EP Lab Digest - February 2008 - (Page 30)

CRYOTHERAPY ROUNDTABLE Continued from page 29 UPDATE FEBRUARY RAJJIT ABROL, MD: Thirty seconds of thawing. The concern now is during that 30 seconds of time of whether or not you stay in the same spot to refreeze. In the time to effect back to minus temperature, it’s quite quick, about 14 seconds or so. We’ve noticed that if the catheter is moved to a different spot, it takes longer for that to come up, even if you come back to that spot again a few minutes later, you can refreeze in the same spot and it comes down quickly. We also look at the time it takes to thaw to predict how much of a consistent lesion you have. PETER J. WELLS, MD: Right, so with that information in mind as far as best practices for cryo, let’s now discuss AV node reentry, which is the hallmark arrhythmia for this device. George, why don’t you bring us up to speed on pediatrics? GEORGE F. VAN HARE, MD: First just a couple of comments on technical aspects about how to do this kind of work in children. We do most of our patients under general anesthesia, and this means that AV node reentry is often not inducible. Therefore, we end up having to use isoproterenol to induce it, and we get what we call the “Goldilocks” phenomenon, which means sometimes too much, sometimes not enough, and sometimes just right. Trying to achieve that dose of isoproterenol that will allow you to repeatedly induce sustained AV node reentry, so we test a number of different doses. We find that the strictly defined jump in AH interval — a 50 msec jump in A2H2 in response to a 10 millisecond decrement — is often not present in children and even teenagers, and so we actually substitute this other criterion which we call PR greater than RR (or crossover). It’s an essentially consistent or persistent conduction down the slow pathway so that the conduction essentially skips an R wave. We do obviously like to make a diagnosis, and the fastest way in our lab to do that is to rule out atrial tachycardia by terminating this from the ventricle without advancing the A. I didn’t make this point before, but in the large multicenter RF ablation series in children, we found that the risk of heart block was 2% for RF; we think 2% is too high in children. RAJJIT ABROL, MD: On the isoproterenol issue, I think it’s extremely important to point out also that with RF cases, we try to induce and not get induction, induce them on isoproterenol, turn off their isoproterenol, come back in the baseline state, and then potentially chase targets that may or may not exist in the baseline state, then go back on and off isoproterenol. Cryotherapy is excellent because of the adherence and the controllability, especially with the 8mm tip catheter. It’s not uncommon to do AVNRT cases on isoproterenol or at least even a little bit of isoproterenol so that you can look for those endpoints. GEORGE F. VAN HARE, MD: You could certainly run isoproterenol with an adhered catheter and test during the lesion. First a couple of examples: one patient did not have sustained tachycardia in a baseline state under anesthesia, but we could get two to three beats of nonsustained tachycardia. Nonetheless, we went ahead. Here we show the unusual occurrence of retrograde dual AV node pathways.This is somewhat helpful in certain cases. It allows you to map that slow pathway a little bit better. In this case, by giving isoproterenol we were able to induce sustained AV node reentry, so the last paced beat is actually not the R wave following the last stimulus artifact but is in fact the next R wave. This is PR greater than RR, or as you say, crossover. It is a very characteristic finding for induction of AV node reentry and the presence of a slow pathway. One important point that we need to make is that the electrogram morphology that we seek for a successful site is in fact different than what we were all taught to use for RF. With radiofrequency, we’ve usually used an AV ratio on our ablation catheter of 1:2, hopefully with a Haissaguerre potential, a little bump between the A and the V. However, what we’ve found through trial and error using cryoablation is that we get better results if we use a higher AV ratio. In other words, an AV ratio of about 1:1. GEORGE F. VAN HARE, MD: One thing that we find useful to do in children and in large children and teenagers is to image the coronary sinus directly.This is an LAO view of an injection through a 7 Fr lumen decapolar catheter in the coronary sinus.This is useful in LAO view because it actually identifies where the coronary sinus really is in relation to the coronary sinus electrodes.You might have imagined that the coronary sinus was adjacent to CS 9-10, but this injection in fact shows you that it’s adjacent to 7-8. It allows you to go to the septum with your catheter.To show the ablation catheter location in RAO view, we’ve placed this 6mm catheter through a positioning sheath (a Daig SR0), and in this view, we are adjacent to the AV annulus. In the LAO view, we are just above the coronary sinus.This is actually a different case than I showed you with the injection in the coronary sinus, but you get the sense of how adherent the catheter is to the myocardium with that electrogram. It’s not moving around too much. Or I should say, it’s moving exactly with the coronary sinus, which means it’s nicely adhered to the myocardium. PETER J. WELLS, MD: Why don’t we stop at this point and field a question from the audience? RAJJIT ABROL, MD: Okay. The first question I have from the audience is: “What catheter do you use for AV node reentry ablation, and what can you say about the stiffness of the different catheters?” GEORGE F. VAN HARE, MD: I can start off. I think that as a pediatrician, I find the fact that we have multiple tip sizes to be an excellent feature.There are situations where I want to make sure I make a very small lesion, so if I have to do AV node reentry, say, in a 4-year-old who might weigh around 20 kilos, I’m very happy about the availability of the 4mm catheter. But for anyone over the age of 12 or 13, I’m using 6 and often 8mm catheters.The stiffness is an important feature, and you need to know about that. We will occasionally see transient AV block due simply to catheter contact.The catheter is quite a bit stiffer than the RF catheters that we’re used to using, and it’s changed our approach. Instead of placing the catheter, finding the His potential and then curving the catheter down, as we might do with a radiofrequency catheter, I actually teach our fellows to place the catheter in the right ventricle and then go clockwise to the slow pathway region rather than getting anywhere close to the region of the fast pathway. PETER J. WELLS, MD: Raj, do you want to speak about adults? RAJJIT ABROL, MD: For the AVNRT cases, I usually use a 6mm catheter just because I’m more comfortable with using it. I think over the course of time, I’m going to start using the 8mm catheter more often. I think the stiffness of the 8mm catheter has kind of scared me — again, being a young electrophysiologist — and I don’t want to have complications with tamponade or anything with a stiffer catheter; bumping the node can obviously be an issue with that as well. I’m sure it’s a much bigger issue in pediatrics than it is for us, but when I use a 6mm catheter to do AV node reentry, I usually use an SRO sheath like Dr.Van Hare had. For the few cases that I’ve done with an 8mm catheter — we did a series of AV junction ablations with the 8mm — I haven’t had to use a sheath because that catheter is extremely well positioned and is able to maneuver very well in the posterior septum. In fact, there is something that you can do that I just learned recently: disconnect the coaxial cable from the catheter itself to try to get maneuverability with the catheter in the 8mm catheter — this can help if you think it’s going to be very stiff. So there are different things you have to learn about this technology in order to help you use it, because it’s extremely different from RF. How about you, Pete? PETER J. WELLS, MD: Well, George, you may want to speak to this.We here at Baylor have never taken these catheters retrograde across the aortic valve, but I think you’re braver.You’ve done it with the 4mm catheter, have you not? GEORGE F. VAN HARE, MD: Yes, I did it once or twice when cryoablation first came out, before the information about the high recurrence risk with accessory pathways came along. I generally don’t do that any longer. I use cryoablation for AV node reentry and for any pathway close to the AV node or close to a coronary artery where I’m worried. I’m not really using it for left-sided pathways any longer. There is an excellent question that has come in by email which I’ll read:“I would like to clarify an implication made by the presenters. Just because a cryomapping test does not show AV delay does not mean that the following freeze will be safe, i.e., will not produce AV node or His bundle damage. The sensitive tissue can be just outside the effective zone of a partial freeze but become included in the ice ball as the temperature drops and the ice ball grows to full size subsequently, damaging the sensitive tissue.” I would entirely agree. I would say that one excellent habit to get into if you are using cryoablation for AV node reentry or any time you are close to the AV node is your eyes do not leave the screen during the entire four minutes of your lesion.You need to watch, because we have occasionally seen patients at three and a half minutes have their PR interval start to prolong. We use a mapping feature on the GE Prucka system that allows us to see within a beat whether the PR interval has prolonged even as much as 5 or 10 milliseconds; when that happens, we immediately come off. Often what happens then is that the PR gets a little bit longer while we’re waiting for the ice ball to disappear, and then in every single case so far, the PR interval has tightened up and gone back

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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