Lower Extremity Interventions

Ankle-Brachial Index

The ABI is a ratio of the blood pressure in the dorsalis pedis or the posterior tibial artery, whichever is higher, to the blood pressure in the brachial arteries. ABI measurement is one of the most cost-effective methods for assessing PAD of the lower extremity, and it typically is done with a handheld Doppler ultrasound device. This is a noninvasive, fairly reproducible, and inexpensive test. The resting ABI should be used to establish the lower extremity PAD diagnosis in patients with suspected lower extremity PAD, defined as individuals with one or more of the following: exertional leg symptoms, nonhealing wounds, age 65 and older, or 50 years and older with a history of smoking or diabetes. The ABI should also be measured in both legs in all new patients with PAD of any severity to confirm the diagnosis of lower extremity PAD and establish a baseline. ABI results should be uniformly reported: noncompressible values are defined as greater than 1.40, normal values are 1.00 to 1.40, borderline is 0.91 to 0.99, and abnormal is 0.90 or less. The most widely accepted definition of lower extremity PAD is a resting ABI of less than 0.9, which is usually associated with 50% or greater angiographic arterial stenosis with a reported sensitivity of 95% and close to 100% specificity. A resting ABI of 0.4 to 0.9 is suggestive of mild to moderate PAD, and a resting ABI below 0.4 is suggestive of severe PAD ( Table 39.2 ). Resting ABI measurement can be artifactually high in the setting of tibial artery calcification usually seen in diabetics. The toe-brachial index (TBI) should be used to establish a diagnosis in patients in whom lower extremity PAD is clinically suspected but in whom the ABI test is not reliable because of noncompressible vessels (usually patients with long-standing diabetes or advanced age). A TBI below 0.7 is considered abnormal.

The use of exercise ABI may be helpful in equivocal cases. For this, the patient walks on the treadmill at a constant speed of 1 to 2 miles per hour and at a 10% to 12% incline for 5 minutes, or the exercise can be done with active pedal plantar flexion. A decrease of at least 15 mm Hg in the ankle systolic pressure following the exercise challenge is considered an abnormal test. Patients with no significant PAD are expected to have an increase or no change in their ankle systolic pressure. Exercise treadmill tests may also be performed in individuals with claudication who are to undergo exercise training (lower extremity PAD rehabilitation), so as to determine functional capacity, assess nonvascular exercise limitations, and demonstrate the safety of exercise.

Pulse Volume Recording

Plethysmography is used to detect volumetric changes in the lower extremity blood flow and is performed with pressure cuffs inflated to 60 to 65 mm Hg at various segments of the lower extremity. A normal tracing will have a rapid systolic upstroke and downstroke with a prominent dicrotic notch. This pattern changes as PAD develops and progresses, with a noted attenuation and widening of the arterial waveform. Ultimately, the waveform becomes flat (nonpulsatile) in patients with advanced PAD ( Fig. 39.2 ). Pulse volume recordings are reasonable to establish the initial lower extremity PAD diagnosis, assess localization and severity, and follow the status of lower extremity revascularization procedures.

Segmental Blood Pressure

For this test, a series of blood pressure cuffs are placed at the level of the thigh (one or two cuffs), calf, ankle, foot, and the big toe. These cuffs are then inflated sequentially to about 20 mm Hg above the systolic pressure in that segment. The cuff pressure is then released slowly, and a continuous-wave Doppler probe is used to obtain the pressure at each segment. A decrease between two consecutive levels of 30 mm Hg or more indicates the presence of a stenosis in the segment proximal to the blood pressure cuff. Also, the presence of a 20- to 30-mm Hg difference in the pressure at one limb, when compared with the contralateral limb at the same level, is suggestive of significant PAD proximal to the cuff in that limb.

Duplex Ultrasonography

Duplex ultrasound uses a 5- to 7.5-MHz transducer to assess and characterize suprainguinal and infrainguinal PAD with a high sensitivity and specificity (over 90%). Doppler velocities are obtained (60-degree Doppler angle) to complement two-dimensional ultrasonography. Traditionally, arteries are classified into five categories based on the degree of stenosis: category 1 is considered normal, 2 indicates stenosis of 1% to 19%, 3 is stenosis of 20% to 49%, 4 indicates 50% to 99% stenosis, and 5 signifies total occlusion. Duplex ultrasonography may be useful to operators in planning access to a lesion that is amenable to endovascular therapy. It is also very helpful in identifying iatrogenic traumatic lesions and pseudoaneurysms. Direct ultrasound-guided compression or thrombin injection to repair femoral artery pseudoaneurysms is widely used in treating such lesions without the need for surgical procedures. One important limitation of Duplex ultrasonography is that it may overestimate residual stenosis following interventions, which limits its usefulness as a follow-up tool in this setting. Duplex ultrasound is recommended for routine surveillance after femoral-popliteal or femoral-tibial-pedal bypass with a venous conduit. Minimum surveillance intervals are approximately 3, 6, and 12 months and then yearly after graft placement.

Computed Tomography Angiography

The use of spiral computed tomography angiography (CTA) in assessing lower extremity PAD has 93% sensitivity and 96% specificity in detecting greater than 50% stenosis with high accuracy when compared with digital subtraction angiography (DSA). A systematic review and meta-analysis suggested that CTA is highly accurate for assessment of PAD in detecting stenosis of the aortoiliac and femoral arteries. However, diagnostic accuracy of CTA in below-knee vessels is poor and contrast angiography should be considered where below-knee disease needs to be accurately identified. CTA correctly identified hemodynamically significant lesions and also accurately distinguished between greater than 50% stenoses and occlusions. Ninety-four percent of occlusions and 87% of nonoccluded segments with more than 50% stenosis detected by contrast angiography were correctly identified by CTA. The accuracy of CTA may potentially be even higher than reported in this study because all studies used contrast angiography as the reference standard but did not report whether biplanar views were used routinely. Because CTA reconstructions allow three-dimensional (3-D) assessment, significant disease may be detected by CTA but may not be recognized by angiography, which may lead to the underestimation of specificity. CTA has advantages over magnetic resonance angiography (MRA) in patients with pacemakers and defibrillators and in those with metal clips, stents, or prosthesis (no significant artifact is seen in CTA as opposed to MRA), and it is significantly faster to perform than MRA. However, CTA requires the use of iodinated contrast, and it entails exposure to ionizing radiation. Dose-saving algorithms are very effective in reducing radiation exposure and should be used whenever possible.

Magnetic Resonance Angiography

The use of gadolinium-enhanced magnetic resonance angiography (GEMRA; Fig. 39.3 ) in the assessment of lower extremity PAD has been compared with standard catheter angiography, with a reported sensitivity and specificity for detecting stenosis greater than 50% of about 90% and 100%, respectively. Most contemporary studies report an agreement of 91% to 97% between MRA and catheter angiography. GEMRA is superior to duplex ultrasound in detecting greater than 50% stenotic lesions (sensitivity of 98% vs. 88% and specificity of 96% vs. 95%).

Limitations of this technology include the tendency to overestimate the severity of stenosis and the fact that metal clips may give the impression of total occlusion, and metal stents can obscure vascular flow as well. In addition to these limitations, certain subsets of patients may not be able to be studied with MRA, such as those with pacemakers and defibrillators and those with certain types of cerebral aneurysm clips. The principle role of MRA is in the initial evaluation for PAD, especially in patients with inflow disease, using “bolus chase” 3-D imaging, in which a single bolus of contrast is followed to the foot.

Contrast Angiography

Despite recent advances in noninvasive evaluation of lower extremity PAD, contrast angiography remains the gold standard. Traditionally, a pelvic/abdominal aortogram in the anteroposterior projection is done using a straight pigtail catheter (5 or 6 Fr) placed at the level of the L1-L2 vertebrae. Approximately 10 to 15 mL of isoosmolar contrast is injected at a rate of 15 mL/s with DSA technology. This allows an excellent view of the distal aorta, the origin of the common iliac arteries, and the external iliac and common femoral arteries. Angulated views (left anterior oblique [LAO] of 30 degrees) can then be used to visualize the iliac and femoral bifurcations without overlap. Next, the pigtail catheter is placed above the aortic bifurcation (L3 to L4) and DSA with bolus chase, 8 mL/s for 10 seconds, is used to assess the outflow and distal runoff. Selective injections and sheath injections can then be used to further define the territory of interest as needed. The use of “road map” technology can be used subsequently to help operators in their intervention and placement of balloons and stents. Contrast angiography remains the most readily used and widely available imaging technique in patients with PAD of the lower extremity when revascularization is contemplated. The use of noninvasive technologies, such as MRA or CTA, may be used prior to contrast angiography to help identify the potential culprit lesion and plan the best approach (access point, catheter selection, etc.) to study such a lesion invasively. Contrast angiography may be associated with vascular access complications (bleeding, infections, pseudoaneurysms, and vascular disruption), atheroembolism, contrast nephropathy, and contrast-induced anaphylactoid reactions. These complications, although rare, should be considered in the decision-making process with regard to the assessment of PAD.

Overall, contrast angiography provides detailed information about arterial anatomy and is recommended for evaluation of patients with lower extremity PAD when revascularization is contemplated. When conducting a diagnostic lower extremity arteriogram in which the significance of an obstructive lesion is ambiguous, transstenotic pressure gradients and supplementary angulated views should be considered.

Indications

The indications for iliac artery (or aortoiliac) percutaneous intervention include (1) symptom relief in patients with IC who failed medical therapy; (2) management of CLI (rest pain, ulceration, or gangrene) prior to a planned distal lower extremity bypass surgery to restore or to preserve the inflow to the lower extremity; (3) in preparation for other invasive procedures, such as the placement of an intraaortic balloon pump (IABP); and (4) for treatment of flow-limiting dissection following invasive catheterization-based procedures.

Revascularization Options

Occlusive disease confined to the iliac arteries appears to occur in relatively young patients and may therefore have a greater impact on productivity and lifestyle. For instance, the mean age of the cohort in the Dutch Iliac Stent Trial was approximately 59 years. These patients, over 90% of whom were smokers, were otherwise healthy compared with those with infrainguinal disease or more diffuse PAD. In general, any type of revascularization for this subset of patients can offer satisfactory long-term results. Historically, aortobifemoral bypass surgery has been the gold standard for PAD that involves the iliac arteries, because this procedure is associated with excellent long-term patency rates (85% to 90% at 5 years, 75% to 80% at 10 years, and 60% at 20 years); however, it may be associated with an intraoperative mortality of roughly 1% to 3% and a major complication rate of 5% to 10%. This, combined with the excellent intermediate- to long-term patency rates following percutaneous intervention, has led to the emergence of percutaneous revascularization as an attractive alternative to surgery in patients with suitable lesions for such intervention. In a Swedish randomized controlled trial (RCT) in which 37% of randomized patients had iliac artery stenosis, equivalence in outcomes was evident between percutaneous transluminal angioplasty (PTA) and surgery. In the iliac disease subgroup, the patency rate at 1 year was 90% in the PTA arm versus 94% in the surgical arm. Table 39.3 summarizes the recommendation of the Trans-Atlantic Inter-Society Consensus (TASC) working group for the revascularization strategy of iliac lesions. The TASC group classifies peripheral arterial lesions into Type A, B, C, or D according to anatomic distribution, number and nature of lesions (stenosis, occlusion), and according to the overall success rates of treating the lesion percutaneously or surgically.

Techniques

Access and Recanalization Techniques

In patients with a unilateral stenotic iliac lesion that does not involve the CFA, ipsilateral access through the CFA with retrograde PTA is usually preferred because it provides direct access to the diseased segment and provides a coaxial alignment of the equipment ( Fig. 39.4 ). Contralateral access with the use of a crossover sheath is reserved for patients with disease that involves the ipsilateral CFA ( Fig. 39.5 ) when the surgeon plans to intervene on more distal lesions in the same limb or when jeopardizing flow to the affected limb by placement of the sheath in the ipsilateral CFA is a concern. Various crossover sheaths are available; the ArrowFlex sheath (Arrow International, Reading, PA) is more flexible and can be helpful in crossing over acute aortic bifurcation angles, but it provides less support than the Flexor Ansel, Raabe, and Balkin sheaths (Cook Medical, Bloomington, IN); these provide more support but are less compliant. If the iliac artery is occluded, both approaches may be needed. For aortic bifurcation lesions, a bilateral retrograde approach is used; the placement of kissing balloons—and, subsequently, kissing stents—is the optimal approach in this setting.

In lesions distal to the aortic bifurcation (in the body of the common iliac artery or the external iliac artery), PTA is attempted, and if satisfactory results are achieved (<5 mm Hg residual gradient and <30% residual stenosis with no flow-limiting dissection), stenting may not be indicated. However, ostial lesions of the common iliac arteries (i.e., aortoiliac bifurcation lesions) are preferably stented with kissing stents. In general, 0.035-inch guidewires are used in PTA and in stenting of the iliac arteries, but 0.018- or 0.014-inch guidewires may be used as well. In nonocclusive lesions, a regular nonhydrophilic guidewire can be used; however, if crossing such lesions is difficult, the use of a hydrophilic wire is indicated.