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Overview of Renal Interventions and Devices
The data and tools necessary for treating renal vascular disease.
By Aravinda Nanjundappa, MD, RVT; and Robert S. Dieter, MD, RVT
Renal artery stenosis (RAS) is a relatively common disease occurring in up to 5% of hypertensive patients.1 Atherosclerosis is the leading cause of RAS. Population-based series indicate that significant RAS (defined by duplex ultrasound as 180 cm/s) is seen in 6.8% of the general population.2 A higher prevalence of RAS is noted in autopsy series. One series by Holley et al showed the prevalence of RAS (defined by diameter stenosis of 50%) to be 27%.3 Prevalence of RAS increases with age, diabetes mellitus, concomitant coronary artery disease, and aortoiliac disease.2,4-6 Among patients with coronary artery disease, significant RAS (luminal stenosis >50%) was noted in 11% to 40% of patients.7-9 RAS is noted in 40% of patients with peripheral vascular disease, especially those patients with aortoiliac disease.10
The first case of percutaneous renal artery angioplasty was performed by Felix Mahler, MD, in 1978.11 However, a few days later, Andreas R. Gruentzig, MD, performed a renal artery angioplasty for renovascular hypertension and was the first to publish.12 During the past 3 decades, several innovations have modified the technique of percutaneous balloon angioplasty.13,14 Adjunctive therapy with atherectomy, laser ablation, cryoplasty balloon, and brachytherapy failed to show superiority over renal artery stenting.15-18 Uses of distal protection devices, such as filters and distal balloon occlusion devices, have shown promising results.19
INDICATIONS FOR RENAL ARTERY REVASCULARIZATIONS20,21
The indications for renal artery stenting are hemodynamically significant RAS22 (luminal diameter >50%) with one of the following: (1) uncontrolled hypertension (systolic blood pressure >150 mm Hg while taking two blood pressure medications), (2) recurrent congestive heart failure/pulmonary edema, (3) preservation of renal function, and (4) uncontrolled angina.
Surgical Revascularizations
Initially, a flurry of surgical revascularization was noted;23 however, it is now performed less frequently. Table 1 depicts the case series of surgical revascularization21 performed for renovascular hypertension. Of 523 patients who underwent surgical revascularization for renovascular hypertension, 26% were cured, 64% had improvement, and 10% failed to improve.
The ease of percutaneous renal artery interventions (PRAIs) and lower complication rates has drastically reduced the number of cases of surgical revascularizations. The current indications21 for surgical renal artery revascularizations include (1) RAS with concomitant abdominal surgery for aneurysm repair, dissection, or aortoiliac disease; (2) RAS with uncontrolled hypertension not amenable to PRAI; (3) renal artery aneurysm not amenable to PRAI; and (4) preservation of renal function with RAS.
Surgical revascularization techniques28 include endarterectomy, aortorenal bypass with an autologous hypogastric artery, saphenous vein, PTFE graft, and hepatorenal and splenorenal bypass. Surgical revascularizations for ischemic renal disease restored renal function in selected patients.29 Despite the optimism of surgical revascularization to treat RAS, 3-year follow-up of 304 patients showed improvement in renal function in only 27%, worsened function in 20%, and no change in 50% of the patients.30
PERCUTANEOUS TRANSLUMINAL RENAL ARTERY ANGIOPLASTY
Percutaneous renal artery angioplasty (PTRA) was performed mostly in a nonrandomized fashion, and several case series were published. A review of three randomized clinical trials of 210 patients showed that PTRA, when compared to medical therapy, had minimal effect on blood pressure, and the procedure was safe, with few complications.31 Webster et al32 reported 27 patients with unilateral RAS who were randomized (13 to medical therapy and 14 to angioplasty). At 6 months, there was minimal reduction in the blood pressure and the number of antihypertensive medications. Ploulin et al33 compared medical therapy in 26 patients versus angioplasty in 23 patients. At 6 months, there was a trend in reduction of blood pressure and the number of antihypertensive medications. The Dutch Renal Artery Stenosis Intervention Cooperative (DRASTIC) study by van Jaarsveld et al34 reported 106 patients with atherosclerotic RAS (>50% stenosis) and serum creatinine <2.3 mg/dL who were randomized to medical treatment or angioplasty. At 12 months, the study concluded that balloon angioplasty had little or no benefit over medical therapy.
These trials have several limitations; a small number of patients were enrolled and, by design in the DRASTIC34 study, the PTRA group did not receive adequate medical therapy. Furthermore, 44% of the DRASTIC study medical group patients were allowed to cross over to the PTRA group. Despite the conclusion that little or no benefit was achieved, the PTRA group had better blood pressure control (68% vs 38%; P<.005) at 1 year. These clinical trials did not adequately use renal artery stents in the PTRA group. The use of renal artery stent35,36 placement improves the short- and long-term outcomes of PTRA.37,38
PERCUTANEOUS RENAL ARTERY STENTING
Dorros et al39 demonstrated the superiority of renal artery stenting over balloon angioplasty alone. A total of 21 patients underwent bare metal stenting, which significantly reduced or eliminated the obstructive renal disease. Van de Ven et al40 reported a study of 85 patients with RAS comparing stent placement to balloon angioplasty. The group with renal artery stenting had a higher success rate and better long-term patency. In an analysis of 14 clinical trials21 of renal artery stenting that consisted of 678 patients who were followed for 16 months, the technical success rate was 98%, and cure and improvement of hypertension was seen in 20% and 49%, respectively. Renal function improved or remained stable in 30% and 38%, respectively.
Despite high immediate success rates of renal artery stenting, 10% to 20% of RAS patients have deterioration of renal function.41 The postulated cause is atheromatous embolization of the plaque debris during renal artery stenting.42 Use of distal protection to capture the atherosclerotic debris and prevent atheroemboli is being pursued vigorously. Henry et al43 studied the use of distal occlusion balloon during PRAI in 56 patients with atherosclerotic RAS. At 6 months, none of the patients had worsening of their renal function; eight patients showed improvement. Recently, an NIH prospective, randomized study comparing renal artery stenting with/without the use of distal protection devices (RESIST)44 was completed. RESIST compared the outcomes of PRAI and adjunctive use of large-molecule glycoprotein IIb/IIIa inhibitors with and without distal protection devices; the results are pending. The GREAT (Palmaz Genesis peripheral stainless steel balloon-expandable stent, comparing a Sirolimus-coated vs a bare stent in Renal Artery Treatment) study compared use of drug-eluting stents versus bare metal stents in renal artery stenting. Binary restenosis defined as >50% of the in-stent narrowing and the target vessel revascularization were reduced in half.45
ADJUNCTIVE MEDICAL THERAPY
All modalities of renal artery revascularization mandate adjunctive medical therapy. Medical therapy includes aspirin, clopidogrel (after renal artery stenting), HbA1C <7.0 in diabetic patients, ACE inhibitor therapy,46 lipid therapy, tobacco cessation, and regular exercise.
DISCUSSION
The number of PRAIs performed in the US for RAS has increased rapidly in recent years.47 However, the clinical advantage of PTRA has not been proved, and the cardiovascular outcomes in terms of mortality, quality of life, and morbidity are not known. The postulated explanations are (1) despite progression of the disease, only a fraction of these patients will develop renal artery occlusion,48 (2) reduction in the renal function in the nonstented kidney and proteinuria in the stented kidney,49 (3) predictors of poor outcomes of renal artery stenting include age, diabetes mellitus, baseline renal insufficiency, and concomitant kidney disease,50 and (4) poor patient selection and difficulty in accessing the severity of angiographic RAS.51
An important clinical trial is CORAL,52 an NIH-sponsored, randomized, multicenter prospective study. CORAL is recruiting patients with clinically significant atherosclerotic RAS to optimal medical therapy versus PRAI with distal protection device plus optimal medical therapy. The patients will be followed for 5 years, and the cardiovascular outcomes will be studied.
SUMMARY
Renovascular disease carries a high morbidity and mortality rate if left untreated. Renal artery stenting is safe, has a high degree of success, and a low risk of complications. Renal artery interventions can result in worsening of renal function in 10% to 20% of patients. There are no large-scale randomized trials to prove the advantages of angioplasty compared to medical treatment. The CORAL trial will determine the benefits of renal artery intervention compared to optimal medical therapy and cardiovascular outcomes.
DEVICES USED IN RENAL ARTERY INTERVENTIONS
Access Sites
- 90% from femoral artery approach
- 10% from brachial artery approach
DIAGNOSTIC EQUIPMENT
Sheath Size
- A short 10-cm, 5-F sheath
- .035-inch, J-tipped wire
- If tortuous aorta: a long 25-cm, 5-F sheath
Catheters
- Nonselective angiogram
- 5-F, 90-cm, bright-tipped straight pigtail catheter
Selective Angiogram
- 5-F internal mammary artery diagnostic catheter or 5-F Simmons 1 curve
- If arm access, a 5-F, multipurpose curve diagnostic catheter
Diagnostic Wires
- .035-inch, J-tipped wire for placement of the catheters
- If iliac arteries are tortuous, .035-inch Wholey wire is used
- If Simmons 1 curve catheter is used, a Bentson wire is used
Diagnostic Notes
- We use a pigtail catheter as the diagnostic nonselective catheter in the majority of the cases
- If renal function permits, use isosmolar contrast at 20 mL/s for a total of 30 mL at 1,200 psi via an automated injector
- Digital subtraction with a large (at least 15 inches) image intensifier will provide quality images
- Instruction for breath holding is important
- If selective imaging is required, most of the cannulation is performed with a 5-F internal mammary artery catheter using a .035-inch J-tipped wire in a "no-touch fashion"
- Aspirate all catheters and confirm good arterial tracing on the monitor before injections
- Most of the renal artery is well visualized in a straight anterior posterior projection.
- Occasionally, a 15° left anterior oblique projection is needed to visualize the renal artery ostium
- If the lesions are intermediate <70% stenosis, a translesional gradient is measured. A translesional gradient of >20 mm Hg is considered significant
Contrast Used
- If the renal function is stable, isosmolar contrast is used
- If there is significant impairment of renal function, we use gadolinium for selective angiography
INTERVENTIONAL EQUIPMENT
Access
- Majority are femoral (90%)
- If diagnostic imaging shows a downward takeoff of renal arteries or severe aortoiliac occlusive diseases, we use brachial access
Sheaths
- 25-cm, bright-tipped, 7-F sheath
Catheters
- 7-F, short renal guide, 45-cm, internal mammary artery, hockey stick, or Judkins right curve
- 5-F internal mammary artery catheter
- .014-inch, 200-cm-long coronary steerable guidewire
Balloons
- Semicompliant balloons over the wire or rapid exchange
Stents
- Balloon-expandable stents, open cell or closed cell with thick struts
Distal Protection Devices
- Retrograde with filter or balloon occlusion system
Interventional Notes
- Do not give any heparin until the sheaths have been placed. Heparin at 70 U/kg body weight is used. Ten minutes after heparin administration, activated clotting time (ACT) is measured; goal ACT is >250 seconds
- The 7-F, short, internal mammary artery catheter with a 5-F internal mammary artery catheter is used with a .035-inch, J-tip wire in a telescoping fashion to avoid plaque embolization. Aspirate and flush all catheters before injection
- Use a .014-inch, steerable coronary wire (medium stiffness) to cross the lesions
- We use intravascular ultrasound for majority of the cases. It helps in vessel sizing, and adequate stent deployment
- We use distal protection with a filter device in all cases that have favorable anatomy
- Avoid using hydrophilic tip wires to cross lesions
- Predilation of renal arteries helps to estimate vessel size, lesion compliance, and response to balloon angioplasty
- Stents are used in 95% of the cases, except for fibromuscular dysplasia
- Balloon-expandable stents require a 1:1 ratio for vessel sizing. All ostial lesions must be covered. Use of bony landmarks is helpful. Lesions involving the midsegments of the renal artery may need self-expanding stents
- Care should be taken while re-engaging the tip of the guide catheter into the ostium of the renal artery without crushing the stent
- Poststenting images should be carefully analyzed for perforation, vessel dissection, and distal embolization
- Keep bailout equipment handy: coils for embolization, covered stents, and protamine to reverse the effects of heparin
Aravinda Nanjundappa, MD, RVT, is Director of Vascular Medicine and Peripheral Interventions, Division of Cardiology, and Assistant Professor of Internal Medicine at East Carolina University, Greenville, North Carolina. He has disclosed that he holds no financial interest in any product or manufacturer mentioned herein. Dr. Nanjundappa may be reached at dappamd@yahoo.com.
Robert S. Dieter, MD, RVT, is assistant professor of vascular, endovascular, and interventional cardiology at Loyola University in Maywood, Illinois. He has disclosed that he holds no financial interest in any product or manufacturer mentioned herein. Dr. Dieter may be reached at rdieter@lumc.edu.
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