Cryothermal Energy: Interview With Dr. James Irwin

I understand that you purchased your cryo system as soon as it was market released in April of 2003. What prompted you to start using cryo as an energy source for ablation? What makes cryo an ideal ablation source?

When I do an ablation, I tell patients we are going to fix the problem. We are very good with AV node reentry, WPW, flutter, and atrial tachycardia, unless it is very close to the AV node. I have treated about a dozen patients with atrial tachycardias around the AV node and also a case of anteroseptal bypass tract; however, it can be very scary when you are ablating these, for fear of heart block. Cryo seemed like an ideal solution in that now we could work in and around the AV node without the fear of heart block. It has always been disappointing when you tell a patient it is too risky to ablate because of fear of heart block now this has been eliminated so that I no longer have to explain to patients why although we should be able to cure them, and we cured the person in the next bed, we are going to put you on medicines instead. Now I never have to tell someone that again; this is one of the main reasons why cryo appealed to me.

What arrhythmias have you used cryo on so far?

Quite a few. Obviously we started with AV node reentry, and then very quickly we extended it out to atrial tachycardias as well as those patients with perinodal arrhythmias. Early on, in June of 2003, I started ablating pulmonary veins with the Freezor ^® Xtra catheter. The reason I started going out to pulmonary veins is that with radiofrequency (RF), you have the risk of pulmonary vein stenosis. With cryo, there is no risk of pulmonary vein stenosis, so I can use a Lasso mapping catheter and freeze, with Xtra, just like we would use an RF catheter. So very quickly I started doing pulmonary veins with cryo. We also started doing atrial tachycardias in and around the phrenic nerve. In November 2003, I was one of three US sites that participated in the Arctic Circler clinical trial. The trial used a novel expanding loop cryo ablation catheter (Arctic Circler ^®) to isolate pulmonary veins to treat AF. The trial also allowed me to use Freezor ^® MAX to ablate the cavo-tricuspid isthmus to treat atrial flutter. One other area where I have used cryo was with RV outflow tract VT. Occasionally when the RV outflow tract VT is in the lower part, or is very close to the His bundle, I ll use cryo. Also, if the RVOT VT appears to be on the anterior free wall instead of the septum, I ll use cryo. Another area in which we use cryo is with the ESI mapping system, which is very good for mapping tachycardias, although sometimes the ST segment gets in the way, particularly for atrial tachycardias. In cases like these, I have used cryo mapping, in which we cool the AV node to -30 º to intentionally induce reversible heart block, and then enhance the ESI mapping system by getting rid of the ST segment. The other alternative is adenosine, to put the node to sleep temporarily, but this can also terminate the tachycardia. I have actually used cryo mapping to aid ESI mapping in adenosine-sensitive atrial tachycardias.

Which catheters and tip sizes do you prefer?

For the most part, I use Freezor Xtra instead of the Freezor. There are two catheters currently released; one is the Freezor Xtra, which is a 6 mm tip it gets a little deeper than the Freezor, which is a 4 mm tip. The Freezor has cryo mapping capabilities, which means it allows you to set the temperature to go down to -30 º, make sure there is no heart block, and then you can take it down to -75 º. In the European version, Freezor Xtra has mapping, but in the US version, it doesn t have mapping capabilities, just ablation mode. With cryo, heart block is a temperature vs. time phenomenon what I mean by that is when you see the PR interval start to prolong you have time to turn off the machine to prevent the ice ball in the tissue from growing further and permanently affecting the AV node. This is a great example that demonstrates the benefit of cellular hypothermia, that is, putting the cells to sleep electrically at temperatures that are not ablative. Having learned this temperature/time relationship, I now feel very confident using Freezor Xtra (without the cryo mapping button) in and around the AV node. Therefore, it has become my cryo catheter of choice.

Describe your involvement in the ICE CAFE Trial.

We were one of three sites Massachusetts General Hospital in Boston, Memorial Hospital in Colorado Springs, and my hospital, St. Joseph's Hospital in Tampa in a Phase 1 clinical trial looking at the safety in utilizing the Arctic Circler for ablation of atrial fibrillation. The patient criteria was that you had to fail two drugs, have at least four episodes of documented atrial fibrillation in a two-month period, have a left atrium of less than 4.5 centimeters, and be less than 70 years old. It was a great experience being able to go in and freeze the pulmonary veins in very short order and eliminate pulmonary vein potentials. In fact, we also demonstrated electrical disconnection of the pulmonary veins in a couple of patients where you can see the vein marching through, independent of the rest of the heart. It is comforting to have a tool where you can go in and you know you are not causing damage, since there is no risk of pulmonary vein stenosis. As part of the clinical trial, we had to get MRI scans at pre-, three months, six months, and a year afterwards; for the most part, there has been no pulmonary vein stenosis. I say for the most part because when you get scans of the heart, it is hard to measure a pulmonary vein, and we have had a few that have been 25% narrowed and some with a 45% increase in size. I know ablation will not increase the size of the pulmonary vein, but I do believe there is some variation in how you measure a pulmonary vein in one scan from another. Nevertheless, there does not appear to be any narrowing of the pulmonary vein, and that is very comforting. With the Arctic Circler, our procedure times were about three and a half hours; in which time we could isolate all four pulmonary veins and create a linear lesion along the tricuspid-IVC isthmus with Freezor MAX. It was wonderful, because for the first time I felt this was a clinically viable tool for ablation of atrial fibrillation. To me, that was the most exciting thing I saw a light at the end of the tunnel for people who are struggling with atrial fibrillation ablation. Remember, cryo won't cause perforation, and in none of our 10 patients did we see any perforations. Obviously I ve had some perforations with radiofrequency pulmonary vein isolation.

Is it true that cryoablation is actually virtually painless for the patient?

Yes, it is, which is one of the wonderful things about cryo energy, especially because in the case of ablating patients with atrial flutter, there is often a lot of discomfort felt during the RF energy pulses. A lot of pulmonary patients have flutter, and I have seen a handful of patients in the last year that have such bad lungs you can t sedate them enough to use radiofrequency. However, cryo is absolutely painless, and the energy source can t perforate, which is another huge advantage. Also, there is cryoadhesion, so I don t have to fluoro the entire time. The only downside is it takes a little longer.

How does Freezor MAX differ from traditional RF catheters for the treatment of atrial flutter?

I do about 60 flutters a year; the catheter that I am currently using is the Chilli ^® (Boston Scientific, Natick, Massachusetts). I like the Chilli because it gets a lot deeper than standard RF it will get about 7 mm deep. When I put my isthmus line in, I look for three things: 1) if they are in flutter, does the tachycardia slow and terminate, 2) do we have bidirectional block at the end, and 3) there are no recordable electrograms when I finish. With standard RF, you still have recordable electrograms, but with saline-cooled RF, there are no recordable electrograms, it is like turning that tissue the isthmus -- into leather. With Freezor MAX, there are also no more electrograms; that tells me we are getting a big, deep freeze. There is a higher recurrence with flutter in standard RF, but I haven t seen it with Chilli, and I haven t seen it in the 10 patients we did with Freezor MAX.

How is the 9 French 8 mm tip more powerful than the 7 Fr 6 mm tip?

Well, don t forget that cryo works by cooling tissue, so by using the bigger catheter such as the 9 Fr 8 mm tip there are bigger tubes for more refrigerant flow. If there is more refrigerant flow, you can pull out more heat from the tissue. With Freezor MAX, you are getting a much deeper freeze that kills out more quickly than you do with a smaller catheter.

What catheter(s) do you currently use for treating atrial flutter?

For atrial flutter, I am using Chilli; the reason is because when we are done, I can t even record electrograms. I have tried other catheters, such as the standard 4 mm tip catheters. I have not tried the 150-watt catheter. However, at least with the saline-cooled catheter, I get a deep burn, and my recurrence rate is just about zero, which is a lot different than most people using RF.

How will the availability of Freezor MAX change how you treat atrial flutter?

It would help because, again, we actually getting as deep a freeze with the Freezor MAX as we are getting with saline-cooled RF. It has a couple of other advantages as well. It is pain-free, which is important for those people with severe lung disease. Flutter ablation, particularly saline-cooled RF, is one of the most painful things a person can go through, and it always takes general anesthesia.For patients who have severe lung disease, have just gotten extubated, and have only a marginal pulmonary reserve, I am currently not ablating them with saline-cooled RF. The other thing is that because of the depth you get with saline-cooled RF, physicians are very concerned about the potential for perforation, particularly as you come over the isthmus going into the vena cava. Personally, I tend to take a deep breath, because it is very easy to perforate. However, with Freezor MAX, you don t have to worry about perforation. I think Freezor MAX is also going to have a role in other arrhythmias as well. For example, I have a patient right now with RV outflow tract VT, and with standard RF I am starting to affect it, but I can t kill it off unless I go a little deeper. With Freezor MAX, I don t have to worry about perforation, so that would be an ideal location. In Europe, I know they are using Freezor MAX in the pulmonary veins to get a bigger deeper kill zone very quickly. Another place I can envision using Freezor MAX would be with ventricular tachycardia, either endocardially or epicardially. Remember, with cryo, you don t get near the clot formation that you do with RF. There is less of a stroke risk with Freezor MAX than with standard RF in the left ventricle. The Freezor MAX is a little shorter of a catheter it is 90 centimeters in length as compared to 110 for a standard catheter and that may pose a problem reaching certain areas, such as in particularly big patients.

What are the differences when comparing energy sources or ablation techniques between RF and cryo?

When I do a RF ablation, for example, for AV node reentry, I have always taken the approach that after our last burn I am going to wait 45 minutes before I put an end to the procedure. I approach my cryo cases in the same way. I don t think there is a difference in technique or success rates between cryo or RF; the only thing cryo does is give me comfort to know I can t perforate, and I can't get pulmonary vein stenosis. Also, cryo is probably a little bit more lenient towards the phrenic nerve and other structures, and I can get in and around the AV node and know what it is going to do before I make it permanent. Therefore, I think cryo is more of a comfort factor to me I could do the same thing with RF, but it is so much more comforting doing cryo. I think if cryo had come out before RF, then radiofrequency would never have been invented. Look at the biggest problem we are currently facing, which is atrial fibrillation. I don t see anyone doing active clinical trials on atrial fibrillation ablation with RF. However, with cryo, both CryoCath and CryoCor are actively doing clinical trials looking at the success rates of treating atrial fibrillation. AF is the final frontier. I don t know which is worse atrial fibrillation or pulmonary vein stenosis. However, I do know that with cryo I have taken a lot more of an aggressive approach towards ablation of atrial fibrillation than I did prior to the availability of cryo.

What changes in ablation have you seen in the course of your career? Also, now that cryo has been available for a while, what do you see as the future of cryothermal energy?

You are talking to somebody who started out with D/C His bundle ablation way back from 1985-1988. I started out at Duke doing D/C AV node ablation and some D/C posteroseptal pathways. When I left Duke in 1988, there was a big controversy between a technique called low-energy D/C versus this new pioneer radiofrequency. In 1990, I started doing radiofrequency, and haven t looked back since. As I said, it was wonderful to cure people, but I felt so bad when I came across critical structures such as in and around the AV node, that I became hesitant. Other things like fasicular VTs on the left, if it mapped down low, I had no problem ablating; however, when they mapped up high, then you have to determine at what point you get heart block. Now with cryo, I can tell if I am going to get heart block before I make it permanent or not. We were the ninth in the nation to get cryo, and I only see cryo taking over more and more. The only thing I currently use RF for now is flutter, and once the Freezor MAX comes out, I may change over 100 percent to cryo. Again, it is a wonderful technology, and I probably won t miss RF a bit. There is a misconception about cryo, though some feel it s a misunderstood product because it s only approved for AV node reentry. Guess what? RF is only approved for AV node reentry and WPW, and we use it for all of these other things. Therefore, I believe once people start to realize that cryo is just another tool, and that tool has certain advantages over radiofrequency, then change is going to take place. I am doing my AV node reentry just as fast with cryo utilizing Freezor Xtra as I ever did with RF.

Is there anything else you'd like to add?

It is exciting what it is going on now with cryo, but I think the most exciting thing is the potential particularly taking it to the left atrium in the pulmonary veins and eliminating pulmonary vein stenosis. Also, I suspect, although I don t have proof yet, that cryo will be safe enough to prevent the esophageal left atrial fistulas that we have had with RF. I think the potential for what cryo can do is just amazing, and now it is simply waiting for the tools to be FDA approved. I keep hoping one day I am going to win the lotto I would put an aircraft carrier 12 miles off shore and provide state of the art technology which is available to the rest of the world, but is several years away because of the US FDA approval process in this country.