Medical Device Daily Contributing Writer

SAN DIEGO— The 43rd annual meeting of the Society of Thoracic Surgeons (STS; Chicago), just concluded, drew excellent attendance as cardio-thoracic (CT) surgeons gathered to meet and gain up-to-date information on their subspecialty. With declining volume in recent years in perhaps their most important procedure, coronary artery bypass grafts (CABG), CT surgeons are definitely more open than ever to find new procedures that can serve their patients and generate incremental volume.

The surgical treatment of atrial fibrillation (AF) would certainly appear to offer such an opportunity, and there are several reasons why AF looks so promising at this juncture.

First, it is a disease with a huge prevalence. Until several months ago, the domestic pool was generally agreed to be about 2.2 million persons. However, an article in the July 11, 2006 issue of Circulation, titled ”Secular Trends in Incidence of Atrial Fibrillation in Olmsted County, Minnesota, 1980 to 2000, and Implications on the Projections for Future Prevalence,” revealed that AF has been dramatically underestimated and that the prevalence exceeds 5.1 million. Moreover, by 2050, it is expected to balloon to nearly 16 million patients. Second, the current “gold standards” for treating AF are not working well.

Anti-arrhythmic drugs are generally regarded as ineffective in 40% to 50% of AF patients, and the blood thinner Coumadin, given to prevent ischemic stroke, has dismal compliance. Hence, many patients suffer an ischemic stroke because of their AF. The percutaneous, catheter-based approach also shows dismal results.

According to an article in the April 2006 issue of the Journal of Interventional Cardiac Electrophysiology, the long-term, single-procedure efficacy of catheter ablation of AF is 28%. Moreover, a major complication occurred in 8% of the patients.

In spite of this, it was estimated at the Boston Atrial Fibrillation Symposium this January that 30,000 to 35,000 “off-label” AF catheter ablations were performed in the U.S. in 2006. These procedures, which increased significantly over 2005, are being performed by electrophysiologists with catheters that are not expressly FDA-approved for AF treatment.

Meanwhile, surgical ablation has grown significantly in the past few years, reaching about 22,000 procedures in the U.S. in 2006. The goal of surgical ablation is to destroy the atrial tissue that is causing the chaotic electrical activity in the atrium. After an ablation, these aberrant electrical impulses cannot cross the burn scars that separate the areas of the atria, thereby halting the atrial fibrillation.
At this year’s STS, the treatment of AF was a key highlight of the meeting.

Atricure (West Chester, Ohio) sponsored an evening boat cruise and program titled “Late Breaking AF Clinical Data Symposium,” with three of the most knowledgeable physicians in the AF arena presenting information concerning this rapidly emerging field.

Patrick McCarthy, MD, chief of the division of cardiothoracic surgery at Northwestern Memorial Hospital (Chicago), strongly advocated that all AF patients undergoing either a CABG or valve procedure should receive a concomitant AF ablation.

He said that in his institution, the percentage of patients in this category has risen in the past couple of years from 38% to 86% and would be 100% except for those few patients contraindicated for an ablation procedure.

“I believe that AF ablation is a safe and successful procedure and that the vast majority of these patients should be treated,” McCarthy stated.

Ralph Damiano, MD, chief of cardiac surgery at Barnes-Jewish Hospital (St. Louis), wholeheartedly agreed with McCarthy, saying that his group’s results of a concomitant surgical ablation in treating paroxysmal (intermittent) AF were excellent, with more than 92% AF-free at 12 months.
Similarly, cardiac surgeon James Edgerton, MD, from the Texas Hospital of the Southwest (Plano, Texas), was ebullient about AF ablation, backed by perhaps the most impressive clinical data. Based upon an extremely rigorous definition of success — freedom from any episode of AF lasting three seconds or longer — Edgerton reported an 89% success rate with his cohort of patients who received a concomitant AF ablation.

He also reported impressive results with his Minimally Invasive Surgical Ablation (MISA) trial, in 111 patients treated thus far. This approach is different than the concomitant one, in that it is performed through two small non-rib-spreading mini-incisions, one on each side of the chest. It is far less invasive for the patient than a concomitant one, where the chest is already for open for a CABG or valve surgery.

This approach is called minimally-invasive although technically it is not, since it does not utilize endoscopic port access. There are other energy sources either FDA-approved (e.g., microwave and high intensity focused ultrasound) or nearing FDA approval (YAG laser) that can be delivered endoscopically.

These three prominent physicians all employ the Atricure bi-polar radiofrequency (RF) devices.

Analysts following the company estimate that Atricure has captured 45% to 50% of the concomitant ablation market and about two-thirds of the far smaller but rapidly growing minimally-invasive stand alone market.

At the STS, AtriCure highlighted its new Synergy RF system. Whereas its first generation device utilizes one parallel electrode, this system utilizes two parallel electrodes embedded in the jaws of the clamp that pulse on and off alternately to create a cumulative heat base in the middle of the tissue.

The company believes that this new design will allow for increased depth of penetration, with wider and more consistent lesions. Based upon numerous talks at STS, it is clear that the most important feature of any ablation device is the ability to produce full thickness, transmural lesions that are reproducible.

Atricure expects an FDA 510(k) approval imminently and will commence a full commercial launch for the concomitant version of Synergy before the end of 1Q07. The company hopes to launch Synergy for minimally-invasive procedures in the third quarter of 2007. Although this year’s STS was very upbeat for AF ablation, it is important to note that this field is still in a state of flux.

For example, Damiano acknowledged that despite all the progress that has been made, “I am not sure that we know which lesion sets or energy source will deliver the best results for our atrial fibrillation patients.” And he said that the CT community needs better clinical trial results to convince its key referral sources (i.e., electrophysiologists and cardiologists) that “we know what we are doing.”
The need for an effective, endoscopic, minimally-invasive procedure was emphasized by Edgerton, who noted that “in our patients, we always opt for a less invasive procedure.”

Thus far, there is no FDA-approved device that fills that bill. Indeed, the results from a rigorous trial of microwave energy delivered endoscopically showed a disappointing efficacy rate of only 42%. The presenter, Dr. J. Crayton Pruitt, a CT surgeon from Cardiac Surgical Associates (Clearwater, Florida), concluded that improvements to the technology are needed. This device is marketed by Boston Scientific (Natick, Massachusetts).

Another AF luminary, Dr. Marc Gillinov, surgical director of the Center for Atrial Fibrillation— Cleveland Clinic Heart Center (Cleveland, Ohio), discussed the merits of removing the left atrial appendage, a thumb-like structure in the heart that some physicians believe can host clot formation that can precipitate an ischemic stroke.
His comments on its merits were: “we think so, we hope so, but we just don’t know for sure.”

Such is the state of AF ablation today — promising but needing better information.