Medical Device Daily Washington Editor

WASHINGTON — The last day of the 2007 meeting of the American Association of Thoracic Surgeons (Beverly, Massachusetts) included a number of the debates that bring sizzle to these conventions, and the topic of one such discussion was whether stentless heart valves increase risk without benefit as compared to a stented heart valve.

Valve disease can distort the adjacent chamber of the heart, and any replacement has to approximately restore the pressure gradient to the vessels and heart chambers involved. The use of a stent, or wire mesh around the outside of the valve, decreases the inside diameter of the valve, a difference of between 2 mm and 4 mm. Some physicians are also of the opinion that stentless valves, which are usually xenografts from pigs, more effectively mimic the flow of blood (hemodynamics) than the stented version. On the downside, installation of the stentless version appears to be a more complicated procedure.

Arguing that stentless valves increase risk for no discernible benefit was George Christakis, MD, associate professor of cardiac surgery at the University of Toronto (Canada), who warned that "anyone who thinks I came to Washington having taken a diplomacy course, you're wrong."

Regarding sub-coronary implantation of stentless valves, he posed the question "What the hell are the benefits?"

Ease of implantation is obviously not a benefit, Christakis said, and regarding hemodynamics, he indicated that published studies suggest that "there is a decrease in the peak gradient" with stentless valves but "I don't think I'd be sold on that." He referred to a study published in the Annals of Thoracic Surgery in 2005 by a team led by Michael Borger, MD, also of the University of Toronto, that concluded that pre-discharge echocardiograms "revealed that stentless patients had significantly lower mean transvalvular gradients … and larger effective orifice areas." However, the abstract also notes that stentless valves "were associated with improved midterm survival by univariate analysis, but not by multivariable analysis."

Of a number of other randomized, controlled trials, Christakis said "the majority of them show no significant difference in gradient or effective orifice area, or left ventricular mass regression, and the ones that do show a statistically significant difference" show differences, he said, that were not clinically significant.

Christakis also said that the stentless valves were not demonstrably more durable than their stented counterparts. "You know what, these valves are coming out. These valves are malfunctioning early."

Taking the opposite position, Neil Kon, MD, chairman of the department of thoracic surgery at the Wake Forest University Baptist Medical Center (Winston-Salem, North Carolina) said that "This debate asks two question," namely whether stentless valves are associated with increased risk and whether they offer an increased benefit for aortic valve replacements.

Of risk, Kon said that Christakis had co-authored a paper used in the moderator's book that indicated that overall mortality for aortic valve replacement was 4.3%. When aortic valves were replaced along with a coronary bypass, the overall mortality rate was 8%, and was 9% when the valve was replaced in a procedure that also repaired an aortic aneurysm. Characterizing this as a baseline for comparison, Kon remarked that Christakis's group "obviously had a lot less operative mortality" overall at 3.5%.

"He said he wasn't a super surgeon, but he must be," Kon quipped.

Kon said that a later publication assigned greater operative mortality to the stentless valve, but that greater surgical experience drives down mortality. Kon also stated that the paper that "contributed the most patients to the Freestyle study group" had a patient population that was "an extremely complex group of patients" and thus skewed the mortality numbers. The Freestyle is a stentless porcine valve made by Medtronic (Minneapolis).

"So what is it that determines risk? You all know what it is. It's not your technique, its not the type of prosthesis that you implant." Age, concomitant procedures, and co-morbidities were the primary drivers of higher risk.

Regarding the benefits of stentless valves, Kon said that "[t]here is tons of stuff published in the literature" and that if a surgeon examined a stented and a stentless valve side by side, "its obvious before you start that one has a bigger effective orifice area than the other," and that stents induce "turbulent flow every time."

"We think the best indication … is a small aortic root and a patient with poor LV [left ventricular] function," Kon said, describing stentless valves as "just another club in our bag."

Kon also noted that "the more you use this club, the better you'll get with it."

One audience member pointed out that Christakis's comments seemed to be aimed at subcoronary implants whereas Kon's remarks were more focused on the aortic root. Christakis agreed that the apples-to-oranges comment was somewhat valid, but "not everyone can do aortic roots" because of the skill needed.

Also of note at the AATS meeting, Edwards LifeSciences (Irvine, California) reported the results of a clinical trial for their Myxo ETLogic annuloplasty ring, with results that suggest greater effectiveness and an easier job for surgeons.

Intended to treat mitral valve disease, the Myxo ETlogic trial indicated that the device is effective at suppressing post-surgical systolic anterior motion (SAM) and can eliminate the need for a lifetime of anticoagulation therapy. Of the 128 enrollees, 92 received conventional annuloplasty rings. The remaining 36 received the ETlogic, a ring designed to accommodate the longer valve leaflets seen in some patients and which features a taller cross-section that provides more space for the posterior leaflet, which reduces systolic anterior motion (SAM).

The median ring size was similar between the two groups, 32mm in the controls versus 34mm in the study group, and while SAM was observed in 5% of controls, only one in the study group exhibited such an effect.

Patrick McCarthy, MD, the chief of cardiothoracic surgery at Northwestern Memorial Hospital (Chicago), said that operations for valves that are damaged due to the accumulation of benign, but abnormal (myxomatous) tissue "are very complex and require intricate valve leaflet resections that are tailored to each individual patient." Many patients acquire a myxomatous state in their mid-fifties, and a mechanical valve would put them on anticoagulants for decades. However, the study suggests that such patients can avail themselves of "a simpler, more straightforward alternative [to other procedures, including the slide annuloplasty] that also frees patients from the lifestyle restrictions associated with anticoagulant therapy." The device, which is not yet available in the U.S., went to market in Europe in the firm's 2007 second fiscal quarter.