EP Lab Digest - February 2008 - (Page 31)

FEBRUARY CRYOTHERAPY UPDATE Figure 2. In this image you can see two atrial paced events, and the last atrial paced event crosses over from the QRS nearest to it and goes to the next one. Figure 3. Clinical SVT, only single echos. Figure 4. The successful ablation site. then immediately when we come off we haven’t yet reached -70 degrees at the AV node, we’re only at 0 degrees.That is very important. Here is a question:“What if you don’t have clear endpoints with cryo? What do you do without junctional tachycardia?”That is a great question.You know, this is one of the criticisms of cryo; the use of cryo in AV node reentry is that junctional tachycardia or accelerated junctional rhythm (AJR) is a very good indicator of where the slow pathway is. It’s not as 100% as we think, but it’s probably about 90% specific.That is, about 5% of the time, you can actually ablate the slow pathway without AJR, but it’s pretty specific. For those of us who have been doing RF ablation for a long time, it definitely provides some comfort that we’re in the right spot. Not only that, it affords us the opportunity to look at retrograde conduction, so when you have accelerated junctional rhythm, it’s going up the fast pathway, and if we ever see retrograde block up the fast pathway, we come off right away. So not having AJR is a limitation, but I don’t think it’s an insurmountable limitation. For example, if you look at one of the cases we did here at Baylor, the second from the bottom electrogram is the distal ablation.This is a little bit different than what George was saying, although we typically do look for AV ratios of about one, but you can see the atrial electrogram is quite a bit smaller than the ventricular electrogram.This is a cryomapping case, so what we do is come on with cryo, stick the catheter to the endocardium, and usually that happens at about 30. However, if you’re looking on fluoro, you can see there will always be a little discordant motion with the catheter and the endocardium until it sticks, so as soon as it’s stuck, now you can see all the hash, which is artifact that is on the distal ablation signal. Then we’ve already practiced pacing and putting in this single atrial extra stimulus that you can see goes down the slow, up the fast, and induces AV node reentry. We know this will happen every time we do it: so we come on with cryo and induce AV node reentry, and five beats later, it terminates. It’s important to know that it terminates with an atrial electrogram, so that means that we’re blocking in the slow pathway.As soon as we terminate, we don’t just sit there and congratulate ourselves. We do the identical activation sequence again that induced AV node reentry. The identical PAC now blocks in the slow pathway. So cryomapping is useful. In the FROSTY trial not all investigators used it, and some of them believed that it was not all that predictive of a successful spot. We use it routinely, though. George, what about in pediatrics? GEORGE F. VAN HARE, MD: Certainly when we have a 4mm catheter, we would. PETER J. WELLS, MD: Okay. Now sometimes we don’t have those kind of endpoints, and this is what George alluded to earlier, the idea of crossover. Here you can see two atrial paced events (Figure 2), and the last atrial paced event crosses over from the QRS nearest to it and goes to the next one. Now, if this is your endpoint for slow pathway ablation, then after you cryoablate the slow pathway, you pace again at the same cycle length. We’re pacing at the same cycle length and we really can’t generate that long AH interval anymore because the slow pathway is gone, so we don’t have PR longer than pace cycle length, we don’t have crossover, and that is a successful site.There is also a case we did of a patient who had already had an RF ablation for AV node reentry; we had an EKG in our hands after that procedure that showed what we thought was clear slow/fast AV node reentry, but sure enough, once we got to the lab, even with the patient wide awake, this was all we had, a single echo.You’ll notice that this was a bit of a different case in that we had ablated where we thought the slow pathway should be and we really couldn’t get it. Therefore, we actually had to search for the posterior leftward AV node extension, which is about 5 to 10 millimeters inside the mouth of the coronary sinus, so you can see a much bigger atrial than ventricular electrogram. Here was our echo (Figure 3) — this was all we had to map with. Here it shows the successful ablation site (Figure 4).You can see the two electrograms from the bottom and how big the atrial electrogram is — twice as big as the V. This is inside the coronary sinus. Postablation, we put in the identical PAC and we don’t go down the slow pathway. I will point out that there is after that atrial extra stimulus an HV, but you can see that if that is conducted, the AH is something on the order of 500 milliseconds, so that is actually just a junctional beat after we block in the slow pathway. RAJJIT ABROL, MD: Speaking of endpoints in AV node reentry, I’ve noticed over the course of time of doing these cases that because you don’t get junctional tachycardia, you actually have to come up with a number of different potential endpoints to check. With the four-minute lesion, you can check for the different types of endpoints, whether it be a change in wenckebach cycle length, induction of tachycardia, with a different cycle length, or with or without isoproterenol. That is part of the process of learning how this technology works, how you can use it. It’s different than RF technology. If you really want to succeed and improve on the numbers that we talk about for AV node reentry, you have to know that you have to put in freeze, thaw and freeze cycles, and you have to know what your endpoints are. To be perfectly honest with you, as a young electrophysiologist, using cryo has helped me improve my EP knowledge of what the endpoints are for AV node reentry and so on and so forth. Of course, I can use RF and get junctional tachycardia and see that the slow pathway is gone, but with this, the precision of this technology and as you learn it, you learn that you’re getting things better. GEORGE F.VAN HARE, MD: Here is a question from a pediatric cardiologist: “Have there been any reported cases of late occurrence of complete heart block after AV node reentry cryoablation?” I think the answer to that is not that I know of, although we’ve heard a rumor from this person’s institution of a patient with other major medical problems who developed a late occurrence of AV block. If it happens, I guess it’s not surprising that one might occasionally have that. There is some inflammatory response that occurs with cryoablation — although very little — but if it does happen, I think that the incidence is going to be quite a bit lower than what we would occasionally see with RF. The second question is:“What does the occurrence of transient AV block during the case mean for long-term follow-up?” PETER J. WELLS, MD: We see transient AV block commonly, and I think one of the advantages of cryo is that when you use it enough, you realize that transient AV block is not anything bad. As far as the adult literature, I think there have been two pacemakers implanted in adults out of about 15,000 worldwide cases. For transient AV block, we probably see, what do you think, 10% of the time? RAJJIT ABROL, MD: Probably. PETER J.WELLS, MD: It almost always just lasts a few seconds, and as George very aptly put it, this is not a technology where you get lulled to sleep. I remember we did a four-minute freeze — I think you may have done this case with me. RAJJIT ABROL, MD:Three and a half minutes in PETER J.WELLS, MD:Yes, three and a half minutes into the refreeze in the identical location, we got heart block. So this is definitely not a technology that you go to sleep when you’re using it, but a transient AV block virtually never causes permanent AV block. GEORGE F. VAN HARE, MD: The question, I think, is whether the outcomes might be better with AV node reentry if you in fact push the envelope some. I’ve See ROUNDTABLE page 32

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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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