A Progress Report on Cryotherapy: One Year After Freezor's Approval by the FDA

EP Lab Digest: Why did you want to bring the cryotherapy system to your lab?

Dr. Lanzarotti: St. Luke's is a leading EP center in the United States. We need to remain at the forefront of the technology curve, so it was essential to add the cryoablation tool to our cupboard of existing radiofrequency (RF) technology. We also wanted to be able to offer our patients an alternative to RF that is both safe and effective. Safety was definitely an important consideration in our decision to use cryoablation. This is especially true in cases where I would feel more trepidation using radiofrequency energy.

Can you give us examples of such cases?

Well, for example, these cases might include parahisian pathways or the more difficult AVNRT cases. With cryo, I have done several ablations in which there was a His on the ablation catheter tracing and still felt comfortable enough to ablate, knowing that by leading with a wave of hypothermia, I can come off quickly without causing permanent AV block.

The success rate with RF ablation for AVNRT and other SVT arrhythmias is very high, with very low complication rates. In light of this, what would be the rationale for using cryothermal energy?

Again, safety is the main consideration. We d been following the progress of cryo first in clinical use in Europe and then in the FROSTY trials in the U.S. and were encouraged both by its safety profile and its efficacy rates. You re right when you say that complications with RF in particular, inadvertent heart block requiring a permanent pacemaker are rare. However, I feel we should do all that is possible to eliminate that risk completely.

How is ablating with cryo different from ablating with RF energy?

The thing that comes to mind is adhesion. With cryo, the catheter adheres to the tissue as the temperature of the tip drops. There is no equivalent to adhesion in RF. Adhesion gives us the ability to ablate during tachycardia without having to worry about the catheter dislodging. There is, however, one slight drawback with adhesion, and that is that you can't drag burn certain arrhythmias, for instance, flutter. Of course, for practitioners who aren t as fond of drag burning, cryoadhesion is primarily viewed as a benefit since it offers good catheter stability and positioning.

How steep a learning curve did you experience when you started out using the cryocatheter?

Not steep at all. Cryoablation is basically an extension of our current ablation techniques.

When you say it is an extension of your current ablation techniques, does that mean that you had to alter your ablation techniques with cryo?

Not really. However, there are a few things to watch out for. You need to pay close attention to time to effect on the pathway or tachycardia. If the time to effect is longer than expected, it is possible that you may not have ablated the target site. It may only mean that the pathway was within the hypothermic zone. During some of our first cases, we experienced early recurrences 15-20 minutes after the ablation lesion during the waiting phase. In all cases, these recurrences were successfully acutely ablated with cryo, during the same session, and our chronic results are very encouraging. These cases show us how precise we must be with cryo and to watch for fast time to effect. In this respect, the 6-millimeter catheter may be more useful and applicable for adult patients with typical SVTs. We also learned that tissue contact is very important with cryo, more so than with RF. More tip/tissue contact will allow the cryocatheter to remove more heat from the tissue to create a proper lesion. Otherwise, an ice ball can form between the catheter and the tissue and lead to a smaller, more shallow lesion. Over time, I've learned to readjust a catheter rather than continue a lesion if the tissue at the tip/tissue interface is taking longer than expected to cool down to mapping temperatures.

What kind of impact do you think cryomapping and cryoablation will have on the field of EP?

There is no RF equivalent for cryomapping where you can test potential ablation sites. In a manner of speaking, with RF, you re learning by burning. With RF, you have to lay down the lesion and then test for effect after the burn is complete. With cryo, you have the ability to test a site for success before making a permanent lesion.

Which arrhythmias are you treating with the catheters that are currently available?

They are useful primarily for septal arrhythmias, including AVNRT and AVRT. We are also using them to treat atrial tachycardia, particularly in the right atrium where there is a concern of ablating near the sinus node or damaging the phrenic nerve.

How do you see cryoablation evolving?

I think it'll play a larger role in treating other atrial and ventricular arrhythmias, especially when catheters with larger tips become available. A larger tip can create a larger lesion, which would be useful in ablating atrial flutter. Of course, cryoablation of atrial fibrillation is also very promising.

Can you elaborate on that, that is, the use of cryo for atrial fibrillation?

Well, atrial fibrillation is the hottest area currently in ablation. Cryo seems to have excellent prospects as a tool that will allow us to advance toward a complete cure via catheter ablation. The ability to go into the pulmonary vein and cryoablate without worry of stenosis is a considerable benefit.

Is there any advice you would offer fellow electrophysiologists as they bring cryo systems into their practices?

I would say it's important to remain vigilant and monitor AV conduction during cryomapping and cryoablation. A lack of AV node disturbances during cryomapping doesn't guarantee that you won t affect the AV node during cryoablation. However, what is comforting is the knowledge that cryo always leads with a wave of hypothermia. What that means is that if you see any conduction disturbances, you can stop immediately, and the effect will only be transient.

As a cryo user, what would you say are its limitations?

As I mentioned earlier, cryocatheters produce precise lesions and adhere well to tissue. These properties limit the use of cryo in the treatment of arrhythmias where I would typically do drag lesions with an 8-millimeter-tip RF catheter, that is, in atrial flutter, atrial fibrillation, or ischemic VT cases. However, I think that larger tip catheters and new tip designs will help solve this problem. For instance, the 8-millimeter cryocatheter available in Europe has done well with atrial flutter.

Has your use of cryotherapy had an effect on the way you counsel patients?

Yes. It has changed the way we discuss risks with our patients. Patients need to understand that there is still a risk of AV block, but that it is very low far lower than with RF. That's very comforting to the more anxious patients, and to electrophysiologists, for that matter. The risk of permanent AV block requiring a pacemaker is a strong deterrent for some patients. We've had several patients who declined an RF ablation for that very reason. We've also had cases where the use of RF might have led to complete heart block due to the proximity of the patients pathways. In all of these cases, we used cryoablation to treat the arrhythmia successfully without complication. 

Could you tell us a little about one or two of your more interesting cases with cryo?

With some trepidation, I went on to cryoablation at this position. We did see PR prolongation, which quickly led to AV block slightly over three minutes into the lesion. We felt it was prudent to stop immediately. AV conduction quickly returned to baseline, demonstrating that the AV block was due to far-field cooling and not because the AV node itself was in the kill zone. We created no further lesions. The patient has not recurred in several months, whereas previously he had several arrhythmic episodes per week on anti-arrhythmic therapy. We have also recently performed several ablations on patients with atrial tachycardia. The most memorable was one that was very close to the SA node and in a position where the possibility of phrenic nerve damage was also a concern. We used cryomapping to confirm termination of the SVT at a point mapped with intracardiac mapping and with the endocardial solution mapping system. We also paced at this location to rule out phrenic nerve stimulation. After one lesion we had a complete cure without effect on either the SA node or phrenic nerve (Figure 1).