Left Ventricular Outflow Tract Obstruction

Definition, Clinical Features, Natural HistoryTop

Left ventricular outflow tract obstruction may develop as a result of defects of the aortic valve, defects of the adjacent parts of the left ventricle (LV), and defects of the ascending aorta that cause obstruction of the outflow of blood from the LV.

1. Classification:

1) Valvular obstruction: The most common type, usually associated with a bicuspid aortic valve.

2) Subvalvular obstruction: In the form of membranous stenosis or a fibromuscular tunnel.

3) Supravalvular obstruction: Usually in the form of an hourglass (with fibrosis of the aortic intima); it may involve a large part of the ascending aorta. Etiology: Williams-Beuren syndrome, congenital rubella syndrome.

2. Symptoms depend on the severity of stenosis and do not differ significantly from those found in patients with acquired valvular aortic stenosis.

3. Signs: In subvalvular stenosis, a loud ejection murmur with a systolic thrill along the left sternal border (in severe stenosis) and diastolic murmur of aortic regurgitation (AR) (common) are present. Similar auscultatory signs are seen in supravalvular stenosis, but usually without the diastolic murmur. Other features include increased accentuation of the second heart sound (resulting from increased aortic pressures proximal to the stenosis), very distinct radiation of the murmur and the thrill to the carotid arteries, and a late systolic or holosystolic murmur caused by stenosis of the peripheral pulmonary arteries. In people with significant stenosis, a fourth heart sound is often present. In those with a congenitally abnormal aortic valve an ejection click is audible. In individuals with supravalvular aortic stenosis, the systolic blood pressure in the right arm is higher than the left arm.

4. Natural history: Congenital valvular stenosis progresses with time to significant stenosis (particularly when valve calcifications occur, usually in patients aged <60 years) and regurgitation with dilation of the aorta (with increased risk of dissection), which require surgery. Subvalvular membranous stenosis can be progressive and often leads to significant aortic regurgitation. Tunnel stenosis is usually severe and requires surgery. The condition is associated with an increased risk of infective endocarditis.

DiagnosisTop

Diagnosis is mainly based on echocardiography. Differential diagnosis includes the individual morphologic forms of the disease. Cardiac magnetic resonance imaging (MRI) or computed tomography (CT) should be performed in individuals with supravalvular aortic stenosis and those with multilevel stenosis to delineate the locations of stenosis and identify additional lesions in the aorta and the peripheral vessels (such as renal arteries). Coronary angiography should be performed in all patients with supravalvular aortic stenosis undergoing surgical correction (CT coronary angiography may be performed).

TreatmentTop

Symptomatic patients with a mean gradient ≥50 mm Hg on Doppler echocardiography require surgery. Asymptomatic patients with severe defects require individual assessment; in asymptomatic patients, surgery may be performed in the presence of LV systolic dysfunction (ejection fraction <50%), with the development of symptoms during exercise stress testing, and in the presence of severe AR and LV dilatation. Surgery may be considered in patients with subvalvular stenosis and progressive AR (on serial assessment) in order to prevent further progression of AR. An independent indication for surgery is a dilation of the ascending aorta >50 to 55 mm. After surgery annual follow-up visits are required.