Using Cryoablation for AVNRT Cases:

Interview With Efrain Gonzalez, MD, Medical Director of Electrophysiology at Baptist Cardiac & Vascular Institute

When did Miami Baptist Cardiac & Vascular Institute begin using cryoablation? We began using cryo here when it first became available, which was about two and a half years ago.

In particular, how long have you been using CryoCath's 6mm Xtra ablation catheter for AVNRT ablation cases? Why did you begin using this catheter for your AVNRT cases? We began using CryoCath's Xtra catheter approximately two years ago. The decision to switch from the 4mm to the 6mm was because it made for a more effective case. The most important reason we began using cryo was because of safety that is the most attractive feature of this technology. Cryo has a low risk of complete heart block in patients, including small-frame patients. In fact, there was a recent article about cryo use in pediatric EP not that we have many pediatric patients here, but apparently it is the safest technology to be utilized for pediatric cases. Therefore, in my opinion, nothing comes close to cryo's safety profile. The 6mm allowed us to speed up our cases over the 4mm.

What is your patient inclusion/exclusion criteria? How much of your ablation practice is cryo? We have primarily utilized it on patients who have AV node reentry tachycardia, and in patients in which we are very concerned about inducing complete heart block, especially in the younger patient population younger meaning less than age 40. Those are the patients that we primarily use it for. We have also successfully used cryo in some patients with idiopathic right ventricular outflow tract tachycardia. In addition, we have used it in a few very young patients with Wolff-Parkinson-White (WPW) syndrome. However, we primarily use it with AV node reentry tachycardia; this includes probably 90+ percent of our cases.

Where do you ablate with cryo? How do you locate the slow pathway to place your cryo lesion? Do you look for an anatomical region or for a certain a/v ratio? We typically use four catheters located in the HRA, RV, the coronary sinus and the His bundle. Traditionally we go very septal; we use a left anterior oblique (LAO) position, and we try to find a slow pathway potential if we can, but very often we go anatomically and using a larger ventricular electrogram deflection of very small atrial inflection: a 2 to 1 ratio, sometimes 3 to 1. In the LAO position, the catheter is going leftwards just anterior and superior from the coronary sinus. This is about 95 percent of our locations.

How does the position of the cryo lesion differ from the placement of a radiofrequency (RF) lesion? At least in our experience, it is pretty much the same anatomical area. It can depend on the patient's age and cardiac size and absence/presence of heart disease, etc.

How has using cryo changed your practice when ablating the slow pathway in AVNRT cases? We can breathe easier! Honestly, it's a sigh of relief. Using cryo, we have not seen complete heart block in two-and-a half years not one case. We've had maybe two or three recurrences in all this time, and we have used this technology on close to 200+ patients. It is a very safe technology, and we really like it.

What is your typical lesion set? We do six minutes, about -74 to -80 degrees, one application.

Describe the six-minute lesion. Why did you choose this method, and what is it based on? We first started with a 4mm tipped catheter. The initial four-minute application did not give us great success. Therefore, at one point we decided we were going to go to six minutes and, using the 4mm tip catheter, we started having great success. After that, we just kept with the six-minute lesions, and the larger 6mm catheter has also worked very well for us. We are averaging 1 - 1.5 freezes per patient.

Do you feel that 1 six-minute lesion is as effective as 2 or 3 four-minute lesions? It is very difficult to say, because we have had very great successes with the six-minute lesions. However, we do not want to go back to the four-minute application. At least in my opinion, the six-minute lesion is actually a very homogeneous lesion, with a very low recurrence rate, judging by our experiences with patients at our institution.

What do you feel is an acceptable endpoint to determine acute success? Non-inducibility is our ultimate goal. However, what we did is kept the mapping technique from the initial theory of when cryo was first introduced in programs for ablation to ascertain whether or not continuous conductivity of the atrial pathway was there or not. We often see that with one application we have complete obliteration of conduction over the slow pathway (if there is no conduction via the AV node under the same conditions, you could lose the jump and induction of the arrhythmia). That is what we follow here in our lab. When I'm working, my lab partner works to look for complete obliteration of conduction via the slow pathway. We accomplish this in probably 95 percent of all our cases. In the other five percent of cases the conduction remains to some degree, but there is no inducibility.

If the tachycardia was inducible without Isuprel infusion, do you use Isuprel in your post ablation testing? In addition, if Isuprel was needed to induce tachycardia, do you ablate with cryo while on Isuprel? We do our ablations on Isuprel. We start Isuprel, apply cryo, and then stimulate on Isuprel for about 20 minutes after the cryo application.

How long is your post ablation waiting/testing period? If the patient had zero conduction via the slow pathway and the AV node refractory has gone up by more than 50 milliseconds, then we consider ourselves basically done after 15 - 20 minutes on Isuprel post cryo. We apply cryo, wait about 2 - 4 minutes, and then stimulate this is all on Isuprel. Using Isuprel, we usually know anywhere from 2 - 6 minutes.

What is the average length of these AVNRT cryo cases? How does that compare with your RF AVNRT cases? Our AVNRT cases using cryo take about 45 minutes to 1 hour. Our RF cases take about the same amount of time 45 minutes on average. There is not much additional time because of cryo our procedure time is about the same. All of our AVNRT cases are now done using cryo.

What have been your success rates (both for acute and chronic cases) for these cryo AVNRT cases? Our success rate is about 98 percent with no recurrence. I can only remember two female patients and 1 male patient who experienced recurrences. The male had dilated cardiomyopathy and a biventricular pacemaker; we had to convert him with RF recently he failed the first two cryoablations.

Was there any one AVNRT case that was particularly challenging or interesting? How was the case handled? I think our most interesting case was our first cryo case. Our first case was an international patient she was the daughter of a dignitary from overseas who came to our institution because she had learned that we had obtained the cryoablation device. The procedure went very well, and she still comes to see us at least once a year for follow-up when she is in the United States. It has been almost two-and-a-half years now.

What is your method for follow-up? We regularly schedule a follow-up in our office for one month after their procedure was done. Most of our patients get referred to us by other cardiologists, so after their cryo procedure, we refer them back to their cardiologists for further follow-up. We get notifications by their physicians regarding their status up to one year, after which time most of the patients, who are mostly young and healthy, don't want to see us anymore! It's nothing personal!

What made you purchase this equipment four years ago, and what do you think the future holds for the technology? Basically we purchased the equipment after I learned about its utility. In particular, we have a long-term goal of utilizing cryo for atrial fibrillation ablation, which I think is going to be the technology for treating atrial fibrillation. Again, its safety profile is so important. In addition, once the Arctic Front balloon is released, cryo is going to be the technology to be utilized, based on European technologies. I was aiming for that from the very beginning as a long-term goal. No matter what, safety comes first.

Is there anything else you'd like to add? I cannot stress enough the safety of this technology and the ease of use as well as patient comfort. There is no discomfort to the patient when cryo is being applied as opposed to radiofrequency application most patients experience some form of chest pain post procedure from RF. Cryo patients have zero discomfort. We've also seen very few patients complaining of palpitations post cryoablation, which can happen (e.g., PACs) with radiofrequency. Patient comfort, patient safety, lack of any complaints post application these are the benefits of cryo. Not to take anything away from RF, it has been the workhorse for so many years and it has worked wonders. We are still doing many RF procedures for WPWs, ventricular fibrillation, and ventricular tachycardia cases, and it works fine. However, taking into account pediatric safety, cryo will be unbeatable, especially if they can just make the catheters a bit more flexible and smaller for these patients. Cryo will continue to grow just look at the atrial fibrillation experience in Europe. It has such potential.