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The Aortopathy of Bicuspid Aortic Valve Disease has Distinctive Patterns and Usually Involves the Transverse Aortic Arch
S. Fazel1, H. R. Mallidi2, R. S. Lee2, M. P. Sheehan2, D. Liang2, R. Herfkens2, S. Mitchell*2, C. Miller*2. 1University of Toronto, Toronto, ON, Canada, 2Stanford University, Stanford, CA,
BACKGROUND:
Bicuspid aortic valve (BAV) affects 0.9-2% of the population and is associated with a poorly characterized connective tissue disorder that predisposes to thoracic aortic dilation and a high likelihood of aortic dissection and/or rupture. Indeed, use of the terms “post-stenotic dilatation” and “post-regurgitation dilatation” in the context of BAV is no longer acceptable.Since no hard criterion exists dictating how much aorta should be replaced, we comprehensively assessed the extent and pattern of thoracic aortic dilatation in BAV patients using computed tomographic or magnetic resonance angiography (CTA, MRA).
METHODS:
Patients with a BAV who underwent CTA or MRA of the thoracic aorta and echocardiographic assessment of aortic valve function were retrospectively identified between January 2002 and March 2006. Orthonormal 2-dimensional (2-D) or 3-dimensional (3-D) aortic diameters were measured at 9 pre-defined aortic levels (aortic annulus to the distal descending thoracic aorta). Agglomerative hierarchical clustering using centered correlation distance measurements and complete linkage analysis was used to detect distinct patterns of aortic dilatation.
RESULTS:
Of 66 patients, 49 were male; age averaged 45±1 years (18 to 75, median=46 years). Twenty patients had a bovine aortic arch and three had aortic coarctation. Measurements of aortic diameter at all levels passed the normality test (P>0.1). Overall inter-observer measurement concurrence was excellent (ICC: 2-D, 0.9; 3-D, 0.9). Agreement between 2-D and 3-D measurements was tight (ICC: 0.9). Mean aortic diameter was 28.1± 0.7 mm at the annulus and 21.7±0.4 mm at the diaphragmatic hiatus. The aorta was largest in the tubular portion of the ascending aorta (45.9±1.0 mm). Aortic diameters proximal and distal to the innominate artery were 36.8±0.8 mm and 30.1±0.8 mm, respectively. When compared to the caliber of the proximal or distal descending aorta, the ascending aortic and arch diameters were larger (P<0.01, at all levels). Cluster analysis revealed that the aortic aneurysmal dilatation predominantly involved: I.) The aortic root alone (n=8); II.) The tubular ascending aorta alone (n=10); III.) The tubular portion and the transverse arch (n=18, or 27%); and, IV.) The aortic root and the tubular portion with tapering across the arch (n=30, or 45%). Cluster I patients were the youngest, and Cluster II were the oldest. Aortic valve function (normal, regurgitation, stenosis), presence of a bovine arch, or coarctation were not associated with any Cluster pattern.
CONCLUSIONS:
Aortic dilatation in BAV patients follows four distinctive patterns that call for a custom-tailored degree of aortic replacement. Patients in Clusters III and IV requiring operation should have the transverse arch replaced and not just the ascending aorta (with concomitant root replacement in Cluster IV). In Cluster I patients, complete aortic root replacement (reimplantation type valve-sparing or composite valve graft) is necessary, whereas in Cluster II patients a supra-commissural ascending aortic graft is adequate. This individualized approach is our practice and should minimize the incidence of late postoperative aortic complications and need for reoperation. 
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