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Treating Popliteal Artery Aneurysms Devices and procedural recommendations for this challenging lesion subset. By Anthony C. Venbrux, MD ACCESS SITES
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 Tips & Tricks: Stent Grafts for Excluding Popliteal Artery Aneurysms Patients with bilateral popliteal artery aneurysms have a 70% chance of having a concomitant abdominal aortic aneurysm, and the overall rate of second aneurysms in patients with popliteal aneurysms is nearly 80%. The most common significant clinical event associated with popliteal artery aneurysms is thrombosis and/or embolization with resultant acute limb ischemia. Based on reports in the literature, if left untreated, the incidence of future thromboembolic events in the asymptomatic patient is high. In one series of popliteal artery aneurysms managed conservatively, only 32% of patients were without a complication at 5 years.1 Recently, use of stent grafts has received increased attention in the medical literature.2-4 Indications for use of stent grafts to treat popliteal artery aneurysms include lack of suitable vein for surgical bypass and severe medical comorbidities (such as pulmonary disease, cardiac disease, etc.), which would make the patient high risk for surgery. An absolute contraindication to the use of stent grafts is bacteremia and/or sepsis. Relative contraindications include lack of "in line" runoff vessels to the ankle/foot (ie, poor runoff arterial anatomy) and elevated creatinine levels or severe contrast allergy. In specific clinical settings, other contrast agents such as CO2 may theoretically be used. PREINTERVENTION IMAGING Ultrasound (US) is useful for confirmation of popliteal artery aneurysms and screening elsewhere in the femoral regions, pelvis, and abdomen (Figure 1). Ideally, multislice thin-section CTA should be performed, which allows preprocedural planning and gives the interventionist an accurate depiction of the patient's anatomy, including an estimate of stent graft sizes required during the procedure. For example, CTA may detect aneurysms in the common femoral arteries, iliac arteries, or abdominal aorta. Iliac artery tortuosity seen on CTA may make an "up-and-over" percutaneous approach technically impossible. MRA may be used, but sluggish flow may limit visualization of runoff vessels. Accurate location of irregular vessel wall calcification is best seen on CT and is often not well visualized on MRA. Placement of a stent graft at sites of irregular wall calcification may result in a suboptimal seal at the landing zones and inadequate aneurysm exclusions. The author has found that an antegrade puncture of the affected limb is optimal. Even an antegrade puncture may prove problematic because the common femoral artery (femoral artery) may be aneurysmal. In such a case, direct percutaneous puncture into the superficial femoral artery (SFA) may be required to avoid puncture of the femoral artery aneurysm. "Preclosure" with commercially available devices may reduce complications associated with larger punctures required for deployment of the stent graft. Initial US-guided percutaneous antegrade vascular access is used to avoid puncturing heavily calcified arterial wall segments. A 6-F vascular sheath is placed and will later be upsized. After sheath placement, the patient is administered intravenous anticoagulation (eg, bivalirudin or heparin). The activated clotting time is measured when using heparin, and the dose is adjusted appropriately. Full anticoagulation is recommended. A 6-F vascular sheath allows for baseline angiography with dilute contrast and digital subtraction technique. A catheter may be advanced down the SFA to approximately the level of the adductor canal. Detailed runoff anatomy may then be acquired with minimal contrast. Because of slow flow often seen in patients with large popliteal artery aneurysms, runoff vessels may not be optimally visualized from a groin sheath injection or on CTA or MRI. The course of the aneurysmal segment may be tortuous and require initial careful negotiation with an angled-tip catheter using road mapping fluoroscopic guidance. Once the aneurysm course has been delineated, it is useful to place a 5-F straight marker catheter to determine overall stent graft length (Figure 2). Contrast may then be injected through the 6-F vascular sheath, if necessary, with attention directed to the proximal and distal landing zones. Accurate stent graft diameter sizing is best achieved using a coronary IVUS catheter. IVUS provides detailed anatomic depiction of proximal and distal landing zones (ie, absence of heavy calcification and lumen irregularity, which may result in a type 1 endoleak). For planning purposes, it is important to try to preserve SFA collaterals (eg, the superior geniculate) or other large branches that may provide collaterals in the event of stent graft thrombosis. However, preservation of collaterals must be balanced against the risk of a type 2 endoleak that may also continue to pressurize the popliteal artery aneurysm sac. Stent Graft Placement Having sized the vessel according to the manufacturer's recommendations, the femoral artery access sheath is upsized. Appropriate stent graft segments are deployed distal to proximal (Figure 3). Ideally, a single device crosses the knee joint. Preservation of arterial blood flow through the anterior tibial, peroneal, and posterior tibial arteries is most important. Once stents have been placed, balloon dilation is used to anchor the proximal and distal landing zones, overlapping segments and intragraft stenoses. It may be necessary to use different diameter stents due to tapering of the vessels. In such cases, the smaller-diameter stents are placed distally. The larger ones are then overlapped and deployed inside the smaller diameter. Given mobility and rotation/torsion movements across the knee joint, overlap of stent grafts by several centimeters (eg, one-fourth overlap) is reasonable. Not infrequently, multiple long overlapping segments are required with post-stent graft deployment balloon dilation, especially in multilobated aneurysmal disease involving the popliteal artery and SFA. Completion angiography is performed (Figure 4). Color-flow duplex US can also be used to detect possible endoleaks, especially in patients with renal dysfunction where there is a need to minimize the use of iodinated contrast. If the completion studies document exclusion of blood flow in the aneurysm sac and no endoleaks, percutaneous or surgical arterial closure (or manual compression) is performed to achieve hemostasis. When using unfractionated heparin, the large sheath may be removed and manual pressure applied when the activated clotting time level is approximately 200 or less. The patient is generally administered a loading dose of the antiplatelet drug (clopidogrel) and started on aspirin. This drug regimen is generally administered for 3 to 6 months. Follow-Up If not already performed, a "baseline" vascular evaluation with color-flow Doppler US is performed to ensure exclusion and absence of endoleaks. Similar to the use of stent grafts for abdominal aortic aneurysms, many type 2 endoleaks will spontaneously thrombose. A type 1 endoleak at the time of completion angiography requires an additional stent graft segment (ie, "cuff") to ensure endoleak exclusion. Although not well documented, a US at 6 months and yearly thereafter for 3 to 6 months unless the clinical situation dictates otherwise is advisable. Controversies After aneurysm exclusion and before percutaneous vascular access is eliminated, a lateral view with the knee in flexion may provide an estimate of graft foreshortening (Figure 5). Should significant change of landing zone sites be noted, the stent graft may be lengthened slightly by adding a stent graft segment(s). This maneuver is controversial because it requires moving the patient's leg with large-caliber vascular sheaths in place. CONCLUSION In selected patients, placement of stent grafts for excluding popliteal artery aneurysms is a technically feasible and reasonable alternative to traditional surgical bypass. Anthony C. Venbrux, MD, is Professor of Radiology and Surgery, and Director, Cardiovascular and Interventional Radiology at George Washington University Medical Center in Washington, DC. He has disclosed that he holds no financial interest in any product or manufacturer mentioned herein. Dr. Venbrux may be reached at (202) 715-5155; avenbrux@mfa.gwu.edu. |
