Tips and Tricks of RAS for High-Risk Patients
Before treating renovascular hypertension or ischemic nephropathy, there are a few things you should know.
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The techniques described in this article have evolved over nearly 25 years of experience. They concentrate on two major goals, which are particularly relevant in the atheromatous patient with compromised renal function: (1) limiting the amount of nephrotoxic iodinated contrast medium; and (2) limiting and simplifying the manipulations in the diseased abdominal aorta and renal arteries.
Aortography demonstrates the presence, location, and extent of atheromatous disease in the aorta and the renal artery, and it also allows for planning the renal artery intervention. Arteriography should begin with an aortogram, and never with selective catheterization in a potentially very diseased aorta. If a proximal/ostial renal artery stenosis is found, selective catheterization is contraindicated, unless an intervention is planned, in which case pressure measurements must be obtained prior to intervention.
The minimum pressure gradient that justifies intervention (using a 4-F catheter) is:
• ≥ 10% peak systolic arterial pressure, or
• ≥ 5% mean arterial pressure
A previous MRA or CTA is very helpful in determining the optimal obliquity for performing diagnostic aortography for renal artery disease (Figure 1).1 Aortography, angioplasty, and stent deployment in the right renal artery is generally performed in the 20º to 30º LAO projection because the right renal artery usually arises approximately 30º ventrally to the "equator" of the aorta and in the AP projection for the left renal artery, which usually originates directly laterally at the "equator."
We use the OmniFlush (AngioDynamics, Queensbury, NY) catheter for aortography because its design prevents cephalad reflux into the celiac and superior mesenteric arteries, which can overlap the renal arteries and also "steal" contrast from the desired areas of interest. Because the renal arteries originate at the L1 vertebral body, the sideholes of the catheter are positioned at the T12–L1 interspace.
As many of these patients have marginal or poor renal function, we try to limit the total amount of iodinated contrast medium. Nephrotoxicity is primarily due to the iodinated part of the contrast molecule; therefore, we use “half-strength” 30% concentration (150 mg I/dL) contrast medium and perform aortography using only 15 mL total volume injected at 15 mL/sec. If the renal artery origins are not satisfactorily demonstrated with the “half-strength” contrast, a targeted repeat aortography can be performed at the now precisely known level of the renal arteries using only 5 mL to 10 mL of “full-strength” contrast.
SELECTIVE RENAL ARTERY CATHETERIZATION
We identify the location of the renal artery and the stenosis in relation to the bony landmarks (spine and ribs) and calcifications in the aorta; the renal artery is visualized using a nonsubtracted aortogram image displayed on a television monitor or as hard copy on a view box.2 We use a SoftVue (soft-tipped) Sos Omni Selective (AngioDynamics) catheter for selective catheterization of the renal artery and for crossing stenoses (Figure 2). This "recurve" design is similar to the Simmons-type configuration, but it has a shorter side arm and is significantly easier and less dangerous to reconstitute its shape. We do not perform contrast test injections during catheterization of the renal artery. Selective catheterization of the stenotic renal artery is performed with the image intensifier in the oblique projection where the origin ("nubbin") of the renal artery is en face.
With its soft, floppy "Bentson"-type guidewire extending approximately 1 cm from the catheter tip, the SoftVue Sos Omni Selective catheter is slowly advanced cephalad with the tip pointed laterally toward the origin of the renal artery. This maneuver deflects the tip of the wire parallel to the aortic wall, pointing slightly toward the lumen. When the funnel-shaped nubbin of the stenotic renal artery is reached, the wire will readily enter it with a lateral flick, at which point it can be gently advanced across the lesion. This maneuver diminishes the volume of contrast used for the diagnostic and therapeutic interventions.
Most occluded renal arteries also have a funnel-shaped origin several millimeters in length proximal to the occlusion, which can be identified and entered as described previously for stenoses; if no nubbin is identified, percutaneous recanalization cannot and should not be attempted. For crossing occlusions, we initially use a straight hydrophyllic guidewire, which is forced (pulled) against the funnel-shaped nubbin of the occluded renal artery by the stiffer AngiOptic version of the Sos Omni Selective catheter.
As soon as a catheter is successfully advanced across the occlusion, its intraluminal position must be documented by hand injection of a small amount of contrast. The hydrophyllic wire should be exchanged out for a nonhydrophyllic wire as soon as is practical, because hydrophyllic wires are more likely to produce iatrogenic vessel perforation, or be withdrawn from the vessel inadvertently. After successfully crossing the lesion, the transstenotic pressure gradient must be documented. In the presence of a significant gradient, the soft guidewire is exchanged for a stiffer wire, such as the TAD II (Mallinckrodt, St. Louis, MO), which can be precurved to fit the course from the aorta into the renal artery. The diagnostic catheter is then exchanged for a device for angioplasty or stenting.
RENAL ARTERY ANGIOPLASTY AND STENTING
Operators should be familiar with alternative choices for puncture sites (femoral, brachial, radial), techniques (balloon or sheath predilation, bareback, guiding catheter or sheath delivery), devices (low-and-high profile, over-the-wire, monorail), and contrast agents (iodinated, gadolinium, CO2,) etc.3
Renal artery stenoses >1 cm away from the aortic lumen usually respond well initially and have good long-term patency with traditional balloon angioplasty.4 Ostial stenoses (within 1 cm of the aortic lumen) almost universally recoil after angioplasty, and require stent placement for lasting benefit.5
There are several techniques for stent deployment. These include predilation with a relatively small (≤ 5 mm) diameter balloon, tapered dilators with a sheath, or no predilation when using lower-profile (0.018-inch or smaller) systems. Our currently favored technique is predilation with a 40-cm to 65-cm-long, 6-F sheath with a long, tapered introducer, such as the Daig (St. Jude Medical, St. Paul, MN), the Bright Tip (Cordis Corporation, a Johnson & Johnson company, Miami, FL), or the Balkin (Cook Inc., Bloomington, IN). Only balloon-expandable stents should be used in the renal artery. In the past we used the Palmaz (Cordis Corporation) stent, but we currently prefer the OmniFlex because of its MR transparency. For balloon and stent sizing, we use the length of the curved tip of the OmniFlush catheter; the distance from the top of the curve to the bottom of the tip is always 15 mm.
The stent, which is premounted on a balloon catheter, is delivered through the 6-F or 7-F guiding sheath (for 0.035-inch wire-based systems) into the stenotic area. The guiding sheath is then withdrawn into the aorta, leaving the balloon/stent combination over the guidewire in place. An angiogram is performed through the sheath to aid in the accurate placement of the stent in the renal artery. Contrast injections for stent positioning are performed using only 5 mL of 30% contrast injected at 10 mL per second. Minor adjustments in the position of the stent can generally be easily performed by advancing or withdrawing the balloon catheter with the mounted stent prior to deployment. The guiding catheter itself can be used to help in stabilizing the position of the stent during these maneuvers but this should only be used as a last resort because the stent could be damaged by the more rigid guiding catheter. Once the stent is in satisfactory position as evaluated by an angiogram in the appropriate oblique view (the x-ray beam should be perpendicular to the long axis of the origin of the renal artery from the aorta), the balloon is inflated and the stent deployed.
We prefer to deploy the stent with several millimeters extending into the aorta and several extending past the stenotic lesion. Palmaz and OmniFlex stents shorten slightly when expanded. The pulsation of the aorta and the renal artery during the cardiac cycle produces a moderate amount of unpredictable movement in the balloon-catheter/stent combination. There may also be some unpredictable and difficult to control movement of the balloon catheter stent combination during balloon inflation. For these reasons, we prefer to deploy 15-mm-long stents for most ostial stenoses. If an inadequate length of stent is used or if it is inaccurately placed, then a second stent partially overlapping the first one must be deployed to cover the entire lesion. This may decrease long-term patency due to extra foreign material and increases the risk of complications. For removing the balloon from the stent after deployment, the sheath should first be gently advanced into the stent as far as it will easily go over the trailing end of the deflated, but “open to air” balloon. This maneuver wraps the balloon to minimize the risk of the balloon “wings” catching in, and inadvertently dislodging the deployed stent.
Following the intervention, completion angiography must be performed to assess the result, retaining the guidewire across the treated lesion, in case further intervention is necessary.
Iodinated contrast-induced nephropathy may occur in up to 25% of cases, especially in diabetics with already compromised renal function. The renal protective benefits of fenoldopam and acetylcysteine in high-risk patients is not clear;6-8 therefore, using contrast sparing techniques is the best way to avoid permanent or transient contrast induced nephropathy. However, because acetylcysteine is inexpensive, easy to use, and has no known serious side effects in the recommended doses, it can be used in appropriate patients. Using our contrast-saving techniques (half-strength contrast, limiting the number and volume of injections), clinically significant acute renal failure occurred in fewer than 5% of our high-risk patients.
During the passage of catheters and guidewires through the atheromatous aorta and renal arteries for dilation and stent deployment, the artery can go into spasm, be occluded, perforated, dissected, or ruptured, and cholesterol crystals may be embolized either into the renal circulation or elsewhere. In situ thrombosis or thromboembolism from areas of manipulation can also occur. These complications each occur in <1% to 3% of cases.9,10
Several embolic protection devices are being evaluated for renal artery stenting; their efficacy is not yet proven in large studies and their deployment is not as safe as in the carotids. The majority of embolic complications in the carotid arteries occur during stent deployment and manipulation, whereas in the renal artery procedures, embolization frequently occurs during attempted selective catheterization from the frequently severely diseased abdominal aorta. These filters have a pore size of ≥ 100 µm; this is larger than the size of microcholesterol crystals, so balloon-occlusion protective devices will probably be more applicable.
In high-risk patients, attention to meticulous technique and contrast-saving strategies during the procedure are essential to achieve successful results and to minimize complications.
Thomas A. Sos, MD, is Professor and Vice Chair of Radiology at the New York Presbyterian Weill Cornell Center, in New York. He has a financial interest in AngioDynamics. Dr. Sos may be reached at (212) 746-2601; email@example.com.
David W. Trost, MD, is Associate Professor of Radiology and Chief of the Division of Interventional Radiology at the New York Presbyterian Weill Cornell Center, in New York. He holds no financial interest in any product mentioned herein. Dr. Trost may be reached at (212) 746-2601; firstname.lastname@example.org.
1. Prince MR, Narasimham DL, Stanley JC, et al. Breath-hold gadolinium-enhanced MR angiography of the abdominal aorta and its branches. Radiology. 1995;197:785-792.
2. Kim P, Lee L, Trost D, et al. Fluoroscopic landmarks for optimal visualization of the proximal renal arteries for diagnostic angiography and renal artery stent placement. Submitted for publication in Radiology.
3. Kerns SR, Hawkins IF. Carbon dioxide administration angiography: expanding applications and technical evolution. AJR. 1995; 735-741.
4. Sos TA, Pickering TG, Sniderman KW, et al. Percutaneous transluminal renal angioplasty in renovascular hypertension due to atheroma or fibromuscular dysplasia. N Engl J Med. 1983;309:274-279.
5. Cicuto KP, McLean GK, Oleaga JA, et al. Renal artery stenosis: anatomic classification for percutaneous transluminal angioplasty. AJR. 1981;137:599.
6. Tumlin JA, Wang A, Murray PT, et al. Fenoldopam mesylate blocks reductions in renal plasma flow after radiocontrast nephropathy. Am Heart J. 2002;143:894-903.
7. Tepel M, van der Giet M, Schwarzfeld C, et al. Prevention of radiographic contrast agent-induced reductions in renal function by acetylcysteine. N Engl J Med. 2000;343:180-184.
8. Brigouri C, Manganelli F, Scarpato P, et al. Acetylcysteine and contrast agent-associated nephrotoxicity. J Am Coll Cardiol. 2002;40:298-303.
9. Trost DW, Sos TA. Complications of renal angioplasty and stenting. Semin Intervent Radiol. 1994;11:150-160.
10. Thadhani RI, Camargo C, Xavier RJ, et al. Atheroembolic renal failure after invasive procedures. Natural history based on 52 histologically proved cases. Medicine. 1995; 74:350-358.