General description of procedure, equipment, technique
Renal artery intervention includes:
revascularization for renal artery stenosis causing uncontrolled hypertension, loss of renal function, or cardiac destabilization with flash pulmonary edema using balloon angioplasty for fibromuscular dysplasia (FMD) and renal stents for atherosclerotic renal artery stenosis
renal denervation, an experimental procedure, employing a variety of techniques (radiofrequency, ultrasound, thermal, and pharmacological) to interrupt renal sympathetic activity to control hypertension
Indications and patient selection
Renal artery revascularization: in the presence of FMD or an angiographically defined “significant” atherosclerotic renal artery stenosis defined as either greater than 70% or a moderate (50-70%) stenosis with a greater than 10mm Hg translesional mean pressure gradient or a greater than 20mm Hg translesional systolic gradient measured with a small (<4-Fr) catheter or a 0.014-in pressure wire.
Uncontrolled hypertension (>140/90 mm Hg) defined as intolerance to medications, or failure of three antihypertensive medications, one of which should be a diuretic, to control blood pressure (JNC-7; The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure).
Ischemic nephropathy defined as worsening renal function with a significant renal artery stenosis.
Cardiac destabilization includes symptomatic coronary ischemia or heart failure, in the presence of a significant renal artery stenosis, not amenable to coronary artery revascularization.
Renal artery denervation for patients with uncontrolled hypertension in the absence of renal artery stenosis. Currently this remains an experimental procedure with definitive indications remaining to be defined.
Renal artery revascularization is contraindicated in patients in whom arterial vascular access cannot be obtained. There is a relative contraindication in patients who have life-threatening reactions to iodinated contrast material unless the procedure can be completed using an alternative guidance technique, i.e., carbon dioxide or ultrasound.
Renal artery denervation is typically contraindicated in patients with renal artery abnormalities, such as renal artery stenosis, or any known secondary cause of hypertension including a glomerular filtration rate of 45 mL/min. Patients with type 1 diabetes, hemodynamically significant valvular disease, implanted pacemakers, or implantable cardioverter defibrillators, or on a treatment that included clonidine, moxonidine, rilmenidine, or warfarin, were excluded from the initial trials.
Details of how the procedure is performed
Renal artery angiography is performed in patients with appropriate indications who have noninvasive computed tomography angiogram [CTA] and magnetic resonance angiogram [MRA] or ultrasound) evidence of moderate to severe renal artery stenosis. Patients with chronically occluded renal arteries are not considered candidates for revascularization. The patient is prepared for the procedure by fasting overnight and being premedicated with daily aspirin (81-325 mg).
Baseline laboratory values including blood counts, blood urea nitrogen (BUN)/creatinine levels, and electrolytes are obtained. Some physicians use a thienopyridine for patients likely to receive a stent, but there is no evidence to justify this practice. Depending on physician or patient preference, vascular access may be obtained in the radial, brachial, or common femoral artery.
Reasons to choose the radial access include a diminution of access site bleeding complications and early ambulation. If imaging of the renal arteries has been obtained, radial or brachial artery access is often preferred if the renal arteries are oriented cephalad for ease of engagement of the guiding catheter and stent delivery.
After access has been obtained, anticoagulation with unfractionated heparin is obtained to prolong the activated clotting time to 250 seconds. Typically the target renal artery is engaged with a long 4-Fr angiographic catheter (internal mammary, Judkins right-4, etc.) placed through the lumen of a 6-Fr guiding catheter (125 cm multipurpose from the arm, or 55 cm hockey stick or renal curve from the femoral access).
The artery is engaged with the less traumatic 4-Fr angiographic catheter, and selective diagnostic renal angiography is performed. Next a translesional gradient is measured with a pressure wire if the stenosis is moderate in severity (50-70% diameter stenosis). If a pressure wire has been used to measure a translesional gradient, it may be left in place to become the working guidewire for the intervention.
If a pressure wire has not been used, once the target lesion and its severity have been confirmed, a 0.014-inch coronary angioplasty guidewire is advanced through the 4-Fr angiographic catheter and across the renal artery stenosis. Next, the 6-Fr guide catheter is advanced over the 4-Fr angiographic catheter to the renal ostium for atraumatic engagement, reducing the risk of atheroembolism.
The 4-Fr angiographic catheter is removed. The reference diameter of the renal artery may be calculated with an on-line quantitative system and the severity of stenosis calculated. The renal artery stenosis is dilated with a monorail angioplasty balloon sized to the reference artery diameter.
The balloon is inflated to nominal pressure, or higher if a waist persists. If the patient complains of discomfort during balloon inflation, the balloon is immediately deflated to avoid potential renal artery rupture. Angiography is performed after balloon angioplasty to assess the result.
For patients with FMD, the procedure is terminated at this time with withdrawal of the wire, balloon, and catheters. For patients with atherosclerotic renal artery stenosis, primary stent placement is the procedure of choice given the significant recoil that occurs routinely after renal artery angioplasty. The postangioplasty angiogram will determine the appropriate stent size and length.
A balloon-expandable stent is then selected and deployed at nominal pressure. Again, if the patient experiences discomfort during stent deployment, the balloon is immediately deflated and smaller balloon may be chosen. An angiogram following stent deployment is performed to assess the adequacy of stent deployment and to rule out any distal edge dissections. The final step is to perform an angiogram with the guidewire removed. The catheters are removed and hemostasis is obtained at the access site.
For renal artery denervation the femoral artery is accessed with the standard endovascular technique and the SymplicityTM catheter is advanced into the renal artery and connected to a radiofrequency generator. Four to six discrete, low-power radiofrequency treatments are applied along the length of each main renal artery. Patients are given heparin to achieve an activated clotting time of more than 250 seconds prior to instrumentation of the artery. Intraprocedural pain that occurs during energy delivery is managed with intravenous anxiolytics and narcotics.
Interpretation of results
Performance characteristics of the procedure (applies only to diagnostic procedures)
Outcomes (applies only to therapeutic procedures)
For renal artery revascularization the results appear to be directly related to the indication for treatment. In general, approximately 70% of patients with renal artery stenosis treated with a renal stent will have improvement in their blood pressure. This response rate can be improved to the mid-80% range if patients are carefully selected by using translesion pressure gradients.
For patients treated to improve renal function, approximately 75% of patients will improve or stabilize and 25% will worsen. It has been presumed that atheroembolism is one of the causes of worsening renal function. For patients with flash pulmonary edema and bilateral renal artery stenosis, a response rate of greater than 90% is expected.
It is too early to conclusively determine the outcome of the experimental trials of renal artery denervation. The SymplicityTM trials have been encouraging, showing an approximately 90% response rate for hypertensive patients.
Alternative and/or additional procedures to consider
The two alternatives to percutaneous renal artery stenting include surgical revascularization or continued medical therapy. For patients with mildly obstructive disease, medical therapy for blood pressure control is appropriate. For patients with moderate to severe renal artery stenosis, stenting is preferred to surgery with comparable patency but much less morbidity.
For patients undergoing surgical repair of an abdominal aortic aneurysm, it is reasonable to surgically bypass renal artery lesions at the same time. In many hospitals including my own, even in patients undergoing abdominal surgery, percutaneous renal stent placement is the preferred therapy.
Complications and their management
Complications of renal artery stenting include vascular access bleeding complications, contrast-induced nephropathy, contrast reactions, renal atheroembolism, renal artery perforation or dissection, and acute stent thrombosis. Major complications related to renal artery stenting occur in 2 to 3% of procedures.
What’s the evidence?
Cooper, C, Haller, S, Colyer, W. “Embolic protection and platelet inhibition during renal artery stenting”. Circulation. vol. 117. 2008. pp. 2752-2760. (Clinical trial comparing four groups of patients demonstrating an interaction between 2b3a glycoprotein antagonists and embolic filter protection for renal preservation.)
Madder, RD, Hickman, L, Crimmins, GM. “Validity of estimated glomerular filtration rates for assessment of baseline and serial renal function in patients with atherosclerotic renal artery stenosis: implications for clinical trials of renal revascularization”. Circ Cardiovasc Interv. vol. 4. 2011. pp. 219-225. (An important paper demonstrating the limitations of using estimated glomerular filtration rate to determine improvement in renal function.)
White, CJ. “Kiss my astral: one seriously flawed study of renal stenting after another”. Catheter Cardiovasc Interv. vol. 75. 2010. pp. 305-307. (Editorial that points out some of the limitations of recently performed trials.)
Esler, MD, Krum, H, Sobotka, PA. “Renal sympathetic denervation in patients with treatment-resistant hypertension (the Symplicity HTN-2 trial): a randomised controlled trial”. Lancet. vol. 376. 2010. pp. 1903-1909. (Clinical trial of renal artery sympathetic denervation.)
Mangiacapra, F, Trana, C, Sarno, G. “Translesional pressure gradients to predict blood pressure response after renal artery stenting in patients with renovascular hypertension”. Circ Cardiovasc Interv. vol. 3. 2010. pp. 537-542. (Important paper on discriminating which patients benefit more after renal artery stents.)
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- General description of procedure, equipment, technique
- Indications and patient selection
- Details of how the procedure is performed
- Interpretation of results
- Performance characteristics of the procedure (applies only to diagnostic procedures)
- Outcomes (applies only to therapeutic procedures)
- Alternative and/or additional procedures to consider
- Complications and their management
- What’s the evidence?