Understanding Objective Performance Goals for Critical Limb Ischemia Trials

Critical limb ischemia (CLI), the most advanced form of peripheral arterial disease, is associated with a high rate of limb loss and substantial mortality. Revascularization remains the cornerstone of limb salvage in the CLI patient, and surgical bypass is the established standard. Endovascular therapies, such as angioplasty, atherectomy, and stenting offer a less-invasive option, but evidence of efficacy is lacking, and no devices are currently approved specifically for CLI. Design and execution of clinical trials in the CLI population are challenging, in part because of the lack of consensus on cohort definitions and relevant endpoints. Recently, the Society for Vascular Surgery undertook an initiative to define therapeutic benchmarks, objective performance goals (OPGs), for CLI. Using surgical bypass with autogenous vein as the standard for comparison, OPGs were developed for nine safety and efficacy measures that could be utilized in the premarket assessment of new devices in CLI. Data from three large randomized controlled trials of surgical bypass for CLI were analyzed. We defined a major adverse limb event (MALE) as a key endpoint for revascularization therapies in CLI—inclusive of amputation (transtibial or above) or any major vascular reintervention (thrombectomy, thrombolysis, or major surgical procedure [new bypass graft, jump/interposition graft revision]) in the index limb. Freedom from perioperative (30-day) death or any MALE (MALE + POD) was suggested as the primary efficacy endpoint for a single-arm trial design in CLI, with an observed rate of 76.9% for the surgical bypass controls at 1 year. Specific high-risk subgroups were also defined from the surgical dataset—based on clinical (age older than 80 years and tissue loss), arterial anatomy (infrapopliteal disease), and conduit quality (inadequate saphenous vein) characteristics. Risk-adjusted OPG were developed for these subgroups of interest. These OPGs define a new set of benchmarks for assessing the performance of revascularization therapies in CLI, and should facilitate clinical trial design and device development in this arena.