A Critical Review of the American College of Cardiology/American Heart Association Practice Guidelines on Bicuspid Aortic Valve With Dilated Ascending Aorta

doi:10.1016/j.amjcard.2008.02.106

The American Journal of Cardiology

Volume 102, Issue 1, 1 July 2008, Pages 107-110

https://doi.org/10.1016/j.amjcard.2008.02.106 Get rights and content

The 2006 practice guidelines from the American College of Cardiology and the American Heart Association recommend prophylactic aortic replacement for even an asymptomatic patient with a bicuspid aortic valve (BAV) when the aortic dimensions exceed arbitrary ranges based on Marfan syndrome, without comparing risk estimates of aortic dissection with operative risks. In the International Registry of Acute Aortic Dissection, which includes >1,000 autopsied subjects, the average age is 63 years; BAVs are found in only 3%, compared with histories of hypertension in 72%. The risk for valve-sparing aortic replacement is 4% and that for late mortality is 10%, on the basis of 5 publications. The aortic dimensions are from guidelines for Marfan syndrome, with a proved genetic weakness of connective tissue, whereas no culprit genes have been demonstrated in BAV. Although cystic medial necrosis is seen in dilated aortas associated with Marfan syndrome and BAV, it is also seen in dilated aortas with other causes. There is no convincing proof that cystic medial necrosis causes dissection or is simply an effect of dilatation. BAV is not associated with dilatation of the pulmonary arteries, in contrast to Marfan syndrome. Hemodynamic explanations for dilatation of the ascending aorta have been largely ignored because of a belief that it requires severe aortic stenosis or regurgitation. In conclusion, vascular dilatation without a genetic weakness is caused by coarse periodic vibrations from even trivial valve disorders, demonstrated experimentally. There is a natural history of progressive deterioration of the BAV, including the valve left in a valve-sparing aortic replacement, that makes the operation ill advised, as opposed to valve replacement with aortic reinforcement.

Section snippets

Histopathology Relative to Inheritance

The guidelines assert that the histology associated with aortic dilatation is cystic medial necrosis¹ and further that this causes aortic dissection in patients with BAVs. Nataamadja et al² drew this conclusion because cystic medial necrosis was associated with BAV and Marfan syndrome. Furthermore, they argued that BAV was associated with premature death, with only anecdotal reports. Unlike patients with Marfan syndrome, who have hereditary tissue weakness, a genetic link has not been

Aortic Dissection Populations

Among the patients with dissections of the aorta in the IRAD, only 3% had BAVs and 5% had Marfan syndrome.⁶ Larson and Edwards⁵ found that 6% of their 161 patients with dissections had BAVs, and Roberts and Roberts¹⁰ found that 7.5% of their 286 patients with dissections had BAVs. In a series of 126 patients who had undergone elective valve-sparing aortic replacement,¹¹ only 3% had BAVs. If one pools the BAV risks weighted by the number of patients in each of these studies, the likelihood of

Poststenotic Dilatation as a Cause of Aortic Dilatation

There is a considerable body of evidence indicating that specific hemodynamics can produce dilatation in all arteries, including central, peripheral, and pulmonary, which is not discussed in the practice guidelines.¹ In 1954, Holman¹⁵ observed that even minor degrees of obstruction of a normal peripheral artery could cause rough periodic turbulence and that this, rather than the severity of the obstruction, produced the subsequent dilatation by means of tissue fatigue. Aortic regurgitation can

The Natural History of Bicuspid Aortic Valve Relative to Valve-Sparing Surgery

The natural history of BAV is relevant to the timing of surgical intervention for aortic valve replacement, relative to replacement of the aorta. Patients with BAVs demonstrate increasing sclerosis after the second decade and calcification with increasing stenosis beginning by the fourth decade.²² In 1968, Campbell²² reported that the same progression seen in BAV ultimately occurs with a tricuspid aortic valve, but several years later. This deterioration with time in BAV and tricuspid aortic

Other Surgical Considerations

The mortality for aortic root replacement is not trivial, considering that the published statistics are usually from centers of excellence. There is no question that mortality is less when replacement is elective in patients with Marfan syndrome as opposed to those with acute dissections, with or without congestive failure. However, from 5 publications concerning elective replacement11, 23, 24, 25, 26 in 717 patients for a BAV with dilatation, early mortality was 4% (a weighted mean), and total

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In this study, the effect of aortic valve (AV) pathology on local hemodynamic conditions was evaluated as a potential trigger for the onset of acute type A and B aortic dissection.
A time- and pressure-related four-dimensional (4-D) computed fluid dynamic model of the aorta was established. In an experimental setup, AV stenosis and AV insufficiency were created. 4-D pressure-related geometry of the aortic root (AR) with valve insufficiency and valve stenosis were determined by high-fidelity (200 Hz) microsonometric crystals. Flow and pressure were obtained at the left ventricle, ascending aorta, and aortic arch.
Expansion of the AR in AV insufficiency was higher with expansion in AV stenosis, at peak ejection, and at the end of systole. In AV insufficiency, there was low shear stress (0 to 0.6 Pa), turbulent flow, and high pressure (80 to 95 mm Hg) at the anterior wall of the ascending aorta, at the proximal aortic arch, and at the aortic isthmus. In stenosis, high shear stress (>2 Pa) and high pressure (>95 mm Hg) were found at the ascending aorta and at the bifurcation of the brachiocephalic trunk.
In AV insufficiency, low shear stresses and turbulent flow regions were documented at the traditional levels of entry tears for acute type A and B dissection. In AV stenosis, high shear stress with elevated pressure at the ascending aorta may be a trigger element for vessel dilatation, aneurysm formation, and intimal tear, which is typical for type A aortic dissection.
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Recent studies have demonstrated that many patients with acute type A aortic dissection (AD) have aortic diameters of <55 mm at presentation, prompting discussion of lowering the prophylactic surgical guidelines. However, risk of dissection at these smaller diameters is poorly defined.
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Using an institutional echocardiography database, we identified 4,654 nonsyndromic adults (age: 68.6 ± 13.1 years; 1,003 women) with maximal ascending aortic diameters of 40 to 55 mm. We performed competing risk analysis to determine the independent risk factors of AD or aortic rupture.
Five hundred eighty-six individuals (12.6%) had bicuspid aortic valves (BAVs). During follow-up (14,431.5 patient-years), AD and rupture occurred in 13 and 1 patients, respectively, which demonstrated a linearized incidence of AD and/or rupture of 0.1% per patient-year. Elective ascending aortic repair was performed in 176 individuals. On multivariable analyses, independent predictors of AD and/or rupture were age (hazard ratio [HR]: 1.06; 95% confidence interval [CI]: 1.01 to 1.12; p= 0.024) and baseline aortic diameters (HR: 1.20; 95% CI: 1.05 to 1.36; p = 0.006). The presence of a BAV was not a significant factor (HR: 0.94; 95% CI: 0.10 to 8.40; p = 0.95). Estimated risks of AD and/or rupture within 5 years were 0.4%, 1.1%, and 2.9% at baseline aortic diameters of 45, 50, and 55 mm, respectively.
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VAR protocol is a prospective, longitudinal, multicenter study. It observes 4 homogeneous small groups of BAV surgical patients (15 patients each): isolated aortic regurgitation, isolated ascending aortic aneurysm, aortic regurgitation associated with aortic aneurysm, isolated aortic stenosis in older patients (> 60 years). Echo analysis is extended to first-degree relatives and, in case of BAV, genetic test is performed. Patients and relatives are enrolled in 10 cardiac surgery/cardiologic centers throughout Italy.
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ReviewA Critical Review of the American College of Cardiology/American Heart Association Practice Guidelines on Bicuspid Aortic Valve With Dilated Ascending Aorta

Section snippets

Histopathology Relative to Inheritance

Aortic Dissection Populations

Poststenotic Dilatation as a Cause of Aortic Dilatation

The Natural History of Bicuspid Aortic Valve Relative to Valve-Sparing Surgery

Other Surgical Considerations

J Am Coll Cardiol

Am J Cardiol

J Am Coll Cardiol

Genet Med

Am J Cardiol

J Am Coll Cardiol

Ann Thorac Surg

Am J Cardiol

J Thorac Cardiovasc Surg

Am J Cardiol

J Thorac Surg

J Am Coll Cardiol

Am J Cardiol

Ann Thorac Surg

J Am Coll Cardiol

Review
A Critical Review of the American College of Cardiology/American Heart Association Practice Guidelines on Bicuspid Aortic Valve With Dilated Ascending Aorta