William P. Robinson III
Presentation
A 74-year-old white male with a history of hypertension, diabetes mellitus (DM), tobacco abuse, coronary artery disease, atrial fibrillation, and end-stage renal disease on hemodialysis presented to the emergency department with a 3-week history of spontaneous ulceration of the left great toe and increasing rest pain in the left foot (Figure 1). Vital signs are normal. On physical exam, there was dry gangrene at that base of the left great toe with mild surrounding cellulitis. The patient had dry and hairless skin of the bilateral lower extremities. The patient has dependent rubor and elevation pallor of the left foot. Bilateral femoral and popliteal pulses were palpable. Pedal pulses were not palpable on either foot, but there was an audible Doppler signal at the left dorsalis pedis. The patient had intact strength and sensation of the lower extremities. The patient walks independently and performs his own activities of daily living.
FIGURE 1 • Left foot with dry gangrene of great toe, dependent rubor, and erythema on dorsum of foot.
Differential Diagnosis
Tissue loss due to arterial insufficiency most often affects the lower extremity due to the predilection of atherosclerotic occlusive disease to occur in the lower extremity. Trauma secondary to diabetic neuropathy and venous hypertension can also lead to lower-extremity ulceration or coexist with arterial insufficiency. Tissue loss secondary to arterial insufficiency typically occurs on the distal aspect of the extremity such as the digits and is often associated with underlying ischemic rest pain of the affected extremity. Tissue loss represents the most advanced form of ischemic secondary to arterial occlusive disease as perfusion is not adequate to maintain tissue integrity. Ischemic ulcerations usually begin as small, dry ulcers of the toes or heel area and progress to frankly gangrenous changes of the forefoot or heel with greater degrees of arterial insufficiency (Figure 2). Such progressive disease, affecting multiple levels of the peripheral vasculature tree, is more frequently encountered in the elderly. Patients with diabetes or renal failure are more susceptible to the development of ischemic pedal ulcers. Disease progression can be very rapid, as up to 50% of patients with critical limb ischemia (CLI) are asymptomatic 6 months before onset of pain or ulceration. The prevalence of peripheral arterial disease (PAD) is between 3% to 10% overall and 15% to 20% in those over age 70. Of those aged >50 with PAD, 1% to 3% will have critical leg ischemia in the form of rest pain or gangrene. The incidence of CLI ranges from 220 to 1,000 new cases per year in a European or an American population of 1 million people. The risk factors for infrainguinal occlusive disease are the same as those for the development of atherosclerosis in general and include age, male gender, hypertension, DM, smoking, dyslipidemia, family history, and homocysteinemia.
FIGURE 2 • Progressive stages of tissue loss from small ischemic ulcerations (A,B) to gangrene (C,D).
Because of the extremely high risk of limb loss, tissue loss from arterial insufficiency must be expeditiously and accurately diagnosed. Although clinical experience indicates that in some patients with CLI small ulcerations may heal with improved cardiac hemodynamics and optimal local wound care, significant tissue necrosis inevitably progresses to limb loss without revascularization. In addition, CLI is associated with an extremely high risk of mortality as it is a marker of advanced comorbidities and cardiovascular disease. Overall, approximately 25% of patients with CLI will die at 1 year, 30% will undergo major amputation, and 45% will be alive with two limbs. The rate of amputation is 10 times higher in diabetics than nondiabetics. The 5-year survival rate for patients with CLI is approximately 50% to 60%.
Workup
A careful physical examination can diagnose the extent of tissue loss and the presence of arterial insufficiency. A lack of a pedal pulse indicates abnormal arterial perfusion and, in the presence of ulceration or gangrene, warrants further investigation. An ankle-brachial index (ABI) is an essential part of the detailed vascular examination. An ABI of <1.0 is considered abnormal and <0.4 is generally considered consistent with the potential for tissue loss. Further workup can be conducted using noninvasive arterial testing, most often in a vascular laboratory. Segmental pressures measured at the level of the upper thigh, lower thigh, calf, ankle, and metatarsal level can diagnose the anatomic level of occlusive disease. If vessels prove noncompressible with the blood pressure cuffs inflated to pressures of 225 mm Hg, which is secondary to severe calcification of vessels in the setting of diabetes and end-stage renal disease, then the ABI and segmental pressure are not reliable indicators of perfusion. Pulse volume recordings, which measure the volume blood delivered to each segment of the lower extremity, are then utilized to assess perfusion. In addition, toe blood pressures remain a reliable indicator of distal perfusion. A toebrachial index <0.3 or absolute toe pressure of <30 mm Hg is indicative of severe ischemia and strongly predictive of inability to heal a lower-extremity wound.
Presentation Continued
The patient was started on broad-spectrum intravenous antibiotics. Ankle-brachial indices and segmental pressures were not diagnostic due to noncompressible vessels. Pulse volume recordings were consistent with severe ischemia and indicative of disease at the tibial and pedal levels (Figure 3). The patient had an absolute toe pressure of 0 mm Hg.
FIGURE 3 • Arterial noninvasive testing including measurement of segmental pressures and toe pressure and pulse volume recordings.
Diagnosis and Treatment
The diagnosis of tissue loss secondary to arterial insufficiency is based upon history, physical examination, and noninvasive arterial testing. The goal of arterial imaging is to plan revascularization and is only indicated if physiologic testing has indicated significant ischemia and the decision has been made to pursue revascularization. Imaging options include digital subtraction angiography, magnetic resonance angiography (MRA) and computed tomographic angiography (CTA). Although MRA and CTA are noninvasive, they are subject to artifact and may not provide the anatomic detail necessary to adequately plan infrainguinal bypass. Digital subtraction angiography provides optimal vessel detail and remains the gold standard. In addition, percutaneous endovascular therapy can often be performed at the time of diagnostic angiography if the patient and anatomy is deemed suitable.
Revascularization options for lower-extremity occlusive disease include percutaneous endovascular therapy, open surgical therapy, and combinations of the two modalities. The optimal treatment is dependent primarily upon the extent and location of occlusive disease and on the patient’s operative risk. The goal of either mode of therapy is to establish inline flow to the affected extremity. Percutaneous endoluminal therapy is best utilized for those with less extensive lesions and high surgical risk. The technical success and the durability of endovascular therapy are best for iliac and superficial femoral artery lesions. Extensive popliteal and tibial disease can be treated via endovascular means, but their durability is quite limited. In addition, long segment stenoses and occlusions are less favorable for endovascular therapy than more limited lesions. Endovascular therapy avoids some of the morbidity and mortality associated open surgery, as general anesthesia is not required, and blood loss and wound issues are largely avoided.
Extensive occlusive disease at multiple levels of the circulation is generally required to develop tissue loss secondary to arterial insufficiency. Therefore, open surgical therapy in the form of endarterectomy and surgical bypass is often required. In particular, extensive tissue loss of the foot often requires the restoration of a palpable pulse in the foot for healing and limb salvage. Surgical revascularization provides durable results. For example, the 5-year results of infrainguinal saphenous vein graft using modern techniques have been excellent, with primary and secondary patency rates of up to 75% and 80%, respectively, and limb salvage rates as high as 90%.
Surgical Approach
Percutaneous Endovascular Therapy
Endovascular treatment of iliac disease is generally performed through ipsilateral retrograde femoral access. Infrainguinal lesions are generally treated via a sheath placed “up and over” the aortic bifurcation from the contralateral femoral artery. In general, the principle of endovascular therapy is to cross the diseased segment with a wire and then successively dilate the stenosis or the occlusion with balloon catheters and/or stents over the wire. Keys to success include stable placement of a sheath, which allows controlled wire and catheter manipulation in traversing lesions and accommodates the passage of balloon catheters and stents of adequate caliber for restoring flow. Potential pitfalls of endovascular therapy include atherothromboembolism to distal arteries, access site hematoma and pseudoaneurysm, and contrast-induced nephropathy.
Infrainguinal Bypass
The principle of successful bypass is to perform the shortest bypass possible to re-establish inline flow to the foot. The three principles of “inflow,” “outflow,” and “conduit” are repeatedly emphasized by vascular surgeons. First, flow must be unobstructed to the level of the proximal anastomosis. Second, a site distal to significant disease must be chosen for the distal anastomosis. In general, the target vessel should be the least diseased artery that is the dominant supply to the foot. Finally, the conduit for the bypass must be adequate to support pulsatile flow. For bypass to below the level of the knee, autogenous conduit, preferably ipsilateral greater saphenous vein, provides maximal durability. Prosthetic conduit is preferred for aortoiliac reconstruction and acceptable for femoral to above-knee popliteal bypass when autogenous conduit is not available.
Infrainguinal surgical bypass can be performed under general, spinal, or occasionally regional anesthesia. It is our practice to work from proximal to distal, first exploring the inflow artery and exposing the venous conduit. We then explore the site proposed for the distal anastomosis, as high-quality preoperative imaging has already defined a suitable target vessel. Having determined the suitable donor and target arteries, vein of sufficient length is then harvested and prepared for use by gentle distension and testing for leaks with heparinized saline solution. The proximal anastomosis is performed prior to the distal anastomosis. This allows confirmation of adequate inflow before the bypass is performed and allows the graft to be tunneled and tailored to appropriate length under arterial pressure. Prior to vessel occlusion for the proximal anastomosis, the patient is systemically anticoagulated with 5,000 to 7,000 units of intravenous heparin and additional heparin is given as necessary. Blunt tunneling with placement of umbilical tapes through the tunnels is completed before heparin is administered to prevent bleeding. Atraumatic vascular clamps are placed proximally and distally and the donor artery is incised. The vein is then spatulated and a beveled proximal anastomosis carried out. Typically, a 5-0 polypropylene is used for the femoral anastomosis and a 6-0 used at the popliteal level. If a nonreversed orientation is used, the vein valves are then lysed with a valvulotome under arterial pressure. The vein is carefully brought through the tunnel under pressure and pulsatile flow confirmed with brief release of the clamp. The graft is then tailored to appropriate length and the distal anastomosis is then completed after occluding the target vessel. 7-0 prolene suture is generally used at the tibial or pedal level. If extensive calcification of the vessel risks significant injury from clamping, bleeding can be controlled by occlusion balloons placed intraluminally. A pneumatic tourniquet is particularly advantageous for arterial control when sewing to diminutive distal tibial or pedal targets, where crush injury or plaque dislodgment could cause graft failure. Flow through the graft and the outflow arteries is assessed following completion of the bypass with a continuous-wave Doppler and pulse examination. An angiogram is performed by directly cannulating the proximal graft. This allows for immediate repair of any technical defects that are identified. Intraoperative completion duplex ultrasonography is an additional sensitive screen for hemodynamically significant abnormalities within the graft.
Pitfalls of infrainguinal bypass that lead to early graft failure include attempted anastomosis to highly calcified vessels inappropriate for anastomosis and use of inadequate conduit. Technical defects not corrected at time of operation are sure to precipitate early graft failure. In addition, adequate hemostasis and meticulous attention to wound closure are necessary to prevent hematoma and wound dehiscence, which incur significant morbidity and can precipitate graft failure. Key steps of infrainguinal bypass with ipsilateral saphenous vein are outlined in Table 1.
Special Intraoperative Considerations
Adequate preoperative planning based on high-quality angiography generally avoids unanticipated intraoperative findings. Occasionally, the necessity of improving the inflow to support an infrainguinal graft is determined intraoperatively, either by direct visual assessment of inflow at the desired donor site or by comparison of a transduced pressure tracing from the donor site with that of a systemic pressure tracing. Aortoiliac angioplasty and stenting is increasingly becoming the preliminary procedure performed to attain sufficient inflow prior to construction of a more distal bypass graft. At times, saphenous vein will be found to be inadequate on exploration despite appearing adequate on preoperative mapping. Alternative autogenous conduit, such as contralateral saphenous vein and arm vein, must then be available and utilized for bypass below the level of the knee.
Postoperative Management
The most common major complications of infrainguinal bypass surgery are cardiac in nature. These are best prevented with perioperative optimization including use of beta blockade, statin therapy, and careful attention to volume status. Wound infection and dehiscence and skin flap necrosis can best be avoided by gentle tissue handling and careful avoidance of skin flaps during vein harvesting. Leg elevation in the early postoperative period minimizes leg swelling and healing complications. Aggressive mobilization and rehabilitation maximizes return to function. All patients are maintained indefinitely on aspirin or clopidogrel following surgical bypass. When a graft is at increased risk of failure, as in cases in which there is compromised outflow or only marginal conduit available, the anti-platelet agent may be supplemented with heparin and then warfarin. Serial duplex ultrasound scanning is necessary to identify hemodynamically significant stenoses within the vein graft that threaten graft patency. Duplex ultrasonography is generally done at 1, 6, and 12 months with yearly scans thereafter.
TABLE 1. Key Technical Steps and Potential Pitfalls of Infrainguinal Bypass Graft with Nonreversed Saphenous Vein
Debridement is avoided or deferred until after revascularization is complete unless infection necessitates it. Small, uninfected ulcerations of the toe or foot often can be safely managed conservatively. However, larger, gangrenous lesions of the toe, forefoot, or heel usually require debridement of all necrotic tissue after revascularization. If the ischemia is particularly severe or infection is present, a toe or transmetatarsal amputation may be necessary in order to achieve a margin of healthy tissue. Pressure offloading is often necessary to facilitate healing.
Case Conclusion
The patient underwent left lower-extremity angiog raphy via a right common femoral approach. There were no significant stenoses in the iliac, femoral, and popliteal vessels. There was severe tibial disease with single vessel run-off via a peroneal artery that was occluded in the distal leg (Figures 4A,B). A dorsalis pedis artery was reconstituted in the foot with patent vessels in the pedal arch (Figure 4C). He underwent below-knee popliteal to dorsalis pedis bypass with ipsilateral reversed greater saphenous vein. Intraoperative angiogram revealed no technical defects (Figure 5). Bypass resulted in a palpable pulse in the dorsalis pedis artery distal to the graft and greatly improved perfusion of the foot. He was discharged on post operative day 3 on ASA. The wound healed with gentle serial debridements done as an outpatient.
FIGURE 4 • Lower-extremity angiogram showing preservation of below-knee popliteal artery with posterior tibial and anterior tibial artery occlusion and single vessel runoff via the peroneal artery (A), occlusion of the peroneal artery in the distal calf (B,C), and reconstitution of the dorsalis pedis artery in the foot (C).
FIGURE 5 • Intraoperative completion angiogram demonstrating excellent result of below-knee popliteal to dorsalis pedis vein bypass graft.
TAKE HOME POINTS
· The diagnosis of tissue loss due to arterial insufficiency is made based on patient symptomatology, physical examination, and noninvasive tests, such as segmental pressure measurements and pulse volume recordings.
· Patients with tissue loss secondary to arterial insufficiency are at high risk for limb loss and death.
· Tissue loss secondary to arterial insufficiency represents the most advanced form of CLI and mandates revascularization for limb salvage.
· Percutaneous endovascular therapy is often applied as first-line therapy in appropriate patients with limited extent of anatomic disease and/or prohibitive operative risk.
· Due to the extensive, multilevel atherosclerotic occlusions present in patients with tissue loss, open surgical revascularization remains the gold standard for restoring durable perfusion to the threatened limb.
· Infrainguinal bypass surgery performed with autogenous vein conduit offers durable patency and excellent limb salvage
· Debridement of nonviable tissue should be delayed until perfusion is restored to the limb unless uncontrolled infection is present. Many patients will require one or more adjunctive operative procedures for salvage of their foot.
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