For subjects with critical limb ischemia, identify patient, physician/hospital, and geographic factors associated with variations in treatment strategies; compare treatments and outcomes, including quality of life, cost and cost effectiveness, at 6, 12 months.

The study will be a prospective multicenter registry evaluating the real world therapeutic strategies, clinical outcomes, and costs associated with patients presenting with critical limb ischemia.

Population: Patients over age 18 presenting with critical limb ischemia After initial enrollment at 40 study sites throughout the US. participants will complete follow-up 6 months and 12 months via call center telephone calls.

The study plan calls for enrollment of approximately 1,200 participants throughout the US that will then have 12 month followup that includes collection of medications, hospitalizations for collection of events.Additionally, the BEST-CLI trial will be gathering quality of life data and cost data using similar instruments, thus providing an opportunity for comparison between cost and quality of life analyses in a clinical trial versus in a real-world registry and collection of Quality of Life using validated instruments: EQ-5D, VASQOL, SF-12.and bill review to determine economic impact of disease.

Inclusion Criteria:

• Male or female
• age 18 years or older
• Infrainguinal peripheral artery disease (occlusive disease of the arteries below the inguinal ligament)
• Critical limb ischemia, defined as arterial insufficiency with gangrene, non-healing ischemic ulcer, or rest pain consistent with Rutherford categories 4-6
• Documented consideration for enrollment in the BEST-CLI Trial with documented failure to meet inclusion / exclusion criteria. Phase ll After BEST CLI official enrollment ends, this inclusion criteria will be removed.
• Willingness to comply with vCLI protocol, attend follow-up appointments, complete all study assessments, and provide written informed consent.

Exclusion Criteria:

• Presence of a popliteal aneurysm (> 2 cm) in the index limb
• Life expectancy of less than 2 years due to reasons other than peripheral artery disease
• Active vasculitis, Buerger's disease, or acute limb-threatening ischemia
• Current chemotherapy or radiation therapy
• Pregnancy or lactation
• Administration of an investigational drug for peripheral artery disease within 30 days of randomization
• Participation in a clinical trial (except observational studies) within the previous 30 days
• Prior enrollment or randomization into the BEST-CLI trial

Patients presenting with critical limb ischemia Phase I: While the BEST-CLI Trial is actively enrolling, the BEST-Registry will only enroll patients who first screen fail from BEST-CLI.

Phase II: After BEST-CLI officially finishes enrollment, screen failure for BEST-CLI will no longer be required for enrollment into the BEST-Registry

1200 patients, across approximately 40 sites participating in BEST-CLI clinical trial.