UK Medical Devices Agency Issues AAA, Breast Implant Device Updates

Endovascualar prosthesis treatment outcomes remain contingent on factors such as aneurysmal remodeling and patients' vascular anatomy, the UK's Medical Devices Agency concludes in a ¹ May update on devices for abdominal and thoracic aortic aneurysms.

The update outlines trends for the devices culled from postmarket experience and provides patient management recommendations.

"As clinical experience with each model has increased, certain trends and limitations have emerged," the agency points out. "As a result, there have been numerous device recalls, 'cease sale actions,' market withdrawals, and subsequent release of modified designs aimed at addressing these limitations."

While MDA notes that "such trends have not been seen in the more recent device models/design iterations," the UK agency remains cautious, suggesting that the lack of adverse incidents may be attributable to "insufficient clinical exposure to date."

MDA recommendations in the update urge clinical vigilance for endovascular prostheses and reflect the fact that the technology is still evolving. The worldwide AAA market is expected to top $1 bil. by 2008.

According to the agency, a common problem for AAA devices is post-implantation fractures. "Stent fractures have been identified among the implanted population of virtually all fully supported models of endovascular prostheses," MDA reports.

The UK device agency has issued several device alerts over the last several years, warning of device fractures. For example, in November 2000, MDA posted a device alert for Medtronic's AneuRx after the discovery of nitinol frame fractures (² (Also see "AneuRx Resolves U.S. Field Action, Is Featured In Separate U.K. Device Alert" - Medtech Insight, 4 Dec, 2000.), p. 9).

"Separation of the top rows of the stent frame, usually where there has been breakage of suture ties intended to attach the frame to the graft, has been found among some models of endovascular prostheses with the most clinical experience," the update also notes.

In January 2001, Boston Scientific's Vanguard was the subject of a device alert related to upper stent row separation. The device was subsequently pulled from the European market.

Graft materials also have deteriorated post-implantation, MDA notes, citing reports of graft holes, seam separation and excessive porosity and/or weave separation.

In addition, deployment complications have been a problem associated with some endovascular graft devices. For instance, Guidant pulled the Ancure off the market temporarily in March 2001 following problems with device deployment (³ (Also see "Guidant 's Ancure" - Medtech Insight, 19 Mar, 2001.), p. 24).

Endoleaks remain a major concern. "The risk of Type I endoleak and/or graft migration, especially in the event of aneurysmal neck dilation, depends upon the effectiveness of the proximal fixation and sealing mechanism used by the endovascular prostheses," MDA points out.

Devices on the European market utilize a variety of fixation mechanisms such as hooks (Boston Scientific's Vanguard, Guidant's Ancure and Cook's Zenith ), radial force and column strength (Medtronic's AneuRx and Talent ) and radial force and anchors (WL Gore & Associates' Excluder and Edwards Lifesciences' LifePath ).

"Consideration should be given to the method by which the device achieves proximal seal and fixation," MDA advises in its section on patient and device selection.

A point that has been made by both industry and regulatory authorities is that physicians should keep apprised of various patient selection criteria for AAA devices and make sure that they select appropriate candidates for treatment with the devices.

Mismatching a patient with an inappropriate AAA device can have serious consequences. Anatomical incompatibility was cited as a potential factor underlying increased risk of aneurysm rupture in a May 2000 safety notice from Medtronic for its AneuRx.

"Special care should be taken in patient selection to ensure that the aneurysm's proximal neck length, neck diameter and angulation are fully compatible with the advice on prosthesis usage given in the manufacturer's instructions," MDA urges in the update.

Participants at an FDA-sponsored AAA workshop last summer reached a similar conclusion about the role aortic neck angle, length and shape play in graft success (⁴ (Also see "Aortic Neck Length, Angle Are Key Determinants Of Graft Success - Workshop" - Medtech Insight, 6 Aug, 2001.), p. 9).

Another point emphasized by the MDA is that "all clinicians involved with device placement should be fully familiar with the manufacturers' instructions and have detailed knowledge of the specific deployment techniques associated with each iteration of each individual model [emphasis MDA's]." The update goes on to note that these iterations "can vary considerably."

Medtronic's AneuRx and Guidant's Ancure are the only endovascular AAA grafts to have received premarket approval in the U.S.

Many of the devices that have been on the European market for several years (or next generation versions) are currently undergoing U.S. clinical trials (⁵ (Also see "J&J/Cordis Teramed Alliance Suggests Swifter Access To $1 Bil. AAA Market" - Medtech Insight, 24 Dec, 2001.), p. 8). For example, U.S. launch of Medtronic's Talent is expected by the end of fiscal 2003.

MDA issued a May device alert noting that connector bar fractures and spring fractures on the Talent had surfaced during the U.S. studies (⁶ (Also see "Medtronic Talent Stent Graft Draws MDA Alert; Firm Eyes 2003 U.S. Launch" - Medtech Insight, 27 May, 2002.), p. 10). After receiving FDA approval in December 2001, Medtronic is enrolling patients in a limited clinical trial of an enhanced version of the Talent that incorporates a medially aligned connector bar and an enhanced surface finish that the firm anticipates will increase the device's durability. The pivotal arm of the U.S. trial has already been completed, however, according to Medtronic. A CE mark for the redesigned version is pending.

Last year, French regulatory authorities requested additional information on in vitro testing and U.S. clinical trial data before they would agree to put the Talent on the French market. The requested information is under review by French authorities, Medtronic says.

With regard to the iteration of the Talent cited in the May MDA device alert, Medtronic points out that fractured devices appear to continue to perform as intended, showing stable or decreased aneurysm diameters.

Long-term clinical effects of devices that show structure damage are still unclear in many cases, underscoring the importance of monitoring patients who have been implanted with the devices.

Ongoing, prospective, randomized clinical trials of AAA devices in the UK under the aegis of the UK Department of Health's Health Technology Assessment Programme are expected to generate published results by mid-2004. Begun in September 1999, the Endovascular Aortic Aneurysm Repair (EVAR) trials are examining overall efficacy of endovascular AAA treatment compared with open repair. MDA hopes that the trials will "help clarify particular patient populations and clinical circumstances for which endovascular repair is best suited."

In the U.S., patients implanted with Medtronic and Guidant AAA devices are being tracked via the Lifeline registry. FDA recently praised the approach and urged other firms to use similar, independently established registries to satisfy FDA's post-approval requirements (⁷ (Also see "Postmarket Problems: FDA Struggles To Achieve Manufacturer Compliance" - Medtech Insight, 20 May, 2002.), p. 3).

Separately, MDA recently issued an update on breast implants examining known safety information for various implant filling materials.

Like the AAA update, the ⁸ MDA breast implant device update reviews technology that has been subject to a number of MDA device alerts and for which studies on long-term clinical effects are ongoing.

Among the types of breast implants included in the May update are silicone, saline, Trilucent (soybean oil) and hydrogel-filled implants (including Novamedical Novagold and Poly Implant Prosthesis Cloverleaf Hydrogel implants).

Risks associated with breast implants and debate over classification of the devices is a topic that has garnered attention both in the U.S. and abroad.

In the update, MDA notes that it is not aware of any safety concerns for saline or silicone filled implants. The two hydrogel filled implants noted in the update were removed from the UK market in December 2000 following concerns over inadequate safety data. The agency has recommended since June 2000 that women consider removal of Trilucent implants because the filler material is thought to degrade into a potentially toxic substance (⁹ (Also see "Trilucent Breast Implants Should Be Explanted - UK Medical Devices Agency" - Medtech Insight, 12 Jun, 2000.), p. 12).