Durability of Endovascular Infrarenal Aneurysm Repair: When Does Late Failure Occur and Why?

The first commercially available stent grafts were unable to withstand the hemodynamic forces of the vascular environment. The past 15 years have seen a gradual improvement in long-term stent graft performance as designs evolved through the elimination of features associated with late failure and the replication of features associated with durable success. Clinical experience provides the following principles on which to base device design and implantation techniques. Few patients have an adequate length of non-dilated aorta distal to the aneurysm to allow implantation of an aorto-aortic stent graft; bifurcated stent grafts are usually required for AAA repair. Friction, column strength and tissue ingrowth do not prevent migration of the stent graft from its attachment within the neck into the aneurysm; some form of active fixation is required, usually in the form of barbs. Any movement between the apex of a stent and the overlying graft material will erode the fabric; stents and grafts need to move as a single unit. Nitinol is versatile, but fragile; Nitinol components must be polished to eliminate all surface irregularities and they cannot be subjected to compression loading, or excessive pulsatile movement. The neck of an aneurysm is unstable; it will dilate unless protected by a securely fixed, non-compliant stent graft. The aneurysm does not heal; freedom from risk of rupture depends on durable depressurization of the sac. The sole objective of image-based follow-up is the early detection, and catheter-based correction, of device failure. Once any given design has been in use long enough to identify its failure modes, the frequency of follow-up studies can be adjusted accordingly. However, it takes a long time to identify all the potential forms of late failure, and pre-clinical testing remains an imprecise science. New, or recently modified, devices cannot necessarily be assumed to be as durable as their predecessors.