Endovascular Treatment of Renal Artery Stenosis

Historical Background

In 1978 Grüntzig and colleagues were the first to describe angioplasty for the treatment of atherosclerotic renal artery disease, and in 1991 early experience with balloon-expandable and self-expanding stents for treatment of renal artery stenosis was reported. Stent placement was subsequently demonstrated to be superior to primary angioplasty and has lead to a marked increase in the number of patients treated for renal artery disease, with more than 90% of all contemporary renal artery revascularization procedures being performed by endovascular techniques. In 2001 the use of a distal embolic protection device was introduced as an adjunct to renal angioplasty and stenting to decrease the adverse effects of atheroemboli.

Indications

Recent randomized clinical trials have demonstrated no benefit in renal function retrieval, blood pressure control, or survival when renal artery stent placement was compared with medical therapy alone. However, these trials were limited by inclusion and exclusion criteria that likely resulted in study groups with significant numbers of patients with only moderate renal artery stenosis and patients unlikely to benefit from revascularization. Furthermore, those data are limited in their power to examine selected patient groups thought by many experts to be more likely to receive benefit from renal artery revascularization. A significant amount of existing nonrandomized clinical trial data suggests that patients with high-grade renal artery stenosis and truly refractory hypertension, renal insufficiency with concomitant severe hypertension, and flash pulmonary edema or other cardiac disturbance syndrome may benefit from restoring renal perfusion.

Preoperative Preparation

• Warfarin is held for at least 72 hours before renal artery stenting, and intravenous bridging heparin is used as needed.

• Clopidogrel therapy is initiated 1 week before renal artery stenting and continued for at least 4 weeks after revascularization. For those who cannot tolerate clopidogrel, aspirin is used at a daily dosage of 81 or 325 mg. Data demonstrate that antiplatelet therapy reduces renal artery embolization during renal artery stenting.

• 3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, or statins, are prescribed to all patients who do not have a documented history of adverse reaction. Evidence suggests that statin therapy reduces restenosis after renal artery stenting.

• Patients should not ingest food or fluids after midnight the evening before the procedure but should shower with chlorhexidine.

• Iodinated contrast agents can lead to impaired renal function, especially in patients with diabetes, dehydration, and chronic renal insufficiency. Preoperative administration of N -acetylcysteine, vitamin C, and normal saline hydration are recommended. Sodium bicarbonate hydration is used in lieu of normal saline for patients with severe preexisting renal insufficiency, with an estimated glomerular filtration rate of less than 45 mL/min. These measures may decrease the risk of contrast-induced nephropathy.

• At the time of admission, nonsteroidal antiinflammatory, diuretics, and metformin are held to minimize the risk of deterioration in renal function.

• Agents that target the renin-angiotensin system, such as angiotensin-converting enzyme inhibitors and angiotensin receptor antagonists, are discontinued on the day of renal artery stenting and reinitiated 1 week later to minimize deleterious intrarenal vascular shunting in the setting of a hyperemic kidney after revascularization.

• Routine antihypertensive medications are taken on the morning of the procedure with a sip of water.

• A first-generation cephalosporin antibiotic, or vancomycin if the patient is allergic, is administered intravenously 30 minutes before the procedure.

Pitfalls and Danger Points

• The decision to intervene. Some anatomic variants are best treated by means other than renal artery angioplasty and stenting, including congenital renal artery stenosis, branch level renal artery disease, and disease involving multiple, small renal arteries. Initial technical success can often be achieved in these situations; however, the response to treatment both clinically and anatomically is often short lived, and renal artery angioplasty and stenting may complicate the secondary application of surgery to definitively correct the problem.

• Wire access. Translesion crossing must be intraluminal, and subintimal crossing must be avoided. This can best be accomplished by avoiding doubling back of the wire and avoidance of treating occluded renal arteries with stenting in all but the most highly select situations. Once the lesion is crossed, maintenance of guidewire position is critical until the procedure is complete. The terminal renal arteries and parenchyma are soft, and wires can easily perforate these tissues if they are allowed to migrate distally. Furthermore, angioplasty and stenting are occasionally complicated by dissection of the distal renal artery. This complication can usually be treated by additional stent placement but may be impossible to remedy if guidewire access is lost. Finally, once a stent is positioned with extension into the aorta, reaccess of the stent orifice can be challenging, making proper treatment of inadequate stent results difficult if access is lost before satisfactory completion of the procedure.

• Stent deployment. Inaccurate stent deployment can lead to permanent loss of access and occlusion of major renal artery branches if distal deployment occurs. This is best avoided by frequent angiography to optimally position the stent before deployment. The risk of inaccurate stent deployment is greatest if the lesion is nonostial or if the main renal artery is short.

Endovascular Strategy

Angiographic Anatomy

Angiographic visualization of arterial anatomy is a fundamental element of both diagnosis and endovascular treatment of atherosclerotic renovascular disease. Initial anteroposterior (AP) images of the visceral aorta are obtained using power injections of contrast through a multiside-holed flush catheter positioned just beneath the diaphragm at the level of the first lumbar vertebra. In patients with severe renal insufficiency, initial localizing views can be performed using carbon dioxide. Dilute (50%) iodinated contrast can be used for imaging purposes in the vast majority of cases. Initial AP views provide an overview of the renal artery and perivisceral aortic anatomy ( Fig. 38-1 ). Further nonselective images of the renal arteries should be obtained after repositioning the catheter to a location below the origin of the superior mesenteric artery to prevent contrast opacification of the visceral vessels that may obscure anatomic details of the renal arteries, especially the ostia. Care must be taken to identify accessory renal arteries, which may be present in up to 18% of kidneys and may not be identified during screening renal duplex sonography.

The ostia of the renal arteries usually arise from the anterolateral or posterolateral aspect of the aorta. Therefore lesions within the renal ostia are frequently not seen or may appear insignificant in an AP aortogram. Oblique aortography or oblique selective renal arteriography projects these portions of the vessel in profile and often better identifies lesions. The most useful projections to visualize the renal ostia are usually moderate ipsilateral anterior oblique views, although contralateral oblique views may also be necessary. Previously obtained axial images of the renal origins via computed tomography imaging may assist in estimating the required obliquity and thereby decrease iodinated contrast and ionizing radiation.

Lesions within the body of the renal artery may require selective arteriographic views for full delineation. Selective cannulation is usually performed using an angled catheter, such as a Cobra, Sos, renal double-curved, or inferior mesenteric catheter, in combination with a directional guidewire. Before selective renal artery cannulation, intravenous heparin is administered. Once the guidewire and catheter are gently advanced into the renal artery ostia, a hand injection of contrast should be performed to ensure an intraluminal position. Selective images can then be obtained using hand-injected angiographic images. The proximal third of the left renal artery usually courses anteriorly, the middle third courses transversely, and the distal third courses posteriorly, whereas the right renal artery pursues a more consistent posterior course. Oblique and cranial-caudad rotated images may be necessary to fully delineate lesions in these various segments.

Considerations in the Treatment of Branch Vessel Disease

Potential problems in dealing with branch vessels must be recognized when considering renovascular disease that affects a very short main renal artery, the distal main renal artery, or the branches themselves ( Fig. 38-2 ). Specifically, the risk of covering or excluding a major branch ostium is significant and must be avoided.