Reactive Luminal Stenosis Associated with Severe Arterial Stenosis in the Aortic Arch: Implications for Stent Angioplasty

Abstract

Percutaneous balloon and stent angioplasty for aortic obstructions has become part of the routine armamentarium in dealing with vascular obstructions. Deployment of balloon expandable stents requires a good understanding of the underlying pathology and anatomy of the stenosis. We report 4 cases of long-segment stenosis that behaved differently during endovascular therapy. Based on this experience, we conclude that not all long-segment stenoses require long stents, as stenoses distal to a focal lesion are likely to be reactive and easily expanded. Predilation with a smaller balloon may delineate the behavior of such lesions prior to stenting.

VASCULAR DISEASE MANAGEMENT 2012;9(4):E51-E56

Key words: coarctation, aorta, stent angioplasty, congenital heart disease

______________________________________________________

The effects of vascular stenosis in the arterial circulation are multifold. When present in proximal conductance vessels such as the aortic arch, it may give rise to profound alteration in vascular tone, reduced arterial compliance, systemic hypertension, and poor ventricular hydraulic power due to adverse ventriculo-arterial coupling. The vascular remodeling that occurs proximally comprises medial hypertrophy and inhibition of normal vasodilatory responses of the endothelium, and resetting of the tonic feedback homeostasis of the carotid body pressure receptors, giving rise to chronic systemic hypertension.

Relieving such proximal aortic obstructions with balloon angioplasty was first demonstrated feasible by Lock and Castenada in post-mortem specimens and subsequently in an animal model.¹ Since then, percutaneous balloon and stent angioplasty for aortic obstructions have become part of the routine armamentarium in dealing with vascular obstructions.^2,3 Deployment of balloon expandable stents requires a clear understanding of the underlying pathology, and anatomy of the stenosis. Sound principles of deployment include use of the shortest stent that will relieve the obstruction, yet ensuring safe placement that bisects the narrowest portion of the obstructed vessel. Stents in the proximal aorta reduce pre-stenotic arterial compliance. Hence, shorter stents are generally preferred. Long-segment obstructions pose a particular challenge to the interventional specialist because conventional stents may not be long enough and because of the inherent problems associated with long stents.

We report 4 cases of long segment stenosis that behaved differently during endovascular therapy. In 3 of the 4 cases there was a post-focal stenotic long-segment luminal stenosis, which was completely relieved with placement of a relatively short stent across only the focal point of tightest stenosis. In the remaining case, there was atresia (extreme coarctation) with a long proximal segment stenosis, which was moderately resistant to balloon distension. Based on this experience, we conclude that not all long segment stenoses require long stents as a stenosis distal to a focal lesion is likely to be reactive and easily expanded. Predilation with a smaller balloon may delineate the behavior of such lesions prior to stenting.

Case Presentations

Case 1

A 38-year-old man presented with symptoms of dyspnea on exertion, orthopnea, and paroxysmal nocturnal dyspnea. An echocardiogram showed a bicuspid aortic valve, mild mixed aortic valve disease, and a dilated left ventricle with mildly impaired systolic function. Cardiac MRI revealed severe coarctation of the aorta with a peak gradient of 50 mm Hg and diastolic continuation of flow across the stenotic area. While awaiting definitive management, he presented with infective endocarditis affecting his aortic valve. He was transferred to our tertiary unit with evidence of worsened aortic regurgitation. He was treated with appropriate antibiotics and definitive treatment was carried out in a hybrid manner with initial stent angioplasty of the coarctation followed by surgical aortic valve replacement while under the same general anesthetic. At cardiac catheterization, vascular access was obtained via the right femoral artery using a 6 Fr sheath. Aortography demonstrated a long segment of stenosis distal to a focal area of severe narrowing (Figure 1). There was a peak-to-peak pullback gradient of 36 mm Hg across the stenosis. The aorta measured 17 mm proximally and 30 mm distally with a total length of 47 mm. A 34 mm covered CP stent (8 zig, NuMED, Inc.) was deployed across the focal stenosis and expanded to 20 mm with 5 atm pressure. This resulted in relief of the obstruction with only a residual 5 mm Hg pullback gradient but no visible obstruction distal to the stent.

Case 2

A 40-year-old male sailor was evaluated after a presyncopal episode while working on a ship. Initial examination revealed severe systemic hypertension. Follow-up evaluation by a cardiologist revealed severe coarctation. CT angiography demonstrated a well-developed left sided aortic arch with normal branching pattern (Figure 2). Though there was a discrete coarctation in the descending aorta, there was distal propagation of the stenotic area in a funnel-like fashion spanning 29 mm. The aortic isthmus proximal to the stenosis was well developed. The total length of the stenotic segment was 49 mm. The stenosis was crossed in a standard fashion and a 45 mm stent deployed with the mid-portion of the stent exactly bisecting the most stenotic area. Though the distal length of the stent did not span the entire funnel-like stenosis, it still resulted in complete relief of the stenosis. No complications were encountered and the patient’s blood pressure was significantly easier to control.

Case 3

A 15-year-old boy was referred for assessment of severe systemic hypertension with a blood pressure of 180/110. He was unresponsive to medical therapy and renovascular causes of hypertension were excluded. Cardiac evaluation demonstrated a severe, atretic coarctation of the thoracic aorta. CT angiography demonstrated a left sided arch, with a well-developed 14 mm transverse aortic arch. There was normal branching of the head and neck vessels. The aortic isthmus was diminutive, measuring 8 mm and narrowing down into a funnel-like long-segment stenosis leading to an atretic segment, which was directly contiguous to the descending aortic segment (Figure 3). The proximal stenotic and “hypoplastic” segment spanned over 31 mm and 25 mm below the atretic segment. There were numerous collaterals communicating with the descending aortic segment. The femoral artery was cannulated and the atretic segment probed from below. It was not possible to cross; hence, right radial access was obtained with a 4 Fr sheath and this permitted passage of an 0.035-inch Terumo wire from the upper thoracic aorta to the descending segment below the atretic portion. The wire was snared using a 10 mm gooseneck snare and exteriorized through the femoral sheath. A 45 mm covered CP stent was then deployed over a 12 mm BIB balloon. The upper stenotic segment above the atretic portion was moderately resistant to inflation to 8 atm and only expanded to 9 mm whereas the lower half of the stent expanded appropriately to the 12 mm. However, the position was stable and there was no residual gradient across the stent. The procedure was uncomplicated.

Case 4

A 66-year-old female presented with a history of uncontrolled hypertension and shortness of breath. Initial transthoracic echocardiogram suggested a coarctation of her aorta and also revealed an unroofed coronary sinus. She underwent cardiac catheterization and angiography demonstrated a tight coarctation measuring 4 mm at its narrowest point (Figure 4). The coarcted segment extended 17 mm proximally and 26 mm distally to this point with a total length of 42 mm. A 34 mm covered CP stent was deployed over a 16 mm

BIB balloon through a 12 Fr sheath. This resulted in complete relief of the obstruction.

All patients demonstrated improved blood flow across that coarcted segment on post-procedural angiography (Figure 5).

Follow-up

In all patients an improvement in post-procedural blood pressure control was noted. Although ongoing dual agent medical therapy was required, blood pressure control was significantly improved. One patient described symptom relief of intermittent claudication following the procedure. At 3 months follow-up there was no significant residual coarctation in all patients. At 1-year follow-up, which we were able to obtain in 2 patients, the findings were similar. Two patients underwent cardiac MRI within the 12 months following the procedure; both demonstrated no significant residual coarctation. In one patient a significant reduction in the size of collateral vessels was noted with improved flow across the native coarctation site (Table 1).

Discussion

Stent angioplasty with balloon expandable stents has become the treatment of choice for endovascular management of arterial and venous obstructions. However, stents are associated with altered vessel compliance, endothelial ingrowth, and restenosis, and may be prone to distortion or fracture around joints or where there is repetitive movement such as in arterial structures. It stands to reason that the shortest possible stent length that permits safe deployment and deals effectively with the stenosis should be selected. In this short series we have reported 4 cases with apparent long-segment stenoses where arguably, a longer stent should have been employed in all cases to overcome the obstruction. However stent angioplasty demonstrated a rather discrete lesion with only apparent long-segment stenosis in case 3 where there was atresia with extensive proximal propagation of the stenosis. This patient also demonstrated significant resistance to balloon inflation consistent with a very different underlying pathology causing true long-segment stenosis. Our experience with these cases has lead us to adopt a strategy of first verifying true long-segment stenosis vs focal stenosis with associated low resistance reactive luminal stenosis by initial submaximal balloon inflation across the stenotic segment. This permits use of a shorter stent without compromising luminal patency.

There are two pathophysiological theories for the development of coarctation of the aorta from a developmental perspective. The first suggests that residual ductal tissue constricts the aorta resulting in coarctation. Immunohistochemistry has demonstrated varying degrees of ductal smooth muscle cells extending into the aorta.⁴ Depending on the amount and distribution of ductal tissue within the aorta, the coarctation morphology may vary greatly in its final appearance. More generous distribution of the ductal tissue may explain longer segment stenosis. Distal propagation of the stenosis may be exacerbated by lack of lateral wall pressure resulting from decreased blood flow across the narrowed segment. Secondary changes within the distal wall may therefore ensue.

The second is the hemodynamic theory, which explains coarctation due to increased ductal flow in utero with the development of a cross point in the dorsal aortic wall opposite the duct. This is described as an adventitial infolding and does not contain ductal tissue.⁵ There is a varying degree of intimal hyperplasia both proximal and distal to this point, which will narrow the aortic lumen. The diminished lateral aortic wall pressure from poor flow beyond the coarctation may enhance distal propagation of the stenosis, particularly once the duct closes. This distal segment may also remain dilated depending on the degree of narrowing and amount of blood flow from the duct through the post-stenotic segment.

In terms of actual observed changes within the aorta, microscopic examination of coarctation tissues in older children and adults reveals that the lumen is constricted by a fibromuscular tissue that protrudes from the dorsal wall of the aorta at the site of insertion of the ligamentum arteriosum. Immediately proximal to the stenosis, the intima runs in fine longitudinal folds that radiate into the orifice of the stenosis. On the distal side of the shelf the intima is grossly irregular with deep longitudinal and transverse folds.⁶ The intima immediately distal to the orifice is covered with a laminated layer, distinct from the elastica, which often gives a positive staining reaction for fibrin. Intimal thickness increases with age in a non-linear manner with large increases in patients over 15 years old. These findings are consistent with the view that the constriction has both a fibroelastic component that is congenital and a fibrous component that is acquired and progressive. Altered flow dynamics are intrinsic to such lesions. In the precoarctation there is flow convergence and dramatic acceleration of blood velocity. Distal to the obstruction there is a spray effect as blood eddies in multiple directions onto the endothelial surface dissipating kinetic energy gained through the flow acceleration. Lateral wall stress may be significantly decreased particularly in more severe stenoses with no ductal flow augmentation. When complete atresia develops as in case 3, flow stops immediately before the atretic segment. There may be proximal propagation of clot and reactive hypoplasia.

Though no literature exists delineating the histology of long-segment coarctation, evidence in stenotic human femoral arteries may provide some insight into possible pathological processes involved.⁷ Femoral vessels with milder degrees of atherosclerotic stenosis, display dilation distal to the obstruction. These vessels by and large have less than 25% luminal stenosis. This phenomenon is well described in coronary arterial lesions and also in non-atherosclerotic congenital lesions such as pulmonary arterial or aortic valvular stenosis. In this context it has often been called post-stenotic dilation.⁸ The pathophysiology appears to be explained by a combination of intrinsic vessel wall weakness and a reaction to fluid hydrodynamic stress to the arterial wall.

In more severe forms of femoral arterial stenosis, distal reactive luminal stenosis occurs more commonly.⁹ This anatomical phenomenon does not correlate with the degree of atherosclerosis and is underscored histologically by a significant contraction of the internal elastic lamina, but there is relative preservation of the remaining vessel wall. It is tempting to speculate that similar pathology may underscore the post focal stenotic extension of luminal stenosis observed in our 3 cases. The easy distensibility of these lesions with a relatively short stent is consistent with such underlying pathology.

Placement of a stent across the main stenosis resulted in relief of the entire long-segment stenosis. Our initial practice was to deploy a stent that spans the entire length of the obstruction, but following our experience with relatively shorter stents in long-segment obstructions we herein propose a new approach to such long-segment stenoses. We suggest initial submaximal balloon dilation of long-segment stenoses should be performed in all cases to determine the nature of the stenosis. It is important to determine if it is reactive post focal stenotic luminal stenosis or if this is truly a long-segment obstruction. The latter needs a longer stent to overcome the true long-segment stenosis.

Conclusion

Long-segment stenosis in aortic coarctation may have quite different underlying pathological mechanisms. In severe focal stenosis there may be a reactive post stenotic luminal stenosis that does not appear to require a long stent but is treatable with a relatively shorter stent that deals primarily with the focal stenosis. In long-segment stenosis associated with atresia, the stenosis is likely to be resistant to balloon distension representing a different underlying pathology. The latter are likely to require long stents.

References

1. Lock JE, Bass JL, Amplatz K, Fuhrman BP, Castaneda-Zuniga W. Balloon dilation angioplasty of aortic coarctations in infants and children. Circulation. 1983 Jul;68(1):109-116.
2. Golden AB, Hellenbrand WE. Coarctation of the aorta: stenting in children and adults. Catheter Cardiovasc Interv. 2007 Feb;69(2):289-299.
3. Rao PS. Stents in the management of aortic coarctation in young children. JACC Cardiovasc Interv. 2009 Sep;2(9):884-886.
4. Jimenez M, Daret D, Choussat A, Bonnet J. Immunohistological and ultrastructural analysis of the intimal thickening in coarctation of human aorta. Cardiovasc Res. 1999 Mar;41(3):737-745.
5. Hutchins GM. Coarctation of the aorta explained as a branch-point of the ductus arteriosus. Am J Pathol. 1971 May;63(2):203-214.
6. Kennedy A, Taylor DG, Durrant TE. Pathology of the intima in coarctation of the aorta: a study using light and scanning electron microscopy. Thorax. 1979 Jun;34(3):366-374.
7. Rodbard S. Physical factors in arterial sclerosis and stenosis. Angiology. 1971 May;22(5):267-284.
8. Wilton E, Jahangiri M. Post-stenotic aortic dilatation. J Cardiothorac Surg. 2006 Mar;1:7.
9. Pasterkamp G, Wensing PJ, Post MJ, Hillen B, Mali WP, Borst C. Paradoxical arterial wall shrinkage may contribute to luminal narrowing of human atherosclerotic femoral arteries. Circulation. 1995 Mar;91(5):1444-1449.

______________________________________________________

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report no conflicts of interest regarding the content herein.

Manuscript received August 22, 2011, provisional acceptance given October 11, 2011, final version accepted November 29, 2011.

Address for correspondence: Gruschen Veldtman, JRCPTB, Wessex Cardio-thoracic Unit, Congenital Cardiac Centre, Southampton General Hospital, Tremona Road, Southampton, SO 16 6YD, United Kingdom. Email: gruschen.veldtman@suht.swest.nhs.uk