Infrapopliteal Bypass

Infrapopliteal bypass is a major lower-extremity arterial reconstruction, the goal of which is to establish inline flow to target vessels such as the tibial, peroneal, or pedal arteries. Arterial supply (inflow) sites therefore include the common femoral, deep femoral (profunda femoris), superficial femoral, and popliteal arteries. Occasionally, a tibial artery may become the inflow vessel.

The primary indication for infrapopliteal bypass is critical limb ischemia (CLI) due to atherosclerotic peripheral arterial disease (PAD). This method of surgical arterial reconstruction can be applied to patients with nonatherosclerotic conditions such as aneurysmal disease and traumatic arterial injuries. The bypass conduit should usually be composed of autogenous vein, but prosthetic material can be used in the absence of suitable autogenous conduit. ^[1]

With regard to conduit type, vein grafts are superior to all prosthetic conduits for infrapopliteal bypass, regardless of target vessel. ^{[2, 3, 4]} The great saphenous vein (GSV; also referred to as the long or greater saphenous vein) is the most commonly utilized autogenous conduit; however, the small saphenous vein (SSV; also referred to as the short or lesser saphenous vein), the superficial femoral vein, ^[5] and spliced vein grafts from the arm can also be used. ^{[6, 7]}

Numerous varieties of prosthetic conduits are available; options include the following:

• Dacron
• Heparin-bonded Dacron
• Human umbilical vein
• Polytetrafluoroethylene (PTFE)
• Heparin-bonded PTFE

Of these, PTFE is the most commonly used material. All prosthetic grafts perform with similar patency rates in the infrapopliteal position and are inferior to autogenous grafts, regardless of type; composite grafts appear to be no better than prosthetic grafts in this regard. ^[3] The 1-year patency rates of vein conduit in the infrapopliteal position reach 70-80%, whereas those of prosthetic grafts reach 30-50% at best. ^[2] If a prosthetic graft is used in the infrapopliteal position, an adjunctive vein cuff at the distal anastomosis improves patency. ^[8]

Indications for infrapopliteal bypass include the following:

• Symptomatic lower-extremity ischemia (eg, disabling claudication, rest pain, or tissue loss)
• Aneurysmal disease
• Traumatic arterial injury

In 2019, the Global Vascular Guidelines were published via a joint effort from the the European Society for Vascular Surgery (ESVS), the Society for Vascular Surgery (SVS), and the World Federation of Vascular Societies (WFVS). ^[9]  The GVG program endorsed the SVS Threatened Limb Classification system, based on grading of Wounds, Ischemia, and foot Infection (WIfI). It also proposed the Global Anatomic Staging System (GLASS), which involved defining a preferred target artery path and then estimating limb-based patency, from which three stages of complexity for intervention were derived.

Contraindications for infrapopliteal bypass include the following:

• Debilitated patient with severe comorbidities
• Lack of an appropriate distal target for revascularization
• Unaddressed inflow disease
• Severe joint contractures
• Nonambulatory patient

Best practices

The principles of surgical revascularization are based on the following three components:

• Inflow
• Outflow
• Conduit

The inflow vessel (ie, the artery from which the bypass will originate) must have adequate flow and pressure and allow suturing. Significant vascular calcification or atherosclerotic disease of the inflow artery can present technical challenges. The outflow vessel should be the least diseased vessel with runoff to the foot. On imaging, inflow and outflow arteries must be well characterized. If disease exists in the proposed inflow vessel and a less diseased more proximal artery cannot be accessed or used because of bypass graft length constraints, an adjunctive procedure to address the inflow disease (eg, endarterectomy) must be added to the operative plan.

The distal target artery must be confirmed to be the dominant vessel to the foot. Tissue distribution of the outflow vessels must correlate with the operative indication. For example, whereas revascularization of the pedal arteries will aid in healing of ischemic foot ulcers, it will not improve calf claudication. In general, shorter reconstructions, if feasible, have better long-term patency. ^{[2, 10]}

With regard to conduit assessment, duplex vein mapping is vital for ensuring a graft of appropriate size and quality. The venous conduit should be at least 2.5 mm in diameter and soft throughout the length needed to perform the bypass. Calcified or sclerotic veins should not be used.

Complication prevention

Measures to help prevent complications include the following:

• Thorough preoperative assessment of the inflow and target vessels
• Thorough assessment of the vein conduit
• Strict attention to sterile technique in the handling of prosthetic grafts
• Systemic heparinization of patients before vessel clamping and after graft tunelling
• Assessment of the reconstruction at the time of the operation with duplex ultrasonography (US) or intraoperative arteriography

Popplewell et al evaluated outcomes in a subgroup of 104 patients with infrapopliteal disease from the BASIL (Bypass vs Angioplasty in Severe Ischaemia of the Leg)-1 trial who were treated with infrapopliteal vein bypass (VB; n = 56) or plain balloon angioplasty (PBA; n = 48). ^[11]  There were no significant differences in amputation-free survival (AFS) or overall survival (OS). The VB group had significantly quicker relief of rest pain but did not show significantly improved tissue healing. Median length of index hospital admission was significantly greater in the VB group (18 vs 10 days) but median total hospital stay between randomization and the primary endpoint was not (43.5 [VB] vs 42 [PBA] days).

Subsequently, Popplewell et al published prospectively gathered data on 137 consecutive patients with CLI from infrapopliteal disease who underwent PBA or VB in their unit between 2009 and 2013. ^[12]  Outcomes were similar to those reported in BASIL-1. Bypass patients spent more days in hospital during the index admission (median, 9 d vs 5), but not out to 12 months (median, 15 d vs 13). They had a higher rate of 30-day morbidity (36% vs 10%), mainly due to infective complications, but not of 30-day mortality (3.1% vs 6.8%). AFS and OS were better after bypass, but limb salvage (LS) and freedom from arterial reintervention (FFR) were not.

Morisaki et al retrospectively studied treatment outcomes in 99 CLI patients (106 limbs) who underwent infrapopliteal bypass either as initial treatment (n = 75; 82 limbs) or after initial endovascular therapy (n = 24; 24 limbs). ^[13]  Outcome measures included graft patency, limb salvage, AFS, and OS. Primary patency at 1 and 2 years was 72.0% and 67.5% for the bypass-first group, compared with 53.1% and 47.2% for the endovascular-first group. There were no differences in secondary patency, limb salvage, AFS, or OS.

Yan et al studied in-hospital and follow-up (≥1 y) outcomes of 32 patients who underwent infrapopliteal bypass surgery for treatment of atherosclerosis (ASO; n = 14) or thromboangiitis obliterans (TAO; n = 18). ^[14]  In-hospital patency rates were 77.8% for TAO patients and 92.9% for ASO patients. Patency rates at follow-up were 44.5% for TAO patients and 85.7% for ASO patients. Despite the lower patency at 1 year, TAO patients experienced relief of ischemic symptoms and improvement in ABI.