Aetiology
Outflow obstruction to the left ventricle can be at the valve itself (valvular), above it (supravalvular) or below (subvalvular). About 1% of cases of 'aortic stenosis' are supra or sub valvular. Supravalvular stenosis is a congenital form of atresia of the ascending aorta, and is associated with acharacteristic 'elfin' facies. Subvalvular stenosis is eithera congenital ring lesion (which is amenable to surgery) or a variable muscular obstruction produced by hypertrophic obstructive cardiomyopathy.
Valvular aortic stenosis can result from
:• Congenital aortic stenosis, presenting in childhood, the valve having one, two or three cusps;
• Bicuspid aortic valve presenting in adulthood. About1% of the population are born with two, instead ofthree, cusps. About one-third of these develop calcific aortic stenosis, one-third mixed aortic valve disease, and one-third have no significant valvular abnormality. The valve itself seems to be mechanically unsatisfactory andsuffers mechanical stresses, which lead to progressive damage;
• Rheumatic heart disease. This involves the aortic valve inabout 50% of cases of rheumatic valvular disease, most frequently producing aortic regurgitation, often a mixed lesion but sometimes pure stenosis;
• Senile aortic calcification. Although calcification of thevalve ring is commonly benign, it can invade the cuspsand produce a calcified tricuspid valve as it renders the cusps immobile. This aetiology is more common over theage of 70. The valve cusps are not fused.
Pathophysiology Outflow obstruction to the left ventricle leads to:
• Concentric left ventricular hypertrophy
• Compensatory enlargement of the coronary arterial circulationas the metabolic demands of the hypertrophied left ventricle increase;
• A relatively fixed cardiac output. A resting pressure gradientof l00mmHg would have to become 400mmHg forthe flow velocity through the valve to double. The heartis incapable of generating such a pressure, and is the reforenear its limit at rest.
Clinical features
Aortic stenosis may remain asymptomatic until it is verysevere, and is then life-threatening. The symptoms are:
• Left heart failure. Shortness of breath on exertion mayprecede paroxysmal nocturnal dyspnoea and orthopnoea,or the patient may present with acute pulmonary oedema.
• Angina. The thickened myocardium is perfused by a lower than normal perfusion gradient owing to low aortic diastolic pressure and a high left ventricular end diastolic pressure. For these reasons, angina can occur without any coronary narrowing, although coronary artery disease often coexists in older patients.
• Syncope on exertion. This is a sinister symptom which indicates a fixed cardiac output and presages sudden death. The mechanisms may be: skeletal muscle vasodilatation causing a drop in blood pressure; a rise in ventricular pressure producing reflex bradycardia and vasodilatation; myocardial ischaemia triggering ventricular arrhythmia.
• Sudden death, probably resulting from myocardialischaemia and ventricular irritability, leading to a fatal arrhythmia. This may be provoked by exertion.
• Right heart failure. Rarely the presentation is right heartfailure supervening on left.
• Emboli from a heavily calcified valve. These are usuallyfairly small and cause small strokes or visual disturbances.
Although the systolic ejection murmur suggests the possiblediagnosis, the most important physical sign is the slow rising poor volume pulse, best felt at the carotid, where asystolic thrill may also be evident. The heart is not enlarged unless the patient has been in failure, but the left ventricular apex beat is powerful and 'pressure loaded'.
Differential diagnosis from a 'flow murmur' is based on the slow-rising pulse, the presence of left ventricular hypertrophy and the absence of the aortic component of the second heart sound. The loudness of the murmur is a poor index of severity and the murmur may even be absent in heart failure. In congenital aortic stenosis there may be an ejection click as the valve cusps tent as they tension.
investigation
Electrocardiography A normal ECG virtually rules out significant aortic stenosis,except in congenital disease when the trace may remain remarkably normal despite a large gradient. A number of ECG changes are seen in aortic stenosis:
• Left ventricular hypertrophy. Often widening of QRS and T wave changes of 'strain' predominate over voltage change. T-wave inversion over LV leads may be the only feature. Loss of anterior R waves may occur.
• Left axis deviation and, eventually, left bundle branchblock may occur either from severe hypertrophy or invasionof the conduction system by calcium from the valve.
.• Left atrial hypertrophy or 'P mitrale\ A large negativecomponent to the P wave in VI indicates raised left ventricularfilling pressure.
• Complete heart block.Chest X-rayThe chest X-ray can be normal but may show a post stenotic dilatation of the ascending aorta, prominence of the left ventricle and a calcined aortic valve on lateral chestX-ray. The latter in a patient under 55 suggests tight stenosis;above this age the valve may calcify even with an insignificant gradient. Significant enlargement of the left ventricle occurs with heart failure or coincident aortic regurgitation.M-mode echocardiography M-mode echocardiography can display thickening and calcificationof the valve cusps, but is less useful in congenital stenosis. The compensatory hypertrophy of the left ventricularwall is well shown. 2D echocardiography may give a good view of the aortic valve orifice.Doppler ultrasound Doppler ultrasound measures the jet velocity and predictsthe valve gradient. A high blood velocity (>4m/s) indicates a surgically significant gradient, but as jet velocities can be under estimated, a low jet velocity record is a less reliablefinding.Cardiac catheterization Measurement of the valve gradient by cardiac catheterizationis not essential if the diagnosis is well established. Catheterization is usually indicated where there is doubt about the site or degree of stenosis, a not-infrequent occurrencein older patients, who may be poor ultrasound subjects. It also allows analysis of ventricular function.Coronary angiography is now considered essential prior to operation in all but the very elderly.
Management
SurgicalTight aortic stenosis has such a poor prognosis that surgery should be offered to all patients. Valvuloplasty or valvotomy in children may gain sufficient time for them to reach a reasonable size before having aortic valve replacement. For adults, valve replacement is the only treatment. If the ventricle has already been badly damaged the results are less good, but in the patient with a normal ventricle the left ventricular hypertrophy regresses fairly rapidly.Lesser degrees of stenosis need serial follow-up, as the stenosis may become more significant with time at a rate averaging about 8mmHg/yr, although this may be veryvariable.
Outflow obstruction to the left ventricle can be at the valve itself (valvular), above it (supravalvular) or below (subvalvular). About 1% of cases of 'aortic stenosis' are supra or sub valvular. Supravalvular stenosis is a congenital form of atresia of the ascending aorta, and is associated with acharacteristic 'elfin' facies. Subvalvular stenosis is eithera congenital ring lesion (which is amenable to surgery) or a variable muscular obstruction produced by hypertrophic obstructive cardiomyopathy.
Valvular aortic stenosis can result from
:• Congenital aortic stenosis, presenting in childhood, the valve having one, two or three cusps;
• Bicuspid aortic valve presenting in adulthood. About1% of the population are born with two, instead ofthree, cusps. About one-third of these develop calcific aortic stenosis, one-third mixed aortic valve disease, and one-third have no significant valvular abnormality. The valve itself seems to be mechanically unsatisfactory andsuffers mechanical stresses, which lead to progressive damage;
• Rheumatic heart disease. This involves the aortic valve inabout 50% of cases of rheumatic valvular disease, most frequently producing aortic regurgitation, often a mixed lesion but sometimes pure stenosis;
• Senile aortic calcification. Although calcification of thevalve ring is commonly benign, it can invade the cuspsand produce a calcified tricuspid valve as it renders the cusps immobile. This aetiology is more common over theage of 70. The valve cusps are not fused.
Pathophysiology Outflow obstruction to the left ventricle leads to:
• Concentric left ventricular hypertrophy
• Compensatory enlargement of the coronary arterial circulationas the metabolic demands of the hypertrophied left ventricle increase;
• A relatively fixed cardiac output. A resting pressure gradientof l00mmHg would have to become 400mmHg forthe flow velocity through the valve to double. The heartis incapable of generating such a pressure, and is the reforenear its limit at rest.
Clinical features
Aortic stenosis may remain asymptomatic until it is verysevere, and is then life-threatening. The symptoms are:
• Left heart failure. Shortness of breath on exertion mayprecede paroxysmal nocturnal dyspnoea and orthopnoea,or the patient may present with acute pulmonary oedema.
• Angina. The thickened myocardium is perfused by a lower than normal perfusion gradient owing to low aortic diastolic pressure and a high left ventricular end diastolic pressure. For these reasons, angina can occur without any coronary narrowing, although coronary artery disease often coexists in older patients.
• Syncope on exertion. This is a sinister symptom which indicates a fixed cardiac output and presages sudden death. The mechanisms may be: skeletal muscle vasodilatation causing a drop in blood pressure; a rise in ventricular pressure producing reflex bradycardia and vasodilatation; myocardial ischaemia triggering ventricular arrhythmia.
• Sudden death, probably resulting from myocardialischaemia and ventricular irritability, leading to a fatal arrhythmia. This may be provoked by exertion.
• Right heart failure. Rarely the presentation is right heartfailure supervening on left.
• Emboli from a heavily calcified valve. These are usuallyfairly small and cause small strokes or visual disturbances.
Although the systolic ejection murmur suggests the possiblediagnosis, the most important physical sign is the slow rising poor volume pulse, best felt at the carotid, where asystolic thrill may also be evident. The heart is not enlarged unless the patient has been in failure, but the left ventricular apex beat is powerful and 'pressure loaded'.
Differential diagnosis from a 'flow murmur' is based on the slow-rising pulse, the presence of left ventricular hypertrophy and the absence of the aortic component of the second heart sound. The loudness of the murmur is a poor index of severity and the murmur may even be absent in heart failure. In congenital aortic stenosis there may be an ejection click as the valve cusps tent as they tension.
investigation
Electrocardiography A normal ECG virtually rules out significant aortic stenosis,except in congenital disease when the trace may remain remarkably normal despite a large gradient. A number of ECG changes are seen in aortic stenosis:
• Left ventricular hypertrophy. Often widening of QRS and T wave changes of 'strain' predominate over voltage change. T-wave inversion over LV leads may be the only feature. Loss of anterior R waves may occur.
• Left axis deviation and, eventually, left bundle branchblock may occur either from severe hypertrophy or invasionof the conduction system by calcium from the valve.
.• Left atrial hypertrophy or 'P mitrale\ A large negativecomponent to the P wave in VI indicates raised left ventricularfilling pressure.
• Complete heart block.Chest X-rayThe chest X-ray can be normal but may show a post stenotic dilatation of the ascending aorta, prominence of the left ventricle and a calcined aortic valve on lateral chestX-ray. The latter in a patient under 55 suggests tight stenosis;above this age the valve may calcify even with an insignificant gradient. Significant enlargement of the left ventricle occurs with heart failure or coincident aortic regurgitation.M-mode echocardiography M-mode echocardiography can display thickening and calcificationof the valve cusps, but is less useful in congenital stenosis. The compensatory hypertrophy of the left ventricularwall is well shown. 2D echocardiography may give a good view of the aortic valve orifice.Doppler ultrasound Doppler ultrasound measures the jet velocity and predictsthe valve gradient. A high blood velocity (>4m/s) indicates a surgically significant gradient, but as jet velocities can be under estimated, a low jet velocity record is a less reliablefinding.Cardiac catheterization Measurement of the valve gradient by cardiac catheterizationis not essential if the diagnosis is well established. Catheterization is usually indicated where there is doubt about the site or degree of stenosis, a not-infrequent occurrencein older patients, who may be poor ultrasound subjects. It also allows analysis of ventricular function.Coronary angiography is now considered essential prior to operation in all but the very elderly.
Management
SurgicalTight aortic stenosis has such a poor prognosis that surgery should be offered to all patients. Valvuloplasty or valvotomy in children may gain sufficient time for them to reach a reasonable size before having aortic valve replacement. For adults, valve replacement is the only treatment. If the ventricle has already been badly damaged the results are less good, but in the patient with a normal ventricle the left ventricular hypertrophy regresses fairly rapidly.Lesser degrees of stenosis need serial follow-up, as the stenosis may become more significant with time at a rate averaging about 8mmHg/yr, although this may be veryvariable.