ALERT FOR A NEW PROSTHETIC VALVE

July 15, 2009 (St Louis, Missouri) — A surgeon at the Washington University School of Medicine, in St Louis, MO, says she and her colleagues have no good explanation for what they term "alarmingly early stenosis" seen in patients treated with the Medtronic Mosaic bioprosthetic valve in the aortic position. According to a brief communication they've published in the June 2009 issue of the Journal of Thoracic and Cardiovascular Surgery, Dr Jennifer S Lawton and her coauthors, prompted by an initial case of early stenosis, followed all 122 patients in whom they'd used the device, ultimately turning up four cases of severe stenosis requiring valve replacement within just three to 44 months after implantation.

Durability of the Mosaic, a third-generation porcine valve, is typically assumed to be between 10 and 15 years, Lawton told heartwire . "We did not find any other reports of this: that's one of the reasons we felt we should try to get it into the literature; we felt others should know about it."

Medtronic, for its part, says Lawton et al's finding is solely related to patient-level factors, and the company staunchly defends the safety, durability, and efficacy of its product.

Early Stenosis

According to Lawton et al's report, all four valves, implanted by two different surgeons, have a "strikingly similar appearance of thickened material resulting in immobility of the leaflets."

Patient-prosthesis mismatch was excluded as a possible cause, as were other patient- or procedure-related factors, Lawton told heartwire . "Explanted valves were examined by a pathologist at the Washington University School of Medicine and by a pathologist after return of the valves to Medtronic, and no cause for the stenosis could be determined in any case," they write.

Contacted for comment, however, a Medtronic spokesperson pointed out that the Mosaic is the only stented heart valve with "proven third-generation performance," with more than three decades of tissue valve design improvements behind it.

"It is the valve of choice for many cardiac surgeons throughout the world," Joseph McGrath told heartwire . "Based upon the collective body of evidence of peer-reviewed journal articles that have demonstrated satisfactory clinical results with the device, Medtronic confidently stands behind its conviction that the Mosaic heart valve offers both surgeons and patients alike a safe and efficacious product."

The Medtronic analysis of the valves--sent to the company by Lawton and colleagues--indicated that pannus (a flap of tissue or scarring) and/or thrombus was the reason for explantation in all four cases. "These events are caused by patient factors extrinsic to the valve," McGrath said. Medtronic has subsequently published a formal statement about the Mosaic's durability online in response to Lawton et al's paper [2].

Lawton is not entirely reassured, however, and says she is not using the Mosaic--it had previously been her go-to device--until she has further information supporting its safety and durability, noting that there are many other options for valve replacement. She hopes other hospitals will be prompted to review their cases and see whether this phenomenon is occurring anywhere else. "I really didn't want to subject any of my patients to a similar problem, and I honestly don't know how to prevent it, so I've been choosing different types of valves."

She added that she didn't think there was any reason for alarm in patients who had already received the Mosaic, since the numbers of patients affected is seemingly so small. "Any patients with a valve replacement should follow up regularly with their physicians, and that means an echocardiogram periodically. If they have symptoms of shortness of breath, swelling in the legs, or chest pain, they should see their doctor and obtain an echocardiogram."

An Issue Worth Raising

Also asked to comment on the paper for heartwire , cardiothoracic surgeon Dr Jeff Tyner (Scripps Clinic, La Jolla, CA) emphasized that Lawton et al's report was "not enough to condemn the Mosaic, although it's a possible problem that you'd want to track."

He added that he himself has not used the Mosaic, because it has only eight to 10 years of data supporting its safety and durability. That said, he added, "It is a third-generation device, which means it should do very, very well long term. If others find this, however, it's a big deal. You have to wonder what the mechanism for this is."

Possible explanations, said Tyner, include underlying endocarditis (although patients with endocarditis were excluded from Lawton et al's series), subsequent chemotherapy, operator-related issues (including the kinds of rinses or other medicines/techniques used during the procedure), and finally something specific to the valve itself.

"I don't know what you do at this point other than raise the issue and get people to kind of track their patients," Tyner said. Since surgeons often do not end up following up with these patients, it's important for news of the potential problem to reach the cardiology and echocardiography communities, he added.