Historical Background
The distal aorta and iliac segments are among the most common sites of chronic atherosclerotic disease. This disease is usually segmental, generally produces a constellation of characteristic symptoms, and is amenable to durable surgical reconstruction. Direct surgical correction of aortoiliac occlusive disease (AIOD) has developed rapidly since the 1940s and 1950s. Although AIOD commonly coexists with disease below the inguinal ligament, correction of inflow disease alone can often provide effective symptomatic relief and is of paramount importance if durable results of further distal arterial revascularization are to be expected.
Indications
Accurate assessment of disease severity is performed on the basis of the history and physical examination and a combination of imaging and physiologic testing. A history of intermittent claudication, diminished sexual potency, and absent femoral pulses accurately describes the triad of Leriche syndrome. Some patients with AIOD present with proximal claudication symptoms in the thigh, hip, and buttock distribution, whereas others with significant inflow disease may complain principally of calf claudication. Disabling symptoms of intermittent claudication that significantly impair a patient’s occupation or desired lifestyle can be considered appropriate indications for intervention. Ischemic rest pain and tissue necrosis are unequivocal indications for revascularization.
On physical examination, audible bruits over the lower abdomen or groins, elevation pallor, rubor of dependency, and shiny atrophic skin are all characteristic findings. Areas of ischemic ulceration, necrosis, or gangrene are often observed in advanced stages of the disease. Some patients may present with distal microemboli secondary to thromboembolism, the so-called blue toe syndrome.
With regard to conservative management, complete cessation of smoking, weight reduction, treatment of hypertension and diabetes, antiplatelet therapy, and aggressive serum lipid lowering are all desirable. A regular exercise program may enhance ambulatory function by improving muscle metabolic function. Finally, pharmacologic agents, such as cilostazol (Pletal), may provide benefit in a limited number of patients based on previous trials; however, this is rarely successful in patients with severe disease.
Preoperative Preparation
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Pulmonary, renal, or coagulation function abnormalities should be addressed. Corrective action, such as a brief period of chest physiotherapy and bronchodilator medication and correction of a prerenal cause of renal impairment, should be pursued.
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Evaluation of the carotid circulation should be performed.
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Preoperative coronary evaluation is necessary and the most important modifiable risk factor in patients undergoing vascular operations. Open aortic reconstruction qualifies as a high-risk procedure compared with, for example, percutaneous endovascular revascularization. Preoperative thallium imaging has been used to identify high-risk patients for perioperative myocardial infarction ; however, most such tests suffer from a poor predictive value, and it is best to manage all vascular patients as potentially having coronary disease.
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Segmental limb Doppler pressure measurements and pulse volume recordings are useful for diagnostic confirmation, establishing an objective baseline and localizing the disease process. They also provide useful quantification to establish whether a lesion has the potential to heal without revascularization. The addition of pre- and post- exercise ankle-brachial indices adds diagnostic sensitivity to noninvasive studies.
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Angiography has long been considered the gold standard for delineating the location, extent, and severity of AIOD, but advances in imaging have allowed computed tomography angiography and magnetic resonance angiography to often obviate the need for catheter-based angiography. In select patients, measurements of femoral artery pressures may be of considerable value. In assessing the hemodynamic significance of AIOD, a resting peak systolic pressure difference of more than 5 mm Hg, or a fall of more than 15% when reactive hyperemia is induced pharmacologically by intraarterial administration of 30 mg of papaverine or by inflation of an occluding thigh cuff for 3 to 5 minutes, implies hemodynamically significant inflow disease.
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Assessment of infrainguinal runoff is indicated because the status of the distal vessels has a considerable influence in the outcome of the proximal procedure. It also helps plan for adjunctive future distal bypass procedures.
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Appropriate antibiotic prophylaxis (cefazolin) should be administered before the operation and through the perioperative period.
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A radial artery cannula is routine in many units. Selective placement of a Swan-Ganz pulmonary artery catheter is reserved for select patients such as those with significant cardiac disease, likely requiring suprarenal clamps, or at risk of having significant hemodynamic disturbances.
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A combination of epidural and general anesthesia is used, which limits postoperative pain medication administration.
Operative Strategy
A simple classification by disease pattern (type I-III) can affect symptom presentation, affect progression of the disease, and help determine the appropriate operative strategy ( Fig. 28-1 ). Type I lesions are confined to the distal abdominal aorta and common iliac arteries. This least common pattern of disease usually occurs in younger patients presenting with symptoms of claudication in the hips and buttock region. At least half of these patients are women, usually heavy smokers with a characteristic pattern called hypoplastic aortic syndrome. Type II patients (about 25% of cases) present with disease that is confined to the abdomen. Type III patients (about 65%) have disease that extends above and below the inguinal ligament, are typically older, are more greatly affected by diabetes and hypertension, and manifest symptoms of more advanced ischemia.
End-to-End Versus End-to-Side Proximal Anastomosis
An end-to-end aortic anastomosis is preferred for most patients for several reasons. All flow is through the graft, which avoids competitive flow and an increased risk of graft limb thrombosis. An end-to-end anastomosis provides a superior hemodynamic configuration with less perianastomotic turbulence and less recurrent atheroma or anastomotic aneurysms. It is less likely to cause distal atheromatous embolization and is easier to cover with retroperitoneal tissue, with less chance of graft-enteric fistula.
An end-to-side anastomosis is preferred for certain anatomic configurations, such as for patients with a sizable accessory renal artery arising from the infrarenal abdominal aorta, patients with a patent inferior mesenteric artery that needs to be maintained, and patients in whom most disease is located in the external iliac arteries. In this instance, retrograde flow to the hypogastric arteries to maintain pelvic circulation may be limited, which can lead to impotence, colonic ischemia, or even lumbosacral spinal or cauda equina syndrome.
Procedure Selection
The optimal method of revascularization represents a controversial area in the management of aortoiliac disease. Surgical risk, extent of disease, personal bias, and previous surgical training may all play parts in decision making. Anatomic or direct reconstructive procedures, extraanatomic bypasses, and catheter-based methods each plays a role.
For low-risk, young patients with extensive disease and mild comorbid conditions, aortobifemoral grafting is the preferred choice and remains the gold standard. Angioplasty, femoral-femoral bypass, or unilateral iliofemoral grafting may be considered for patients with limited disease. Aortoiliac endarterectomy may be used for a small number of patients with distal aortic disease, confined to the distal aorta and common iliac arteries, although stenting has largely replaced this open surgical method in contemporary practice. For high-risk patients with bilateral iliac disease or heavy retroperitoneal scarring or contamination, an axillobifemoral bypass can be considered even though it may have lower long-term patency.
Aortoiliac Endarterectomy
Appropriate for patients with type I disease, aortoiliac endarterectomy is only infrequently performed today. Its advantages include the lack of prosthetic material, no infective potential, and continuity of antegrade inflow to the hypogastrics. Contraindications include evidence of aneurysmal change, total occlusion of the aorta to the level of the renal arteries, and extension of the disease into the external iliac and distal vessels. Although percutaneous transluminal angioplasty (PTA) and stents have replaced endarterectomy as first-line therapy for localized aortoiliac disease for many patients in current practice, endarterectomy remains a viable option for select patients and cases ( Fig. 28-2 ). From a technical standpoint, the atherosclerotic disease should terminate at the iliac bifurcation to obtain satisfactory results and achieve a good endpoint no farther than 1 to 2 cm into the external iliac arteries. Bilateral longitudinal arteriotomies, one extending from the distal aorta into one common iliac artery and the other confined to the common iliac artery, are performed. The proper endarterectomy plane, to the level of the external elastic lamina, should be obtained. Patch closure, either with vein or prosthetic, can be used. Tacking sutures may also be used to secure the distal endpoint.
Graft Selection
Both Dacron and polytetrafluoroethylene (PTFE) grafts are used in current practice. Dacron grafts are preferred by many surgeons because of flexibility and easy handling, although they have been known to dilate by 10% to 20% when exposed to arterial pressure. Proper sizing of the graft, more than graft type, prevents the development of sluggish flow and later potential fragmentation and dislodgement of laminar clot, which often builds up in oversized grafts. A graft that is 16 × 8 or 14 × 7 mm for female patients is a frequently used size.
Totally Occluded, Calcified, and Small Aortas
Surgical management of patients with a totally occluded aorta hinges upon extension of the occlusion into the juxtarenal segment. Occlusion that is limited to the distal aorta, usually up to a patent inferior mesenteric artery or lumbar branch, is managed in the usual way with placement of an aortic graft. With extension of thrombus into the juxtarenal segment, however, the operative approach requires control of the aorta above the renal arteries and protection of the renal arteries with bulldog clamps to avoid migration of thrombus into the renal arteries. After removal of the occluding thrombus in the juxtarenal aorta, relocation of the clamp to an infrarenal position is typically possible. Graft implantation is then carried out in the usual fashion.
A second problem may arise with dense calcification of the aorta. The anastomosis can usually be accomplished in these circumstances by constructing it close to the renal arteries, where the aorta may be more normal, or by endarterectomizing the proximal aortic cuff to the level of the proximal clamp. In this case interrupted pledgeted sutures are recommended for the anastomosis ( Fig. 28-3 ).
