the clinical data that we have right now for cryo, the largest cryo trial reported was in the HeartRhythm Journal in 2004.1 It was a prospective registry called the FROSTY trial, and it covered 14 centers — three in Canada and 11 in the United States. There were 166 patients in the trial. The arrhythmias studied in the trial included AV node reentry, ORT or ART, and atrial fibrillation, of which patients underwent AV junction ablation with a 4mm catheter. The cryomapping option was available at that time with the 4mm, and was performed at -30 degrees Centigrade for less than 80 seconds. The cryoablations were then done for four minutes with no refreeze. Another point to make about what we have learned using cryotherapy is that by putting in a freeze, thaw, and refreeze, you can actually get a more permanent, more stable lesion than just doing a lesion in and of itself. It’s possible to explain the results of the FROSTY trial based on the fact that they just did a freeze but no refreeze. The endpoints for the FROSTY trial, which were understandable, were not exactly the endpoints that we use clinically in the lab. They used acute success as less than 15 seconds of supraventricular tachycardia (SVT) or the development of complete heart block (which is an endpoint in the lab). If you develop complete heart block, you must quit. However, if you had less than 15 seconds of SVT, with or without isoproterenol, then chronic success was looking at no recurrence at six months. If you look at the outcomes of the FROSTY trial data, the AV node reentry group of 103 patients had an acute procedural success of 91%, with a confidence interval between 84 and 96%. Of the ORT and ART patients with accessory pathway tachycardias, there were 49 patients with acute procedural success at 69% using the 4mm catheter. The numbers here are about what people quote when referring to the success of cryo. They’ll say, “Well, See ROUNDTABLE page 28

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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