Case Study: Utilizing the Cryoballoon for Atrial Fibrillation Patients

Dr. Irwin was among the first in the United States to treat atrial fibrillation (AF) patients using cryoballoon technology. In this article, Dr. Irwin discusses his use of the technology, including his participation in the STOP-AF (Sustained Treatment of Paroxysmal Atrial Fibrillation) clinical trial.

Introduction

The Arctic Front^® Cardiac CryoAblation Catheter System (Medtronic, Minneapolis, MN) received FDA approval December 17, 2010 for the treatment of paroxysmal atrial fibrillation (PAF). The Arctic Front system consists of a cryoballoon, which comes in a 23 mm or 28 mm diameter, and a 12 French steerable delivery sheath. This system received FDA approval without going to panel based on the results of the STOP AF clinical trial. Bay Heart Group in Tampa, Florida, was one of 25 centers in the United States and Canada making up the pivotal clinical trial. As a part of the phase 1, 2, and 3 FDA trials, we have had access to the balloon for the past 5 years. Having used the device for the last 5 years, I have grown to appreciate both the ability and limitations of the cryoballoon. The STOP AF trial was a randomized clinical trial comparing cryoballoon ablation to drug therapy in patients with highly symptomatic atrial fibrillation. The inclusion criteria were that the patients have a left atrial size of 5 cm or less. Patients needed to have at least 2 episodes of PAF per month, failed at least 1 membrane active antiarrhythmic drug and have no more than 2 cardioversions in the prior 2 years. Patients could not have had a previous left-sided ablation. Patients were randomized in a 2:1 ablation versus a drug arm. Patients randomized to drugs were required to be treated with either sotalol, Rythmol or Tambocor. The drug needed to be new to the patient or at a higher previously failed dose. Patients randomized to the drug arm could cross over to the ablation arm if at the end of the 6 months if they were still having AF. Patients who crossed over to the ablation arm could have one attempt at ablation with the cryoballoon. Patients originally randomized to ablation could have a repeat ablation if done within 90 days of the first ablation.

Case Description

DH was a 51-year-old male enrolled in the STOP AF clinical trial. Being very symptomatic at the time of enrollment, he was hoping for ablation. At the time of randomization he had a left atrial size of 5 cm. He was randomized to the drug arm of the clinical trial. Despite drug adjustment he continued to have PAF over the next 6 months. At the time of crossover to the ablation arm, the patient’s left atrium had grown to 5.8 cm. A pre-procedure TEE showed the patient had smoke in the left atrium and poor left atrial appendage velocity, but no clot. The patient was in sinus rhythm at the time of the TEE, which occurred at the start of the ablation procedure. The patient underwent cryoballoon ablation using both the 23 and 28 mm cryoballoon. The 2 balloon sizes were required to get complete occlusion on each of the 4 pulmonary veins. The 2 sizes of balloon ablate different areas of the pulmonary vein antrum. Because of this, when I have to use 2 different sizes of the balloon, I always apply additional ablations with the second size balloon to previously ablated veins. Post ablation the patient did significantly better but still had paroxysmal AF off drugs. His desire was to be off both antiarrhythmic agents and coumadin. Because of the TEE findings, it was recommended that the patient stay on coumadin. At the end of one-year post ablation the patient felt better, but demanded to be off all drugs. At the patient’s request, an open-chest surgical ablation was performed. During the surgical Maze procedure, a fiberoptic scope was inserted into the left atrium for filming the extent of the ablation one year earlier. At the time of the surgical Maze, the ablation lines from the prior year were clearly visible (Figure 1). This figure shows the right inferior vein in the foreground. The pump sucker is present in the left inferior pulmonary vein. As can be seen in the figure, the extent of the ablation extends well beyond the pulmonary vein ostium. The ablation line is clearly visible. The tissue within the ablation line appears to be very uniform without visible gaps. The other pulmonary veins showed a similar antral ablation as seen with the right inferior pulmonary vein. Post-surgical Maze, the patient has been AF free and off all drugs including coumadin.

Discussion

This case showcases several aspects seen with cryoballoon ablation. In the STOP AF clinical trial, patients enrolled had PAF with a left atrium of 5 cm or less. Another important limitation was the fact that patients were limited to 2 cardioversions over the previous 2-year period. After the patient was enrolled, they could have cardioversions as necessary directed by the investigator. In addition, at the end of the 6-month drug arm, the patient could cross over to ablation despite having a left atrium above 5 cm. By the time our patient crossed over to ablation, his atrium had grown to 5.8 cm and he received cardioversions that would not have been allowed at time of enrollment. Post ablation he did much better, but was not cured by the procedure. Once the left atrium grows above 5 cm or the patient’s AF becomes persistent, the results of ablation will fall off from that seen by the clinical trial. Because of this case, I try to stick to the enrollment criteria from the STOP AF trial when selecting patients for ablation now that the device is market released. The level of ablation with the cryoballoon has been debated. On the basis of three-dimensional mapping, it has been felt that these ablations are limited to the pulmonary vein ostium.¹ As can be seen from Figure 1, the cryoballoon extends to the antrum. When a balloon ablation is done, the balloon must be outside of the vein to prevent injury to the vein. The entire balloon is cooled by the liquid nitrous oxide expansion in the balloon to the gas phase. Because the size of the balloon is larger than the mouth of the vein, any part of the balloon out of the vein in contact with the wall of the heart can result in extra ostial ablation. In particular, using a 28 mm balloon can result in a significant amount of ablation outside of the ostium. The cryoballoon has been available in Europe since 2004. Several investigators have reported their results compared to spot ablation with radiofrequency (RF). One of the most common observations contrasting RF with the cryoballoon is the absence of left atrial flutter and left atrial tachycardia post-balloon ablation. As an AF ablator, I find this a welcome relief. The extent of the ablation is seen from Figure 1, and it is clear why this may be the case. Clearly the ablation appears to have a discreet line demarcating ablated versus non-ablated tissue. The lack of apparent “holes” in the ablated tissue may account for the lack of proarrhythmia seen with the cryoballoon. The extent of the ablation seen at the time of the surgery was a surprise. The ablation line extends about one centimeter beyond the mouth of the vein. This raises several possibilities. The distance of unablated tissue between the left- and right-sided veins is very limited. This means that it may be relatively simple to place connecting lines for the treatment of persistent AF. As can be seen from Figure 1, the distance required to create a mitral isthmus line would be very short. This may make creating a line for mitral flutter much easier.

Summary

Recently, the 2011 ACCF/AHA/HRS updated Atrial Fibrillation guidelines were published in Circulation.² The new guidelines now list ablation as a Class 1 indication for the treatment of drug refractory atrial fibrillation in patients with a small atrium and normal LV function. This pertains to catheter ablation performed in experienced centers. The cryoballoon is well suited to play a major role in giving cardiologists the ability to follow the guidelines. The learning curve for the cryoballoon appears to be very small, and it appears that the technique translates well from major academic centers to small private practices.³ Our average time for performing an AF ablation with the cryoballoon is 3 hours, and in the STOP AF trial, our success rate was greater than 90%.

References

1. Reddy VY, Neuzil P, D’Avila A, et al. Balloon catheter ablation to treat paroxysmal atrial fibrillation: What is the level of pulmonary venous isolation? Heart Rhythm 2008;5:353-360.
2. Wann LS, Curtis AB, January CT, et al. 2011 ACCF/AHA/HRS focused update on the management of patients with atrial fibrillation (Updating the 2006 Guideline): A Report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Circulation 2011;123:104-123.
3. Kowal R, et al. Rapid Impact of Incremental Experience on the Outcome and Procedure Times Using Cryoballoon Ablation to Treat Paroxysmal Atrial Fibrillation. Boston Atrial Fibrillation Symposium, 2011.

———————————————————— Disclosures: The author has no financial stock to disclose. Dr. Irwin also reports he is a physician advisor to Medtronic CRDM, cryoballoon trainer for AF Solutions (Medtronic), and physician advisor to Bard EP. Currently the only active research funding reported is Medtronic for phase 3 cryoballoon and Medtronic’s chronic lead study. ———————————————————— Editor’s Note: This article underwent peer review by one or more members of EP Lab Digest’s editorial board.