Percutaneous Vascular Interventions

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CHAPTER 86 Percutaneous Vascular Interventions

Jonathan Liaw, Benjamin Pomerantz, Sanjeeva P. Kalva

The first known use of angiography was performed on a cadaver hand in 1896, a year after Roentgen developed the first x-ray. The progress of angiography was initially slow because of the lack of a suitable in vivo contrast medium. Eventually, a contrast agent was developed based on linking iodine to carbon, a formula fundamental to all current iodinated agents. Vascular access remained a problem until 1954, when Seldinger described the technique for percutaneous vascular access.¹ This allowed safe vascular cannulation and resulted in the rapid development of techniques for diagnostic percutaneous angiography.

Percutaneous vascular therapeutic interventions evolved from the successes of diagnostic angiography. The first case of percutaneous revascularization was performed by Dotter and Judkins,² who successfully dilated a superficial femoral artery stenosis in 1964 using serial dilation over a percutaneously inserted guide wire. Since then, many technologic innovations in hardware materials, such as balloons, metallic stents and guide wires, have led to the rapid progression of percutaneous vascular interventions. Advances in contrast media and imaging technology, such as digital subtraction angiography, CT, and MRI, have also ushered in new approaches and methods to identify and treat a wide array of vascular diseases through the percutaneous approach. One such example of great clinical usefulness is the use of carbon dioxide (CO₂) as a contrast material for arteriography in digital subtraction angiography system.³ The knowledge gained through such arterial interventions has been applied for cancer therapy to achieve temporary tumor devascularization in preparation for surgery or to treat the tumor through a combination of chemotherapy and vascular occlusion materials.

In this chapter, we will briefly discuss the tools, principles, and methods of diagnostic arteriography and percutaneous arterial interventions. We have broadly divided arterial interventions into revascularization procedures and vascular exclusion procedures. Our intention is not to provide detailed descriptions of procedures but to provide an overview of the indications, principles, complications, and results. For detailed descriptions of these procedures, refer to the subsequent specialized chapters in this book.

EQUIPMENT AND TOOLS

The essential tools for diagnostic arteriography are catheters, vascular sheaths, and guide wires. In addition to these, revascularization procedures use various types of balloons, metallic stents, and aspiration and infusion catheters. Vascular occlusion and exclusion procedures use particulate materials, metallic coils, detachable balloons, liquid embolic agents, and stent grafts.

Catheters

A catheter commonly serves as a delivery conduit for contrast materials, drugs and embolic devices. Catheters are long hollow tubes made of various materials, usually polyethylene or polyurethane. The size (diameter) refers to the outer diameter of a catheter, with typical sizes varying from 4F to 9F. The inner lumen of a diagnostic catheter is constant, and allows a 0.038-inch diameter guide wire. Within the shaft of a catheter, there is a layer of fine braided wire, resulting in a flexible, kink resistant, torqueable structure. The luminal surface is coated with Teflon or other low-friction substances to provide a low-friction surface for passage of the guide wire and other devices used for peripheral arterial interventions. The tip of the catheter is soft and often tapered. Some catheters have a preformed shape. This may help manipulate the catheter across a vessel or allow selective cannulation of a vessel. Various tip configurations are currently available. Catheter selection depends on the angle at which the target vessel arises from the parent vessel. Several catheters have a reverse curve (e.g., Simmons, SOS omni), which require reformation in a larger vessel to return to the original curve of the catheter.⁴ Other catheters have multiple side holes at the tip and allow injection of a large volume of contrast material at a high flow rate.

Microcatheters are generally 3F or smaller in diameter and can be passed through a diagnostic catheter. A microcatheter allows superselective cannulation of a small or tortuous vessel.

Vascular Sheaths and Dilators

Vascular sheaths are generally larger catheters of varying lengths, with a hemostatic valve on the proximal end of the sheath. A side arm is connected to the hemostatic valve. These catheters are inserted over a wire following needle cannulation of the vessel. An inner dilator is present and removed following cannulation of the vessel with the sheath. After removing the dilator, the vascular sheath provides hemostatic access to the vascular system, greatly reducing trauma to the vessel associated with repetitive catheter insertion and manipulation. Most procedures require the use and manipulation of multiple catheters that can be introduced atraumatically to the vessel lumen via the sheath. In addition, sheaths provide support for catheter manipulation and interventions. Sheaths are available in varying sizes, shapes, and lengths. The size (diameter) of sheaths is described in a similar fashion as catheters but, in the case of sheaths, the inner diameter of a vascular sheath is used as the metric, which therefore corresponds to the largest catheter diameter that the sheath will accommodate.

Dilators are short, stiff catheters with a smoothly tapered end. They are passed over a guide wire into the vessel and are used to create a smooth, minimally traumatic tract from the skin surface to the vessel lumen. These are particularly useful for scarred tissue and serial dilations can be performed to enlarge a soft tissue tract to accommodate larger catheters and sheaths. The dilator shape and size are closely matched to the sheath to facilitate nontraumatic introduction of the sheath to the vessel.

Guide Wires

Guide wires are crucial in supporting and steering catheters to the target vessels. They consist of an inner core of stainless steel, wrapped with a smaller wire mandrel. There are multiple guide wire diameters, lengths, stiffnesses, and coatings. The tip of the wire can be angled, flexible, or J-shaped. The length of the flexible tip varies from 1 to 6 cm. A J tip can have a 3-, 5-, 10-, or 15-mm curved radius. Guide wires are typically coated to reduce friction. Some guide wires have a hydrophilic coating, which when wet develop low friction coefficients, thus facilitating advancement in tortuous vessels. Guide wire selection is based on the catheter being used, location of the target vessel, and intervention being performed.

Balloons

Although the first percutaneous angioplasty was described by Dotter and Judkins ² in 1964, Gruentzig devised the first successful balloon angioplasty in 1976, and this method became widely accepted.⁵ The primary mechanism of balloon angioplasty is controlled tear and shearing of the atheromatous plaque, the intima, and the media beneath the plaque.

The characteristics of a balloon depend on the material and its construction. There are essentially two types of balloons, compliant and noncompliant. All balloons have a nominal diameter at a given pressure as well as a predetermined burst pressure.

Atherectomy Devices

Atherectomy devices (e.g., SilverHawk Plaque Excision System; U.S. Peripheral Products, Plymouth, MN) use a small rotating blade to cut and remove vessel wall atheroma. Theoretically, atherectomy offers the following advantages over conventional percutaneous transluminal angioplasty. It reduces focally and selectively the degree of stenosis by debulking the atheromatous mass, which increases immediate technical success, given the absence of subintimal dissection and local trauma. Although short-term results show a favorable trend toward decreased restenosis rates, long-term efficacy data of this technique is not yet available.⁷

Stents

The first endovascular stent (endovascular splint) was used by Dotter in 1969.⁸ Since then, stent technology has grown significantly and revolutionized the percutaneous management of vascular disease. Currently, there are two basic devices, balloon-mounted and self-expanding stents.

Balloon-Mounted Stents

Balloon-mounted stents (e.g., Palmaz, Cordis, Warren, NJ; WaveMax, Abbott, Santa Clara, Calif; Omni-Flex, AngioDynamics, Queensbury, NY;, Express, Boston Scientific; LifeStent, Bard Peripheral Vascular, Tempe, Ariz) are made of stainless steel and require balloon dilation to expand the stent to its working dimension. These stents have high radial strength but are less flexible. If deformed, these stents will undergo permanent plastic deformation and thus should not be placed in locations subject to flexing or compression. When deployed, balloon-mounted stents undergo minimal foreshortening, which allows precise placement; this is particularly useful for the treatment of lesions adjacent to an ostium, bifurcation, or side branch. These stents are not contained within a delivery system, and thus the delivery sheath should be long enough to cover the balloon and stent until deployment. During deployment of these stents, the final length of the deployed stent is inversely related to the final diameter of the deployed stent. The stent used needs to be large enough to prevent stent migration with minimal coverage of the normal adjacent vessel.

Self-Expanding Stents

Self-expanding stents (e.g., Wallstents, Boston Scientific; SMART stents, Cordis) are made from an alloy of nickel and titanium (Nitinol) or stainless steel. Nitinol stents have a thermal memory, which allows them to expand to a predetermined diameter at body temperature. Self-expanding stents will not undergo permanent plastic deformation and therefore are ideal for placement across flexing or compressing regions. They should also be used when relatively longer coverage is needed or in the presence of an associated dissection at the target vessel.

Nitinol stents are somewhat radiolucent, requiring the use of radiopaque markers, which are strategically placed on the stent to allow visualization of the proximal and distal aspects of the stent. In general, a self-expanding stent needs to be 1 to 2 mm larger in diameter than the target vessel. Often, after deployment, an angioplasty balloon is needed to expand the stent fully. Following deployment, self-expanding stents undergo minimal foreshortening, generally less than 7%.

Drug-Eluting Stents

Following angioplasty and stent placement, smooth muscle cells in the arterial wall may undergo hyperplasia, resulting in neointimal hyperplasia and subsequent stenosis within the stent. Drug-eluting stents are designed to decrease stent restenosis rates. Drug-eluting stents contain three components, a metallic stent, a slow-release chemical coating, and a drug. The drug acts locally on the vascular smooth muscle cells, theoretically reducing neointimal hyperplasia that results in decreased stent restenosis. To date, the most promising drugs include sirolimus, zotorolimus, everolimus, and paclitaxel. Long-term data are lacking but multiple studies are underway to assess the efficacy of drug-eluting stents.⁹

Stent Grafts

Stent grafts are covered stents that serve as a vascular conduit. The covering material is generally a synthetic textile such as Dacron, extruded polytetrafluoroethylene (ePTFE), or polyethylene terephthalate (PET). Stent grafts may be balloon-mounted (e.g., Fluency stent, Bard Peripheral) or self-expanding (e.g., Viabahn, W.L. Gore, Flagstaff, Ariz). Common indications for stent grafts are treatment of ruptured or unruptured aneurysm, repair of an inadvertently ruptured vessel during angioplasty, and helping prevent restenosis.¹⁰

PERCUTANEOUS ARTERIOGRAPHY

High spatial resolution catheter-based angiography is crucial for diagnostic and interventional procedures. It is necessary to provide fine anatomic detail of the target lumen. It is important to optimize the technique to obtain temporal and spatial resolution.

Percutaneous Vascular Access

Vascular access techniques have evolved little since Seldinger described the technique of percutaneous access using a removable core or hollow needle, which allows the insertion of a guide wire.¹ The choice of the vascular access site is based on the procedure being performed, the location of the target vessel, and the degree of focal atherosclerotic disease in the affected vascular region. The access vessel should be readily free of disease. Access may be performed using a single-wall or double-wall technique. Regardless of the technique, once the vessel is accessed, a nontraumatic wire is passed through the lumen of the needle into the vessel. The entrance site to the vessel should be located over a bone whenever possible. This provides a stable object against which to compress the vessel following completion of the procedure and removal of the catheters and sheaths.

Common Femoral Artery Access

The common femoral artery (CFA) is the most common access site used for peripheral diagnostic angiography and intervention. The CFA is a large-caliber artery that can accommodate a large sheath size with minimal trauma to the vessel. The entire vascular system can be accessed from this site.

The CFA may be punctured in a retrograde (toward the head) or an antegrade (toward the foot) direction. In the retrograde direction, the access needle’s tip should be aimed at the level of the mid-femoral head. The bifurcation of the CFA is commonly just distal to the mid-femoral head. Fluoroscopic guidance may be used to help identify the appropriate access location.

An antegrade puncture is generally more difficult and the risk of bleeding is increased, particularly in obese patients. To puncture the CFA, the skin entrance site must be higher; the needle needs to be angled at 60 degrees toward the feet, aiming at the mid-femoral head. A combination of fluoroscopic and ultrasound guidance can be used to ensure accurate cannulation.

Brachial and Radial Artery Access

Brachial and radial artery access offers a lower risk of bleeding complications. However, the vessels are small, limiting the usable sheath sizes. In addition, there is an increased risk of distal ischemia if the sheath obliterates the vessel lumen. Also, if instrumentation crosses the origins of the great vessels from this approach, there is an increased risk of embolization to the cerebral and contralateral limb circulation.

Micropuncture access sets are normally used for brachial and radial punctures. Brachial artery puncture is performed with the patient’s arm and forearm supinated and slightly abducted. The artery is punctured near the medial antecubital fossa, with care taken to avoid puncturing the artery near the radial nerve. Radial artery puncture is performed with the wrist extended and the forearm supinated.

The brachial and radial arteries are more prone to vascular spasm and thrombosis, particularly during catheter manipulation. Administration of a vasodilator, such as nitroglycerin, or heparin is often given intra-arterially to reduce the incidence of these complications.

Popliteal Artery

Popliteal artery access is usually reserved for revascularization procedures involving the superficial femoral artery (SFA). It is performed with the patient in the prone position. In general, ultrasound-guided arterial puncture is recommended to avoid puncturing the popliteal vein, which may lie superficial to the artery.

Choice of Contrast Agent

The best tolerated and least nephrotoxic iodinated contrast material is nonionic iso-osmolar contrast. Many different brands are available, all of which are generally equal in efficacy.

For patients with renal impairment, the best strategy is to prevent further renal deterioration by avoiding the procedure unless absolutely necessary. Other diagnostic procedures such as magnetic resonance angiography (MRA) or color Doppler sonography may be performed for vascular diagnosis. However, if an endovascular therapeutic intervention is essential for management, catheter angiography can be safely performed if the patient is well hydrated prior to the procedure; the amount of contrast material used during the procedure should be minimized. In addition, oral N-acetylcysteine may be beneficial to reduce the risk for contrast-induced renal impairment.

Gadolinium chelate contrast agents and CO₂ are alternative contrast materials for catheter angiography in renal function–impaired patients. The disadvantage of these contrast agents is that vascular imaging is often suboptimal. In addition, gadolinium chelate contrast materials are associated with increased risk, albeit small, for nephrogenic systemic fibrosis in patients with severe renal impairment.

Specific Regions of Interest

Arch Aortography

Arch aortography is commonly performed for the assessment of atherosclerotic vascular disease, such as stenosis of the origin of the great vessels—the innominate, carotid, and subclavian arteries (Fig. 86-1). It is also used in the evaluation of thoracic aortic aneurysms and dissections, post-traumatic vascular injuries and, in some cases, congenital anomalies of the aorta and/or great vessels, especially if therapeutic intervention is desired.

FIGURE 86-1 Arch aortography in a patient suspected of left subclavian stenosis. A pigtail catheter is placed in the ascending aorta and angiography is performed. There is mild stenosis (short arrow) of the left subclavian artery. The long arrow points to a patent coronary bypass graft.

Abdominal Aortography

Abdominal aortography is commonly performed to evaluate abdominal aortic aneurysms and atherosclerotic vascular disease causing stenosis or occlusion in the aorta, mesenteric, or renal arteries. Additionally, abdominal aortography is routinely performed as the initial step for endovascular procedures involving the mesenteric, renal, and pelvic vasculature.

Pelvic Angiography

Pelvic arteriography is indicated for the diagnosis and management of suspected iliac artery occlusive disease, pelvic trauma, hematuria from the bladder, and arteriovenous malformations in the pelvis.

Carotid and Cerebral Angiography

Carotid and cerebral angiography is indicated for diagnosis and endovascular therapy of steno-occlusive disease, aneurysms, and arteriovenous malformations. Preoperative embolization of intracranial tumors may also be performed. Another less common indication is to assess cross-cerebral perfusion before sacrificing the ipsilateral carotid artery in cases of large inoperable carotid artery aneurysms and during resection of head and neck tumors.

Upper Limb Angiography

Arteriography of the upper limb is commonly performed to investigate vascular compression by bone or ligament (thoracic outlet syndrome), Raynaud’s syndrome, subclavian aneurysm, and ischemia (often secondary to embolic occlusion, Buerger disease, or iatrogenic trauma). Atherosclerotic disease is usually focal and located at the origin of the great vessels.

Lower Limb Angiography

Lower extremity arteriography is indicated for the diagnosis and endovascular management of limb ischemia (Fig. 86-2), trauma, vascular malformation, and tumors. Vascular access may be gained through a femoral, brachial, or radial route.

FIGURE 86-2 Right femoral angiography in a patient with rest pain. The catheter is in the right external artery. There is complete occlusion (arrows) of the right common femoral artery. The profunda femoris artery is seen in the leg being reformed through collaterals. The superficial femoral artery is also occluded.

Pulmonary Angiography

Historically, pulmonary angiography had been extensively used for the diagnosis of pulmonary embolism. Currently, its role is limited to interventional procedures for the treatment of massive pulmonary embolism with pharmacomechanical thrombolysis and for pulmonary arteriovenous malformations and aneurysms. With the advent of noninvasive imaging alternatives, notably pulmonary CT angiography, pulmonary angiography is rarely performed for surgical planning in patients with chronic pulmonary thromboembolism. Relative contraindications for pulmonary angiography are the presence of left bundle branch block and severe pulmonary arterial hypertension.

Renal Angiography

Renal angiography is indicated for the diagnosis and management of suspected renovascular hypertension (Fig. 86-3), hematuria of unknown origin, trauma, preoperative assessment of a donor kidney, and postoperative evaluation of a transplanted kidney. It may also be performed for the devascularization of renal tumors prior to surgery or as a palliative therapy.

FIGURE 86-3 Left renal angiography in a 24-year-old woman with hypertension and neurofibromatosis. The angiogram shows a dysplastic left renal artery (long arrow) with mild stenosis. There is also an intrarenal aneuyrsm (short arrow).

Hepatic and Mesenteric Angiography

Hepatic and mesenteric arteriography is indicated for suspected mesenteric ischemia, gastrointestinal bleeding, and vasculitides and for the assessment of variant anatomy prior to catheter-based and colonic interposition procedures. Mesenteric arteriography is also performed as part of an endoleak repair if the inferior mesenteric artery is the source of the endoleak. Other indications of mesenteric arteriography include diagnosis of vascular tumors such as islet cell tumors of the pancreas and assessment of portal venous anatomy through indirect portography.

Indications and Contraindications

Indications for percutaneous arteriography are as follows:

1 Diagnosis and treatment of primary vascular disease—vascular occlusive disease, aneurysm, and arteriovenous malformations

2 Diagnosis, localization, and delineation of highly vascular tumors, such as pancreatic islet cell tumors

3 Evaluation of percutaneous endoluminal therapies such as angioplasty, stenting, atherectomy, embolization, and thrombolysis

4 Diagnosis and treatment of vascular complications in various disease states (e.g., trauma, malignancy)

Contraindications

Few contraindications exist for diagnostic arteriography. Renal insufficiency or renal failure is a relative contraindication for the use of nephrotoxic contrast material. However, iodinated contrast material is cleared by conventional hemodialysis and postprocedural dialysis can reduce the toxicity concerns of iodinated contrast agents. In some cases, CO₂ may be a better alternate contrast material, but its use necessitates digital subtraction angiography. Other relative contraindications for catheter angiography are the presence of septicemia, active vasculitis, or infection at the vascular access site. Patients with an allergy to iodinated contrast material often require premedication or the use of a noniodinated contrast material such as CO₂ or a gadolinium (Gd) chelate contrast agent. Often, the amount of contrast agent used for diagnostic procedures may be less than that required for a diagnostic CT scan.

In pregnant patients, the risks to the fetus also need to be considered in addition to those to the mother relative to the benefits of catheter angiography. In pregnant patients, a noninvasive imaging study such as ultrasound or MRA, without the use of a Gd chelate contrast agent, may be able to provide sufficient diagnostic vascular information for appropriate management of the patient or at least to minimize the extent of catheter intervention, if required.

Outcomes and Complications

Complications of angiography are generally related to the arterial puncture site and nephrotoxic effects of the contrast material.¹¹^,¹² The most common puncture site complication is local hemorrhage, which occurs in fewer than 3% of patients. Large hematomas may require transfusion or vascular surgical repair. The risk of hemorrhage is increased with large-caliber catheters, multiple sheath or catheter changes, and patients with bleeding diathesis, local aneurysmal or atherosclerotic arterial disease, or inadequate compression of the puncture artery. In addition to hematoma, false aneurysms (less than 0.5%) and, rarely, arteriovenous fistula formation (less than 0.1%) may occur.

Arterial thrombosis at the puncture site is a rare complication. Arterial spasm, the use of large-caliber sheaths, multiple punctures, polycythemia, hypercoagulable states, and excessive compression of the puncture site also increase the risk of thrombosis.

Subintimal dissection may occur secondary to wire, dilator, or catheter malpositioning. This complication occurs more commonly in the femoral or iliac artery during initial puncture. Frank perforation of the arterial wall is rare.

Embolization into the distal arterial tree occurs most frequently in the lower limbs, given the overwhelming predominance of femoral arterial access. Embolization is caused by thrombus stripping off the guide wire or catheter or by dislodgment of an atheroma (cholesterol emboli) during catheter manipulation. The administration of systemic anticoagulation during the procedure helps reduce the incidence of distal embolization. The use of embolic protection devices during lower extremity interventions also may reduce the incidence of clinically significant distal embolization.¹³

Complications with the use of iodinated contrast material include allergic reactions, renal failure and, rarely, cardiac failure. Premedication with prednisone or diphenhydramine is recommended for patients with a history of minor allergic reactions to contrast materials. As noted, the nephrotoxic effects of contrast can be minimized by preprocedural hydration and possibly the use of N-acetylcysteine. Cardiotoxicity is related to the high osmolarity of the contrast material, largely a historical complication given the widespread current use of low iso-osmolar, nonionic iodinated contrast agents.

Imaging Findings

Preprocedural Planning

Although cross-sectional imaging is often unnecessary for planning angiography, noninvasive imaging with CT angiography (CTA) and MRA is increasingly being used for screening and/or primary diagnosis. CTA and MRA often provide important information concerning the extent of the disease and aid in optimal planning for endovascular interventions. This information may also enable limiting the extent of catheter angiography, thereby decreasing the overall ionizing radiation dose to the patient and potentially the contrast material dose requirement. In addition, CTA and MRA can provide information regarding the presence and extent of arterial disease at the access site or intervening anatomy that may affect the choice of percutaneous approach or even the preference of therapeutic intervention.

Three-dimensional reformations of CTA or MRA data provide spatial representation of vascular anatomy that often enables improved appreciation of vascular origins and complex geometries of vascular segments. This information aids in the proper selection of angiographic catheters, wires, and therapeutic devices. Radiographic image acquisition during catheter angiography is also optimized if preprocedural knowledge of vessel orientation, course, and branching pattern is obtained on CTA or MRA.

Postprocedural Surveillance

Following diagnostic catheter angiography, all patients are observed for arterial access site complications and distal hypoperfusion. Catheter angiography is generally an outpatient procedure and patients are discharged within 6 hours of the angiographic procedure.

ANGIOPLASTY

Angioplasty was initially described by Dotter and Judkins,² who successfully carried out angioplasty of a superficial femoral arterial stenosis using serial dilation. Later, balloon technology was developed by Gruentzig in 1976. Since then, balloon angioplasty has become the standard for revascularization procedures. Successful angioplasty requires careful attention to patient work-up, high-quality angiography, selection of proper hardware, and careful postprocedure management. In general, short-segment stenoses and occlusions respond well to angioplasty.

In addition to routine laboratory work-up and noninvasive vascular studies prior to a planned revascularization procedure, patients should ideally be treated with antiplatelet drugs (e.g., clopidogrel and/or aspirin). Depending on the location of the stenosis or occlusion, an antegrade or retrograde approach is undertaken. In general, a guide catheter or large sheath is placed at the arterial access site to allow angiography of the segment being treated and a balloon catheter to be used. Heparin (70 to 100 U/kg) is administered intravenously prior to crossing the stenosis. The stenosis or occlusion is crossed first with a hydrophilic wire and then with a catheter. The intravascular location of the catheter distal to the stenotic segment is confirmed by contrast material administration and then a stiff working wire (e.g., Rosen or Amplatz wire) is positioned across the stenosis. The catheter is exchanged for a properly sized balloon. The diameter of the balloon is determined by the vascular segment being treated and the size of the normal adjacent vessel. The balloon is inflated, deflated, and removed. Inflation devices are helpful to treat the lesion adequately. A postangioplasty diagnostic arteriogram is obtained (Fig. 86-4) to confirm the therapeutic result. A successful angioplasty is revealed by the absence of any significant residual stenosis (i.e., residual stenosis less than 30%), normalization of intravascular pressures across the stenosis (pressure gradient less than 10 mm Hg), and disappearance of collaterals. Postprocedure, heparin may be infused intravenously for 24 hours.

FIGURE 86-4 62-year-old man with right leg claudication. A, Right femoral angiogram shows a short-segment occlusion (large arrow) of the distal superficial femoral artery. The popliteal artery is patent and is reconstituted by collaterals (small arrow). The occluded segment was treated by balloon angioplasty. B, Postangioplasty femoral angiogram shows areas of residual stenosis (arrows). This was subsequently treated by placing a self-expanding stent. C, Poststent, the femoral angiogram shows no residual stenosis and disappearance of collaterals.

Special Considerations

Severe or Tight Calcified Stenosis

Wire negotiation through a tight or very severe high-grade stenosis can be challenging. The use of the roadmap feature with digital subtraction angiography is often helpful. A curved guide wire and catheter can be helpful for negotiating across a complex stenosis. In some cases, a subintimal channel with re-entry distal to the lesion may be made (subintimal angioplasty). A very tight or calcified lesion may require progressive dilation with sequentially larger balloons.

Chronic Occlusions

Crossing chronic occlusions presents a particular challenge. New hardware, simultaneous antegrade and retrograde access, and subintimal angioplasty are often useful in such cases. Recently developed tools to help cross chronic occlusions include catheters (e.g., CTO catheter, Cordis), re-entry devices (e.g. Outback, Cordis), an ultrasound-guided re-entry needle for subintimal angioplasty, thermal ablation devices such as a radiofrequency ablation wire (e.g., Safe-Cross wire, IntraLuminal Therapeutics, Menlo Park, Calif), and laser wires (e.g., Excimer laser wire, Spectranetics, Colorado Springs, Colo).

Acute Dissection

Acute dissection during angioplasty may be asymptomatic or may lead to vessel occlusion and/or thrombosis. It may be treated with prolonged balloon inflation across the dissection or with the placement of an intravascular stent.

Acute Thrombosis

Acute thrombosis during the procedure is typically treated with local thrombolytic infusion and/or mechanical thrombectomy or thrombosuction.

Restenosis and Elastic Recoil

Unsuccessful angioplasty caused by recoiling of the vessel may be treated with placement of an intravascular stent. The incidence of postangioplasty neointimal hyperplasia may be reduced with the use of cryoplasty balloons, but data are still lacking concerning their efficacy.

Indications and Contraindications

The main indications for angioplasty vary based on the specific arterial region. They include life- limiting claudication and chronic critical limb or organ ischemia (e.g., rest pain, ulcer, gangrene), bypass graft stenosis, and clinically significant arterial stenoses in the renal artery, mesenteric circulation, and other arterial territories. Angioplasty may also be performed to treat in-stent stenosis (Fig. 86-5). Specific indications for each vascular territory are discussed in subsequent chapters.

FIGURE 86-5 In-stent stenosis treated with angioplasty. A, Right femoral angiogram shows multiple areas of severe stenosis (black arrows) within a stent. The stenoses were crossed with a wire and angioplasty was performed. B, C, Postangioplasty, there is restoration of the vessel lumen, with no residual stenosis within the stent.

Absolute contraindications for angioplasty include a hemodynamically unstable patient and the presence of an ulcerative plaque secondary to its high risk for distal embolization. Multifocal long-segment stenoses and calcified eccentric stenoses respond poorly with angioplasty. Relative contraindications include allergy to contrast material and the presence of renal dysfunction. Pregnant patients present additional considerations related to risks to the fetus. In all cases, discussion and careful assessment of the risks and benefits related to catheter intervention are essential.

Outcomes and Complications

The optimal clinical outcome is a durable improvement of the patient’s symptoms. Many early failures of angioplasty were caused by technical problems encountered at the time of the procedure, such as an occlusive dissection adjacent to the intervention site, elastic recoil of a fibrotic lesion, or perhaps an unrecognized lesion that continued to impair flow. Delayed failure occurs when there is restenosis of the treated segment. This is typically seen from 3 months onward and is predominantly caused by neointimal hyperplasia. Late failure occurs as the disease progresses in the inflow and outflow tracts. Vessel patency rates following angioplasty vary significantly, depending on the vascular territory, length of the stenotic lesion, complications during the procedure, and preexisting or unaltered patient factors such as smoking, lifestyle, and the use of antiplatelet medications.

As noted, access site complications include hematoma, pseudoaneurysm, arteriovenous (AV) fistula, and thrombosis. Atheroemboli causing blue toe syndrome occur in less than 1% of patients; dissection and occlusion of the branch vessels occur at a rate of 0.5%. Another rare complication is rupture of the vessel during angioplasty. Predisposing factors for arterial rupture include long-term therapy with corticosteroids and underlying vascular abnormalities such as Marfan syndrome and Ehler-Danlos syndrome. Immediate reinflation of the balloon across the rupture or proximal to the lesion can be a lifesaving maneuver. Urgent surgical repair or endovascular therapy with a stent graft is usually required to stop bleeding. Systemic complications are relatively uncommon and include sepsis (0.2%) and transient acute tubular necrosis (0.3% to 1%).

Imaging Findings

Preprocedural Planning

It is paramount to review previous noninvasive studies (e.g., CTA, MRA, Doppler, ankle-brachial index [ABI] testing) and any prior arteriograms. These are reviewed to assess the extent of the steno-occlusive disease, disease at the access site, anatomy, and disease affecting the distal arterial bed. Imaging studies such as Doppler provide hemodynamic information about the severity of the stenosis. Careful clinical evaluation and recent clinical laboratory studies, in particular renal function, are essential. Administration of antiplatelet medications prior to a planned angioplasty may also improve clinical outcome.¹⁴

Postprocedural Surveillance

Antiplatelet therapy with aspirin and/or clopidogrel is generally recommended following angioplasty.¹⁴ The duration of antiplatelet therapy is debatable and many interventional interpreting physicians prefer to treat the patient for at least 6 months following angioplasty. It is essential to carry out a postprocedure assessment such as a Doppler ultrasound examination or ABI testing at 24 to 48 hours postangioplasty. Long-term follow-up (e.g., at 1, 3, 6, and 12 months) is also important to monitor patient outcome. Imaging studies such as Doppler or CTA may be performed if there is suspicion of residual or recurrent disease. Secondary interventions with repeat angioplasty or stent placement may be performed to increase the assisted patency following angioplasty.

REVASCULARIZATION WITH STENTS AND STENT GRAFTS

When angioplasty alone is ineffective for treating a stenosis or occlusion, stents and stent grafts provide an alternative solution. It is necessary to have a normal vessel both proximally and distally to allow internal fixation of the device and prevent disease recurrence. Today, many designs are approved by the U.S. Food and Drug Administration (FDA) and numerous devices are being used commercially or in clinical investigations. Stent grafts can also be used to treat aneurysmal disease.

In general, self-expanding stents are preferable for revascularization. However, the design and nature of the delivery system do not allow a precise deployment of the stent in complex locations. As such, balloon-expandable stents are used when location of the stent deployment is complex, as in the treatment of osteal stenosis of the subclavian and renal arteries and intracranial arterial disease.

Primary stenting—direct placement of a stent without prior angioplasty—is often practiced for the treatment of iliac, renal, and subclavian artery disease when the stenosis affects the ostium or is a result of an eccentric ulcerated plaque (Fig. 86-6). Secondary stenting following failed angioplasty or a complication of angioplasty is more commonly done.

FIGURE 86-6 Left subclavian stenosis treated with primary stenting. A, Left subclavian angiogram shows a severe stenosis (arrow) at the origin of the vessel. Mild poststenotic dilation is also seen. The stenosis was treated with a balloon-expandable stent. B, Poststent, there is no residual stenosis.

The procedure involves the same steps as angioplasty. The stenosis or occlusion is crossed with a wire. The extent, location, and size of the diseased artery are measured and an optimal stent is chosen. The stent is deployed across the disease segment as per the manufacturer’s guidelines. Angioplasty of the stent is often performed to bring the stent to the optimal size. If multiple stents are required, deployment of the distal stent should be performed first and adequate overlap of the stents achieved. The deployment of a stent graft for steno-occlusive disease is similar to that used for regular stents. However, when stent grafts are chosen to treat an aneurysmal disease, proper planning with regard to the size of the proximal and distal arteries is essential to prevent residual perfusion of the aneurysm.

Indications and Contraindications

Indications for arterial stenting are residual stenosis after angioplasty, postangioplasty dissection, restenosis, eccentric ulcerated plaque with risk of distal embolization, and ostial stenosis of the renal or subclavian arteries. Stent grafts are often used for steno-occlusive disease with an intent to reduce in-stent restenosis. Indications for stent grafts include the treatment of abdominal or thoracic aortic aneurysm, iliac aneurysm, ruptured aneurysm, pseudoaneurysm, ruptured vessel during angioplasty or arterial trauma, and aortic dissection.

The main contraindications for stent grafts include the presence of active infection, bacteremia, or a mycotic aneurysm. Other contraindications for stents include those listed earlier (“Angioplasty”).

Outcomes and Complications

In general, stents provide better patency rates compared with angioplasty in the treatment of renal artery disease, subclavian stenosis, and iliac artery disease. The role of stenting has been debated for the treatment of femoropopliteal and infrapopliteal disease. It appears that stents provide better short-term patency rates in the treatment of superficial femoral artery disease.¹⁵ The role of stent grafts in the treatment of aneurysms is now well established for abdominal aortic and iliac artery aneurysms.

The complications of stenting are similar to those for angioplasty. However, stenting carries the risk of stent migration, stent fractures, thrombosis, and restenosis.

Imaging Findings

Preprocedural Planning

Preprocedural planning for stenting is similar to that for angioplasty. It is important to understand the location, extent, and size of the diseased segment and characteristics of the plaque. The distal and proximal normal arterial segments should be assessed for patency, size, and branch vessel origin. In general, stenting across a joint is not preferred because this may increase fracture or crushing of the stent. Similarly, when stent grafts are used for the treatment of steno-occlusive disease, the covering of branch vessels may jeopardize the blood supply to distal organs. Furthermore, covering patent vessels may prevent the formation of collateral pathways in case of stent occlusion.

Postprocedural Surveillance

Surveillance following stent placement for steno-occlusive disease is similar to that for angioplasty. When stent grafts are used for the treatment of aneurysmal disease, imaging surveillance to assess aneurysm size and reperfusion is mandatory at 1 to 3 months and then every year thereafter.

THROMBOLYSIS

Thromboses in the peripheral vascular system are a major cause of morbidity and mortality. An arterial or venous thrombosis can lead to ischemia and tissue infarction. The aim of thrombolysis is to restore blood flow to the ischemic limb or organ and to identify the underlying lesion for treatment via an endovascular approach or surgery.

Several pharmacologic agents are available for thrombolysis, including streptokinase, urokinase and recombinant tissue plasminogen activator (rt-PA). Each has a slightly different mechanism of action but they generally exert their effects by converting plasminogen to plasmin. Plasmin is an enzyme that degrades multiple blood plasma proteins, most notably fibrin (fibrinolysis), the predominant component of fibrin clots. At present, rt-PA has emerged as the most commonly used agent.

During vascular access, care is taken to ensure a single wall puncture to the artery. A diagnostic arteriogram is obtained to assess whether the event is secondary to in situ thrombosis or embolization. Angiography may also provide information about the chronicity of the problem. The arterial inflow, extent of thrombosis, and patency of distal arterial bed are assessed. The thrombus is crossed using a wire and an infusion catheter with multiple side holes is placed within the thrombus. The tip of the infusion catheter should be advanced beyond the thrombus, if possible, and the side holes within the thrombus.

There are multiple regimens for thrombolytic infusion. The most common is a bolus infusion of the thrombolytic agent followed by a continuous infusion for 24 to 48 hours. The catheter may be repositioned during thrombolysis to provide a more even distribution of the thrombolytic agent. Repeat angiograms are obtained at regular intervals to evaluate the progression of thrombolysis. Concomitant low-dose heparin therapy is administered through the arterial sheath or an intravenous route. The patient’s activated partial thromboplastin time (aPTT) and hematocrit should be followed during thrombolysis. In addition, serum fibrinogen levels are determined to assess the degree of fibrinolysis, which may correlate with the risk of hemorrhagic complications.

During thrombolysis, there may be a distal embolization as the thrombus fragments. Continued upstream thrombolytic infusion is usually sufficient to lyse any distal thromboemboli. If no improvement occurs within several hours, the infusion catheter can be repositioned within the distal emboli.

Thrombolytic therapy is terminated once antegrade blood flow is established and no significant thrombus remains. In general, thrombolytic therapy is stopped after 48 hours if there is no significant clinical improvement. Thrombolysis is terminated sooner if hemorrhagic complications arise.

After a successful thrombolysis, the patient should be evaluated for any underlying vascular lesion or clotting disorder. If identified, these lesions should be treated to prevent further recurrence.

Special Considerations

Thrombosuction

This technique is done as an adjunct to pharmacologic thrombolysis when there is a large thrombus burden, or in a situation in which chemical thrombolysis alone has failed to clear the thrombus adequately. A large-lumen, nontapered straight catheter is placed into the thrombus. The thrombus is aspirated and suction is maintained while withdrawing the catheter in a smooth motion. These steps are typically repeated several times. This method may also be used when pharmacologic thrombolysis is contraindicated.

Mechanical Thrombolysis

Mechanical thrombectomy devices are used as an adjunct to pharmacologic thrombolysis. These devices excel in the treatment of acute limb ischemia caused by thrombotic occlusion. In addition, there is increasing interest in the use of these devices for the treatment of acute deep venous thrombosis (DVT). Also, these devices allow thrombectomy when pharmacologic thrombolysis is contraindicated or has failed. Several mechanical thrombectomy devices are available.

AngioJet (Possis Medical, Minneapolis) uses retrograde fluid jets to create a negative pressure gradient directed toward the catheter lumen (Bernoulli principle). The thrombus is drawn into the catheter, where it is fragmented by the jets and evacuated from the body. The device consists of a catheter, disposable pump bag and nondisposable motorized drive unit. The catheters have two lumens. The larger lumen allows debris evacuation and guide wire passage while a small profile inner lumen allows the pressurized perfusate to be removed. The pump set pressurizes the saline that energizes the catheter and creates the vacuum. The drive unit activates the pump, monitors safety, and ensures balanced flow and volume of the saline solution. This monitoring and control allow the system to theoretically remain iso-volumetric.

The Arrow Trerotola device (Arrow International, Reading, Pa) is a direct contact mechanical fragmentation device that uses a spinning wire to macerate the thrombus. The device consists of a motor-driven fragmentation cage attached to a drive cable. The cage and drive cable are housed in a 5F catheter containing a self-expanding cage, with a soft rubber distal tip. Once the cage is unsheathed, the cage expands to a predetermined diameter (9 mm). The open cage is rotated within the graft at a fixed speed (3000 rpm) using a separate handheld rotator unit. This device has FDA approval for declotting dialysis access in patients with arteriovenous fistulas and synthetic grafts.

As its name suggests, the ultrasound thrombolytic infusion catheter (EKOS, Bothell, Wash) combines the use of catheter-directed pharmacologic thrombolysis with ultrasound. Ultrasound functions to alter the structure of the thrombus by temporarily increasing its permeability while providing an acoustic pressure gradient that helps move the drug into the thrombus to speed its dissolution (Fig. 86-7).

FIGURE 86-7 Acute thrombotic occlusion of femoropopliteal stent. A, Right femoral angiogram demonstrates complete occlusion (arrows) of femoropopliteal stent. B, Distally, there is reconstitution of the below-knee popliteal artery (arrow) through collaterals. An EKOS catheter was placed in the thrombus and thrombolysis was performed with rt-PA for 12 hours. C, D, Following thrombolysis, there is complete restoration of flow through the stent, with patent run-off vessels.

Indications and Contraindications

Indications for thrombolysis are as follows:

1 Acute thrombotic events with viable extremities and organs. Therapy should be initiated within 4 to 6 hours.

2 Acute thromboses occurring during diagnostic angiography or transcatheter therapy

3 Thrombosis of a mature bypass graft in the presence of demonstrable run-off vessels. However, if it occurs within 4 weeks of bypass graft surgery, it is unlikely to be successful. Surgical thrombectomy with graft revision is often necessary.

4 Thrombosis of dialysis related to arteriovenous graft or fistula

5 Acute thrombotic stroke (anterior circulation, less than 6 hours; posterior circulation, 12 to 24 hours)

6 Intracranial venous sinus thrombosis

7 Massive pulmonary embolism with impending cardiorespiratory collapse

8 Central venous access catheter occlusion

9 Extensive peripheral deep vein thrombosis

Thrombolytic therapy is absolutely contraindicated in patients with bleeding diatheses, cerebrovascular accident within 6 months, intracranial surgery within 6 months, gastrointestinal hemorrhage within 10 days, major surgical procedure, and trauma within 10 days. Other absolute contraindications include uncontrolled blood pressure (higher than 180/110 mm Hg), intracranial neoplasm, and arteriovenous malformation. Relative contraindications include renal impairment, hepatic impairment, recent transient ischemic attack, diabetic retinopathy, pregnancy, thrombocytopenia, and coagulopathy.

Outcomes and Complications

The technical success rate is around 80% with urokinases or rt-PA for acute thrombotic occlusions.¹⁶ The success rate decreases with the age of the occlusion. In general, infusion duration is much shorter with rt-PA.

Complications include the following:

1 Transient distal embolization is common in up to 20% of patients and manifests as a transient increase in rest pain. This resolves in a few hours in most patients.

2 Bleeding complications include hematoma at the vascular puncture site (incidence, 15%), gastrointestinal bleeding (10%) and, less frequently, hematuria. The most significant complication is hemorrhagic stroke. The reported risk is up to 2%, with an apparently higher risk with rt-PA. The risk continues for at least 12 to 24 hours following termination of therapy.

3 Systemic complications include acute renal failure (0.3%) and acute myocardial infarction (0.2%).

Imaging Findings

Preprocedural Planning

Careful clinical and laboratory work-up, including a review of all previous angiograms and noninvasive vascular studies, is essential to plan the access site, route to the location of the thrombus, and potential postprocedural issues, such as the placement of indwelling sheaths for ongoing thrombolytic therapy. It is important to assess the extent of thrombus, involvement of branch vessels, and patency of distal arterial flow. Previous imaging studies may provide information about preexisting stenosis or occlusion. It is also important to assess the heart for atrial fibrillation and left atrial thrombus.

Postprocedural Surveillance

Immediate success of thrombolysis is determined by angiography along with noninvasive assessment using ultrasound. Long-term patency rates are improved if the underlying lesions are treated promptly by surgery or percutaneous techniques.

ATHERECTOMY

The concept of removing an obstructive plaque by a catheter-based excision technique was first introduced by Höfling and colleagues.¹⁷ There are several different types of atherectomy devices available, including directional atherectomy devices (e.g., SilverHawk), orbital atherectomy devices (e.g., Diamondback 360, Cardiovascular Systems, Minneapolis), rotational atherectomy devices (e.g., Pathway Jetstream, Pathway Medical Technologies, Kirkland, Wash; Rotablator, Boston Scientific), and laser atherectomy devices (e.g., Excimer laser wire).¹⁸ At present, no specific recommendations have been established for the treatment of lower limb disease with atherectomy devices and there are no long-term results of peripheral application of atherectomy. The procedure involves crossing of a stenotic lesion with a wire and repeatedly passing the atherectomy catheter over the wire to remove the plaque. The size of the atherectomy device depends on the target vessel diameter.

Indications and Contraindications

Currently, no specific recommendations exist for performing atherectomy in the peripheral vascular system. As experience increases, the indications and applications will become more apparent. Certainly, a focal subtotal occlusion, complex stenotic lesion, or discrete lesion within a previously bypassed vessel or stented vessel would be a candidate for atherectomy.

It is clear that atherectomy is contraindicated in certain situations, such as limb-threatening ischemia, total occlusion, occlusion secondary to thrombotic emboli, and multifocal disease in heavily calcified vessels.

Outcomes and Complications

Few large studies exist evaluating the efficacy of atherectomy compared with balloon angioplasty.¹⁹^,²⁰ However, there are several theoretic advantages. Physical debulking of the atheromatous plaque compared with fracturing of the media would seem to provide better long-term patency. However, studies have demonstrated that the long-term patency obtained with atherectomy catheters is no better than that achieved with traditional balloon angioplasty.²⁰^,²¹

Complications associated with atherectomy are similar to those seen when procedures necessitate the use of large sheaths, including hematoma, dissection, pseudoaneurysm, and complications related to emboli. Additionally, complications from the atherectomy device itself may be encountered, including dissection, tissue emboli or atheroemboli, thrombosis, and vessel damage or perforation.

Imaging Findings

Preprocedural Planning

All patients undergoing atherectomy should be started on antiplatelet therapy with aspirin and clopidogrel prior to the procedure. Evaluation of previous imaging studies is mandatory to assess the lesion of interest as well as any other concomitant peripheral vascular disease. The use of distal embolic protection devices may be indicated, depending on the complexity of the lesion, the device being used, and the operator’s preference.

Postprocedure Surveillance

Patients should be maintained on antiplatelet therapy for at least 6 months. Routine postprocedural evaluation with physical examination, ABI tests, and noninvasive vascular studies should be carried out. If there is any suspicion of disease progression, a definitive imaging study should be obtained.

EMBOLIZATION

Embolization refers to the percutaneous therapeutic blockage of blood vessels to stop or prevent hemorrhage, devitalize an organ or tumor, reduce blood flow through a vascular malformation, or redistribute blood flow.

Embolic Agents and Devices

A variety of embolic agents are available, including the following:

1 Particulate agents—gelfoam, polyvinyl alcohol (PVA) particles, trisacryl gelatin microspheres

2 Mechanical occlusion devices—coils, balloons, Amplatz vascular plug

3 Liquid agents—alcohol, n-butyl cyanoacrylate, ethylene–vinyl alcohol copolymers, sodium tetradecyl, sodium morrhuate

Particulate Agents

Gelfoam

Gelfoam is composed of sterile gelatin and is the oldest embolization agent currently used. Because it is biodegradable, it is a temporary embolization agent. Gelfoam is absorbed completely and allows vessel recanalization within days to weeks. Gelfoam is available as a powder or sheet. The powder consists of small particles (40 to 60 µm) and is used for small vessel occlusions. The use of gelfoam powder is associated with a high risk of tissue ischemia and is generally not recommended. Gelfoam sheets are cut to the size required by the operator and are used to occlude larger vessels.

Polyvinyl Alcohol

Currently available particles range from 150 to 1000 µm in size and are homogeneous in size, calibrated by the manufacturer. They are not absorbable and cause near-permanent occlusion. The particles lodge at the arteriolar and capillary level, leading to luminal thrombosis. PVA particles have been extensively used for renal, liver, spleen, and uterine artery embolization.

PVA is usually administered in a mixture of contrast medium under fluoroscopy. Some PVA suspensions have a tendency to clump or float in a suspension. Frequent mixing is therefore required, otherwise clumping of the particles in the catheter or blood vessel may result in a false angiographic end point. Also, during administration, especially when there is slow flow, frequent evaluation for reflux is crucial to avoid nontarget embolization.

Trisacryl Gelatin Microspheres

These particles are hydrophilic, compressible, nonabsorbable, and precisely calibrated. They are available in various sizes, ranging from 40 to 1200 mm. They cause permanent embolization. Similar to PVA particles, they are mixed with contrast material and injected under fluoroscopic guidance. These microspheres can tolerate temporary compression of 20% to 30% to facilitate their passage through the delivery catheter.

Mechanical Occlusion Devices

Coils

Most coils are made of platinum or stainless steel. They are permanent embolic agents used to occlude a vessel or pack an aneurysm sac. Occlusion is a result of coil-induced thrombosis rather than mechanical occlusion. The thrombogenic effect is further improved by Dacron fibers attached to the coils. Coils have three variables—size of the formed coil, length of the coil wire, and diameter of the coil wire. Coils are slightly oversized to pack tightly in the vessel and help reduce the chance of coil migration. Coils are precisely positioned under fluoroscopic guidance. After placement of the first coil, additional coils are deployed until total cessation of blood flow occurs. Mechanical and electrically detachable coils are currently available that allow precise coil placement in more difficult locations.

Balloons

These are permanent embolic agents used to occlude large, high-flow blood vessels. Currently, balloons are rarely used. They have the risk of deflation and migration.

Amplatz Vascular Plug

This plug is made of thin Nitinol wire mesh formed into a plug shape. The Nitinol mesh is radiolucent and it has a platinum band on each side to serve as a marker. The device is secured to the delivery system by a single steel microscrew and is deployed by unscrewing the device from the delivery wire. The delivery system allows precise placement of the plug in the target vessel. The manufacturer recommends oversizing the devices by 30% to 50% to occlude the vessels and prevent risk of distal malposition. The plug occludes the vessel and thrombosis ensues distally because of stasis of blood flow. Often, a single plug can effectively block a blood vessel that would have required many pushable coils, which makes it a very efficient and cost-effective alternative to coils or surgery.

Liquid Embolic Agents

These agents include sclerosants, glue, and thrombin. Common sclerosant agents are absolute ethanol and sodium tetradecyl (STD). Common glue agents are cyanoacrylate and an ethylene–vinyl alcohol copolymer (Onyx Liquid Embolic System, Micro Therapeutics, Irvine, Calif).

Alcohol

This is a permanent embolic agent and is the most commonly used. It causes cell death by dehydration and is highly toxic. Ethanol is administered with contrast material and frequent check angiograms are obtained to assess thrombosis and reflux. Total occlusion of the lumen occurs within minutes. Extravasation should be avoided because this can result in soft tissue swelling and tissue necrosis. Similarly, central nervous system depression, hemolysis, and cardiac arrest can occur if a large amount of absolute alcohol enters the systemic circulation. Balloon-assisted injection of alcohol is often practiced to prevent the systemic spread of alcohol.

n-Butyl Cyanoacrylate

n-Butyl cyanoacrylate (NBCA, glue) is an adhesive that quickly polymerizes when it comes into contact with ionic solutions, blood, or intima of a vessel. Because of the rapid polymerization, coaxial catheterization, precise positioning of the delivery catheter, and considerable skill are required when NBCA is used for embolization. The polymerization can be delayed by adding lipiodol, which allows more distal embolization. When a target location is reached by using a microcatheter, the catheter is flushed with 5% dextrose to clear it of any blood or contrast medium. Under real-time fluoroscopic control, a mixture of NBCA and lipiodol is delivered. As soon as a cast of the vascular tree is seen fluoroscopically, the delivery microcatheter is quickly removed so that the catheter tip does not adhere to the vessel. Again, the catheter is flushed quickly with 50% dextrose so that it can be reused during the same procedure. A foreign body inflammatory reaction is the primary disadvantage of the use of this embolic material.

Sodium Tetradecyl

STD (Sotradecol) is less painful and less toxic than absolute alcohol. It is commonly used for vascular malformations, varices, and varicoceles.

Ethylene–Vinyl Alcohol Copolymer

Onyx is an ethylene–vinyl alcohol (EVOH) copolymer dissolved in an organic solvent and dimethyl sulfoxide (DMSO). Micronized tantalum powder is added to this mixture to make it radiopaque. When Onyx comes into contact with blood, the DMSO rapidly diffuses, leaving the EVOH to precipitate and solidify at the tip of the catheter in a shape that conforms to a lesion (e.g., an aneurysm). Unlike other liquid embolic agents, Onyx is a nonadhesive material; after it solidifies, it does not adhere to the endothelial wall, and no cases of catheter tip adherence have been documented. The disadvantage of this agent is severe vasospasm precipitated by the rapid injection of DMSO.

Onyx has been used since 1996 in the treatment of cerebral aneurysms and cerebral and peripheral arteriovenous malformations (AVMs; Fig. 86-8).

FIGURE 86-8 Right forearm arteriovenous malformation embolized with Onyx. A, Right brachial arteriogram shows an AVM (arrow) bed through branches of the radial artery. B, There is early opacification of the veins (short arrows; AVM, long arrow). C, D, This was treated with Onyx, with a favorable result.

Thrombin

Thrombin is a topical agent that induces rapid thrombosis when injected intravenously. It is commonly use to treat pseudoaneurysms. Thrombin is reconstituted in saline and contrast material may be added before instillation. Thrombosis is usually achieved within minutes and thus it is important to prevent reflux into the systemic circulation. Gentle injection of contrast material helps monitor the progress of thrombosis to ensure no washout to non-target locations. Lesions with rapid blood flow should not be treated with thrombin.

Principles of Embolization

A detailed description of various embolization procedures is beyond the scope of this chapter. Here we will briefly discuss the principles of embolization.²² When distal arteriolar or capillary embolization (as in tumor embolization) is desired, particulate or liquid embolizing agents are used. It is important to occlude all collateral supply to the tissue to achieve complete devascularization. When a distal arterial bed needs to be reperfused through collaterals (as in splenic artery embolization for splenic trauma), proximal embolization with mechanical devices is carried out. During therapy of aneurysms and pseudoaneurysms, the arterial inflow and outflow should be occluded to prevent persistent perfusion of the aneurysm. Another option is to completely pack the aneurysm sac with mechanical coils. In the treatment of arteriovenous malformations, all the branch vessels supplying the nidus or the entire nidus should be completely embolized. Arteriovenous fistulas can be treated with coil embolization of the communication or by excluding the communication with a stent graft.