Percutaneous Vascular Interventions

Published on 25/02/2015 by admin

Last modified 25/02/2015

Print this page

This article have been viewed 2449 times

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.