Arterial Occlusive Disease

Arterial Occlusive DiseaseAlthough atherosclerosis is the dominant cause of arterial occlusive disease, other etiologies such as congenital and anatomical anomalies, arterial dissection, and remote thromboembolism can also result in arterial obstruction. Symptoms of occlusive vascular disease primarily are end-organ dysfunction and, in the muscle beds, pain with exercise and tissue necrosis.AtherosclerosisAtherosclerosis can be seen in any artery, with plaques most commonly developing in areas of low shear stress, such as at arterial branch points. Lesions are usually symmetrically distributed, although the rate of progression may vary. Early lesions are confined to the intima. In advanced lesions, both intima and media are involved, but the adventitia is spared. Preservation of the adventitia is essential for the vessel's structural integrity and is the basis for all cardiovascular interventions.The hemodynamic circuit consists of the diseased major artery, a parallel system of collateral vessels, and the peripheral runoff bed. Collateral vessels are smaller, more circuitous, and always have a higher resistance than the original unobstructed artery. The stimuli for collateral development include abnormal pressure gradients across the collateral system and increased flow velocity through intramuscular channels that connect to reentry vessels. Adequate collateral vessels take time to develop but often maintain tissue viability in patients with chronic major arterial occlusions.Generally, arterial insufficiency occurs in medium-sized and large arteries with a 50% reduction in arterial diameter. This correlates with a 75% narrowing of cross-sectional area and enough resistance to decrease downstream flow and pressure. Compensatory dilation of the vessel wall may preserve lumen diameter as the atherosclerotic lesion develops, but with continued growth, lesions overcome this adaptation and result in flow limiting stenoses.Atherosclerosis develops over decades. Significant luminal narrowing with reduced flow may produce ischemia with increased demand (exercise), or the presenting event may be sudden thrombosis. If there is adequate collateral flow, single stenoses or even occlusions are reasonably well tolerated. Severe ischemia is usually associated with multiple levels of disease.Libby P: Atherosclerosis: the new view. Sci American 2002;286:46. [PMID: 11951331]

Dav G, Patrono C: Platelet activation and atherothrombosis. N Engl J Med 2008;358:1638. [PMID: 19476184]

Chronic Lower Extremity Occlusive Disease

Operative TreatmentInterventional procedures, open or endovascular, are performed both for limb salvage and for incapacitating claudication. The choice of operative procedure depends on the location and distribution of arterial lesions and the patient's comorbidities. Recognition of coexistent cardiopulmonary disease is particularly relevant, because many patients with peripheral vascular disease also have ischemic heart disease and/or chronic lung disease associated with tobacco use. Preoperative cardiac functional assessment is sometimes necessary, but preoperative myocardial revascularization is not beneficial in patients with reasonable cardiac reserve. All patients undergoing vascular surgery should have preoperative risk assessment. Randomized trials have shown that perioperative beta-blocker, angiotensin-converting enzyme (ACE) inhibitor, and statins may reduce cardiac morbidity in patients undergoing vascular surgery. Evidence is also emerging demonstrating the importance of maintaining statin therapy throughout the perioperative period.Endovascular TherapyEndovascular therapy consists of image-guided techniques to treat diseased arterial segments from within the lumen of the vessel. Access to the arterial system is established by the insertion of valved sheaths, usually percutaneously, into the access vessel, often the common femoral artery. Steerable wires and catheters are then passed through the vasculature under fluoroscopic guidance to the target lesion (Figure 343). Once the target lesion is accessed, therapeutic maneuvers, such as angioplasty, or devices, such as stents, can be delivered. In many arterial beds, endovascular therapy is more commonly utilized than open surgical therapy because of its minimally invasive nature and reduction of short-term morbidity and mortality. However, many questions remain concerning the long-term durability of endovascular repairs, and open surgery still plays a major role in the treatment of patients with arterial disease.Figure 343.

Endovascular gear. A: Sheath. Inserted using Seldinger technique into access vessel. Wires, catheters, and devices pass through the sheath. Sheaths provide stable working access points and protect artery. B: Catheter. Variable length, stiffness, coating, and shape (examples: B.1, cobra; B.2, pigtail; B.3, mesenteric selective). Catheters help steer wires through vasculature and also maintain access in vessel. C: Guidewire. Variable diameter, length, stiffness, and shape. Used to gain access into vasculature, cross lesions, and deliver devices. D: Balloon catheter. E: Peripheral stent graft. F: Peripheral nitinol self-expanding stent. G: Aortoiliac stainless steel/Dacron stent-graft.

Percutaneous transluminal angioplasty, with or without placement of an intravascular stent, is often the treatment of choice when stenoses or even occlusions are relatively short and localized. As the angioplasty balloon expands, it stretches the adventitia, fracturing and compressing plaque, expanding the artery to widen the lumen. Energy losses associated with a stenosis are inversely proportionate to the fourth power of the radius; therefore, even small increases in radius can result in substantial increases in blood flow, although durability of the procedure is improved with the reestablishment of a normal lumen. Concomitant stenting is frequently performed to improve luminal expansion and the arteriographic appearance of the lesion. Stent grafts (stents with fabric covering) may also be used in selected cases or to repair the inadvertent rupture of an artery during angioplasty (Figure 344).

Figure 344.

Aortoiliac occlusive disease. A: Aorta. B: Severely stenotic/occluded iliac arteries. B.1: Widely patent iliac arteries following balloon angioplasty and stenting (C).

Both stents and stent grafts are commonly used from the aortic bifurcation to the distal popliteal artery. Stenting is rarely performed below the knee, but angioplasty of tibial disease is now common with the use of small catheters and wires. Percutaneous mechanical and laser atherectomy are other options in removing obstructing lesions in lower extremity atherosclerotic occlusive disease. Mechanical atherectomy removes plaque by shaving with a cutting or rotating catheter.For short, stenotic segments in larger, more proximal vessels, the results of endovascular therapies are good with 1-year success rates of 85% in common iliac disease and 70% in external iliac disease. The results with superficial femoral and popliteal lesions are lower (Figure 345). The success of endovascular therapy for lower extremity occlusive disease is inversely related to the complexity of the lesion, defined by the number and length of stenoses treated.Figure 345.

Superficial femoral artery occlusion, angioplasty and stent-graft. A: Common femoral artery. B: Occluded superficial femoral artery. B.1: Recannulized, stent-grafted superficial femoral artery. C: Profunda femoris artery. D: Stent-graft.

Since disease may recur more frequently after angioplasty than after bypass surgery, the patient should be closely followed up using noninvasive tests. Repeat angioplasty or stenting may be indicated for recurrent disease, but the improvement in morbidity and mortality of endovascular interventions may be offset by the need for multiple repeat procedures. In general, minimally invasive percutaneous treatment of lower extremity occlusive disease is best used in patients of high operative risk and severe, limb-threatening ischemia (Figure 346).Figure 346.

Comparison of outcomes for surgical and endovascular intervention in lower extremity occlusive disease.

Surgical TreatmentAortoiliac ReconstructionOpen operations are indicated for aortoiliac occlusive disease in younger patients with low operative risk or patients with severe disease not amenable to endovascular therapy. To completely bypass the aortoiliac segment, an inverted Y-shaped prosthesis is interposed between the infrarenal abdominal aorta and the femoral arteries, creating an aortofemoral bypass. The goal of operation is restoration of blood flow to the common femoral artery or, when occlusive disease of the superficial femoral artery is present, to the profunda femoris artery. The clinical results of aortofemoral reconstruction are excellent, although the mortality and morbidity clearly are higher than for endovascular therapy. The operative death rate is 5%; early patency rate, 95%; and late patency rate (510 years postoperatively), about 80%. Late complications may be as high as 10% and include graft-intestinal fistula formation, anastomotic aneurysm formation, renal failure, and erectile dysfunction.Lower risk procedures may be preferable in high-risk patients. If the clinically important lesions are confined to one side, a femoral-femoral or iliofemoral bypass graft can be used. A graft from the axillary to the femoral artery (ie, axillofemoral graft) can be used for bilateral disease. Unfortunately, these "extra-anatomic" methods of arterial reconstruction are more prone to late occlusion than are direct reconstructions.Femoropopliteal ReconstructionWhen disease is confined to the femoropopliteal segment, femoropopliteal bypass is used. The principal indication for these operations is limb salvage. In patients with claudication alone, the indications for femoropopliteal bypass are more difficult to define but must include substantial disability from claudication. For limited lesions of the superficial femoral artery, endovascular therapy is often attempted first, with surgery reserved for extensive disease or angioplasty failure.The best graft for femoropopliteal bypass is an autologous greater saphenous vein. The saphenous vein may be left in situ or removed and reversed. In the former instance, the venous tributaries are ligated, and special instruments are used to render the valves incompetent. Expanded polytetrafluoroethylene (PTFE) may also be used as a conduit, particularly for bypass to the suprageniculate popliteal artery. Below the knee, PTFE conduits produce much lower patency rates than saphenous veins. Operative death rates are low (2%), and 5-year patency rates range from 60% to 80%. Limb salvage rates are higher than graft patency rates.The profunda femoris artery perfuses the thigh and acts as an important source of collateral flow when the superficial femoral artery is diseased. When there is a stenosis of the profunda, profundoplasty alone can be performed for limb salvages with success rates of 80% when the suprageniculate popliteal artery is patent and 4050% when the popliteal artery is occluded. Isolated profundoplasty is rarely helpful for treating claudication.Tibioperoneal Arterial ReconstructionReconstruction of tibial arteries (ie, distal bypass to the tibial, peroneal, or pedal vessels) is performed only for limb salvage. Advancing technology allows better endovascular therapy in the tibial vessels, with decreased short-term morbidity and mortality, and similar gains in limb salvage when compared to bypass surgery. However, endovascular techniques are not as widely used in the tibial vessels, and bypass still remains the primary mode of therapy for these patients. Autogenous saphenous veins are preferred because prosthetic conduits have high failure rates. Due to smaller vessel size, extensive disease, and probably the length of the bypass conduit, these grafts are not as durable as femoropopliteal bypass, so the limb salvage rate is substantially higher than graft patency. The operative death rate for these procedures is about 5%.AmputationAmputation of the limb is necessary within 510 years in only 5% of patients presenting with claudication. Amputation is more common if patients continue to smoke cigarettes. Patients with multiple risk factors for atherosclerosis and short-distance claudication are also at increased risk for eventual limb loss. Of patients who present with ischemic rest pain or ulceration, 510% require amputation as initial therapy, and most eventually will require amputation if not revascularized. Successful revascularization results in lower costs than primary amputation and an infinite improvement in quality of life. Occasionally, primary amputation may be preferable to revascularization if the likelihood of successful bypass is low, extensive foot infection is present, or the patient is nonambulatory. Amputation levels, options, and the special needs of amputees are covered in the section on Lower Extremity Amputation.Hirsch AT et al: ACC/AHA 2005 guidelines for the management of patients with peripheral arterial disease (lower extremity, renal, mesenteric, and abdominal aortic): a collaborative report from the American Association for Vascular Surgery/Society for Vascular Surgery, Society for Cardiovascular Angiography and Interventions, Society for Vascular Medicine and Biology, Society of Interventional Radiology, and the ACC/AHA Task Force on Practice Guidelines (Writing Committee to Develop Guidelines for the Management of Patients with Peripheral Arterial Disease) endorsed by the American Association of Cardiovascular and Pulmonary Rehabilitation; National Heart, Lung, and Blood Institute; Society for Vascular Nursing; TransAtlantic Inter-Society Consensus; and Vascular Disease Foundation. J Am Coll Cardiol 2006;47:1239. [PMID: 16545667]

Norgren L et al: Inter-Society consensus for the management of peripheral arterial disease (TASC II). TASC II Working Group. J Vasc Surg. 2007;45(Suppl S):S5.