ATLANTA -- An investigational cryoablation system was substantially better than antiarrhythmics in treating paroxysmal atrial fibrillation, a multicenter, randomized STOP-AF trial showed.
Through one year, 69.9% of patients who underwent cryoablation remained free from treatment failure, compared with just 7.3% of those on medical therapy (P<0.001), according to Douglas Packer, MD, of the Mayo Clinic in Rochester, Minn.
Although five patients had serious ablation-related complications, the overall rate of serious adverse events was similar in the two groups (12.3% with cryoablation versus 14.6% with medical therapy, P=0.69), he reported at the American College of Cardiology meeting here.
"I find [the trial] very exciting," commented Ralph Brindis, MD, a cardiologist at Kaiser Permanente in Oakland, Calif., and president-elect of the ACC.
Action Points
- Explain to interested patients that the cryoablation system evaluated in this study has not been approved for use in the U.S.
- Note that this study was published as an abstract and presented at a conference. These data and conclusions should be considered preliminary until published in a peer-reviewed journal.
"I think it may lead to increased utilization of ablation technologies for the paroxysmal afib population because it may actually lead to the ability to not be on a lot of medications and to not need to be on long-term anticoagulation," said Brindis, who moderated a press briefing at which the results were presented.
He had some concerns, however, including the likely increased need for interventionalists to learn how to treat pulmonary vein stenosis, which was infrequent but more often in the cryoablation group (3.1% versus 2.4%).
STOP-AF was a pivotal trial evaluating the Artic Front cryoballoon ablation system, which is not approved for use in the U.S. It involves threading a catheter into the opening of a pulmonary vein and expanding a balloon, which is used to freeze the target area.
Packer said the technique has advantages over radiofrequency ablation because the vein can be isolated using a few freezes, instead of ablating multiple isolated spots with the tip of a catheter.
The trial was conducted at 26 centers in the U.S. and Canada. To be included, patients were required to have had at least two atrial fibrillation episodes in a two-month period, with ECG documentation of at least one, as well as treatment failure with a least one antiarrhythmic.
All patients had symptoms, most commonly palpitations, rapid heart beat, and fatigue.
The level of underlying cardiac disease was low.
Patients were randomized in a 2:1 ratio to cryoablation (163 patients) or medical therapy (82 patients).
After randomization, there was a 90-day blanking period in which cryoablation could be re-performed, if necessary, and the drug dose could be optimized. Patients were then followed for another nine months.
Overall, 31 patients required a repeat ablation procedure, and 65 eventually crossed over from the drug group to the cryoablation group.
The mean duration of the cryoablation procedure was 371 minutes (range 200 to 650). It was successful in 98.2% of patients, as defined by the isolation of at least three pulmonary veins.
At 12 months, significantly more of the patients in the cryoablation group were free from treatment failure, defined as no detectable atrial fibrillation, no use of nonstudy drugs, and no interventions for atrial fibrillation.
Nearly all patients in the cryoablation group were taking antiarrhythmics and warfarin at baseline, but at 12 months, only 26% were still taking antiarrhythmics and 24% were taking warfarin.
The number of patients with atrial fibrillation symptoms in the cryoablation group was reduced from 100% to 19.6%.
The number of procedure-related serious adverse events was significantly lower than the projected 14.8% (P<0.001).
Phrenic nerve paralysis occurred 29 times in 28 patients; 25 of the cases resolved by the one-year follow-up, but four persisted.
There was one death, from MI, in the cryoablation group. It occurred on day 288 of follow-up.
Out of 927 total pulmonary veins that were ablated, 10 in seven patients became stenotic.
Packer said that complications would likely be reduced as those performing the ablation procedure become more experienced. He said there is a large learning curve involved in the adoption of the relatively new technology.
The study was limited in that there was a large proportion of patients from the drug-treatment group who crossed over to cryoablation, and re-do ablations were allowed within 90 days of the first procedure.
Also, there was a limited choice of antiarrhythmics, and cross-sectional area was used instead of diameter to asses pulmonary vein stenosis, which tends to overestimate the problem, Packer said.
Disclosures
The study was funded by Medtronic CryoCath.
Packer reported providing consulting services in the past year to Boston Scientific, Biosense Webster, Biotronik, CyberHeart, InnerPulse, Medtronic, nContact, sanofi-aventis, Toray Industries, and St. Jude Medical, although he did not receive personal compensation.
He reported receiving research funding from the NIH, Medtronic, Siemens AG, EP Limited, the Minnesota Partnership for Biotechnology and Medical Genomics/University of Minnesota, Biosense Webster, and Boston Scientific.
Primary Source
American College of Cardiology
Source Reference: Packer D, et al "Cryoballoon ablation of pulmonary veins for paroxysmal atrial fibrillation: first results of the North American Arctic Front Stop-AF trial" ACC 2010; Abstract 3015-6.