Transcatheter Pulmonary Valve Prone to Stent Fracture

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More than one-fourth of transcatheter pulmonary valves used to treat right ventricular outflow tract (RVOT) dysfunction suffer stent fracture by 3 years, according to data published online November 9, 2011, ahead of print in Circulation: Cardiovascular Interventions. But, according to the findings, prestenting the implant site may greatly lower this risk.

Researchers led by Doff B. McElhinney, MD, of Children’s Hospital Boston (Boston, MA), looked at 150 patients enrolled in the prospective, nonrandomized, multicenter Melody valve (Medtronic, Minneapolis, MN) IDE trial to determine the incidence and predictors of stent fracture and valve dysfunction. The Melody transcatheter pulmonary valve consists of a trileaflet bovine jugular vein sutured into a balloon-expandable stent.

The median patient age was 19 years, with the most common primary diagnosis being tetralogy of Fallot (51%) followed by Ross procedure for aortic valve disease (20%). Overall, 34% had new prestents placed at the Melody implant site in an attempt to increase radial strength.

Stent Fractures Common at 3 Years

At 3 years, 39 of 148 (26.4%) patients available for follow-up experienced a Melody stent fracture, most occurring during the first 2 years (11 at 3 months, 15 at 6 months, 6 at 1 year, 6 at 2 years, 1 at 3 years). The fractures were type I in all but 6 cases, with 17 either initially diagnosed as type II or progressing from type I to type II.

Freedom from stent fracture as well as valve dysfunction decreased steadily over the study period (table 1).

Table 1. Melody IDE Trial: 3-Year Outcomes

Freedom from valve reintervention also decreased from 92 ± 2% at 14 months to 86 ± 4% at 27 months. In all, 20 patients underwent RVOT reintervention, including 16 secondary Melody valve implantations and 1 surgical RVOT conduit replacement. All of the valve reimplantations and the surgical conduit replacement involved a stent fracture, all but 2 of which were type II fractures. Among patients with a Melody stent fracture, freedom from RVOT reintervention after fracture diagnosis was 49 ± 10% at 2 years.

On multivariable analysis, prestenting or prior placement of a bioprosthetic valve was associated with a reduced likelihood of Melody stent fracture, valve dysfunction, or valve reintervention (table 2).

Table 2. Effect of Prestenting/Placement of Bioprosthetic Valve

 

For stent fractures, when the combined variable was limited to prestenting alone, the risk reduction remained significant.

Factors that increased the likelihood of stent fracture with the Melody valve included substantial apposition to the chest wall and compression of the valve.

“Given that [Melody stent fracture] is a function of fatigue stress, we suspect that there will be an ongoing hazard for new [Melody stent fractures] and for progression of minor [stent fractures] to more substantial [stent fractures],” the researchers conclude, adding that “these findings suggest that prestenting is likely to be beneficial and may be indicated when substantial chest wall apposition or conduit obstruction are present.”

Still, although the practice of prestenting prior to Melody valve placement has become common in clinical practice, the researchers caution that the current study “should not be construed to support universal prestenting.”

According to Robert J. Sommer, MD, of Columbia University Medical Center (New York, NY), the frequency of Melody stent fracture in the study is not surprising, especially since for the period of the original protocol, clinicians were not permitted to use pre-stenting.

Everybody Does It

“You could only put the valve in,” he told TCTMD in a telephone interview. However, despite the study authors’ caveat, “nobody does it that way anymore, everybody prestents the conduit.”

The reason, Dr. Sommer explained, is the anatomy involved. “Where they have to place these conduits is right under the sternum, and a lot of the conduits get distorted by the pressure between the heart and the sternum,” he said. “What we do is we’ll put in a stent in the conduit and inflate it, and after we deflate the balloon, if there’s a lot of recoil or pressure on the stent, we’ll put another stent inside that one bolstering it so there’s a sturdy sheath for the valve to be implanted [in].”

Even with the risk of fractures, though, Dr. Sommer stressed that transcatheter pulmonary valve therapy is here to stay. “Now that it exists, you can’t go back because it has so changed the way we do things,” he said. “Techniques and materials and valve design will get better with time, but it’s a done deal. Even if there are some stent fractures, it’s a part of the risk that doctors will discuss with the patients ahead of time just as you would taking a patient for a coronary procedure. It’s just part of the consent now.”

However, as far as stent fractures go, these should be few and far between with prestenting. “It makes a huge impact,” Dr. Sommer said. “We don’t have long-term data; but in the short term, there’s been a dramatic reduction [in stent fracture]. I think it’s going to virtually eliminate the problem.”

 

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Source:
McElhinney DB, Cheatham JP, Jones TK, et al. Stent fracture, valve dysfunction, and right ventricular outflow tract reintervention after transcatheter pulmonary valve implantation: Patient-related and procedural risk factors in the US Melody valve trial. Circ Cardiovasc Interv. 2011;Epub ahead of print.

 

 

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