Using Cryoablation to Treat Pediatric Patients: Interview With Peggy Strieper, DO, Director of Pacing and Electrophysiology

Cryoablation is making its way as the preferred technology in the treatment of arrhythmias. Dr. Strieper, of Children's Healthcare of Atlanta (CHOA), recently began using the procedure in pediatric patients. In this article, she describes the procedure and its success rates.

Briefly describe the cryoablation procedure. What are the benefits of using cryo?

In standard ablation, we heat the tissue of an accessory pathway or short circuit within the heart and kill those cells so SVT cannot occur. The problem with doing radiofrequency (RF) ablation is that when you go on, it is a permanent damaging of the cells, and so we don't use RF ablation in places that are close to the AV node. Cryoablation, instead of heating the tissue, cools the tissue. A benefit of cryoablation is that you can test the spot first by cooling the tissue to -30 ºC. If you are in the correct spot, you will eliminate the pathway. There will be evidence that you are in the right spot, and you are not causing any harm such as complete heart block. The next step is to drop the temperature a bit further to -70 ºC, which will cause the permanent cell damage, and then you can perform the ablation. In cryoablation, you are able to get rid of the pathway by cooling, but you have a portion of the temperature curve in which things are still reversible, so if you are causing heart block or some other complication occurs, you can come off and things will reverse themselves.

How many patients have been treated so far at CHOA?

We just acquired this system about a month ago, so we have only done five patients so far. However, in the coming week, we have another five patients scheduled. We have been selectively choosing our patients, because there are some limitations with cryo as well. In addition, we still continue to use RF ablation for the majority of our patients; we use cryoablation for the patients that we think would benefit from this, including those that have a substrate closer to the AV node.

Have they all been pediatric cases?

Yes. We are a truly pediatric center, we treat very few adult patients. All of our patients have been young less than 18 years of age. On occasion we have an adult congenital patient, but most of our patients are less than 18 years old.

Is this the first instance of cryo being used in pediatric patients?

No, there are some other centers that are doing it as well. Toronto Sick Children's Hospital has been doing cryoablation for a couple of years in fact, they were one of the pilot sites. From my understanding, they have a lot less stringent regulation for getting new technology in Canada than we do in the United States. Actually, when we did our first five cryoablation procedures, we had one of the pediatric cardiologists from Toronto Sick Children's, Dr. Joel Kirsch, come down and walk us through the procedure so that we would be comfortable with the process.

When was the first cryo case performed? How is that patient doing today?

I don t remember the exact date, but it was about four weeks ago, so not very long ago. The patient was a little 8-year-old who had a tachycardia that was not well controlled with medication. Her pathway was fairly close to the AV node, which is the normal pacemaker within the heart. Since this patient was hard to control on medication, she was also at higher risk for an ablation procedure and for complications. We went ahead and offered cryoablation, and everything went well.

What has the success rate been so far? What complications, if any, have you seen in the cryo cases performed?

We have not had any complications with cryoablation in the first five patients treated so far. My understanding is that the complication rate is lower across the board because you do have reversability with cryo. There are some limitations of the procedures it is not for everybody but it is certainly beneficial in cases such as septal pathways where it is close to the AV node.

What cryoablation equipment is used at CHOA?

Instead of using a RF generator, the generator uses nitrous oxide. The liquid nitrous oxide that goes in through a lumen in the catheter is converted to a gaseous state at the tip when heat is removed from the surrounding tissue. The nitrous oxide is then evacuated from the catheter. The nitrous oxide does not leave the catheter or enter the body at all it stays within the closed circuit and gets pumped through. The equipment we use is made by CryoCath.

How does cryoablation differ in pediatric cases versus adult cases? Are there different risks? Is there different equipment?

The same equipment is used for both pediatric and adult cases. This is actually one of the challenges we face in the field of pediatrics, because we have to use the adult equipment and must adapt things for our pediatric patients. The difference is that the patients we are going to use cryo on are the kids that have either failed medicine or are having difficulties with their medication, so these are kids that would really benefit from ablation, especially because of where their pathways are located. Generally, with standard techniques such as RF, we would not do the septal ablation and continue medications. By offering cryoablation, we can limit the number of times the patient has to come to the emergency room and the patient can come off their medication.

How soon can you ablate in pediatric cases? Are there any age limitations?

There is no age limit, but for the most part, in any kind of ablation we don't perform these procedures on infants. Their hearts are still growing and ablating will cause scar tissue to form in the heart, so we prefer for the patient to be larger. Generally, we will start doing elective ablations at approximately 20 kilograms (or about 50 pounds). There are times where a child just isn t tolerating medicines or is having a lot of breakthroughs, so we may do smaller patients. If it is truly more elective, we will wait until they are preteen or approximately 10-12 years of age. Therefore, it depends on what problems the patient is having, how many medications they have been on, how many visits to the er, etc.; there are a lot of different reasons why we will go ahead with the ablation sooner or later, depending on the situation.

Had you previously used RF ablation?

Yes, that is our standard method. Last year we performed 129 RF ablations on pediatric patients and had a very good success rate. The only children we didn't offer ablation to were kids that we felt had pathways that were just too close to the av node. We have been using RF since 1993 at CHOA.

What are some of the advantages of cryoablation versus RF ablation? Do you expect cryoablation usage to increase?

The main advantage is that we can treat kids that we normally wouldn't ablate because it would be too close to their AV node those kids have gained the most benefit from cryoablation. You can use cryoablation for other substrates and for varying locations of pathways, but I am not sure there is going to be a whole lot of advantage to ablating those patients with cryo. We have had such a good success rate with RF and we know its long-term results on children. I expect we will continue to use RF primarily, and then for those additional patients we will go ahead and use cryo.

What advances do you hope to see in the coming years?

I think some of the other advances in electrophysiology that have come out recently is biventicular pacing or cardiac resynchronization therapy. Once again, this has been used on adults for the last number of years for patients with cardiomyopathy. Pediatrics is always a little slower to follow the technology for adult patients. We have recently started to utilize some of these cardiac resynchronization devices and pacemakers in cardiomyopathy patients that would otherwise go onto transplantation; we also have had very good results with biventicular pacing. I think we are going to learn a lot more about this on patient selection and timing. Regarding ablation, I think we are going to see improvements in different ablation techniques and mapping.

Is there anything else you would like to add?

I think we will keep learning as we use the cryoablation techniques more and more. It will be interesting after we see these five patients this week these five in particular have been in the lab before and we haven't been able to ablate them because the pathways were too close to the AV node. In addition, these kids have not tolerated medicines at all. I am anxious to see how this next week goes and to follow the children long-term. For more information about CHOA, please visit www.choa.org.