When Device Failure Translates to Therapeutic Efficacy

Implantable devices, including valves, stents, occlusion devices, pacemakers, and debrillator systems, have become widespread and indispensable tools for cardiovascular therapy. Subjected as they are to the incessantly dynamic mechanical environment of a beating heart, a fundamental component of demonstrating safety, and one of the basic regulatory challenges, is testing to ensure their physical resilience and resistance to fatigue failure. Fracture of such devices in situ has traditionally been considered a mark of failure, not simply in the material sense, and although such failures are not always catastrophic, they are still cause for concern. With the introduction of ultra-noncompliant angioplasty balloons, it is now conceivable and feasible to impose intentional overload fracture of some vascular and valvar prostheses for therapeutic rather than for detrimental effect. The report by Chhatriwalla et al1 in the current issue of Circulation: Cardiovascular Interventions adds to a growing literature on such innovations, which include deliberate fracture of intravascular stents in patients with congenital heart disease2,3 and of the support framework of surgical valves in patients undergoing transcatheter valve-in-valve replacement.4–6See Article by Chhatriwalla et al Stented surgical bioprosthetic valves (BPV) are constructed from a single- or multicomponent rigid or semirigid framework that typically forms a ring at the base of the leaflets and supports for the commissural posts.7 These frames may be composed from various alloys and polymers and are typically covered with a woven polymer fabric and a felt or silicon sewing ring. The commissural posts have some degree of play and can splay outward quite a bit, so these structural elements of the BPV do not usually limit the diameter that can be achieved with valve-in-valve therapy. The ring at the base of the device, however, is of fixed circumference and, insofar as it remains intact, …