Endovascular Treatment of Infrarenal Aortic Stenosis: Importance of Multimodality Imaging

ABSTRACT: We sought to describe the evolution in imaging and interventional options for endovascular treatment of significant infrarenal aortic stenosis. Balloon angioplasty and stent implantation for infrarenal aortic stenosis has generally required large-sized arterial access sheaths in the past, and was typically guided by visual size assessment. Computerized tomography angiography enables accurate preprocedural assessment of severity and extent of aortic atherosclerosis, degree of calcification, and luminal dimensions at both stenosis and reference sites, and visualizes possible aneurysm. Intraprocedural pressure gradient measurements evaluate the hemodynamic response to revascularization. On the other hand, intravascular ultrasound can further verify accuracy of equipment sizing. Small-profile stents and balloons can be used via small-sized sheaths, thereby rendering the procedure possible in patients with extensive peripheral arterial disease or small iliofemoral arteries. Improved non-invasive and intravascular imaging can guide with great accuracy infrarenal aortic stenosis procedures and may enable the use of reduced-size access sheaths and devices in fragile patients with vasculopathies.

J INVASIVE CARDIOL 2011;23:E192–E196

Key words: CT scan, intravascular ultrasound, renal artery stenosis

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Atherosclerotic infrarenal aortic stenosis is an infrequent, though difficult to treat condition. Previous studies have indicated very good long-term patency with endovascular treatment.^1–5 However, the unfamiliar sizing of interventional equipment in very large vessels (with the potential risk of catastrophic aortic rupture) and the relatively large-diameter access sheath requirement in these arteriopathic patients can pose unique technical challenges. Recent advances in imaging techniques and interventional equipment enable preprocedural and intraprocedural planning and assessment, and ultimately safer performance of these complex cases. We hereby present a case of infrarenal aortic stenosis, performed with multimodality imaging.

Case Report. This case involved a 80-year-old female with a body mass index of 28.3 m/kg², chronic renal insufficiency with estimated glomerular filtration rate (GFR) of 49 ml/min per 1.73 m² and significant comorbidities including refractory hypertension, cervical spinal cord compression (awaiting surgery), coronary artery disease recently treated with bare-metal stent implantation in the left anterior descending coronary artery, and peripheral vascular disease manifesting as severe bilateral claudication (right greater than left). The patient was taking aspirin 81 mg daily and clopidogrel 75 mg daily for 1 month following the coronary stent implantation.

At the time of the coronary procedure, severe diffuse aortic atherosclerosis was documented fluoroscopically, with significant pressure gradients as follows: (i) thoracic aorta to right brachial artery: 40 mmHg; (ii) thoracic aorta to left brachial artery: 40 mmHg; (iii) thoracic aorta to distal infrarenal aorta: 65 mmHg; and (iv) distal infrarenal aorta to left common iliac: 40 mmHg. In addition, significant angiographic stenoses were documented in all ostia: (i) 50–60% aorto-ostial stenoses of the great vessels; (ii) 90% bilateral renal artery stenoses; (iii) 99% right common iliac stenosis; and (iv) 80% left common iliac artery stenosis. The extent of the infrarenal aortic disease was classified as category III according to the American Heart Association Task Force on Peripheral Angioplasty.⁶

The combination of identified angiographic stenosis, significant pressure gradient accompanied by bilateral exertional lower extremity weakness, and incapacitating claudication justified infrarenal and bi-iliac revascularization, especially given the anticipated need for rehabilitation during her anticipated postsurgical course (for cervical spinal stenosis). In addition, the presence of refractory hypertension with end-organ damage and resistance to multiple medications supported bilateral renovascular intervention. Alternatively, since there was a lack of symptoms/signs related to the brachiocephalic stenoses, there was no indication for revascularization in those territories.

In preparation for the endovascular procedure, a computerized tomography (CT) angiogram of the abdominal aorta and iliacs was performed on an outpatient basis, which verified absence of aortic aneurysm and allowed for precise measurement of aortic lumen dimensions at proximal and distal reference sites as well as at the target lesion, and also of distance between target lesion and both renal arteries (Figures 1A and 1B and Figures 2A–2D). Based on this information, the infrarenal aortic procedure was planned with use of a balloon-expandable 10-mm diameter stent with plans to postdilate with a 12 mm balloon. Both devices could be delivered via a 7 Fr sheath. The bilateral ostial iliac stenosis precluded the use of larger-sized sheaths.

After ascertaining left and right common femoral artery access, aortography was performed and a 20 MHz intravascular ultrasound imaging catheter was used over a 0.014˝ support wire in order to further assess the infrarenal aorta and the left common iliac artery stenosis (the left side was selected, since less obstructive and calcified than the right common iliac). Important measurements with these 2 imaging modalities as well as key angiographic images are shown in the Table and also in Figures 1 and 2 in correlation with the respective tomographic measurements that were utilized for device sizing.

After removal of the ultrasound catheter, the dilator was replaced in the sheath, which was then advanced across the ostial common iliac lesion. The same was performed with the right-sided sheath. A 7.0 x 27 mm balloon-expandable stent was positioned across the left ostial common iliac artery lesion and a 7.0 x 37 mm balloon-expandable stent across the right ostial common iliac artery lesion; the sheaths were retracted to uncover the stents in an inverse-V position. The stents were deployed sequentially at 14 atm and then simultaneous (“kissing”) balloon inflations were performed at 6 atm. A compliant 8.0 x 20 mm balloon was then used at 10 atm for 30 seconds to selectively expand the distal aspect of the right common iliac artery stent that was located at an area of poststenotic dilation distal to the ostium.

Following removal of the balloon catheters, a marker 5 Fr pigtail catheter was advanced to the level of the renal arteries from the right side, while the dilator was reinserted in the left side sheath, which was subsequently advanced across the infrarenal aortic stenosis, which was ~75% obstructive angiographically. The dilator was then exchanged for a 10 x 37 mm balloon-expandable stent and the sheath was retracted in order to uncover the stent in position. Guiding angiography from the marker catheter was used (Figure 3, left panel) to avoid stent deployment across the renal arteries, and then the diagnostic catheter was withdrawn. The stent was deployed with one inflation at 10 atm and subsequently postdilated at 14 atm with a 10 x 12 mm balloon, resulting in excellent angiographic and ultrasound results (Figure 3). The thoracic aorta to femoral pressure gradients were eliminated bilaterally.

Attention was subsequently paid to the renal arteries. Using a no-touch technique, an internal mammary (IM) 6 Fr, 55 cm guiding catheter and a 190 cm, 0.014˝ wire, a compliant monorail 4.0 x 15 mm balloon was inflated at 14 atm across the 80% stenotic right renal artery lesion. A 5.5 x 15 mm balloon-expandable stent was subsequently deployed at 12 atm and flared. Using similar technique, a 5.0 x 18 mm balloon-expandable stent and a 5.0 x 12 mm balloon-expandable stent were serially deployed at 12 atm after predilatation across the left renal artery lesion (90% stenotic, approximately 18–20 mm long). Final flow and angioraphic results were excellent.

The entire case was completed with limited iodinated contrast use (60 cc). Heparin (3,000 units intravenously) was used for anticoagulation, allowing the sheaths to be removed 2 hours after the procedure without complication. No decrease in hematocrit or increase in serum creatinine was observed postprocedure or at follow-up laboratory analysis.

Discussion. Endovascular treatment of infrarenal aortic stenosis has been described previously with very good long-term patency. However, device choice has been a limiting factor. Investigation of a possible concomitant aortic aneurysm is important, since the treatment strategy would then involve the use of stent grafts. Absence of aneurysm allows treatment of the stenosis with bare-metal stents rather than stent grafts, but operators must always consider a possibly catastrophic aortic perforation. This has been evident from the careful, conservative procedural approach as described in previous reports, especially limiting balloon size if the patient reports pain during the inflations.^1–5 Furthermore, several factors may contribute to procedural difficulty. Specifically, in patients who tend to have extensive arteriopathies and comorbidities, the aortic diameter at the lesion and reference sites cannot be accurately estimated by the two-dimentional angiography. Excessive angiographic aortography may increase the contrast-media load during the procedure, leading to an important risk for acute kidney injury. Last, but not least, the size of devices used are significantly larger than those used in classic peripheral arterial intervention and typically necessitate a very large arterial access sheath, which itself poses significant risks or can be considered impossible in cases with severe iliofemoral atherosclerosis.

In the current case, this old, small-sized woman with extensive arteriopathy in multiple vascular territories (coronary, thoracic, and abdominal aorta, bracheocephalic, renal, infrarenal aortic, and common iliac) would pose unique problems to a large-sheath approach. First, the sheath would need to be advanced through the aortic stenosis lesion for safe delivery of the stent. However, passing a larger than 7 Fr (up to 11–12 Fr) sheath through the heavily calcified, stenosed, and angulated common iliac area would likely not have been possible or safe, given the risk of perforation either at the ostial iliac or aortic stenosis level. Second, the close proximity of the target lesion to the renal arterial ostia might pose a unique challenge during placement of a stent type that may move upon deployment; the pre-mounted stent was therefore clearly an advantage. Third, her diffusely calcified (non-distensible) aorta poses by itself a risk of disruption even by passing very large-sized sheaths that pose stretch/straightening risks. A stable balloon-expandable stent system with a maximum 10 mm diameter is available and can be delivered via a smaller sheath (7 Fr) without movement and expanded up to 12 mm with subsequent dilation. Nevertheless, selection of small-diameter equipment in the aorta necessitates an accurate measurement to avoid stent dislodgement.

The reason that self-expandable stents were not selected in the aortoiliac bifurcation lesions was due to their lower scaffolding support relative to the balloon-expandable stent. Moreover, ostial common iliac lesions are typically calcified, unyielding, and frequently prone to recoil.⁶ The common iliac arteries were not stenotic after the end of the ostium-involving lesions; for this reason, there was no need for additional stents, which could have been self-expanding as they would involve the mid-distal common iliac or proximal external iliac segments.

While decision-making points can be performed during the interventional procedure, this involves increased procedure time and contrast media. However, we consider a short, well-targeted procedure to be the key to fewer complications in such high-risk arteriopathic patients. Therefore, we used CT angiography on an outpatient basis (two weeks before the intervention in order to separate the contrast media injections) to accurately measure the aortic size (outer wall diameters) and the key distances from other vital arteries to be avoided. The use of IVUS further reduced the need for angiography with iodinated contrast and verified in real-time the aortic and iliac lumen sizes at the key locations. Indeed, accurate measurements allowed the procedure to be executed swiftly, with small contrast load and via very small femoral sheaths, which in turn facilitated their uncomplicated removal and rapid patient mobilization. Availability of pre-mounted balloon-expandable stents in larger diameters might facilitate performance of such procedures even in patients with larger-sized aortas.

Conclusion. Improved non-invasive and intravascular imaging can guide infrarenal aortic stenosis interventions with great accuracy and may enable the use of smaller-sized equipment in fragile vasculopathic patients, with less radiation and contrast use.

References

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From the ¹Mount Sinai Medical Center and ²Cardiovascular Research Foundation, New York, New York.
The authors report no conflicts of interest regarding the content herein.
Manuscript submitted December 17, 2010, provisional acceptance given February 1, 2011, final version accepted February 4, 2011.
Address for correspondence: George Dangas, MD, PhD, Cardiovascular Institute, Mount Sinai Medical Center, One Gustave L. Levy Place (Box 1030), New York, NY 10029. Email: george.dangas@mssm.edu