Angioplasty and Stenting for Aortoiliac Disease: Technique and Results

History of Endoluminal Treatment

The concept of endovascular therapy of atherosclerotic occlusive disease was introduced in the 1960s when Dotter performed the first transluminal angioplasty in a patient with ischemic extremities. His novel technique, however, could not reliably maintain luminal patency and did not receive wide acceptance as a treatment of vascular occlusive lesions. Subsequent device modifications led to the development of an angioplasty balloon composed of latex material. The clinical success of this new construct was limited, in part because of its improved compliance, and could not fully dilate a calcified lesion. The introduction of an angioplasty balloon made of polyvinyl chloride in 1976 by Gruntzig and Hopff, followed by rigid balloons composed of polyethylene and polyethylene terephthalate, marked a significant advance in endovascular therapy. The latter angioplasty balloons displayed a low compliance and high radial force in a fully inflated condition. As the technology and techniques of endovascular therapy continued to improve and become more widely accepted as outcomes data became available, transluminal balloon angioplasty evolved to an important modality in the treatment of peripheral vascular disease.

Despite numerous studies demonstrating the short-term clinical success of transluminal angioplasty, it has several limitations, in part because of the architectural variation of atherosclerotic lesions. Early restenosis or occlusion following angioplasty can occur because of elastic recoil of the arterial wall or intimal dissection. Vessels that are heavily calcified, completely occluded, or that contain ulcerated plaques might not be amenable to balloon angioplasty. Moreover, residual luminal irregularities following angioplasty occasionally trigger mural thrombus formation, leading to thrombotic occlusion. Late restenosis following angioplasty can occur as a result of intimal hyperplasia or atherosclerotic progression.

In an effort to improve the results of transluminal angioplasty, researchers proposed the concept of intravascular stents as a means of maintaining vessel patency against the restenotic process and improving the clinical outcome of balloon angioplasty. Since Dotter first reported his successful deployment of intravascular stents in canine femoral and popliteal arteries in 1969, a variety of stent devices composed of various materials have been introduced. Intravascular stenting is recognized as a potentially effective modality in overcoming elastic recoil of the arterial wall, stabilizing intimal dissection at the site of angioplasty, and maintaining the luminal patency of arteries with calcified and eccentric atherosclerotic plaques.

Classification of Aortoiliac Occlusive Disease

The 2000 Trans-Atlantic Inter-Society Consensus (TASC) guidelines were developed to assist physicians in the management of peripheral arterial disease. The classification of inflow of aortoiliac lesions was updated in 2007 as TASC II to reflect the advances in endovascular technology. General guidelines included in the TASC II document state that lesions classified as TASC A ( Table 24.1 ) should be treated preferentially with endovascular techniques, whereas lesions classified as TASC D should be treated preferentially with open surgery. The recommendations for lesions classified as TASC B or C are not as clear. Good surgical judgment including surgical experience, available technology, and patient overall health needs to be considered when deciding on the appropriate initial treatment plan.

General Principles of Endoluminal Stents

The desired characteristics of an intravascular stent depend on the anatomic placement and lesion characteristic for which it will be used. In general, the optimal stent needs to be encased in a low-profile device to cross high-grade lesions, and the stent should be deployed easily and accurately. Flexibility and durability are important characteristics that need to be combined with a low thrombogenic nature and high radial force. Moreover, the stent should have noticeable radiographic opacity to facilitate visualization. Finally, the ideal stent would be biocompatible, to promote endothelialization without causing intimal hyperplasia.

Intravascular stents can be separated into three distinct types: self-expanding stents, balloon-expandable stents, and covered stents ( Table 24.2 ). Within each of these categories, there are numerous stents with different structural materials, deployment devices, and biocompatible characteristics. In addition, there are many stents undergoing clinical trials. Table 24.3 lists the commercially available stents that can be used to treat aortoiliac occlusive disease with the US Food and Drug Administration (FDA) indication status. Some stents are tested and marketed in noniliac positions but have found use in the clinical world for arterial occlusive disease. Additionally, medicated stents and drug-coated balloons have been approved for arterial occlusive disease but are currently FDA approved only for iliac lesions. The Bard Lutonix balloon catheter (Bard Peripheral Vascular, Tempe, Arizona) and the Impact Admiral balloon catheter (Medtronic Vascular, Santa Rosa, California) have also been approved to treat superficial femoral artery (SFA) lesions, but they have also been reported for use in the iliac arteries.

Self-Expanding Stents

Self-expanding stents are generally manufactured so that the stents are constrained within a delivery sheath. The prosthesis is placed intravascularly through an introducer sheath that is advanced over a guidewire for deployment. Deployment is achieved by withdrawing the constraining sheath while keeping the stent in position, thus permitting the stent to self-expand and anchor to the vessel lumen ( Fig. 24.1 ). Stents in this category are generally noted for their ease of deployment and high degree of flexibility for meandering around the curves typically found in an iliac artery. These characteristics are advantageous because self-expanding stents can be used across arteries of varying diameters, specifically from the common to the external iliac. Compared with balloon-expandable stents, however, they may have lower radial force, or resistance to radial compression. These stents require oversizing by 2 to 3 mm to maintain outward radial force after deployment. Most self-expanding stent delivery systems have a smaller diameter compared with those of balloon-expandable stents. In addition, the Wallstent and the Gianturco-Z stent (Cook, Bloomington, Indiana) are available.

Another type of self-expanding stent is the nitinol stent, which was first introduced by Dotter and colleagues in 1983. Nitinol is a nickel-titanium alloy that has a unique temperature-associated memory property. The nitinol wires can be shaped into a coil spring configuration to serve as a stent when heated to 500°C. As it cools down to 0°C, the nitinol coil straightens into a linear alignment that can be constrained into a delivery catheter for stent deployment. The exposure to warm body temperature after deployment causes the nitinol stent to resume its original coil spring shape. Several clinical studies have evaluated the application of these stents in vascular occlusive lesions.

Balloon-Expandable Stents

The balloon-expandable stent is first mounted and compressed onto an angioplasty balloon. The original stents were all operator mounted; newer stents are premounted by the manufacturer. Once the stent is positioned intraluminally, it is deployed by inflating the balloon to expand the stent ( Fig. 24.2 ). Unlike a self-expanding stent, the balloon-expandable stent can be expanded beyond its nominal diameter by using a larger angioplasty balloon catheter. Most balloon-expandable stents are characterized by excellent radial strength because of intrinsic stent rigidity once deployed, which can be advantageous in treating stenotic vessels containing calcified plaques. The rigid property of such a stent, however, can create a technical dilemma when treating lesions in tortuous vessels. Moreover, it makes a contralateral approach for iliac artery stenting a challenge, although newer stents are more trackable and flexible.