The normal aortic valve is composed of three thin cusps that project from the wall at the origin of the aorta. Aortic stenosis (AS) refers to a tight valve.
Aortic sclerosis is usually considered to be the precursor of calcified, degenerative AS but sclerosis is rather more common than stenosis.

Epidemiology.

AS has become the most frequent type of valvular heart disease in Europe and North America. It most often presents as calcific AS in adults of advanced age (2-7% of the population aged over 65 years).
AS occurs in almost 10% of adults over the age of 80 years, with a mortality rate about 50% at two years unless outflow obstruction is relieved.
The second most frequent cause, which dominates in the younger age group, is congenital.
Rheumatic AS has become rare in developed countries.

Risk factors
A congenital bicuspid valve predisposes to both AS and regurgitation.

Presentation
Aortic valve stenosis is the most common form of valvular heart disease in the elderly population and occurs frequently in conjunction with coronary artery disease.

Symptoms include shortness of breath on exertion, angina, dizziness or syncope.

The characteristic murmur may occasionally be faint and so the patient may present as heart failure of unknown cause.
The disappearance of the second aortic sound is specific to severe AS, although not a sensitive sign.

Symptoms
Even with a quite marked pressure gradient across the valve, patients may be asymptomatic for many years but they may still be susceptible to sudden events. However, only 4% of sudden cardiac deaths in severe AS occur in asymptomatic patients.

AS predisposes to angina and is a reason to auscultate the chest when a patient presents with angina. Angina occurs in approximately two thirds of patients with critical AS, of whom 50% have significant coronary artery disease.

It can also cause syncope on exertion and even sudden death and so violent exertion should be avoided.

Symptoms of congenital disease often appear between ages of 10 and 20 years.

The classic triad of chest pain, heart failure and syncope are found in only 30-40% and usually after the age of 50 years.
Fatigue may be the presentation in children.
Syncope, especially on exertion, may be caused by arrhythmia or the sudden onset of heart failure with decline in cardiac output.

Signs
Examination of the pulse in significant AS reveals a slow-rising, flat character called pulsus parvus et tardus.
Blood pressure will show a narrow pulse pressure (difference between systolic and diastolic pressures). In the elderly, a rigid aorta may make this sign less obvious.

Examination of the cardiovascular system includes palpation of the cardiac apex.
There may be a thrill. In regurgitation the left ventricle is enlarged as each beat has to pump the required cardiac output plus that which regurgitates. In AS the left ventricle hypertrophies as more force is required to eject the blood past a tight valve.
In laminar flow, the resistance to flow is proportional to the 4th power of the radius so that a small reduction in calibre has a marked effect on resistance.

AS murmur:

A2 is soft in AS. In aortic sclerosis, A2 is normal or loud.
Both conditions are associated with an early, harsh systolic murmur that is transmitted to the carotids. A similar murmur may occur without stenosis if turbulence is due to aortic aneurysm causing dilation of the proximal aorta. Such pathology may cause leakage from the valve too and with it an early diastolic murmur.
The typical murmur of AS is a crescendo-decrescendo systolic ejection murmur shortly after the first heart sound that ends just before the second heart sound. It is a rough, low-pitched sound that is loudest at the base of the heart and most commonly heard in the second right intercostal space.
If congestive heart failure leads to a fall in cardiac output, the murmur will be quieter.

An ejection click may be present, especially with bicuspid valves. Ejection sounds are more obvious in children in whom the valves are more mobile than in older people.
A fourth heart sound indicates left ventricular hypertrophy (LVH) in severe AS. If the left ventricle dilates and fails, a third heart sound may be heard.

Differential diagnosis
Other causes of murmurs that are, or appear to be, from the aortic valve include:

Aortic sclerosis.
Aortic regurgitation.
Subacute bacterial endocarditis.
Dilatation of the root of the aorta (may also lead to a leaking valve).
Flow murmurs (turbulence from high cardiac output in anaemia, thyrotoxicosis and marked aortic regurgitation).
Murmurs originating from the pulmonary valve with disease of that valve or atrial septal defect (the pulmonary and aortic areas are very close).
NB: flow murmurs can be normal in children and in neonates. Interpretation of cardiac sounds in children can be very difficult. Aortic valve disease is often not detected until the child is about 2 years old.

ECG may show evidence of LVH or left ventricular strain.
CXR may show cardiac enlargement, calcification of the aortic ring or evidence of other disease. It is often normal except in advanced disease.
Echocardiography:
Is the key diagnostic tool. It confirms the presence of AS, assesses the degree of valve calcification, left ventricular function and wall thickness, detects the presence of other associated valve disease or aortic pathology and provides prognostic information.

Trans-oesophageal echocardiography should be considered when transthoracic echocardiography is of insufficient quality.
Doppler echocardiography is the preferred technique for assessing AS severity.

Exercise testing:
Is contra-indicated in symptomatic patients with AS but it is recommended in physically active patients for unmasking symptoms and in the risk stratification of asymptomatic patients with severe AS.
Exercise testing is safe in asymptomatic patients, provided it is performed under the supervision of an experienced physician while monitoring for the presence of symptoms, changes in blood pressure, and/or ECG changes.

Multi sliced computerised tomography MSCT, Cardiac
Magnetic resonance:
Provide additional information on the assessment of the ascending aorta when it is enlarged.
MSCT may be useful in quantifying the valve area and coronary calcification, which aids in assessing prognosis.
MSCT has become an important diagnostic tool for evaluation of the aortic root, the distribution of calcium, the number of leaflets, the ascending aorta, and peripheral artery pathology and dimensions before undertaking transcatheter aortic valve implantation (TAVI) .

Natriuretic peptides have been shown to predict symptom-free survival and outcome in normal and low-flow severe AS and may be useful in asymptomatic patients.
It may still be necessary to undertake cardiac catheterisation to measure pressures across the valve to assess the severity of disease and the need for intervention
.
Coronary angiography may be indicated as part of the assessment of coronary artery disease.
The risk factors for aortic sclerosis are similar to the risk factors for coronary heart disease and so similar investigations should be undertaken.

Management options can be supplied if needed.

G Mohan.

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