Manufacturer evaluations of endograft modifications.

The motivation to modify the design of a vascular device can arise from a number of sources. Clinical experience with the unmodified device could suggest new design modifications to improve device performance or clinical outcomes. Similarly, clinical success with a device often suggests modifications that could broaden the applicability of the device to enable treatment of different or more advanced disease states. As a specific example, both of these scenarios have arisen during the last decade in the evolution of endovascular grafts for the treatment of abdominal aortic aneurysms, with modifications enabling the treatment of patients with shorter infrarenal necks, more angulated anatomy, and smaller access vessels. These modifications have been made by manufacturers and additionally by physicians who create branched and fenestrated devices. The experience to date with the use of fenestrated devices and the development of chimney, snorkel, and periscope techniques suggests that modifications to off-the-shelf devices may provide some clinical benefit. This experience provides additional motivation for manufacturers to develop devices to address the clinical needs not met with their current product lines. For manufacturers, the device development process includes an assessment of the new device design to determine the appropriate evaluation strategy to support the safety and effectiveness of the modified device. This report provides a high-level overview of the process generally followed by device manufacturers to evaluate a proposed device modification before market release, in accordance with local country regulations and recognized international standards such as the International Organization of Standardization (ISO) standards for endovascular grafts (ISO 25539 Part 1).

Evolution and future of preclinical testing for endovascular grafts.

The preclinical testing of endovascular grafts has evolved significantly since the creation and early testing of these devices; however, there are continued limitations in using preclinical testing to predict clinical performance. Early testing was conducted in the absence of standards and guidance specific to endovascular grafts, and references available for vascular grafts and stents did not adequately account for the complexity of endovascular graft systems. Failure of early-generation devices suggested that the testing being conducted was inadequate and that there was a lack of understanding of the in vivo environment. These concerns led to several efforts to improve preclinical testing. The Food and Drug Administration (FDA) sponsored a workshop to discuss the limitations inherent in testing of endovascular grafts, and an ISO standard for endovascular grafts was developed. Publication of the standard in 2003 succeeded in standardizing testing and reporting across device manufacturers; however, several clinical failure modes, such as migration and stent fractures, continued to be unpredicted by current preclinical testing. This, coupled with knowledge gained from additional clinical experience, led the FDA to hold a second workshop to discuss the benefits and limitations of current testing and propose future testing that may better predict device performance. This workshop was successful in accurately describing past testing, determining what has been learned, identifying issues that have not been adequately addressed, proposing modifications to address these limitations, and discussing how the proposed modifications should be implemented. While significant progress has been made in endovascular graft testing, continued collaboration among industry, academia, regulators, and clinicians will provide continued improvement in the predictability of device performance.