Percutaneous Vascular Interventions

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CHAPTER 86 Percutaneous Vascular Interventions

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.

Balloons

Although the first percutaneous angioplasty was described by Dotter and Judkins2 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.

Compliant and Noncompliant Angioplasty Balloons

Compliant balloons are made of latex, silicone, or polyurethane. These balloons elongate and conform to the vessel rather than dilate as pressure is applied. They are particularly useful for temporary vascular occlusion, embolectomy, or the molding of a stent graft.

Noncompliant balloons are made of noncompliant polymers with high tensile strength. The balloon reaches a nominal predetermined diameter during inflation. These balloons are useful for angioplasty.

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.

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.

Specific Regions of Interest

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.