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Moderating AFib to Prevent Strokes

Freezing atrial tissue, or cryoablation, is gaining popularity as an effective, less painful alternative treatment.

One of the top causes of stroke is atrial fibrillation (AFib), an irregular heartbeat that occurs when the two upper chambers of the heart beat irregularly and do not coordinate with the two lower chambers. The chaotic rhythm can cause blood to pool in the heart and form clots, which can then travel to the brain and cause a stroke.1

Though medication can be used to control AFib, some cases require more invasive treatment to restore a normal heart rhythm. "Treating AFib is a procedure that is based on a patient's anatomy," said Robert Winslow, MD, a cardiac specialist and electrophysiologist at the Western Connecticut Health Network's Danbury and Norwalk hospitals.

"A lot of abnormal heart rhythms that we treat, we try and specifically map and identify the exact area electrically where the abnormal heart rhythm emanates. AFib has some challenges in that we cannot definitively locate exactly where the abnormality is, so our procedure is based much more anatomically in that there are areas in the heart that we want to electrically sequester or isolate from the rest of the heart."

These areas are the pulmonary veins that bring blood back from the lungs to the left atrium, where the triggers for AFib originate. John Novella, MD, also a cardiac electrophysiologist at Norwalk and Danbury Hospitals, explained that electrically isolating the tissue just outside the pulmonary veins essentially "prevents that tissue from triggering episodes of atrial fibrillation by preventing electrical triggers from emanating out of the vein."

Traditionally, AFib is treated with radiofrequency-based ablation, a procedure that isolates these veins with a radiofrequency catheter. "To isolate those areas would often take a number of point ablation lesions - twenty, thirty, forty - for each group of veins," Winslow said. However, an alternative technique called cryoablation, which freezes the atrial tissue, is gaining popularity as a quicker and generally less painful alternative for treating AFib. The minimally-invasive procedure takes about two hours and only requires restricted intense physical activity for 48 hours.2

Cryoablation

Cryoablation delivers extreme cold energy by way of a balloon catheter, also called a cryoballoon. "The cryoballoon is nice because it essentially acts as a mechanical "plunger" that is specifically designed to incorporate the entire circumference of the vein and deliver a circumferential line of electrical block," Novella said. This technique creates a larger circumferential lesion around the pulmonary vein rather than requiring point-by-point lesions like heat-based ablation.

Physicians insert the balloon catheter into a blood vessel, typically in the upper leg, and then thread it through the body until it reaches the heart. Utilizing a dye that can be seen in the vein under live x-ray, physicians confirm that the balloon has occluded the pulmonary vein. Once confirmed, cold energy is delivered through the catheter and the damaged tissue is destroyed.3

Novella recently treated a patient with cryoablation at Danbury Hospital. "He was having multiple daily episodes of drug-refractory atrial fibrillation," Novella said in an April 26 Danbury Hospital press release. "On the day of the procedure, he arrived in atrial fibrillation. During his procedure, his abnormal heart rhythm was restored to normal rhythm shortly after we began applying Cryoballoon energy to his largest pulmonary vein. Since his procedure, he has not had one episode."2

Advantages

One advantage of cryoablation is that it gives the ability to cool tissue before freezing in order to ensure that the targeted area is the one causing the abnormal heart rhythm. If it is not, the site's normal electrical function can be restored just by allowing the tissue to warm up again.3

Using cold energy instead of heat can also reduce the chances of affecting healthy heart tissue and the structures that surround it. There tends to be less of a perforation risk, less risk of esophageal injury, and less risk of clot formation, according to Novella.

"Ultimately it can help reduce procedure time, and it's also something that is easier for lab throughput, in terms of setting patients up, monitoring patients, and the aftercare of patients," Winslow said.

Potential for Growth

Though cryoablation has been used to treat AFib for about five years, it has only really gained popularity within the past two years, due in part to a better design in the second generation cryoballoon technology.

There are not many centers that offer this technology, however. "It's not widespread in the sense that radiofrequency is," explained Novella. "It's new or novel in that regard."
Cryotechnology is also an extra capital outlay for hospitals, as Winslow explained. "The extra cost to get this sort of equipment when most places have all the traditional radiofrequency equipment to do the traditional kind of ablation is another reason that it's not being adopted everywhere," he said.

Nevertheless, this technique may see greater use throughout hospitals in the near future. "I think there are definitely people that are adopting it because of some of the advantages in the technique, in terms of patient throughput, less anesthesia time, and the shorter procedure time," Winslow said.

Cryoablation also offers the advantage of technical uniformity, another reason that Novella sees potential for it to gain popularity as a treatment for AFib. Radiofrequency ablation tends to take more time to learn because it requires very fine movements, while cryoablation is comparatively simpler and associated with less variability among operators.

"If I was to perform a cryoballoon ablation and one of my colleagues was to perform one as well, each patient would theoretically receive equivalent quality ablations because of the inherent technical uniformity of cryoablation," Novella explained. "This is not the case with radiofrequency ablation and therefore allows greater standardization of the ablation procedure itself."

Kirsten Malenke is a staff writer at ADVANCE. Contact:kmalenke@advanceweb.com.

References

1: Mayo Clinic. Atrial Fibrillation. http://www.mayoclinic.org/diseases-conditions/atrial-fibrillation/symptoms-causes/dxc-20164936  
2: Danbury Hospital. Can Freezing the Heart Prevent a Stroke? - Danbury Hospital Pioneers Use of Cryoablation to Treat Afib and Reduce Stroke Risk. http://www.danburyhospital.org/newsroom/articles/cryoablation-to-treat-afib
3: Massachusetts General Hospital. Cryoablation for the Treatment of Atrial Fibrillation. http://www.massgeneral.org/heartcenter/services/procedure.aspx?id=2232  


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