Peripheral arterial disease is narrowing of arteries in the legs, and sometimes in the arms, which restricts blood flow and causes pain. In severe cases, gangrene (death of tissues supplied by the vessels) may develop.
In most affected people, peripheral arterial (vascular) disease is caused by atherosclerosis, in which fatty deposits form on the inner walls of arteries. The greatest risk factor for developing atherosclerosis is smoking. Other risk factors include hypertension (high blood pressure), a high-fat diet, and poorly controlled diabetes mellitus. Diseases of the peripheral arteries that are not caused by atherosclerosis include Buerger’s disease and Raynaud’s disease.
Symptoms and complications
The first symptom of narrowed arteries due to atherosclerosis is usually an aching feeling in the leg muscles (usually in the calf) when walking. The pain may be relieved by resting for a few minutes, but recurs after the same amount of walking as before. Prolonged use of the arms may also cause pain. Symptoms then become worse until, eventually, pain is present even when the person is at rest. The pain may be severe and continuous, even disrupting sleep. By this stage, the blood supply to the affected leg is dangerously low. The affected limb is cold and numb, with dry, scaly skin, and leg ulcers may develop after even minor injuries. In the final stage, gangrene (tissue death) develops, initially appearing in the toes and then spreading up the leg. Sudden arterial blockage sometimes occurs, causing acute ischaemia (insufficient blood supply to an organ or tissue). This arterial blockage may be due to the rapid development of a clot on top of a plaque of atherosclerosis, by a dissecting aneurysm (splitting of an arterial wall), or by an embolism arising from a clot formed in the heart and carried to a peripheral artery. It causes sudden, severe pain. The affected limb becomes cold and pale or blue, with no pulse. Movement and feeling in the limb are lost.
Diagnosis and treatment
A diagnosis is often based on the results of Doppler ultrasonography, which shows the flow of blood through the affected vessels, or angiography, which will reveal signs of narrowing or other structural abnormalities. Exercise and giving up smoking are important aspects of treatment. For peripheral vascular disease of the legs, the affected person needs to take scrupulous care of the feet in order to prevent infection and minimize the risk of gangrene. Arterial reconstructive surgery, bypass surgery, or balloon angioplasty may be needed to widen or bypass the affected blood vessels. Amputation is necessary if gangrene has developed.
Peripheral arterial disease in detail - technical
The most common presentations of peripheral arterial disease are intermittent claudication and abdominal aortic aneurysm. In patients under 50 years of age the cause of disease is most likely to be genetic, congenital, immunological, infectious, or traumatic; over 50 years the principal risk factor is smoking.
Diagnosis—the main diagnostic method used to confirm the diagnosis of peripheral arterial disease is Doppler ultrasonography, in particular to estimate the ratio of systolic blood pressure at the ankle and in the arm, the ankle–brachial pressure index (ABPI; normal value 1.0–1.4, <0.9 abnormal). Ultrasonography is the standard technique for demonstrating abdominal aortic aneurysms, usually defined as being when the maximum aortic diameter exceeds 3 cm.
Critical leg ischaemia is defined as gangrenous change, ulceration, tissue loss, or rest pain lasting for 2 weeks, with an absolute ankle pressure of less than 50 mmHg.
Acute leg ischaemia
Presents as a painful, pale and pulseless limb, and is usually caused by thrombosis at the site of an atherosclerotic stenosis. Requires administration of analgesia and, if appropriate, rapid surgical intervention: (1) for irreversible ischaemia the options are amputation or palliative care; (2) for severe but potentially reversible ischaemia (white leg), surgery is usually the treatment of choice; and (3) for moderate limb ischaemia (no paralysis and only mild sensory loss), arteriography with consideration of thrombolysis, endovascular angioplasty/stenting, or surgical embolectomy/endarterectomy/bypass.
Chronic leg ischaemia
Most commonly presents with claudication affecting the calf and thigh. This is associated with high cardiovascular risk, but only 5% will go on to lose a limb, and surgical or endovascular intervention is not usually required. Key elements in management are smoking cessation, aspirin, and statins.
Abdominal aortic aneurysm
Ruptured abdominal aortic aneurysm typically causes collapse and severe back or abdominal pain: less than 20% reach hospital alive, and almost half of those undergoing emergency surgical die within 30 days.
By standard definition, more than 5% of men older than 55 years have an abdominal aortic aneurysm, but most of these are small (3–5.5 cm). These should be managed by ultrasound surveillance, with attention to modification of cardiovascular risk factors.
Repair is generally recommended for asymptomatic aneurysms greater than 5.5 cm (perhaps >5 cm in women), or symptomatic aneurysms of any size. Minimally invasive endovascular aneurysm repair has an operative mortality of about 2%, which is only one-third of that associated with traditional open repair, but within 2 years the mortality advantage of endovascular repair has been lost and long-term outlook is unknown.
Peripheral arterial disease, defined for the purpose of this chapter as diseases of the abdominal aorta and its branches, has risk factors and features that overlap with, but can be distinguished from, those of coronary artery disease. The two conditions often coexist, but patients with coronary disease are almost always referred directly to physicians, whereas those with peripheral arterial disease are referred directly to vascular surgeons, particularly in regions where angiology is a poorly developed specialty, since medical therapies are limited. Vascular surgeons also manage patients with arterial disease in the carotid vessels and upper limbs.
The most common presentations of peripheral arterial disease are intermittent claudication and abdominal aortic aneurysm. Most peripheral arterial disease remains asymptomatic. It is not a new disease that results from a modern Westernized lifestyle. Atherosclerotic disease, partially occluding the peripheral arteries, has been described in the mummies of ancient Egypt. Life as a cavalry officer was associated with an increased risk of popliteal aneurysm, a condition treated by ligation by John Hunter, the pioneering 18th-century surgeon. Albert Einstein died of a ruptured abdominal aortic aneurysm.
Techniques for repairing abdominal aortic aneurysms were not developed until the middle of the 20th century. This was the golden era for the development of vascular surgery as a specialty, with the increasing use of bypass surgery that reduced the need for amputation. Today newer, less-invasive approaches are being employed—angioplasty and endovascular stenting—but few specific medical therapies are on the horizon.
Aetiology and epidemiology
Peripheral arterial disease may occur in the young, but the prevalence increases sharply with age. Both young and old may suffer from occlusive (stenosing) disease of the peripheral arteries or dilating (aneurysmal) disease, while vasospastic disease is uncommon. However, the underlying causes of peripheral arterial disease in those below and above 50 years of age tend to be very different.
Peripheral arterial disease in patients less than 50 years old
In younger patients, the cause of disease is most likely to be genetic, congenital, immunological, infectious, or traumatic. Patients with familial hypercholesterolaemia and related inherited disorders of lipid metabolism may present with peripheral limb ischaemia. There are also congenital causes of early onset leg ischaemia. These include aortic hypoplasia, which occurs during the embryonic fusion of the distal aortas, and popliteal entrapment, where the popliteal artery takes an unusual course through the head of the gastrocnemius muscle, with exercise involving knee flexion causing intermittent occlusion of the artery and calf pain that resembles intermittent claudication. A fierce immunological inflammatory response to smoking causes Buerger’s syndrome, which involves the artery, vein, and associated nerves in both the legs and the arms. This disease, seen principally in men, is particularly prevalent in the Indian subcontinent, and may resolve if the patient stops smoking. Sudden thrombotic occlusion of the iliac and distal arteries may occur in those below 50 years of age, suggesting the presence of an inherited thrombotic disorder. Embolic occlusion from a proximal source is also possible.
Marfan’s syndrome may sometimes be confirmed only after a patient has presented with a ruptured abdominal aortic aneurysm. In some variants of Ehlers–Danlos syndrome, patients with mutations in type III collagen present with visceral artery aneurysms. In South Africa (and elsewhere), aneurysms of the abdominal, femoral, or popliteal arteries in those under 50 years have been attributed to infectious causes, from HIV to tuberculosis. Syphilitic aneurysms, which used to affect principally the thoracic aorta, are now rare.
Peripheral arterial disease in patients over 50 years old
For patients over 50 years of age, the principal risk factor for peripheral arterial disease—stenosing, aneurysmal, or vasospastic—is smoking. The pathology is atherosclerotic change with superimposed thrombosis. Of patients who present with peripheral arterial disease, less than 5% have never smoked. For this reason, more men than women presented with peripheral arterial disease in the past, but recently more women are affected, perhaps a reflection of the increasing number who smoke. Nevertheless, unlike Buerger’s disease, cessation of smoking is not associated with an immediate dramatic improvement in symptoms and it may take several years without smoking to improve prognosis.
Diabetes is another important risk factor for stenosing peripheral arterial disease. Other risk factors include hypertension, raised levels of plasma fibrinogen, and hyperlipidaemia, with elevated plasma triglycerides being a common finding. The risk factors for dilating arterial disease are similar, with the exception of diabetes, which is rare.
For aortic aneurysms, although strong familial clustering has been observed, no specific common genetic mutations associated with aneurysmal disease have been identified yet and atherosclerotic change is commonplace. White and northern European populations appear to be at higher risk of aneurysmal disease than black populations. Stenosing and aneurysmal disease are associated with degenerative changes of the artery wall, the prevalence of both diseases increasing sharply with age (Table 1). Epidemiological studies also indicate a difference between stenosing and aneurysmal disease, with death from aneurysmal disease (aortic aneurysm) being more common amongst those of higher social classes and in affluent geographical areas.
|Table 1 The increasing prevalence of peripheral arterial disease with age in the populations of northern Europe|
Most peripheral arterial disease, both stenosing and dilating, is asymptomatic. The data have been derived from several studies and geographical variation may occur. ABPI, ankle–brachial pressure index.
Clinical features of leg ischaemia
The terms acute and chronic relate purely to the length of time that symptoms have been present and must not be confused with terms related to severity, such as critical limb ischaemia.
Critical leg ischaemia
Critical leg ischaemia is defined as gangrenous change, ulceration, tissue loss, or rest pain lasting for 2 weeks, with an absolute ankle pressure of less than 50 mmHg, although patients with diabetes are difficult to include in this classification.
Acute leg ischaemia
The incidence of acute leg ischaemia, which presents as a painful, pale, and pulseless limb, is 1 in 12 000 patients per year. It can be due either to an embolic event or thrombosis of an atherosclerotic stenosis. The commonest cause of a peripheral embolus used to be rheumatic heart disease in a patient with atrial fibrillation, but this is now uncommon, and other sources of emboli, such as an aortic aneurysm, must be considered. The development of a thrombosis at the site of an atherosclerotic stenosis, either in the superficial femoral artery or popliteal artery, is undoubtedly now the commonest cause of acute leg ischaemia. However, it should be stressed that, whatever the cause, there is no difference on clinical examination of the acutely ischaemic limb.
Arterial trauma due to road traffic accidents and knife or gunshot wounds is becoming commoner, as is iatrogenic trauma following the insertion of intra-arterial catheters for diagnosis or therapy. A rare but dramatic cause of acute leg ischaemia is phlegmasia cerulea dolens, in which massive thrombosis of all the major veins of the limb occurs with gross swelling that obstructs the arterial supply.
Patients with a thrombosis of a popliteal aneurysm may present with classic symptoms of pain, paralysis, loss of power, paraesthesia, pallor, lack of pulse, and perishing cold. If the blood supply is not restored, fixed blue staining of the skin is a further sign of irreversible ischaemia, as is a tense calf with plantar flexion. However, most patients presenting with acute ischaemia have symptoms that are less severe.
Chronic leg ischaemia
Chronic leg ischaemia is much more common than acute ischaemia (Table 1, and its main cause is atherosclerosis. In the young patient, one should also consider cystic adventitial disease, entrapment of the popliteal artery, and occasionally fibromuscular hyperplasia of the iliac arteries, particularly in women.
Symptoms are pain on walking, claudication affecting the calf and thigh, rest pain, ulceration, and gangrenous change. Less commonly, patients may present with buttock claudication and impotence (Leriche’s syndrome). Although the differential diagnoses of the acutely ischaemic limb are few, in the chronically ischaemic limb pain may be due to spinal stenosis or nerve-root compression (spinal claudication) or arthritis of the hip or knee. Classically the patient with claudication will complain of cramp-like pain in the calf, appearing after walking a particular distance, relieved by a few minute’s rest, and recurring again at the same distance if the patient resumes walking. Failure of the pain to disappear on resting, or its reappearance after a shorter distance after each rest, suggest a possible musculoskeletal cause, particularly if distal pulses are present on examination. However, it should also be remembered that distal pulses may be felt at rest in the limbs of patients with claudication due to peripheral vascular disease, but disappear on exercise to the point of pain.
Investigation of the patient with an ischaemic leg
The main diagnostic method used to confirm the diagnosis of peripheral arterial disease is Doppler ultrasonography (duplex scanning). The ratio of systolic blood pressure at the ankle and in the arm, the ankle–brachial pressure index (ABPI), provides a physiological measure of blood flow at the level of the ankle. At rest, in a normal leg, the ankle–brachial pressure index lies between 1.0 and 1.4. As the blood flow in the leg is compromised, the ABPI falls sharply and values below 0.9 are considered abnormal and likely to confirm the diagnosis of peripheral vascular disease. To emphasize the important overlap between this condition and coronary artery disease, a reduction in ABPI nearly always signals the presence of coronary artery disease, which is the cause of death in most patients with peripheral arterial disease.
Exercise testing provides an objective method of assessing walking distance and helps with the identification of disease processes, such as angina, that may be limiting. It only needs to be used in those people who have a history of claudication but have normal resting ABPI, and can be used as a way of eliminating or suggesting other diagnoses.
In addition to establishing the diagnosis of peripheral arterial disease, duplex ultrasonography is able to determine the site of disease and indicate the degree of stenosis or length of an occlusion and hence aid in the planning of interventional treatment. Other imaging modalities such as CT scanning and magnetic resonance (MR) angiography can provide three-dimensional reconstructions of the diseased vessels and may be used for planning surgical treatment. Angiography is only required as an adjuvant to endovascular treatment, for surgical planning in some circumstances, or in the management of the acutely ischaemic limb.
Management of critical and acute limb ischaemia
Critical limb ischaemia requires administration of analgesia and rapid surgical intervention. The severity of ischaemia will determine the treatment options considered. However, all patients with a severely ischaemic limb should be given adequate analgesia and 5000 units of heparin intravenously. Many will be old and frail, with significant medical comorbidities. These issues must be considered in deciding whether or not surgical intervention is appropriate for any individual case, with action taken to improve those aspects of the patient’s medical condition that can be improved before surgery, or as part of continuing medical management.
For a patient with irreversible ischaemia (fixed skin staining and tense muscles), the main decision is whether a primary amputation or palliative care should be offered. If severe but potentially reversible ischaemia is present (white leg), surgery is usually the treatment of choice. Delay while thrombolytic therapy is tried is not advisable in this group. For patients with moderate limb ischaemia, where there is no paralysis and only mild sensory loss, arteriography with consideration of the potential use of thrombolysis should be performed. However, it should be remembered that thrombolysis is associated with numerous potential complications, most notably gastrointestinal haemorrhage and stroke. If the limb is salvageable, it may be possible to offer the patient an endovascular procedure, such as an angioplasty (with or without stenting). Surgical treatment can involve simple embolectomy, but may require a bypass procedure or endarterectomy, and in the severely ischaemic limb fasciotomies may be needed to treat or prevent a compartment syndrome. For at least 10% of patients, it will not be possible to offer revascularization: a few of these may benefit from the use of a prostacyclin analogue (iloprost), which might diminish amputation rates and alleviate pain. Any benefits of gene therapy, with vascular endothelial growth factor (VEGF) or other molecular mediators, on avoidance of amputation are far from established. Limb-salvage rates for patients presenting with critical limb ischaemia are variable, probably 50 to 60% at 2 years, dependent on the severity of disease.
In a patient presenting with acute leg ischaemia the outlook is poor, with only about 60% leaving hospital with an intact limb. The 30-day mortality for this group of patients can be as high as 30%, the main cause of death being cardiac disease. Controversial areas in the treatment of acute leg ischaemia include the role of arteriography, and which technique of thrombolysis is the safest and most cost effective.
In the patient who has had an embolic event, long-term anticoagulation should not be forgotten, and nor should a search for the source of embolus. If the patient is not in atrial fibrillation, has normal cardiac enzymes and 12-lead ECG, then they should have an echocardiogram to exclude any valvular lesion, a 24-h ECG to look for arrhythmia, an ultrasound to exclude abdominal aortic aneurysm, and a screen for thrombophilia.
Management of the chronically ischaemic leg
In chronic limb ischaemia, management depends upon the severity of the disease. Most patients present with claudication, which is relatively benign: only about 5% will go on to lose a limb, but claudication identifies patients with a threefold increased risk of death from either heart disease or cerebrovascular disease compared with age- and sex-matched controls. It is important when planning treatment that all the potential risk factors are covered. In the past surgical intervention was usually considered unnecessary: at least one-third will have improvement of symptoms with simple medical treatment and exercise. However recent trials have suggested that either angioplasty with adjunct and stents or coated balloons or angioplasty combined with exercise therapy may offer early benefits (to 2 years) and longer term results are awaited eagerly.
Careful attention must be paid to the cleanliness of ischaemic feet to avoid infection, and particular care should be given to the cutting of toenails. In many patients this is best done by a careful younger relative or chiropodist, since apparently minor lacerations can lead to ulcers, infection, and gangrene. Patients are recommended to exercise. Walking to the point of claudication is not harmful, and may improve collateral circulation with beneficial results. Supervised exercise therapy appears to be more effective than merely providing advice to exercise more.
Smoking is by far the most significant risk factor for occlusive arterial disease and every effort should be made to encourage smokers to stop. If patients undergo surgical treatment, then the long-term patency rate following arterial reconstruction is four times greater in smokers who stop than in those who persist.
Since coronary artery disease is the main cause of death in those with peripheral arterial disease, patients with the latter condition should receive similar cardiovascular risk reduction therapy to patients with coronary heart disease. Low-dose aspirin therapy (75–325 mg/day) should be recommended for all. If aspirin cannot be tolerated, ADP-receptor antagonists, such as clopidogrel, are equally effective in reducing the risk of cardiovascular events (stroke, myocardial infarction, and vascular deaths).
Secondary prevention trials have demonstrated the benefits of statin therapy in reducing cardiovascular morbidity and mortality in those with stenosing atherosclerotic disease of the peripheral arteries. Statins also may improve operative cardiovascular morbidity and mortality, but neither fibrates nor chelation therapy offer benefits.
The options for facilitating smoking cessation are increasing and nicotine replacement therapy can be used with either buproprion or varenicline if necessary, although many will not stop smoking until surgery threatens.
There is good evidence that cilostazol (a selective cAMP phosphodiesterase inhibitor) improves walking distance in those with intermittent claudication, although the mechanism of action is not clear, side effects are frequent, and the drug is contraindicated in patients with congestive heart failure.
In general, surgeons are conservative with respect to interventional treatment for patients with claudication, despite a possible early benefit for those having an endovascular procedure. However, in the patient who has severe claudication, with symptoms that significantly affect their quality of life, it is certainly possible and appropriate to offer interventional treatment.
Both endovascular techniques (angioplasty with or without stent) and bypass surgery are effective treatments, with little to choose between the two. For infrainguinal bypass, good-quality autologous vein is the conduit of choice. However, reasonable results can be obtained with synthetic grafts, particularly where the distal anastomosis is above the knee. Below the knee, an adjuvant vein interposition in the form of either a Miller cuff or Taylor patch is used. Stenting is used widely, but its use is contentious, and, at least in the iliac arteries, it may not be of value. The role of exercise therapy compared with angioplasty in the treatment of mild to moderate claudication continues to be debated, but it might be prudent to consider the conjoint treatment of angioplasty with exercise therapy.
Ischaemia of the arm
Ischaemia of the arm is usually a result of embolism from the heart. Occasionally the subclavian artery is diseased or has suffered traumatic injury or radiation damage following radiotherapy. The basic principles of investigation and management are the same as for the leg. However, it should be noted that the upper limb has multiple interconnection of collateral vessels, hence occlusion of the major arterial supply may still leave a viable limb. The other disease process that needs to be considered in differential diagnosis is the thoracic outlet syndrome, which gives rise to symptoms in the arm as a result of arterial, venous, or neurological compression caused by an additional cervical rib or by scalene bands. Management may require surgical intervention, either cervical rib excision or thoracic outlet decompression with the removal of the first rib.
Mesenteric ischaemia is uncommon. Over one-third of cases of acute mesenteric ischaemia are due to arterial embolism, with emboli lodging at the ostium of the superior mesenteric artery in many cases. Patients with acute mesenteric artery thrombosis have often had symptoms of mesenteric ischaemia prior to the acute episode. Chronic mesenteric ischaemia typically presents with weight loss and abdominal pain on ingestion of food, the classic story being that the patient is constantly hungry, but frightened to eat. Other causes of acute mesenteric ischaemia include venous thrombosis and nonocclusive ischaemia secondary to hypoperfusion.
Patients with acute mesenteric ischaemia will usually present with abdominal pain, but the abdominal physical signs may be much less dramatic than would be anticipated from the subsequent clinical course. Suspicion of the diagnosis should be heightened in the presence of atrial fibrillation or widespread atheromatous vascular disease. Patients may deteriorate suddenly and present in shock.
The diagnosis of acute mesenteric ischaemia is difficult to make. In the acute situation, clues to look for include leucocytosis, hyperamylasaemia, and unexplained acidosis. Liver function tests are usually normal. Radiological imaging is rarely able to make a positive diagnosis, although it can be very useful in excluding other possibilities. Angiography is not always accurate. CT scanning can be helpful in the diagnosis of mesenteric venous thrombosis.
Intensive resuscitation to replace fluids is essential. Surgery is usually necessary for the patient to survive, and the possibility of acute mesenteric ischaemia remains one of the dwindling number of reasons for requiring an emergency diagnostic laparotomy. Depending on the findings, resection of small bowel may suffice, but formal arterial surgery may be necessary, and in some unfortunate instances the extent of irreversible ischaemia can preclude any attempt at resection or revascularization. In cases where the surgeon is unsure of the viability of bowel remaining after resection, a second laparotomy may be planned to assess the situation a few days later. Repeat laparotomy may also be required to examine, and if necessary resect, more bowel in the patient who is not ‘doing well’ postoperatively. The prognosis for patients who present with acute mesenteric ischaemia is poor.
For patients who present with chronic mesenteric ischaemia, the aim of treatment is to improve blood flow and to act as a prophylactic procedure to prevent the catastrophic disaster of arterial occlusion. The potential options, having identified the site of the disease process by duplex scanning and angiography, include angioplasty, endarterectomy, reimplantation, or a surgical bypass procedure.
Abdominal aortic aneurysm
There is no fixed definition of an abdominal aortic aneurysm beyond agreement that it is a localized dilatation of the abdominal aorta, usually fusiform, with dilation starting distal to the renal arteries. Some would apply the term when the maximum aortic diameter is more than 1.5 times the diameter of the undilated proximal aorta.
Manual palpation to detect abdominal aortic aneurysms is unreliable, unless undertaken by a specialist on a nonobese patient. The most convenient method of screening for the presence of these aneurysms is ultrasonography, measuring the anterior–posterior diameter. Since the reproducibility of ultrasound measurements of the suprarenal aorta is poor, a convenient working definition of an abdominal aortic aneurysm is when the maximum diameter exceeds 3 cm, which in most people is more than 1.5 times the diameter of the undilated proximal aorta. In practice, it is only aneurysms of 4 cm or greater in diameter that have been of clinical concern.
Population screening studies in northern Europe have shown that the disease is usually without symptoms, much more common in men than in women (Table 2), and is strongly associated with smoking. The associations with hypertension and hyperlipidaemia are inconsistent. The prevalence of large aneurysms (>5 cm in diameter) detected by screening is only about 1% in men and the large majority of screen-detected aneurysms are 3 to 5 cm in diameter. The natural history of abdominal aortic aneurysms is progressive enlargement (with the diameter increasing by 2–5 mm each year) without symptoms, until the aortic wall is so weakened that it ruptures, which is a catastrophic event.
The infrarenal aorta is by far the most common site of aneurysmal dilatation, and usually the abdominal aorta is the only site of dilatation. When patients present with aneurysms of the iliac, femoral, or popliteal arteries, abdominal aortic aneurysm is often present and screening for this is mandatory. This emphasizes the tendency of some patients to have a more generalized form of dilating arterial disease.
Most patients (60%) with abdominal aortic aneurysm die from cardiovascular causes, and up to 25% of other male family members may develop occult aneurysms.
The symptoms of a ruptured abdominal aortic aneurysm are collapse (shock) and severe back or abdominal pain. Rarely a ruptured aneurysm will present with gastrointestinal bleeding from an aortoduodenal fistula or high-output cardiac failure from an aortocaval fistula.
Less than 20% of patients with a ruptured abdominal aortic aneurysm reach hospital alive, and even among those that undergo emergency surgical repair almost one-half will die within 30 days. With this bleak prognosis and the very significant costs associated with emergency repair following rupture, evidence has accumulated that screening of men over 65 years to detect those with the largest aneurysms, at highest risk of rupture, is cost effective. Accordingly, there are plans for national screening programmes for abdominal aortic aneurysm in the United Kingdom and other countries.
Management of ruptured aneurysms requires:
- ◆ Access lines, cross-matched blood, and resuscitation—maintaining moderate hypotension at ∼70 mmHg may be beneficial
- ◆ Confirmation of diagnosis—ultrasound (to show aneurysm); CT scan or experienced vascular surgeon (to confirm diagnosis of rupture)
- ◆ Rapid assessment of whether patient would benefit from emergency repair
- ◆ If yes, immediate surgical or endovascular repair
Aneurysms detected before rupture
Abdominal aortic aneurysms are commonly symptomless, but rupture—as explained above—is catastrophic. However, elective repair of an abdominal aortic aneurysm, a major surgical procedure, is not without risk. Traditionally, larger aneurysms have been repaired by cross-clamping of the aorta and insertion of a Dacron inlay graft at open surgery. This is a durable procedure and effectively ‘cures’ the patient. However, although some specialized surgical centres report an operative mortality of less than 2% associated with this elective procedure, on a population basis the mortality is more likely to be 5 to 8%, which is an important reason for avoiding surgery in those with small aneurysms.
Minimally invasive endovascular aneurysm repair, via femoral access vessels, has developed rapidly. Only about one-half of patients have an aneurysm that is anatomically suitable for this mode of repair, but randomized trials have shown that the operative mortality associated with endovascular repair is less than 2%, which is only one-third of the mortality associated with traditional open repair. However, within 2 years the mortality advantage of endovascular repair has been lost and a significant proportion of patients with endovascular repair require further interventions to ensure continued exclusion of the aneurysm. Hence patients with endovascular repair are likely to require lifelong surveillance. The cost-effectiveness, long-term durability, or patient preference for this new technique has not been established. In the UK endovascular repair now is considered cost-effective for elective procedures (www.nice.org.uk/TA167). The majority of patients would prefer endovascular repair although some still prefer open repair principally because there is no requirement for long-term follow up. The long-term durability of endovascular repair remains to be established and late rupture may be a greater problem than for open repair. Although the endovascular approach initially was developed for patients not considered fit for open surgery because of numerous comorbidities, the operative mortality rises to 9% in this cohort and there is no evidence that endovascular aneurysm repair prolongs patient survival.
Two randomized trials have shown that for aneurysms of 4.0 to 5.5 cm in diameter a policy of early elective surgery confers no long-term survival benefit, and hence early surgery should not be recommended. For such patients surveillance, with measurement of ultrasound diameter every 6 months, is a safe policy that engenders little patient anxiety, and the risk of aneurysm rupture is very low—1% per year. By contrast, for patients with aneurysms greater than 6 cm in diameter the risk of rupture may be as high as 25% per year, and in most such cases elective repair is recommended. Over 90% of the patients enrolled in the trials were men, and it is possible that the diameter threshold for considering surgery should be 5 cm in women.
Repair is also recommended when symptoms are attributed to the aneurysm, whatever its size, the commonest being back or abdominal pain, or tenderness to palpation. It is assumed that such aneurysms are at high risk of rupture and need early repair. As the aneurysm dilates, onion skin layers of laminated thrombus deposit in the lumen, to leave a blood-flow channel of approximately normal aortic diameter. These layers of thrombus are very stable and only in rare circumstances are the sources of emboli to the legs. The aneurysms which most often provoke symptoms have very thick, inflamed, fibrotic walls, which entrap nerves and may become adherent to other tissues. These are known as inflammatory aneurysms and the thickened wall can often be detected by CT or MRI. They are technically demanding to repair. There is no convincing evidence that a course of preoperative corticosteroids is beneficial. In the Japanese population, inflammatory aneurysms have been associated with active cytomegalovirus infection.
Patients with small aneurysms should stop smoking and have their blood pressure controlled. Since screening detects mainly small aneurysms, it would clearly be beneficial if a treatment to limit aneurysm growth were available. Although β-blockers have proved effective in limiting the dilation of the proximal aorta in patients with Marfan’s syndrome, there is no evidence that they are effective for abdominal aortic aneurysms. Furthermore, many patients with abdominal aortic aneurysm have impaired lung function, perhaps through smoking, and β-blockers often are poorly tolerated. However, effective control of blood pressure and cessation of smoking are both likely to minimize the rate of aneurysm growth and the risk of rupture, and statins may also be helpful. Intervention to exclude the aneurysm remains the only available treatment for aneurysms larger than 5.5 cm in diameter.
Just as for patients with limb ischaemia, patients with abdominal aortic aneurysm are at high risk of cardiovascular events. All patients with abdominal aortic aneurysm should be offered statin therapy to reduce the risk of morbidity and mortality from other forms of coexistent cardiovascular disease. Antiplatelet therapy should be considered, and there is some evidence that, for hypertensive patients, angiotensin converting enzyme (ACE) inhibitors minimize the chance of aneurysm rupture.
Conventional surgical management
Preoperative evaluation requires CT or MRI to define the anatomy and extent of the aneurysm. Cardiac, pulmonary, and renal function should always be assessed and optimal treatment instituted before surgery: poor renal and lung function are associated with an increased risk of postoperative morbidity and mortality.
The most common surgical approach to an abdominal aortic aneurysm is through a transperitoneal incision under general anaesthesia. The retroperitoneal approach, which avoids bowel manipulation and permits a more rapid return to oral diet, has similar cross-clamp, operating, and recovery times. The transperitoneal approach offers the advantage of exploring the abdominal cavity for other pathology. In this approach, after the bowel has been removed from the operative field, the aorta is exposed anteriorly from the left renal vein to the bifurcation. The infrarenal neck of the aneurysm is exposed anteriorly and laterally so that an occluding clamp may be applied. Both common iliac arteries are exposed for the placement of the distal occluding clamps. The aneurysm is opened longitudinally on the anterior surface and the remainder of the procedure performed from inside the aneurysm cavity. Usually following a small dose of intravenous heparin, arterial clamps are applied. Clot and debris are evacuated and any back-bleeding lumbar or mesenteric arteries ligated. A Dacron prosthesis is then sutured, end-to-end, to the normal-diameter aorta above the aneurysm. This anastomosis is tested for leaks before the graft is trimmed to appropriate length and sutured in place above the aortic bifurcation. The aneurysmal sac is closed over the prosthesis, before replacement of abdominal contents. Such tube grafts are the most common type, but when the iliac arteries are dilated or diseased a bifurcated prosthesis is used. The cross-clamp time should be less than 1 h and the whole procedure completed within 2 to 4 h. The longest procedures involve inflammatory aneurysms and cases where the proximal aneurysm neck lies above the renal arteries. The patient should be ready to leave hospital 7 to 12 days after the operation, with a durable repair.
Endovascular aneurysm repair
The technique of endovascular repair was introduced in the early 1990s and the technology has now stabilized. The procedure may be performed under general, regional, or even local anaesthesia. This flexibility allows endovascular repair in patients where general anaesthesia is risky, and the avoidance of aortic cross-clamping is an additional benefit for those with limited cardiac reserve.
Preoperative investigation to evaluate the extent and size of the aneurysm (spiral CT or MRI) is of critical importance. The length of the aneurysm neck below the renal arteries, angulation of the aorta, and tortuosity of the iliac arteries must be evaluated precisely so that the correct size of graft can be placed via the femoral artery. The insertion of the graft is performed under fluoroscopic control. This requires the use of significant amounts of contrast material, which may underlie the unfavourable results reported in patients with pre-existing renal impairment. The proximal end of the graft is held in place either by hooks and barbs, balloon, or self-expandable stents.
The length of the procedure is similar to that for open repair but the transfusion requirements are similar to those for open repair but the transfusion requirements are less and the patient recovers more rapidly and is ready to leave hospital within 2 to 5 days. The long-term success of the procedure depends on the successful exclusion of the aneurysmal sac and the security of the proximal attachment to prevent graft migration. Endoleaks may develop when the aneurysm is not completely excluded, the graft migrates or fatigues, or there is back-bleeding from lumbar vessels or the inferior mesenteric artery into the aneurysm sac. These are associated with an important risk of continued aneurysm expansion and rupture. For these reasons, continued vigilance and repeated evaluation of the aneurysm with duplex or CT scanning is necessary at annual intervals.
The endovascular revolution has affected the management of all categories of peripheral arterial disease, although in many instances the advantages and indications for the use of the (often more expensive) endovascular approach are not based on evidence from randomized trials.