Aortic Stenosis (AS)

Anatomy & Physiology

The aortic valve commissures are usually partially fused together preventing the valve from opening properly. Frequently the valve has only 2 effective leaflets (bicuspid). In some instances the leaflets are dysplastic. When the degree of stenosis is significant the left ventricle becomes hypertrophied and eventually may fail. The problem is compounded by the fact that the origin of the coronary arteries is beyond the stenosis - coronary blood flow may thus be reduced in the face of an increased myocardial oxygen supply due to the hypertrophy. Myocardial ischaemia can thus occur - particularly if strenuous exercise is undertaken with catastrophic consequences.

Presentation

6% of CHD although it is less common amongst some Asian races. If severe, aortic stenosis presents with neonatal collapse. Milder disease presents with asymptomatic murmur. When severe the pulse pressure may be diminished. The second heart sound is normal or closely split. There may be a click as the valve opens. The murmur is usually heard best at the 2nd right intercostal space although may also be heard at the mid left sternal edge. There is usually a thrill - best felt in the suprasternal notch.

Investigations

Electrocardiogram

In milder disease this is normal. In severe disease LVH is seen with tall R waves over the lateral limb leads and ST & T wave changes.

ECG showing left ventricular hypertrophy

Chest X-ray

This may be normal or the cardiothoracic ratio increased.

This 10 yr old child had moderate aortic stenosis with marked aortic regurgitation. The volume load on the left ventricle is reflected in the mild increase in cardiothoracic ratio.

Echocardiogram

This allows the aortic valve leaflets to be assessed. Doppler enables the degree of stenosis to be determined and whether regurgitation is also present. The degree of ventricular hypertrophy can also be assessed.

Natural History

Unfortunately, unlike pulmonary stenosis, this lesion is always progressive. Nearly all patients will thus require surgery at some stage although this may not be until later in adult life.

Management

If asymptomatic and the degree of stenosis is mild then restricting the exercise and close observation is all that is required. For those with significant stenosis (more than 50mmHg measured by cardiac catheterisation) then surgical or transcatheter valvotomy is usually advised. This can be repeated provided that there is no significant aortic regurgitation.

Balloon valvotomy entails putting a catheter in the aorta usually from the femoral artery but the brachial artery can also be used. It is passed around the arch, crossing the aortic valve into the left ventricle. A wire is then passed through the catheter into the ventricle and the catheter withdrawn leaving the wire in place. A balloon catheter is then "railroaded" over the wire to the valve and inflated for a few seconds. It is then deflated and removed.

The procedure is usually relatively straightforward however it can prove difficult to cross the narrowed valve and thrombosis of the femoral artery requiring thrombolytic therapy is not infrequent. The most serious complication is the occurrence of aortic regurgitation which if severe may require urgent valve replacement.

Aortic Balloon Valovotomy Animation (file download time 15s)

When the valve cannot be conserved then valve replacement is required with either an autograft, (Ross procedure), homograft or mechanical valve. The method chosen depends upon the age and activity of the person. Homografts have the advantage of not requiring anticoagulation but deteriorate quicker than mechanical valves and thus require replacement more frequently.

Hover the mouse over the heart to see the animation

Hover the mouse over the picture to see the animation

Prognosis

Overall the prognosis is very good. The perioperative risks are 5% or less. Unfortunately re-operations are almost always required and the risks increase for multiple procedures. There is also a significant morbidity of anticoagulation is required.

This page was last edited 16/2/2004

Acknowledgements