Infrapopliteal Revascularization

Marc Sapoval, Massimiliano di Primio, Olivier Pellerin, Thierry Carrères and Pierre-Yves Laffy

In most countries, critical limb ischemia (CLI) has an incidence estimated to be 50 to 100 per 100,000 every year. CLI has a high mortality and morbidity rate and consumes important health and social care resources.1,2 Aging of the population, increasing incidence of diabetes and renal failure, and limitations in the ability to reduce tobacco consumption explain the high likelihood of increased incidence in the near future. Treatment options include amputation, surgical or endovascular revascularization, and novel techniques of arteriogenesis or angiogenesis using stem cell or gene transfer. Amputation should be avoided as much as possible because it carries its own risk of complications and increased mortality.

Bypass surgery requires good-quality saphenous veins (not always present) and routine ultrasound-guided graft surveillance.³ The optimal approach should be selected according to multidisciplinary consensus and is generally based on local and general clinical factors, high-quality anatomic workup, and experience. As stated in the TransAtlantic Inter-Society Consensus (TASC) document in 2000¹ and confirmed by the recent results of the BASIL trial,⁴ the endovascular approach is generally regarded as the initial treatment of choice.

Indications

Based on current evidence, the indication for below-the-knee (BTK) angioplasty is limited to patients presenting with chronic CLI as defined in the TASC consensus document.¹ Indications for BTK angioplasty are based on clinical assessment of the patient and evaluation of the extent of arterial disease. Revascularization is the only method that will prevent amputation and prolong life. These patients are at high risk for limb loss and other vascular events like stroke and myocardial infarction (MI). Studies have shown that 25% of patients who cannot be revascularized will die within 1 year after the initial diagnosis of CLI.^5,6

Clinical examination should follow a sequential approach: (1) documentation of the quality of lower limb pulses, (2) assessment of the skin surface and ankle pressures (should include toe pressure in diabetic patients [critical level < 50 mmHg], and (3) overall evaluation of the patient’s general status (renal function, cardiac and carotid evaluation). Also important is the patient’s social environment because chronic care will be needed in all cases. An appropriate link to a postoperative care network to ensure appropriate global management and nursing is key to optimal clinical management.

Next is appropriate imaging, which should be performed by well-trained radiologic personnel in a hospital environment.

With the endovascular approach, many patients can have successful reestablishment of improved flow down to the foot and healing of any ulcers. Stents may improve the results of angioplasty, but an important breakthrough has been the use of subintimal recanalization, which dramatically increases the number of patients who can be helped by the endovascular approach.

Contraindications

Contraindications to revascularization are rare. This is because endovascular techniques are less invasive and can be undertaken in patients who cannot undergo open repair. However, a patent distal vessel (whether in the lower leg or foot) is an essential prerequisite before an attempt at revascularization should be considered. In patients with CLI who have no patent distal target vessel to justify an attempt at recanalization, work is ongoing looking at the potential for other methods to improve distal arterial perfusion, such as angiogenesis using stem cell therapy or gene transfer. However, beneficial results from clinical evaluation in patients are awaited.

In patients with distal limb infection, urgent amputation should be performed to avoid septicemia and other systemic complications.

Equipment

Imaging

Both noninvasive and invasive imaging techniques are of utmost importance before considering an endovascular or surgical approach.

The initial workup should be by color duplex ultrasound imaging, which can provide (in expert hands) essential anatomic and hemodynamic information. However, the results of duplex ultrasound are variable at the BTK level, so for evaluation of the BTK circulation, many centers use computed tomographic angiography (CTA) or magnetic resonance angiography (MRA).

MRA has several advantages that are well recognized, but it is limited by the possibility of claustrophobia and other well-known contraindications. MRA for the demonstration of BTK lesions has a sensitivity of about 93%, and with recent technical refinements (venous occlusion cuff, parallel imaging), the results should further improve.7,8

Multidetector CTA (MDCTA) is now rivaling digital subtraction angiography (DSA) in the quality of imaging sensitivity and specificity.⁹ MDCTA requires iodinated contrast medium, but careful hydration can overcome most of the problems related to nephrotoxicity. A significant limitation is analysis of small and calcified vessels. The results of high-quality MRA and CTA for the diagnosis of BTK disease are broadly comparable.

The gold standard for imaging BTK circulation is DSA, which has become easier to perform thanks to the development of smaller-caliber diagnostic catheters and less toxic iodinated contrast media. A unifemoral approach, where only the ipsilateral femoral artery is punctured and subsequent angiography limited to the symptomatic leg, requires substantially less contrast medium than required for classic bilateral angiography. Patients taking metformin or other biguanides should undergo interruption of these medications for at least 48 hours after DSA, with reintroduction only after verification of unimpaired creatinine clearance (European Society of Urological Radiology guidelines).¹⁰ In practice, puncture of the ipsilateral common femoral artery (CFA) with a Teflon needle and injection of less than 60 mL of a contrast agent can provide adequate images of the lower limb arterial supply. Delayed images with selective injections, appropriate pixel shifting, and masking are also key elements to allow high-quality images.