Embolectomy/Thrombectomy – Arterial

Description and Special Anatomic Considerations

Lower extremity arterial occlusions resulting from distal embolization or acute thrombosis may manifest as a profoundly ischemic limb and constitute a surgical emergency. Initially, the underlying cause of the occlusion should be determined (e.g., cardiac embolus from atrial fibrillation or myocardial infarction versus in situ thrombosis associated with atherosclerosis). The patient's clinical history and the nature of the symptoms frequently suggest the etiology of the occlusion. Embolic occlusions usually cause more severe ischemia because of the lack of collaterals, whereas thrombosis in the presence of pre-existing disease may be better tolerated because there are established collaterals. The decision about appropriate imaging, such as angiography, is based on the clinical status of the limb, the presumed etiology of the occlusion, and the need to visualize distal runoff. Imaging is important in management as it localizes the level of obstruction, determines if there are multiple levels of occlusion, assesses for inflow and outflow disease, and guides the appropriate site for the arteriotomy. Surgical intervention is usually the primary consideration in treating acute limb ischemia, although endovascular treatment options are available. Surgical thrombectomy with Fogarty balloon catheters is often an effective treatment, but if it is unsuccessful, vascular bypass surgery may be necessary. Some patients may also require surgical fasciotomy if a compartment syndrome has developed. Endovascular options are appropriate when the limb is sufficiently perfused to allow pharmacologic or mechanical thrombolysis.

Treatment of an acutely thrombosed surgical bypass graft may be influenced by additional factors, such as progression of disease involving the native inflow or outflow arteries and the nature of the vascular conduit itself.

Indications

The clinical presentation of the patient and the severity of the limb ischemia usually dictate the appropriate therapy. A classification system for categorization of the acutely ischemic limb serves to direct the intervention. This classification is detailed in Table 77-1-1 .

Contraindications

Thrombolytic therapy may have advantages over surgical thrombectomy, particularly in the treatment of thrombosed surgical vein conduits. Fogarty balloon embolectomy may damage the endothelium of a vein graft and thus increase potential thrombogenicity. Synthetic conduits, however, usually respond well to surgical thromboembolectomy. Patients who have profound limb ischemia are at a high risk for limb loss and thus require rapid revascularization. One must be vigilant for life-threatening reperfusion syndrome; profound acidosis, hyperkalemia, myoglobinuria, renal failure, and even death may occur. Primary amputation may be more appropriate in some patients with irreversible limb ischemia.

Outcomes and Complications

Surgical thromboembolectomy of an acutely ischemic limb with an inflatable balloon catheter is considered a relatively minor and technically simple operation. However, there may be high perioperative mortality that can be attributed to serious underlying cardiac disease or to the consequences of reperfusion of the ischemic limb and subsequent release of toxic metabolites. On occasion, pulmonary emboli may result from secondary venous thrombi, or there may be reactive hyperemia after successful revascularization that may increase cardiac workload of the heart and cause acute cardiac failure. There are studies that report a 30-day mortality rate exceeding 20% and amputation rates above 10% after arterial embolectomy. Several studies have also shown that older patients have a higher mortality rate, and mortality risk is greater with proximal occlusions than with distal occlusions. A short duration of symptoms before embolectomy has been reported to increase mortality, whereas other authors have found no effect on mortality. According to Levy and Butcher, severe ischemia did not increase the mortality rate, whereas Balas and colleagues concluded the opposite. Many studies report higher amputation rates when embolectomy was delayed ; other authors have found no adverse effect of delayed treatment. High amputation rates have also been associated with age, advanced arteriosclerotic disease, severe ischemic symptoms, and thrombotic compared with embolic occlusion. In addition, there is a worse prognosis the more distally the occlusion is located, and the prognosis is also worse with common femoral emboli than at other sites.

Imaging Findings

Patients with clinical evidence of acute embolic or thrombotic occlusion may require emergent CTA or catheter angiography, followed by thromboembolectomy and subsequent endovascular or surgical interventions and vascular reconstruction if there is profound limb ischemia. For patients with moderate ischemia (TASC acute limb ischemia category IIa), initial diagnostic angiography should be performed, followed by primary thrombectomy and subsequent intraoperative angiography with immediate endovascular or operative treatment of remaining vascular problems. As an alternative therapeutic option, if the limb remains well perfused, catheter-directed thrombolytic infusion therapy may be appropriate in selected patients, with the intention of subsequent limb revascularization or unmasking of relevant disease that may allow endovascular or surgical vascular reconstruction.

In either situation, it is important to have preoperative or intraoperative images of the arterial inflow, the compromised vascular segments, and the outflow anatomy. In cases of embolic occlusion, there may be multiple areas of involvement, and emboli may be bilateral. In addition, if the emboli are from a cardiac source, compromise of the renal or mesenteric vasculature must be excluded. Thus, the clinical presentation of the patient will dictate the scope and proper choice of imaging.

Description and Special Anatomic Considerations

In contrast to the surgical management of thromboembolic disease, endovascular therapy employs both mechanical and pharmacologic methods for thrombolysis. With regard to the pharmacologic approach, a catheter is introduced into the occluded segment and a drug is infused that activates plasminogen and thus initiates thrombolysis. A variety of thrombolytic agents have been used, including streptokinase, urokinase, and recombinant tissue plasminogen activator (alteplase, tPA) and its derivative (reteplase, r-PA). The first two agents are now infrequently used for intra-arterial thrombolysis, mainly because of improvements in available agents. The newer plasminogen activating agents are now the agents of choice, with the activity of these agents enhanced in the presence of fibrin. All of these agents eventually fragment and dissolve thrombus and generally are most effective in the presence of acute or subacute thrombosis. When thrombosis is chronic and well organized, thrombolysis is much less successful.

For intra-arterial pharmacologic thrombolysis to be most effective, a catheter must first be advanced across the occluded segment; inability to cross the thrombosed segment generally indicates a more chronic process that will probably respond poorly to thrombolysis. A variety of infusion catheters are available; the majority are constructed with multiple side holes that allow maximal exposure of the surface area of the thrombus to the pharmacologic agent. Thrombolysis may be accelerated by the forceful pulsed injection of the fibrinolytic agent directly into the clot. Newer catheter systems combine pharmacologic with mechanical thrombolysis by use of ultrasound or rheolytic technologies to enhance drug activity ( Figure 77-1-1 ).

There are also percutaneous mechanical thrombectomy devices available that are designed to achieve thrombolysis without use of pharmacologic agents. These devices use a variety of techniques that include forceful fluid jets, suction, lasers, ultrasound, rotating baskets or coils, and impellers. Whereas many of these were originally designed for declotting of dialysis grafts, they are often used intra-arterially.

Indications

Catheter-directed thrombolysis is indicated in the lower extremities when there is symptomatic acute or subacute thrombotic arterial occlusion. It is also used in the treatment of occluded surgical bypass grafts or endovascular stents, for restoration of patency; often, thrombolysis will demonstrate a high-grade stenosis that has progressed to thrombotic occlusion and may be treated with angioplasty or stenting.

Mechanical thrombectomy devices are most effective in fresh thrombus and are often used in patients with a contraindication to pharmacologic thrombolysis. They may also be used in combination with a pharmacologic agent to rapidly reduce the volume of thrombus and thus shorten the duration of treatment.

Contraindications

Thrombolysis is contraindicated in patients in whom there is irreversible limb ischemia because the reperfusion will result in severe metabolic consequences. Patients who are currently experiencing active bleeding, have recently undergone major surgery, have had recent stroke or craniotomy, or have primary or metastatic brain tumors generally are poor candidates for pharmacologic thrombolysis because of the potential for significant bleeding complications. A profoundly ischemic limb may be inappropriate for thrombolysis because the time requirements for successful treatment may be prohibitive; these patients require rapid restoration of arterial circulation to avoid limb loss. Surgical intervention with thromboembolectomy and bypass may therefore be more appropriate in such patients.