Anatomical and Functional Criteria

Patient selection for catheter-based vascular intervention depends upon both anatomical and functional criteria (Table 20-2). Anatomical lesion criteria include ability to gain vascular access, a reasonable likelihood of crossing the lesion with a guidewire, and the expectation that a therapeutic catheter can be advanced across the target lesion (Fig. 20-1). A strategy of “provisional” (bailout) stenting, or use of a stent for a failed balloon dilation attempt (in contrast to “primary” stenting, in which stents are placed with or without balloon predilation), has become the standard of practice for shorter, more discrete lesions. Longer lesions and occlusions are better treated with primary stent placement.^3,5–8

Figure 20-1 A, Tight stenosis of infrarenal aorta amenable to angioplasty. B, Final postangioplasty result.

Availability of endovascular stents (balloon expandable and self-expanding) has significantly extended the anatomical subset of patients who may be considered candidates for peripheral vascular intervention, particularly for longer stenotic lesions and occlusions. The rate-limiting step for nonsurgical revascularization of the aortoiliac vessels is the ability to pass a guidewire across the lesion. Regardless of the balloon dilation result, the option of stent placement offers a reliable and reproducible method to recanalize these large vessels.⁹

Vascular access site complications following catheter-based procedures often can be treated with percutaneous therapy¹⁰ (Fig. 20-2). Patients with hypotension and a high suspicion of bleeding after common femoral artery (CFA) access require urgent diagnostic angiography from the contralateral femoral artery to determine the bleeding site. Rapid identification of the bleeding site may provide an opportunity for lifesaving hemostasis with balloon tamponade.

Figure 20-2 Access site complication with bleeding (A) successfully tamponaded with balloon inflation (B), and final angiogram showing hemostasis.

Functional criteria to select patients for peripheral endovascular revascularization typically include lifestyle- or vocational-limiting symptoms of claudication, critical limb ischemia (CLI; rest pain, nonhealing ulcers, or gangrene), or acute limb ischemia. Asymptomatic patients with anatomically suitable iliac artery lesions may be considered candidates for peripheral vascular intervention to facilitate vascular access, such as for intraaortic counterpulsation balloon placement or for vascular access to perform coronary intervention.

Patients with lifestyle-limiting symptoms of classical claudication or atypical claudication should first have an attempt at pharmacological therapy with cilostazol and supervised exercise training before endovascular intervention is attempted. If exercise training and pharmacotherapy are not effective, if patients are intolerant of cilostazol or cannot be treated with the drug because of heart failure (black box warning), or if a supervised exercise program is unavailable, an attempt at endovascular intervention is appropriate. In general, patients with claudication progress to limb loss at a rate of well under 5% per year, so endovascular revascularization is reserved for those patients with favorable anatomy who either fail conservative therapy and have lifestyle-limiting symptoms or have vocational-limiting symptoms. Therapeutic goals for claudicants are symptom relief, increased walking distance, and improved functionality and quality of life. For this reason, durability of the procedure becomes important; recurrent ischemic symptoms require repeated procedures.

Patients with CLI or limb-threatening ischemia (gangrene, nonhealing ulcer, or rest pain) are candidates for urgent revascularization. When considering a patient with CLI for revascularization, it is important to remember that multilevel disease (iliac, femoral, and tibial) is likely to be present and that simply improving “inflow” without addressing the more distal vascular lesions or runoff vessels may fail to solve the clinical problem. Patients with CLI (rest pain, nonhealing ulcers, or gangrene) typically have more extensive disease than claudicants and require urgent revascularization to prevent tissue loss^3,11 (see Table 20-2).

Prognosis for patients presenting with CLI is poor.¹² Those with tobacco abuse and/or diabetes are 10 times more likely to require amputation. Patients with CLI tend to be older, with almost 50% of patients older than 80 years undergoing amputations. Within 3 months of presentation, 12% will require an amputation, and 9% will die; 1-year mortality rate is 22%. Anatomy suitable for endovascular therapy is often present in one or more below-knee vessels. Therapy should be designed to restore pulsatile straight-line flow to the distal part of the limb, with as low a procedural morbidity as possible. The guiding principle is that less blood flow is required to maintain tissue integrity than to heal a wound, so restenosis does not usually result in recurrent CLI unless there has been repeated injury to the limb. Therefore, the emphasis is less on long-term vessel patency and more on amputation-free survival.

The Bypass versus Angioplasty in Severe Ischaemia of the Leg (BASIL) trial was a multicenter randomized trial comparing an initial strategy of balloon angioplasty to open surgery in 452 patients with CLI.¹³ The primary outcome was time to amputation or death (amputation-free survival). After 6 months, the two treatment strategies did not differ significantly in amputation-free survival. There was no difference between the groups for quality-of-life outcomes, but for the first year of follow-up, costs associated with a surgery-first strategy were higher than for angioplasty. For this reason, the authors concluded that a percutaneous-first strategy was the treatment of choice in patients who are candidates for either surgery or endovascular intervention.

General Measures

Prior to performing peripheral endovascular intervention, the patient should have a complete cardiovascular evaluation, with specific attention directed to the status of atherosclerotic risk factors. Atherosclerosis is a systemic disease, and appropriate risk-factor modification (tobacco-cessation counseling, treatment of lipids to target values), screening tests for cardiovascular diseases, and optimization of medical therapy should be performed.

Prior to performing lower-extremity endovascular intervention, it is necessary to objectively determine the patient’s functional status. A history, physical examination, and appropriate noninvasive testing should be obtained prior to planning peripheral endovascular revascularization. If the patient is ambulatory, a rest and exercise ankle-brachial index (ABI) should be measured, and pulse volume recordings (PVR) should be performed. Other noninvasive modalities, such as vascular ultrasound, or alternative imaging modalities, such as magnetic resonance angiography (MRA) or computed tomographic angiography (CTA), may be helpful to resolve conflicting data and are used at the discretion of the physician (Fig. 20-3). When planning lower-extremity revascularization, status of the inflow and outflow vessels relative to the target lesion must be visualized angiographically. This is usually done with invasive diagnostic angiography, but in selected patients, MRA or CTA may be very useful.

Figure 20-3 Computed tomographic angiogram (CTA) of lower-extremity vasculature.

There is occlusion of arterial segments of the right femoral, popliteal, and tibial segments.

Premedication

The only premedication requirement for peripheral endovascular intervention is aspirin therapy (81-325 mg daily). Use of other antiplatelet agents is optional, since there is no evidence that their use improves procedural success or decreases complications. If the patient is intolerant to aspirin, a thienopyridine drug would be appropriate. There is no evidence supporting use of dual antiplatelet therapy after peripheral endovascular intervention or following peripheral vascular stent placement.

Anticoagulation

There is no standard for anticoagulation therapy, except to state that intravenous unfractionated heparin (UFH), in a dose up to 5000 International Units, is commonly used to achieve an activated clotting time (ACT) of 250 to 300 seconds. At present, there is no evidence that use of glycoprotein (GP)-IIb/IIIa platelet receptor antagonists, low-molecular-weight heparins, or antithrombins improve procedural efficacy or safety for peripheral vascular intervention.

Vascular Access

The first step to ensure a successful procedure is to plan appropriate vascular access. The majority of peripheral endovascular intervention can be performed from multiple arterial access sites (i.e., radial, brachial, femoral, or popliteal arteries). However, cases occasionally require a specific access to achieve a successful result. Consequently, familiarity with a variety of vascular access sites and techniques is one of the most important components of the basic skill set. Ability to gain both retrograde and antegrade common femoral access is a required skill for the interventionalist. An infrapopliteal target lesion may be best approached with antegrade femoral access, whereas a proximal superficial femoral artery lesion may require a contralateral retrograde femoral approach. Occasionally, bilateral retrograde femoral artery access is desirable—for example, when treating a common iliac bifurcation lesion.

Guidewires

Trade-offs include smaller catheters with crossing lower profiles, smaller sheath sizes, and increased flexibility for the smallest 0.014-inch systems, which must be balanced against the increased support and pushability of the larger-profile 0.035-inch systems. It is most common that 0.014-inch systems are used for below-knee intervention where the vessels are smaller, compared to the usual 0.035-inch systems used for the larger balloons and stents placed in the iliac vessels. It is recommended that the interventional laboratory be stocked with several redundant lines of equipment to allow for flexibility in the approach to difficult or complex lesions. In general, the lowest profile system within the smallest vascular access sheath should be used.

Use of coated “glidewires” should be carefully restricted to instances when their unique properties are necessary because these wires are more difficult to control than conventional guidewires and are prone to vascular perforation. Their lack of a “transition point” makes them ideal for negotiating abrupt angles and crossing occlusions. Ideally, once they have crossed the occlusion, it is wise to exchange this potentially dangerous wire for a safer and more controllable wire.

Balloon Catheters

A wide variety of monorail and over-the-wire balloon catheters are available that are suitable for dilating lower-extremity lesions. They come in a variety of diameters, with balloon lengths up to 15 cm. A pressure manometer is recommended to monitor balloon inflation pressure. Although no optimal inflation pressure or duration has been determined, it is generally recommended that the balloon be inflated with adequate pressure to ensure full expansion of the lesion.

Stents

The two categories of stents are balloon expandable and self-expanding. Both types may be covered with material. Balloon expandable stents are intended for use within the axial skeleton to protect them from external compression. This generally limits their use to the iliac arteries, but coronary balloon expandable stents are used to salvage failed angioplasty results in below-knee vessels.^14,15

Balloon expandable stents can be deployed with more precision than self-expanding stents, although there is some shortening associated with their expansion. Self-expanding stents resist permanent deformation and are elastic. Their flexible nature allows them to delivered in longer lengths, and they will fit themselves to a tapering artery. Self-expanding stents may be made of nitinol or a stainless steel alloy. At this time, there is no evidence that either material is associated with any safety or efficacy advantage.^16,17

Adjunctive Devices

Other adjunctive devices, such as laser catheters, atherectomy catheters (rotational and directional), brachytherapy catheters, cryotherapy balloons, and cutting balloons have been developed, tested, and aggressively marketed. With the possible exception of the brachytherapy devices, there is no comparative evidence that these adjunctive devices bring any added value, efficacy, or increased safety over balloons and stents when treating lower extremities.