With the prevalence of atrial fibrillation (AF) in the U.S. believed to exceed 5.1 million – and with the current “gold standards” for treating the heart rhythm disturbance not working well – catheter manufactures have developed a growing range of technologies for soft tissue ablation.

So far none of these devices have been approved specifically to treat AF – but that hasn’t kept companies from trying.

This week, Ablation Frontiers (Carlsbad, California) reported getting the FDA go-ahead to extend U.S. enrollment in its clinical trial for interventional treatment of chronic AF.

The company says its Tailored Treatment of Permanent Atrial Fibrillation (TTOP AF) study is the first U.S. investigational device exemption (IDE) trial of its kind. FDA approval to proceed with the pivotal phase of the study is based on the review of an initial feasibility segment completed in August, Ablation Frontiers said.

The TTOP AF trial is designed to compare the safety and efficacy of tailored ablation therapy against traditional pharmaceutical regimens, and the company said it plans to submit a pre-market approval (PMA) application to FDA when the trial is complete.

With receipt of FDA approval to enter the pivotal phase of the trial in 4Q07, several patients already have been randomized into the study, the company noted. Initial U.S. treatment sites included the Lahey Clinic and Medical Center (Burlington, Massachusetts). Their first patient, with a three-year history of continuous AF, was treated and returned home the next day with a normal heart rhythm, according to the company. Gregory Michaud, MD, performed the two-hour and 10-minute procedure.

“I am really excited about this new technology,” Michaud said. “It has two advantages that are immediately apparent. One, the catheters are simpler to use than the traditional ‘point-by-point’ catheters, thus reducing the time it takes to complete complex left atrial procedures. Second, the depth of the radio frequency energy lesions is controllable, which makes damage to collateral structures, such as the esophagus, less likely.”

The Ablation Frontiers Cardiac Ablation System, being evaluated in this clinical study, was developed under the guidance of Fred Morady, MD, and Hakan Oral, MD, at the University of Michigan (Ann Arbor). Designed to be a versatile tool kit for mapping and ablating areas of the heart where AF is most prevalent, the ablation system combines a radiofrequency (RF) energy source with a series of anatomically-designed catheters, the company said. Ablation Frontiers says its system is also unique because it does not require costly 3-D navigation or robotic steering equipment that can make these types of procedures longer and more complicated.

The TTOP AF study uses an approach that allows cardiologists to customize their treatment strategy and potentially shorten procedure times, improve patient outcomes, and reduce recurrence of the disease, the company noted.

AF is considered the most common form of chronic heart arrhythmia. And as the world’s population ages, it is becoming an increasing problem and drawing increasing attention in the cardiovascular sector.

Medical management – primarily the use of pharmaceuticals – is the first line of treatment for AF. However, it has proven to have poor efficacy and difficult side effects for the majority of patients. Drug therapy fails to work for about 40% to 50% of AF patients, and so device and surgical approaches have become increasingly seen as potential solutions.

Catheter ablation, while not FDA-approved to treat AF, is commonly performed as an off-label use. At the Boston Atrial Fibrillation Symposium in January 2007, the number of these off-label applications was estimated at 30,000 to 35,000 procedures a year.

“The pivotal phase of the TTOP AF trial is designed to demonstrate the clinical safety and efficacy of our catheter ablation system as compared to current drug options,” said Keegan Harper, CEO of Ablation Frontiers. “Based on positive clinical outcomes of our multi-center European study, as well as our ongoing commercial experience in Europe, we believe that the TTOP AF trial will show striking clinical benefits made possible by our technology. We have already demonstrated in numerous procedures in Europe that we can greatly reduce procedure times with our technology.”

Patients will initially be randomized into two treatment groups: one group receiving ablation therapy, and the other group — the control arm — receiving commonly used drug treatments. For every two patients initially receiving an ablation, one will be randomly assigned to the control arm. The trial allows patients in the control arm to receive an ablation if they do not respond to drug therapy.

Ablation Frontiers is a venture-backed company developing products for the treatment of cardiac arrhythmias.

Despite the regulatory challenges associated with the development of devices to treat AF, the list of companies making products for this erratic heart condition continues to grow. In addition to Ablation Frontiers, that list includes CryoCath Technologies (Montreal); CryoCor (San Diego); Cardima (Fremont, California); Medtronic (Minneapolis); St. Jude (St. Paul, Minnesota); Atricure (West Chester, Ohio); Stereotaxis (St. Louis); Symphony Medical (Eden Prairie, Minnesota); Medical CV (Inver Grove Heights, Minnesota); eCardiodiagnostics (The Woodlands, Texas); Estech (San Ramon, California); Atritech (Plymouth, Minnesota); Sorin Group (Mannheim, Germany); ProRhythm (Ronkonkoma, New York); Lechnologies Research (Milwaukee); Siemens Medical Solutions (Malvern, Pennsylvania); and PDSHeart (Conyers, Georgia).