Aortic Stenosis, Subvalvular

KEY FEATURES

ESSENTIALS OF DIAGNOSIS

• With no other congenital heart abnormalities, it is usually asymptomatic

• Low-pitched systolic ejection murmur is heard at the left sternal border radiating to the neck

• Two-dimensional echocardiography defines the anatomy of the obstruction

• Doppler echocardiography estimates the pressure gradient

GENERAL CONSIDERATIONS

• Subvalvular aortic stenosis accounts for 10–20% of fixed left ventricular outflow lesions in children

• Is more common in males

• Associated congenital heart lesions are common, such as:

  • – Ventricular septal defect

  • – Patent ductus arteriosus

  • – Other components of Shone’s syndrome: coarctation of the aorta, bicuspid aortic valve, supramitral valve ring, cor triatriatum, parachute mitral valve, hypoplastic aortic arch, and hypoplastic left ventricle

• Subvalvular stenosis is progressive even after surgical correction

• The pathology ranges from a thin discrete membrane, to a fibromuscular ring, to a tunnel-like narrowing of the left ventricular outflow tract

• Most stenoses are membranes or ridges 5–15 mm below the aortic valve

• The membrane can attach to the anterior leaflet of the mitral valve and cause mitral regurgitation

• Aortic valve thickening and associated aortic regurgitation are common and may persist after membrane removal

CLINICAL PRESENTATION

SYMPTOMS AND SIGNS

• Most patients are asymptomatic or have symptoms related to associated congenital heart disease

• When present, symptoms are similar to those of valvular aortic stenosis:

  • – Dyspnea

  • – Chest pain

  • – Syncope

  • – Palpitation

PHYSICAL EXAM FINDINGS

• A left ventricular lift and precordial thrill may be present

• Auscultation:

  • – A fourth heart sound may be present

  • – There is a low-pitched systolic ejection murmur best heard in the left third or fourth parasternal space

  • – An early diastolic high-pitched murmur of aortic regurgitation is common

• A holosystolic murmur at the apex of mitral regurgitation may be present

DIFFERENTIAL DIAGNOSIS

• Valvular aortic stenosis

• Supravalvular aortic stenosis

• Hypertrophic cardiomyopathy

DIAGNOSTIC EVALUATION

ELECTROCARDIOGRAPHY

• Left ventricular hypertrophy is common

IMAGING STUDIES

• M-mode echocardiography shows coarse fluttering of the aortic valve and early systolic closure

• Two-dimensional echo defines the anatomy of the subvalvular obstruction

• If surgery is contemplated, transesophageal echo better defines the lesion for planning surgery

• Doppler echocardiography is used:

  • – To estimate the pressure gradient across the lesion

  • – If there is a ventricular septal defect or more than 1 obstructive lesion (eg, aortic valve stenosis or a tunnel-like left ventricle outflow tract), the estimated pressure gradient may not be reliable

  • – For assessing other lesions

DIAGNOSTIC PROCEDURES

• Cardiac catheterization is best for distinguishing the hemodynamic contributions of multiple lesions

• Cardiac MRI may be useful to determine the extent of abnormalities, especially of the proximal aorta