CDU Washington Editor
The concept of "one size fits all" is falling more out of favor every day in modern medicine, and a presentation at the 87th annual meeting of the American Association of Thoracic Surgeons (Beverly, Massachusetts) underlined that concept in the cardiac ablation sector.
Fred Morady, MD, a professor of cardiovascular disease at the University of Michigan Health Systems (UMHS; Ann Arbor) titled his discussion "Catheter Ablation for Atrial Fibrillation: Does One Size Fit All Our Patients?" Morady said that the answer "is obviously no," at least not for paroxysmal atrial fibrillation (PAF), which teremd "clearly a different arrhythmia" from chronic AF. Morady's discussion was on circumferential ablation, an approach that eliminates the need for the long and winding percutaneous approach and gets around the need to stop the heart, a requirement of the Maze procedure.
However, Morady also does not rely on a standardized set of lesions to do the job, but induces AF, ablating only after seeing where the heart's electrical system is malfunctioning. The idea is to ablate only the areas that need ablating and no more.
"There are multiple mechanisms that contribute to AF," Morady said, including nerve tissue located in the pulmonary veins and various other musculatures in the area of the atria. He said that AF can be very mechanism-specific, describing the case of a 60-year-old man who demonstrated no rapid pulmonary vein (PV) activity, but had right atrium fibrillation, nonetheless.
"So instead of doing a left-side procedure, all we did was circle" the source of the AF at the right atrium and ablate the external surface of the heart with a Lasso catheter, made by Biosense Webster (Diamond Bar, California).
However, Morady said that circumferential ablation had limits when applied to the PV, including flutters in 3%-30% of patients, some instances of left atrial dysfunction, and the fact that this procedure will be less than adequate in some patients and more than needed in others.
Maze 'gold' but more difficult
Morady said that the Maze procedure offered long-term freedom from AF in 90% of patients, a gold standard that catheter ablation might never match. The Maze procedure was developed by Jim Cox, MD, formerly a professor of surgery at the Washington University School of Medicine (St. Louis, Missouri) and now the CEO and chairman of the World Heart Foundation (Geneva). This procedure, which Cox first performed in 1987, involves a series of incisions made in the right and left atria to interrupt the abnormal conduction of impulses, thus restoring a more normal rhythm and reducing AF.
However, the procedure requires that the heart be stopped and some Maze patients experience fluid retention. Thus, ablation was developed as an alternative.
Morady said that in order to isolate the source of the AF, "we challenge the patient with very high doses of isoproterenol," a beta adrenergic receptor agonist that induces irregular rhythm by enhancing the polarization that immediately precedes a contraction in the affected muscle, thus inducing AF. "We believe it's more specific than pacing" the heart with an external source of electricity.
"Our goal is to try to eliminate the AF with the least amount of ablation" for several reasons. One of these is that too many ablations can impair the function of the left atrium. "The more ablations you do, the more atrial flutters you get," Morady said, and a small number of ablations equals a lower risk of collateral damage.
Morady said he uses orally ingested barium in his practice to visualize the esophagus, which is somewhat prone to shifting about when the patient is only sedated. This is typically not a problem with patients who are under general anesthesia.
Morady also discussed a study published in the April 18, 2006, edition of Circulation describing the outcome of a non-randomized, non-controlled study involving the treatment of 153 consecutive patients with PAF. Of that number, 15 were "encircled" with the Lasso catheter on the right-side pulmonary veins, five only on the left-side pulmonary veins, and both sides in another 50 patients. The remaining needed treatment that did not fully encircle any pulmonary veins.
Twenty-eight patients needed a repeat procedure for AF or atrial flutter (AFL), but in the 12-month follow-up, 118 of the 153 patients were free of AF or AFl, a success rate of 77%. The physicians performed a total of 180 left atrial procedures in that 153-patient group, and two developed pericardial tamponade. The team treated this with percutaneous drainage in one of the two, and by surgery in the other.
The case for this approach in the treatment of chronic AF was likewise compelling. Morady described a controlled, randomized study, also conducted at UMHS, in which each of 145 patients received amiodarone, an anti-arrhythmic agent, and two treatments of cardioversion. The study subjects were treated with circumferential pulmonary vein ablation, and all patients "reported" their cardiac rhythms via telephone for a year.
This study, which appeared in the April 18, 2006, edition of the New England Journal of Medicine, resulted in 74% of ablated patients being free of recurrent AF at one year vs. less than 5% of the controls who had the same outcome. However, the authors stated in the article that "an intent-to-treat analysis showed that 74% of patients in the ablation group and 58% of those in the control group were free of recurrent atrial fibrillation or flutter without antiarrhythmic-drug therapy at one year."
Valves: stentless vs. stented
The last day of the 2007 meeting of the AATS 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 are 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."
As always — risk-benefit debate
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 said 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 there 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.
Myxo Etlogic trial results positive
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, 32 mm 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.