Cryo device targets AV node reentry tachycardia. (Alternative to Radiofrequency Ablation).
Last month, the Food and Drug Administration approved the Freezor Cryoablation System specifically for treatment of atrioventricular node reentry tachycardia (AVNRT). Over 50,000 procedures a year are performed to ablate AVNRT every year, making this the most commonly ablated arrhythmia in this country, according to the manufacturer, CryoCath Technologies, Montreal. The company has agreed to monitor the incidence of heart block in patients after treatment with Freezor, as part of postmarketing surveillance.
Approval was based on safety and efficacy data presented at a meeting of the FDA's Circulatory System Devices Panel in March, where the expert panel recommended 7-3 that the device be approved for treating AVNRT, with conditions including one that the manufacturer reestablish a patient registry to monitor the incidence of heart block and other adverse events.
Although the safety and effectiveness in a multicenter study presented at the meeting were not as good as those expected for radiofrequency (RF) ablation, panel members voting in favor agreed that the results "provided a reasonable assurance" that the device was safe and effective for patients with AVNRT.
"It will be a useful tool for the electrophysiologist," Dr. Richard Page, head of the division of cardiology at the University of Washington, Seattle, said at the meeting. It will provide "a new way of dealing with a difficult problem," said Dr. Salim Aziz of the department of cardiothoracic surgery, University of Colorado, Denver. Those voting against approval expressed their concern that while they believed it was a promising device, the scientific data did not support what their clinical intuition suggested.
Dr. Mark Haigney, director of the division of cardiology at the Uniformed Services University of the Health Sciences, Bethesda, Md., who voted for approval, said that he viewed this as a "niche device," which would not replace RF ablation.
The flexible, single-use cryoablation catheter is designed to create focal lesions to treat high-risk arrhythmias near the atrioventricular node with a generator system, according to the company The tip of the catheter generates temperatures from -68[degrees] C to -75[degrees] C maintained for up to 240 seconds using a nitrous oxide energy source, which freezes the tissues and causes necrosis. At warmer temperatures, with shorter durations of exposure, it can also be used for cryomapping to cause reversible alterations in cardiac conduction, to help identify sites for ablation.
The FDA has allowed information on cryomapping to be in included in the device's usage instructions. The panel had split on whether to approve the cryomapping indication.
Speaking on behalf of CryoCath at the panel meeting, Dr. Jeremy Ruskin, chief of the cardiac arrhythmia service at Massachusetts General Hospital, Boston, noted that cryotherapy had been used safely and effectively in the surgical treatment of cardiac arrhythmias for over 30 years, so the concept of using cryotherapy for this indication is not new The novelty of the Freezor system is the availability of the cold energy source in a catheter-based system, which, when applied to the myocardium, results in "well-demarcated, homogenous, dense fibrous lesions, with minimal or no disruption in the endocardium," said Dr. Ruskin, who is a paid consultant to and owns a small equity position in CryoCath.
The Freezor device was used to treat adults with AVNRT, atrioventricular reciprocating tachycardia (AVRT), or atrial fibrillation (AF), in a single-arm, nonrandomized study at 14 U.S. and Canadian sites, which did not compare results directly to patients treated with RF ablation. Instead, safety and effectiveness of cryoablation were compared with "objective performance criteria" for RF ablation, based on the medical literature on RF ablation, which were at least 85% for acute success of the procedure, 7% or lower for the major complication rate, and at least 80% for chronic success, at 6 months. The device did not meet these criteria for the primary endpoint, the acute success rate for the group overall, which was 83%.
But the company did post-hoc analyses of subgroups, and determined that treatment was successful in 91% of the 104 AVNRT subjects, compared to 69% and 67% of those with AVRT and AF, respectively The long-term success rate for the AVNRT patients who had not been lost to follow-up at 6 months was 91%.
There were no cases of permanent AV block in 151 ablated subjects with AVNRT or AVRT, despite frequent ablations near the AV node, according to the manufacturer.
The company pointed out that heart block occurs in about 1%-4% of AVNRTs that are ablated with RF catheters, although one panelist said that in experienced hands, the incidence of heart block after RE ablation was less than 1%--and was probably lower after cryoablation.
In the study, seven patients--three with AVNRT and four with AVRT--experienced eight acute major complications within 7 days of the procedure, for a major complication rate of 4.2%; none were device related and all patients recovered, CryoCath said.
There were 11 device-related events, 7 that were related to cryoablation. There was one unrelated death in a patient 4 months after the procedure.
During the discussion period, one of the investigators, Dr. Peter Friedman, of Brigham and Women's Hospital, Boston, who presented the study's results for CryoCath, said that comparing the Freezor results to RE technology, which has been available for 20 years, set a very high bar for cryoablation. He also described the clinical scenario of a 20-year-old patient with AVNRT, who has a choice between RE ablation with a 94% chance of success but some risk of ending up with a pacemaker, versus cryoablation with a 91% chance of acute success with no chance of ending up with a pacemaker.
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|Publication:||Internal Medicine News|
|Date:||May 15, 2003|
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