Significance and Use
5.1 Once implanted, active fixation systems are subjected to cyclic loading that can be caused by blood flow, musculoskeletal motion, and other sources. The focus of this document is on axial loading caused by hemodynamics. However, depending on the device design other loading modes could influence AFC or attachment mechanism durability (e.g., radial dilatation could lead to longitudinal foreshortening and axial loading on an active fixation system). Damage to AFCs and/or attachment mechanisms may not necessarily lead to device malfunction, but could cause embolization of portions of the device, device migration, endoleaks, or other patient complications (1-4).4 Therefore, durability testing of AFCs and attachment mechanisms is important to ensure that these components are capable of maintaining structural integrity for a defined lifetime.
5.1.1 A test method developed following this standard guide can be used to determine the durability of AFCs and/or attachment mechanisms under the desired loading which can be used to assess conformance to product specifications, consensus standards, and guidance documents as well as to support regulatory submissions, quality control, and manufacturing.
5.2 This guide provides examples and recommendations so that users can develop an appropriate active fixation durability test for their device design that mechanically challenges either the AFC, the attachment mechanism, or both simultaneously. It should be recognized that both AFCs and attachment mechanisms need to be evaluated to fully characterize active fixation system durability for design verification testing. While testing of the entire active fixation system may typically be preferable, this guide recognizes that there might be situations where this is not practical or desired and allows for independent testing of AFCs and attachment mechanisms. This guide does not contain an exhaustive list of test methods for active fixation durability and methods not included herein may be acceptable for evaluating active fixation durability. Furthermore, this guide does not include information on how to handle all patient complexities such as calcium deposits or weakened aortic tissue. For assistance regarding super-physiological testing, the user is referred to ASTM F3211.
5.2.1 The success of an active fixation durability test method depends on the ability of the test apparatus to consistently induce the desired loading (force and/or displacement) to the test specimen at the applied test frequency for the entire duration of the test.
5.3 For most devices, active fixation durability testing will need to be complemented by other types of durability testing such as pulsatile, axial, bending, or torsional. ASTM F2477 addresses pulsatile durability testing, ASTM F2942 addresses axial, bending, and torsional durability testing, and ISO 25539-1, in part, addresses general in vitro testing and durability testing of endovascular prostheses.
Scope
1.1 This guide addresses how to conduct in vitro durability testing on active fixation components (AFCs) and attachment mechanisms of endovascular prostheses. It does not address the durability of fixation systems that reside solely within the vessel lumen to resist device migration (e.g, radial force and friction, adhesives, or geometric fit).
1.2 This guide was developed to address active fixation durability for aortic stent grafts. It is not intended to address fixation durability for other endovascular prostheses such as inferior vena cava filters, transcatheter heart valves, barbed venous stents, ancillary fixation devices (e.g, staples or adhesives), or cardiac devices (e.g., left atrial appendage device or mitral repair device). However, some of the techniques and guidance within may be applicable to the in vitro testing of those other devices.
1.3 This guide does not directly apply to implants with absorbable AFCs although many aspects of this standard are applicable to those products.
1.4 This guide does not provide the in vivo physiologic loading conditions for endovascular prostheses. It is the responsibility of the user to determine the loading or deformation conditions for their particular device and indication. Typically, an axial loading (force or displacement) mode caused by hemodynamics is used, although other modes are possible and should be considered.
1.5 This guide does not recommend any specific test method or apparatus for evaluating active fixation durability. It is recognized that there are multiple valid ways to conduct active fixation durability testing and as such this guide provides general recommendations and topics to consider so that users can successfully develop a test plan for their device.
1.6 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.8 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
