As lower limb arterial disease most frequently affects the SFA (Fig. 21.5), IC is usually characterized by pain on walking in the muscles of one or both calves. If the iliac arteries are affected then that pain may also be felt in the thigh and even the buttock (internal iliac disease). The pain comes on after a reasonably constant ‘claudication distance’, and usually subsides rapidly and completely on cessation of walking. Resumption of walking causes the pain to return. These and other features distinguish it from neurogenic and venous claudication (Table 21.1).

Fig. 21.5 Angiogram showing diffuse disease in both right and left superficial femoral arteries (arrows).

Table 21.1 Differential diagnosis of claudication

Typically, the superficial femoral artery (SFA) first becomes narrowed at the adductor canal (Fig. 21.6A). Ankle pulses may be palpable but are diminished, and a bruit may be heard at or below the stenosis. The ABPI is often (near) normal at rest but reduced following exercise.

Fig. 21.6 Symptoms and pathology in intermittent claudication.

A Superficial femoral artery (SFA) stenosis at adductor canal B Occlusion of the SFA and development of a collateral circulation between the deep femoral (profunda femoris) artery (PFA) and the popliteal artery C Iliac artery and PFA stenosis leading to worsening symptoms of IC and further collateralisation D Eventually CLI characterised by ischaemic rest pain and tissue loss develops due to multilevel disease affecting tibial arteries and collateral supply

Over the next few months or years, collateral vessels arising from the PFA enlarge so that they carry a higher proportion of the blood flow to the lower leg. As a result, in the majority of patients, symptoms gradually improve or even disappear. But thrombotic occlusion of the SFA (Fig. 21.6B) may lead to a sudden deterioration in walking distance. Ankle and popliteal pulses will be absent at this stage.

Continued development of the collateral circulation may lead to an improvement in symptoms and walking distance. This phase of moderate claudication may remain apparently stable for several years. However, without ‘best medical therapy’ (BMT) (see below) and a change in the patient’s lifestyle, the atherosclerosis will progress to involve other segments, such as the PFA, iliac and tibial vessels (Fig. 21.6C). The IC will progress to become severe, often forcing the patient to stop every 50–100 metres or so, and the scope for spontaneous improvement steadily diminishes. As the disease progresses further in severity and extent, symptoms are likely to worsen to a point where CLI develops due to multilevel disease (Fig. 21.6D). Such patients will often go on to develop night/rest pain and are at risk of tissue loss (see below).

An understanding of this cyclical pattern of exacerbation and resolution in IC is important as spontaneous improvement may mislead the patient into thinking all is well and that there is no longer a need to comply with medical advice (see below); and, in particular, that they can continue to smoke with impunity.

Epidemiology

IC affects up to 5% of people aged over 60 years. Provided patients comply with BMT only a small proportion (1–2%) of those affected by IC will deteriorate to a point where amputation and/or revascularization to prevent amputation is required. However, the annual mortality rate is 5–10% per year, which is 2–3 times higher than an age- and sex-matched non-claudicant population. This is because IC is a powerful marker of widespread atherosclerosis, and most of these patients succumb to MI, stroke and limb loss. The emphasis is, therefore, on the preservation of life; in most patients, measures to reduce cardiovascular mortality and morbidity (MI, stroke) will also improve the functional status of the limb.

Critical limb ischaemia

Whereas IC is usually due to single-level disease, CLI (sometimes also termed severe limb ischaemia, SLI) is caused by multiple lesions affecting different arterial segments down the leg (Fig. 21.6D). These patients usually have tissue loss (ulceration or gangrene) and/or rest (night) pain; their ankle blood pressure is often 50–70 mmHg or less. Without revascularization, such patients will often lose their limb, and sometimes their life, in a matter of months.

Night and rest pain

Ischaemic ‘night pain’ typically develops in the forefoot a few hours after going to bed. The pain is due to the accumulation of metabolites (acidosis) as a result of reduced perfusion consequent upon the loss of the beneficial effects of gravity and the reduction in blood pressure and cardiac output that usually occurs during sleep. The pain is severe and wakes the patient from sleep. At first the pain may be relieved by hanging the limb out of bed but, as the disease progresses, the patient has to get up and walk about to obtain relief. The patient then often takes to sleeping in a chair, which leads to dependent oedema. This increases interstitial tissue pressure and so further reduces arterial perfusion. The patient is then in a vicious cycle of increasing pain and sleep loss. At this point, even a trivial injury to the foot will fail to heal, and the entry of bacteria leads to infection and an increase in the metabolic demands of the foot. The result is the rapid formation of ulcers, gangrene and, without treatment, limb loss and death.

Diabetic vascular disease

Approximately 40% of patients with CLI have diabetes and such patients pose a number of unique problems for vascular specialists:

• Arteries are often calcified, which makes surgery and angioplasty technically difficult

• Calcification also leads to vessel incompressibility which results in spuriously high ankle pressures and ABPI measurements

• Reduced ability to fight infection

• Severe multisystem arterial disease (coronary, cerebral and peripheral), which increases the risks of intervention

• In the lower limbs, diabetic vascular disease has a predilection for the infrapopliteal vessels. Although vessels in the foot are often spared, the technical challenge of performing a satisfactory bypass or angioplasty to these small vessels is considerable

• Frequent coexisting neuropathy may lead to foot ulceration in its own right but may also complicate peripheral ischaemia (see below).

The diabetic foot

This refers to the combination of ischaemia, neuropathy and immunocompromise that renders the feet of diabetic patients particularly susceptible to sepsis, ulceration and gangrene. Diabetic neuropathy affects the motor, sensory and autonomic nerves.

Sensory neuropathy

This renders the patient incapable of feeling pain. Minor trauma – for example, from a stone in the shoe – remains unnoticed. Even severe ischaemia and/or tissue loss that would lead a sensate patient to seek urgent medical advice may be completely painless. For this reason, diabetic patients often present late, with extensive destruction of the foot. Sensory neuropathy also affects proprioception such that, when walking, pressure is applied at unusual sites. This leads to ulcer formation and even joint destruction (Charcot’s joint).

Motor neuropathy

The normal structure and function of the foot depends not only upon ligaments, but also upon the long and short flexors and extensors of the calf and foot. The former are affected more than the latter by motor neuropathy, leading to weakness and atrophy. The result is that the long extensors of the toes are unopposed and the toes become increasingly dorsiflexed. This exposes the metatarsal heads to abnormal pressure, and they are a frequent site of callus formation and ulceration (Fig. 21.7).

Fig. 21.7 Neuropathic ulceration of the first metatarsal head with sinus entering joint space.

Autonomic neuropathy

This leads to a dry foot deficient in the sweat that normally lubricates the skin and contains antibacterial substances. The result is scaling and fissuring of the skin, and the creation of a portal of entry for bacteria. Abnormal blood flow in the bones of the ankle and foot due to loss of autonomic control may also contribute to osteopenia and bony collapse (Charcot’s foot).

Management

If the blood supply to the foot is adequate, dead tissue can be excised in the expectation that healing will occur, provided infection is controlled and the foot is protected from pressure (so-called off-loading). If there is ischaemia as well, the priority is to revascularize the foot, if possible. Sadly, many diabetic patients present late, with extensive tissue loss and ‘unreconstructable’ disease, which accounts for the very high amputation rate.

Management of lower limb ischaemia

Medical management

All patients with atherosclerotic vascular disease should be strongly urged to comply with BMT, which comprises:

• Immediate, absolute and permanent cessation from smoking. This is by far the most important intervention and prognostic factor. In the face of continued smoking, other treatments are rendered largely ineffective and disease progression, limb loss and death (usually from cardiovascular causes) within a few years are the likely outcome.

• Control of hypertension according to current guidelines (for example, see the British Hypertension Society, www.bhsoc.org).

• Control of hypercholesterolaemia according to current guidelines (for example, see the British Heart Foundation, http://www.bhf.org.uk). All vascular patients should be prescribed lipid lowering drugs, usually a statin, so that their baseline total cholesterol is reduced by a third (ideally to below 4 mmol/l). Statins also stabilize atheromatous plaques and prevent the development and progression of aneurysmal disease through as yet incompletely understood anti-inflammatory mechanisms.

• Prescription of an antiplatelet agent (for guidance see National Institute of Clinical and Health Excellence, http://www.nice.org.uk/guidance/index.jsp?action=folder&o=51201). This is normally aspirin (75 mg daily) but clopidogrel (75 mg daily) is a more effective and safer alternative (but is also more expensive). Anticoagulation with warfarin should normally be reserved for patients with AF.

• Regular exercise as possible; it is widely accepted that supervised exercise in a health care environment is more effective than (unsupervised) simple advice to exercise.

• Control of obesity. This will help to bring down blood pressure, cholesterol and the ‘strain’ of walking; diabetes will also be easier to control. Surgical and endovascular intervention is much more difficult and morbid in obese patients.

• The identification and active treatment of patients with diabetes. This includes foot care (for further information see, for example, Diabetes UK, http://www.diabetes.co.uk).

Compliance with BMT increases not only walking distance but also affords very significant protection against cardiovascular events, improves the patient’s quality of life and life expectancy. Unfortunately, many patients fail to comply and, in particular, continue to smoke. Endovascular or open surgery for IC should not normally be considered until the patient is fully compliant with BMT and that therapy has been given adequate chance to effect symptomatic improvement. Intervention in the face of continued smoking is usually clinically and cost-ineffective and represents poor use of limited health care resources. Revascularization is in addition to, not instead of, BMT, a point that often has to be emphasized to patients anxious to return to their previous lifestyle.

By the time a patient develops CLI it is often (but not always) the case that, without surgical or endovascular revascularization, the limb will be lost. However, this does not in any way undermine the value of instituting BMT in such patients. On occasion, BMT may improve the condition of the leg such that intervention is not required or a lesser procedure becomes an option. In those undergoing intervention, BMT undoubtedly reduces the overall risks and increases the success of the procedure.

Endovascular management

Balloon angioplasty (BAP), with or without stenting, has been used successfully in the iliac, femoral, popliteal and crural arteries and is usually performed under local anaesthesia (Fig. 21.8). The arterial lesion to be treated (stenosis or occlusion) is identified and crossed with a wire. A balloon catheter is introduced over the wire and the balloon inflated. This enlarges the lumen by disrupting the atheromatous plaque. In occlusions and complex disease, metal stents may be deployed across the lesion to improve patency and reduce distal embolic complications. Sometimes these balloons and stents are coated with drugs that reduce the arterial scarring (neo-intimal hyperplasia) that follows such intervention and can lead to restenosis and reocclusion (so-called drug eluting balloons and stents). Endoluminal repair of the aortoiliac segment is the treatment of choice in most vascular units because of its high patency rates, and low morbidity compared to open surgery. Infrainguinal BAP and, less commonly, stenting is also widely used in the management of IC and CLI.

Fig. 21.8 Balloon angioplasty and stenting.

A Critical arterial stenosis. B A guidewire is used to cross the lesion. C The guidewire is used to direct a balloon angioplasty catheter across the lesion. D The balloon is inflated. E A metal stent may be mounted on a catheter. The stent may be self-expanding or require expansion with a balloon. In many cases, the first manoeuvre is to cross the lesion with a stent and in this circumstance steps C and D may be omitted. F Metal stent holding open the stenosis.

Intermittent claudication

Endoluminal treatment (BAP, stent) should be used selectively in patients with IC because it may be associated with a 1–2% morbidity rate, rarely mortality, and many patients have a pattern of disease that is unsuitable for current endovascular technologies. There is controversy with regard to its role in the femoropopliteal and infrapopliteal segments because of a perceived lack of durability of benefit. In the future, this may be improved by the use of stents. By contrast, most vascular specialists believe that endoluminal therapy should be considered in patients with IC due to aortoiliac disease (absent or reduced femoral pulses) because they:

• tend to be younger, so that their symptoms have a greater impact on their quality of life and livelihood

• often have short-segment disease that is amenable to BAP, with or without a stent

• often have (relatively) normal infrainguinal arteries, so that restoring flow in the aortoiliac segment effects a dramatic improvement in the perfusion to their leg(s)

• tend to be more symptomatic, with shorter walking distances and bilateral symptoms

• may not achieve a satisfactory increase in walking distance with BMT alone, because the ability of the body to collateralize around aortoiliac disease is not as good as it is around femoropopliteal disease.

Furthermore, the long-term patency of BAP and stenting is optimal in high-flow, large-calibre vessels, leading to a durable clinical benefit in many patients.

Critical limb ischaemia

The role of BAP and stenting in CLI remains controversial and, with present technology, many such patients remain unsuitable for endovascular therapy. The only published randomized controlled trial to compare BAP and bypass surgery (BSX) (http://basiltrial.com) indicates that although BAP is safer and less expensive than BSX in the short term (12–18 months), BSX (with vein) offers a more durable and complete revascularization in the longer term (3–5 years) (EBM 21.1). At the present time, CLI patients expected to only live 1–2 years and who do not have a suitable vein for the construction of a bypass are probably best treated by BAP where technically possible; all other CLI patients are probably best served by BSX. The role for endovascular therapy may increase in the future as technology improves.

21.1 Bypass surgery (BSX) or balloon angioplasty (BAP) for severe limb ischaemia)

‘For patients who survived for at least 2 years after randomization, a BSX-first revascularization strategy was associated with a significant increase in subsequent overall survival and a trend towards reduced amputation free survival. BAP was associated with a significantly higher early failure rate than BSX. Many BAP patients ultimately required surgery. BSX outcomes after failed BAP are significantly worse than for BSX performed as a first revascularization attempt. BSX with vein offers the best long term outcome but BAP appears superior to prosthetic BSX.’

Basil Trial Investigators and Participants. Final results of the BASIL trial (Bypass Versus Angioplasty in Severe Ischaemia of the Leg) Journal of Vascular Surgery 2010; 51(5): 5S–17S.

Indications for arterial reconstruction

Intermittent claudication

Many surgeons are reluctant to perform infrainguinal bypass surgery for IC because:

• The risk of limb loss is very low with BMT

• Those patients who fail to comply with BMT (fail to stop smoking) are those most likely to press for surgery because of on-going symptoms. However, they are also those at greatest operative risk and those least likely to gain durable benefit from their bypass

• Surgery is associated with a significant risk of mortality and major morbidity, the size of that risk depending on the procedure and the patient but probably approaching 3–5% for infrainguinal bypass and 5–10% for aorto-bifemoral bypass

• As most patients have bilateral disease, even if they have unilateral symptoms, successful infrainguinal surgery on one side often reveals limiting IC symptoms on the other, requiring a second operation (the same for endoluminal treatment)

• Grafts have a finite patency, especially in those who fail to comply with BMT and, in particular, continue to smoke (the same for endoluminal treatment)

• As soon as a bypass graft is inserted, collaterals circumventing the original lesion shrink down. For this reason, when the graft occludes, usually suddenly, the patient is normally returned to a worse level of IC than before the operation. A patient who was previously a claudicant may now have acute limb-threatening ischaemia, which then forces the surgeon or radiologist to re-intervene. Secondary interventions are technically more difficult, are associated with higher risk and enjoy a lower patency rate.

As with BAP and stenting, the balance of risks and benefits for open surgery is different in patients with aorto-iliac disease. Although the risk of surgery is higher, the long-term patency rates of such grafts are excellent, and one operation deals with both legs. Whatever the treatment being considered, patients and their families must be made fully aware of the risks and benefits so that they can give fully informed consent. These discussions must always be faithfully recorded in the notes; it is good practice to send copies of this to the patient as well as the GP. Sadly, medicolegal activity continues to grow in the UK and clear and accurate verbal and written communication between the clinician, the patient and their family affords significant protection for all parties concerned.

Principles of arterial reconstruction

Endarterectomy

This involves the direct removal of atherosclerotic plaque and thrombus and is a relatively uncommon operation in modern vascular surgical practice except at the carotid and femoral bifurcations (Fig. 21.9).

Fig. 21.9 Profundaplasty.

A Focal atherosclerotic disease of the left common femoral artery is causing severe ischaemia because it is obstructing flow down the superficial and deep femoral (profunda femoris) arteries. B Local endarterectomy and closure of the profunda femoris using a vein or prosthetic patch (profundaplasty) restores normal flow to both vessels.

Bypass grafting

For a surgical bypass operation (Fig. 21.10) to be successful in the long term, three conditions must be fulfilled:

• There must be high-flow, high-pressure blood entering the graft (inflow)

• The conduit must be suitable

• The blood must have somewhere to go when it leaves the graft (outflow or run-off).

Fig. 21.10 Femorodistal bypass graft.

A Diagram showing femoral to posterior tibial bypass graft. B On-table angiogram showing distal end of vein graft (arrow) anastomosed to the dorsalis pedis artery in the foot.

Two main types of conduit are available:

• autogenous material, most commonly the ipsilateral great saphenous vein (GSV)

• prosthetic material, most commonly expanded polytetrafluoroethylene (ePTFE) or Dacron.

The main advantage of vein is that it is lined by endothelium that is actively antithrombotic and profibrinolytic, and therefore much less liable to induce coagulation than even the most inert of man-made materials. This translates into much better long-term graft patency. Vein is also much more resistant to infection (see below) and less expensive. It is generally agreed that, wherever possible, vein from the leg or arm should be used for infrainguinal reconstruction.

Extra-anatomic bypass

In most bypass operations, the new conduit more or less follows the course of the original artery – so-called anatomic bypass (Fig. 21.11). Where this is not possible and/or desirable, a so-called extra-anatomic bypass can be inserted (Fig. 21.12).

Fig. 21.11 Anatomic aortic bypass.

Reconstruction of an occluded aortoilliac segment by means of aorto-bi-femoral bypass grafting.

Fig. 21.12 Extra-anatomic bypass.

A Unilateral iliac disease may be treated by femoro-femoral crossover graft. B Bilateral aorto-iliac disease may be treated with axillo-bifemoral bypass graft.

For example, if only one iliac artery is blocked, and the patient is unfit for abdominal surgery and unsuitable for endoluminal treatment, a femorofemoral crossover graft can be performed. If both iliac arteries are occluded, then an axillobifemoral graft can be inserted. In general, these extra-anatomic grafts do not have as good long-term patency as anatomic aortoiliac reconstructions. However, they are lesser procedures and so the preferred option in high-risk patients or those that have a limited life expectancy.

Complications of arterial reconstruction

The morbidity and mortality associated with vascular surgery is often high because vascular patients are usually elderly and unfit with widespread vascular disease, and the operations are often lengthy with significant blood loss. Meticulous perioperative care is essential for optimal results, and close liaison between the surgeon, the anaesthetist and the intensivist is essential. Longer term major complications include infection and graft occlusion for which outcome is better when identified early.

Although there is no strong evidence of benefit, many surgeons perform ultrasound scans of their grafts at regular intervals in the postoperative period, typically at 1, 3, 6, 12, 18 and 24 months. This so-called ‘graft surveillance’ is designed to pick up technical problems with the graft that are likely to increase the risk of failure. It is generally believed that it is better to correct a ‘failing’ graft before it has blocked than to try to resurrect one that has already failed.

Infection of prosthetic grafts is a serious and growing problem, largely due to the increasing prevalence of antibiotic-resistant organisms, including methicillin-resistant Staphylococcus aureus (MRSA). Once a prosthetic graft is infected, it must usually be removed to rid the patient of sepsis and/or to prevent life-threatening (anastomotic) haemorrhage. Graft removal of course renders the distal part ischaemic and, where possible, a new graft is inserted through fresh uninfected tissue. This can be extremely challenging, and on occasion is impossible. Measures to avoid graft infection include:

• Using vein wherever possible

• Peri-operative antibiotic prophylaxis

• Strict aseptic technique in the operating theatre and ward

• Always using gloves and washing hands between examining patients.

Amputation

Indications

Amputation should only be considered where arterial reconstruction is considered by a vascular surgeon to be inappropriate or impossible. In some cases, patients are admitted profoundly unwell and septic from spreading gangrene and immediate amputation may be the only means of saving the patient’s life.

Level of amputation

This is determined by local blood supply, the status of the joints, the patient’s general health and his or her age. The broad principle is to amputate at the lowest level consistent with healing (Fig. 21.13). It is important to conserve the knee joint if at all possible, as the energy required to walk on a below-knee prosthesis is much less that required to walk on an above knee prosthesis. However, if the patient has other co-morbidity or disability that would make walking with a prosthesis impossible, there is no point in attempting to conserve the knee joint at the expense of healing. A common situation is where a patient presents with a fixed flexion contracture of the knee. A below-knee amputation in such a patient is usually ill-advised because the contracture will prevent the patient from ever walking and will also result in the stump wound resting on the bed or chair, leading to poor healing and wound breakdown.