Covered Stents in Renal Artery Interventions

Reprinted with permission from the Journal of Invasive Cardiology, May 2010, vol. 22, no. 5. Balloon angioplasty/stenting has emerged as a highly effective revascularization procedure for renal artery stenosis (RAS).¹ The major complications of balloon angioplasty of the renal artery are dissection, perforation and thrombosis.² Use of balloon-expandable stents has decreased the incidence of restenosis. It has also improved the immediate and long-term results of this technique,³ but the risks of life-threatening complications such as free perforations or aortic dissection persist, as well as the risk of distal embolization. In this context, we illustrate the use of covered stents in 2 patients with RAS and discuss the possible role of covered stents in preventing morbidity and mortality associated with this percutaneous procedure.

Case 1

A 69-year-old female patient with RAS was admitted with hypertensive encephalopathy. She was referred for potential renal stenting and angioplasty to optimally control her medically-resistant hypertension. Angiography revealed an 80% stenosis in the proximal left renal artery. The angiographic characteristics of the lesion were suggestive of intraluminal thrombus and mimicked the classic “coral-reef” appearance of an organized thrombus, as described in the carotid vasculature (Figure 1). There was a 10-mmHg gradient across the stenosis, as measured with a 0.014 inch PressureWire (Radi Medical Systems/St. Jude Medical, St. Paul, Minn.). Lack of optimal medical control of her life-threatening hypertension despite five medications necessitated treatment of her RAS. In view of the obvious risk of distal embolization of the thrombotic lesion, the option of surgical treatment was considered but declined by the family of the stuporose patient. Using heparin for anticoagulation and a 7 Fr internal mammary artery guide catheter for support, a FilterWire EZ™ distal protection device (Boston Scientific Corp., Natick, Mass.) was placed beyond the lesion. A QuickCat™ extraction catheter (Kensey Nash Corp., Exton, Penn.) was used for an attempt at aspiration thrombectomy, without success. Options at this stage included stenting and angioplasty of the thrombotic lesion without distal protection or the off-label use of a covered stent graft with an aim to prevent distal embolization of the thrombotic load. Use of a covered stent was preferred by the family and a 6.0 x 15 mm iCast covered stent (Atrium Medical Corp., Hudson, New Hampshire) was deployed over a 0.014 inch Spartacore wire (Guidant Corp., Santa Clara, Ca.). Postdilatation was achieved with a 7.0 x 20 mm OptaPro balloon (Cordis Corp., Miami Lakes, Fl.). There was no residual stenosis and no evidence of distal embolization to any angiographically visible renal artery branch (Figure 2). Her subsequent clinical course was remarkable for recovery from her hypertensive emergency using only three medications and the absence of any renal impairment.

Case 2

An 82-year-old female patient with hypertension, chronic renal insufficiency, rheumatoid arthritis and Paget’s disease was referred for an invasive evaluation and prospective treatment of RAS, diagnosed earlier on magnetic resonance angiography. Angiography confirmed an 80% eccentric stenosis at the ostium of a calcified right renal artery (Figure 3). Using intravenous heparin for anticoagulation and a 6 Fr internal mammary artery guide catheter for support, the ostial stenosis was predilated using a 4 mm balloon advanced over a 0.014 inch Spartacore guidewire (Guidant). A 6.0 x 12 mm Herculink stent (Guidant) was deployed spanning the ostium of the vessel. Control angiography revealed adequate stent expansion and placement, but also demonstrated a persistent contrast staining at the proximal and superior edge of the stented segment (Figure 4). The patient was asymptomatic and hemodynamically stable. The angiographic appearance was concerning due to the presence of a dissection in the wall of the renal artery and the patient was kept under observation on the catheterization table with the guide catheter in place. While contemplating how to proceed, the patient complained of mild diffuse abdominal discomfort approximately 15 minutes after completion of the procedure. A repeat angiogram revealed free flow of contrast medium in a cephalad direction suggestive of either a free perforation or a dissection into the wall of the abdominal aorta. A 5.5 x 15-mm balloon was immediately inflated at the site to “tamponade” the bleed and anticoagulation was reversed with intravenous protamine. The balloon was kept inflated for 20 minutes as the activated clotting time was reduced to Discussion Renal artery angioplasty and stent placement are generally well-tolerated procedures. As compared to stand-alone balloon angioplasty, renal artery stenting is associated with improved immediate results and a decrease in the rate of restenosis.³ Complications include contrast-induced nephropathy, thrombosis, distal embolization, renal artery dissection and perforation.² Distal protection devices are attractive for safeguarding against the effects of distal embolization and currently under investigation.⁴ However, the short length of renal arteries and lack of a safe landing zone for placement of distal protection devices is a limiting factor. An alternative strategy could be the use of covered stents. Covered stents have been used in coronary and peripheral arteries for varied indications. Their cardiac application was initially evaluated in stenotic saphenous vein bypass grafts for protection against distal embolization and prevention of restenosis. The results of the BARRICADE trial⁵ showed an increase in the rate of restenosis with the use of a covered stent as compared to a bare-metal stent in this location, thereby disapproving their application for this indication. However, they continue to be used for treating free perforations in the coronary arteries,⁶ and have proven life-saving in this regard. Their use in the peripheral vasculature is more widespread. Apart from their use in the aorta, they are being increasingly used in the iliac and femoral arteries to treat free perforations⁷ and, aneurysmal dilatations.⁸ Commercially available varieties of stent grafts for non-aortic applications, therefore, conform to the dimensions of the iliac and femoral arteries. Although not intended for use in the renal vasculature, the similarities between the size of renal arteries and either the saphenous vein grafts or the ilio-femoral vasculature makes them potentially usable in this arterial bed. To date, there are no reported cases of the use of covered stents to decrease the risk of distal embolization in lesions with large thrombus burden. Gaxotte et al suggested that stent-grafts could be superior to bare stents in the ability to minimize embolic complications; however, this has never been studied. She described a 6-month patency rate of 92% in 12 patients in which Jomed stent-grafts were placed within the renal arteries.⁹ These stents were placed for a variety of reasons including renal artery rupture, dissection, aneurysm, in-stent restenosis, chronic total occlusions and ulcerated stenosis. Because covered stents could potentially exclude thrombus from within the lumen of lesions with large thrombus burden, there may be a role for these stents in reducing distal embolization, as shown in our case. Iatrogenic renal artery perforation can occur from guidewire, angioplasty balloons, stents or even the guide catheter itself.¹⁰ The incidence of serious iatrogenic injuries of the renal arteries after percutaneous revascularization was 3.4–10.0% after stenting in the late 1990’s.¹¹ Covered stents have been found to be effective in treating both coronary and iliac artery perforations.^2,3,12 Extrapolation from these data has led to the use of covered stents for the treatment of renal artery dissections and perforations.¹³ Aortic dissections most likely occur secondary to balloon-mediated intimal tears within the renal vasculature that eventually extend retrograde into the aorta. Intimal tears with contrast extravasation are the result of separation of the intima from the underlying media. Possible risk factors for aortic dissection after stenting of the renal arteries are similar to those that cause dissection and perforation of the renal arteries after angioplasty. These possibly include a large balloon-to-artery ratio, higher inflation pressures, repeat vessel expansion, presence of aortic atherosclerosis, advanced age, presence of long-standing hypertension, diabetes, stenosis location, eccentricity, severity and calcification.¹⁴ It is necessary to consider these factors prior to any renal artery intervention. The second case described here highlights a life-threatening complication of renal intervention, i.e., aortic dissection. It is important to realize that this can present in a delayed manner after the intervention, as seen in our patient and also described in earlier reports. This should be kept in mind when confronted with a clinical scenario of abdominal pain and hemodynamic compromise after a renal artery intervention, and an early diagnosis and prompt management can prevent a life-threatening situation. The authors can be contacted via Dr. Jolly at: njolly@medicine.bsd.uchicago.edu

References

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