Medical Device Daily Washington Editor

BOSTON – The annual meeting of the Heart Rhythm Society (Washington) took place in this rain-soaked city, which is fortunately just south of some of the worst of the flooding to hit the Northeast. Despite the travel travails encountered by rail, road and plane, attendance at HRS 2006 was robust.

One of the numerous sessions at Heart Rhythm 2006 was a discussion of the latest innovations in treatment of atrial fibrillation (AF). Kenneth Ellenbogen, MD, the Kontos Professor of cardiology at the Virginia Commonwealth School of Medicine (Richmond, Virginia), discussed the use of cryoablation in treatment of non-atrial fibrillation arrhythmias.

Ellenbogen, whose biography states that he is on the editorial board for 22 journals, indicated that radio frequency (RF) ablation of AV nodal re-entry tachycardia had demonstrated some stunning successes, but that the successes were not without room for improvement.

On the positive side, the six studies he displayed on the use of radioablation for non-atrial fibrillation arrythmias enjoyed a success rate of between 93% and 99% in treating AV nodal re-entry tachycardia, but also had a rate of occurrence of complete heart blockage of between .5% and 2.1% after radioablation. One of the studies, a 1999 trial sponsored by Medtronic, indicated a recurrence rate of about 5% “with a relatively limited follow-up,” according to Ellenbogen, adding that practitioners using RF ablation should “be prepared to talk to your patients about the risk of heart blockage.”

Before discussing data on cryoablation, Ellenbogen commented briefly on the various tip sizes used in cryoablation. These tips come in different sizes, but much of the data is based on the use of a 4mm tip. Ellenbogen made a case for tips running 6mm and 8mm, arguing that “you just don't get that much deep freezing” with the smaller tips, further arguing that he has not found the 4mm tip very useful compared to its larger brethren.

In the so-called FROSTY trial, which was reported in the 2004 edition of HRS's journal Hearth Rhythm, it was reported that “there were no instances of permanent and/or inadvertent AV block” using a 4mm tip. Ellenbogen added that the induced lesions were “more focused” than is typically obtained with RF ablation, but pointed out that there is “a learning curve associated with new technology,” suggestive of the possibility that greater efficacy will accrue with experience.

Attempts to optimize the success rate for cryoablation in this use calls for “different catheter positions from RF” ablation, and Ellenbogen stated that “we usually give two or three insurance lesions” to ensure efficacy. He remarked that “we've done a few cases with an 8mm tip, but that even with the larger tip, “cryoablation limits the area of impact compared to RF.”

Ellenbogen posed the question of why cryoablation should be used to treat atrial flutter. “One of the best reasons is that there was a dramatic difference” in the pain perceived by patients as compared to RF ablation. He noted that many patients experience significant pain and discomfort, leading to secondary problems such as difficulty sleeping. He noted that may studies indicated a success rate for RF ablation to treat atrial flutter of more than 90%, describing it as “safe and effective” in this use, but he argued that “there is some data that says that a 6 mm tip can be used” to cryoablate “with almost no incidence of heart block.”

Douglas Packer, MD, also discussed a thermal approach to AF, but by means of cryoballooning as a means of ablation. Packer, who is the director of research for electrophysiology at the Mayo Clinic College of Medicine (Rochester, Minnesota), commented that despite some initial concerns over thermal uniformity, “the entire balloon will be almost the same temperature.”

Many of the balloons used in animal research to date have employed temperatures between -60^o and -80^o Celsius and left in place for a period of four to eight minutes. Packer stated that in a series of 16 applications on eight animals, he had to drive temperatures below the -80^o threshold, and that this is often due to the confounding effect of the warmth of blood. In most cases, he suggested, “colder is better.”

Many of the balloons he has researched have run a little more than 20mm in diameter, but Packer informed the audience that the effect of the balloon is not utterly sensitive to perfectly aligning the maximum diameter of the balloon with the cross section of the blood vessel. “You do not have to have complete, 100% closure of bloodflow,” he stated, but added that a surgeon “may have to reposition the balloon” in cases when shutting down blood flow proves problematic.

Packer concluded his discussion by remarking that “the early data are just that. The numbers are small, but the early results are promising.”