DENVER – An investigational atrial fibrillation ablation catheter that provides the interventionalist with real-time measurement of contact force with the beating heart wall is safe and appears to improve 12-month success rates, according to the SMART-AF trial.
The principle underlying the development of this novel ablation catheter is that the durability of the therapeutic lesion created during AF ablation depends upon the amount of contact between the radiofrequency electrode and target tissue. Conventional catheters require the operator to assess this mainly visually, a hit-or-miss proposition. In contrast, the new catheter uses contact force sensing technology to provide the operator with quantitative feedback as to whether adequate tissue contact is occurring. The Biosense Webster ThermoCool SmartTouch contact force catheter is integrated with a standard 3-D navigation system, so the operator can see the data on the monitor during the procedure, Dr. Andrea Natale explained in presenting the SMART-AF results at the annual meeting of the Heart Rhythm Society.
The primary efficacy endpoint was freedom from documented AF, atrial flutter, and atrial tachycardia episodes through 12 months of follow-up, not including the standard 3-month blanking period immediately post ablation. Seventy-two percent of the 122 patients with symptomatic paroxysmal AF included in the efficacy analysis remained recurrence free at 12 months.
More impressively, the success rate climbed to 84% in cases where the interventionalist maintained contact force in the therapeutic range more than 82% of the time, while dropping to 61% when the contact force time was 82% or less, reported Dr. Natale, executive medical director of the Texas Cardiac Arrhythmia Institute, Austin.
While therapeutic efficacy proved to be a function of time spent in the therapeutic contact force range, adverse events were not, he noted.
The rate of serious adverse events occurring within 7 days of ablation was 9.9% among the 161 patients included in the SMART-AF safety analysis. The efficacy analysis included 39 fewer patients than the safety analysis. Those first 39 patients comprised investigators’ learning curve in the multicenter, prospective, single-arm study.
An independent safety committee deemed the single case of pericardial effusion that occurred in SMART-AF to be the only device-related adverse event. In addition, the committee judged the four cases of cardiac tamponade and the single case of pericarditis to be possibly device related. No strokes, MIs, or thromboembolisms occurred in the study.
The Food and Drug Administration allowed SMART-AF to use historical controls from earlier clinical trials utilizing a similar Biosense Webster ablation catheter which lacked contact force sensing. The required endpoints in SMART-AF were a 12-month freedom from recurrence greater than 50% and an early adverse event rate less than 16.6%, both of which were met.
SMART-AF investigators selected individual contact force target ranges based upon their early experience with the technology along with patient characteristics. To date, it hasn’t been possible to zero in on a fixed quantity of contact force that predicts treatment success regardless of who is doing the procedure.
All patients underwent circumferential pulmonary vein isolation, with additional radiofrequency lesions placed outside the pulmonary vein ostia as warranted.
The contact force sensing catheter utilizes a 7.5 F shaft with an 8 F electrode. Dr. Natale said it’s his anecdotal impression that the catheter results in reduced fluoroscopy and procedure times, but they weren’t measured in the study. What patients and physicians really care about, he added, is therapeutic success.
Asked if he thought ablation catheters using contact force sensing technology, if eventually approved by the FDA, would become the standard of care, he replied that he believes so, as long as the price is reasonable.
Dr. Michael R. Gold, who wasn’t involved in the SMART-AF study, commented that he found the results "very exciting."
"Our ability – using our fingers 3 feet away from a catheter – to know whether we’re making the right amount of contact is limited. Often, we worry, is it too little or too much? Experts like Dr. Natale do it wonderfully, but for the rest of us, it’s a challenge to try to do these ablations. So the concept of being able to know how much force you’re creating, and to optimize it while minimizing the risk of complications [such as] pushing too hard and poking a hole in the heart, is clearly the Holy Grail we’ve been trying to achieve. This is the first step in that direction," said Dr. Gold, professor of medicine, chief of cardiology, and medical director of the Heart and Vascular Center at the Medical University of South Carolina, Charleston.