Coarctation of aorta

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Definition

Coarctation of the aorta is typically a discrete narrowing of the thoracic aorta just distal to the left subclavian artery (preductal, ductal or postductal depending on the position relative to ductus arteriosus).[1][2] However, the constriction may be proximal to the left subclavian artery or rarely in the abdominal aorta. In some cases, coarctation presents as a long segment or a tubular hypoplasia.

Coarctation of the aorta is considered now as part of a generalized arteriopathy, and not only as a circumscript narrowing of the aorta.[3]

Epidemiology

Aortic coarctation accounts for 5–8% of all congenital heart defects. The prevalence of isolated forms is 3 per 10 000 live births[3]. Associated lesions include bicuspid aortic valve (up to 85%), subvalvular, valvular, or supravalvular aortic stenosis, mitral valve stenosis (parachute mitral valve, a complex known as Shone syndrome), or complex congenital heart defects.

Coarctation of the aorta can be associated with Turner, Williams–Beuren, or congenital rubella syndromes, neurofibromatosis, Takayasu aortitis, trauma[3] or congenital aneurysm of the circle of Willis [4]

Pathogenesis

Coarctation of the aorta imposes significant afterload on the left ventricle resulting in increased wall stress, compensatory left ventricular hypertrophy, left ventricular dysfunction, and the development of arterial collaterals. ‘Cystic medial necrosis’ with early elastic fibre fragmentation and fibrosis was found in the ascending and descending aorta, resulting in an increased stiffness of the aorta and carotid arteries.[3]

Echocardiography

Echocardiography provides information regarding site, structure and extent of coarctation of the aorta, left ventricular function and hypertrophy, associated cardiac abnormalities, and aortic and supra-aortic vessel diameters.

Echocardiographic detection of coarctation requires both an index of suspicion and careful recording of the descending aorta from the suprasternal window.[2]

Two-dimensional echocardiography

Two-dimensional echocardiography may identify the location and the extension of the aortic narrowing , the type of coarctation (diaphragmatic or tubular hypoplasia) and poststenotic aortic dilatation.[5]

In children, evaluation of this portion of aorta is straightforward. In adults, however , may occur false-negative resuls from inability to image the most distal aortic arch or false-positive findings from a tangential imaging plane through the vessel, creating the illusion of narrowing.[2]

Dilatation and exaggerated pulsation of proximal aortic arch are further evidence of significant coarctation.

Color Doppler imaging

Color Doppler imaging can detect acceleration and turbulence withing the region of narrowing and permits more accurate alignement of the continuous wave Doppler beam.


Continuous wave Doppler

Continuous Doppler echocardiography showing a peak systolic gradient of 69 mmHg and a low grade antegrade diastolic flow in the descending thoracic aorta (saw tooth), highly specific for significant aortic obstruction, before stent placement
Reduction of the peak systolic gradient at 29 mmHg after stent placement

To estimate the peak pressure gradient, the Bernoulli equation can be used. If proximal aortic flow velocity is less than 1,5 m/s, it can be ignored and simplified equation can be used: Pressure Gradient=4Xmaximum velocity 2 If it is greater than 1,5 m/s, the expanded Bernoulli equation is necessary in order to obtain a more accurate pressure gradient: Pressure Gradient= 4 (V2-V1)2[2]

A pressure gradient that persists into diastole is an indicator of severe stenosis.[2]

Because coarctation gradients are flow-dependent, low-level exercise can be performed in borderline cases and often will result in the development or increase of diastolic gradient , without changing of systolic gradient.[2]

Common mistakes

False-negative

False-negative results of Doppler imaging can occur in the presence of well-developed collaterals or in the presence of patent ductus arteriosus, because of a reduced jet velocity through the coarctation that leads to an underestimation of the pressure gradient.[2]

False-positive

False-positive results are the missinterpretation of mild increase of descending aorta flow velocity (1,5-2 m/s) due to normal acceleration in aortic arch, without evidence of vessel narrowing.[2]

A slow upstroke on the abdominal aortic velocity profile is observed when compared with that seen in ascending aorta.[6]

After surgical repair, increased systolic flow rates may develop, even in the absence of significant narrowing, due to a lack of aortic compliance.[3]

Echocardiography is also used for detecting restenosis in long-term after repair of aortic coarctation.

Transesophageal echocardiography

Transesophageal echocardiography may be used for a more accurate evaluation of coarctation site, narrowing dimensions and of the type of obstruction and also for pressure gradient determination.

Other imaging techniques

CT 3D images showing significant coarctation of the thoracic aorta beyond the origin of the left subclavian artery (arrow) with poststenotic dilatation and hypoplastic abdominal aorta.

Cardiac magnetic resonance and CT are the preferred non-invasive techniques to evaluate the entire aorta in adults. Both depict site, extent, and degree of the aortic narrowing, the aortic arch, the pre- and post- stenotic aorta, and collaterals. Both methods detect complications such as aneurysms, restenosis, or residual stenosis.[3]

References

  1. Agarwala, Clinical manifestations and diagnosis of coarctation of the aorta , 2012, http://www.uptodate.com
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 Congenital Heart Diseases in Feigenbaum's Echocardiography pg. 581-582
  3. 3.0 3.1 3.2 3.3 3.4 3.5 ESC Guidelines for the management of grown-up congenital heart disease (new version 2010) , The Task Force on the Management of Grown-up Congenital Heart Disease of the European Society of Cardiology , European Heart Journal (2010) 31, 2915–2957
  4. Anthony N , Echocardiography in Hurst's The Heart, 12th edition, McGrawHill Medical, pg. 443, ISBN 978-0-07-149929-3
  5. Solinas M ,Aortic coarctation is correlated with bicuspid aortic valve and intracranial aneurysm: a case report and review of the literature, Ital Cardiol (Rome).2006 Feb;7(2):151-4
  6. Webb, Congenital Heart Disease in Braunwald's Heart Disease , eighth edition, Saunders Elsevier, 1607, ISBN 978-1-4160-4106-1
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