Aortic Valve Disease

The aortic valve is composed of 3 thin cusps that project from the wall at the origin of the aorta. These leaflets and their respective sinuses of Valsalva are called left, right, and noncoronary. They should allow unimpeded flow from the left ventricle to the aorta during systole and close swiftly and firmly to prevent backflow during diastole. Disease may impair outflow, permit backflow or a combination of both.

Aortic stenosis refers to a tight valve. A leaking aortic valve is variously called insufficiency, incompetence and regurgitation. It may be argued that a stenotic valve is also insufficient or incompetent and so perhaps regurgitation is to be preferred. They will be abbreviated to AS and AR.

Aetiology

Aortic valve disease may be congenital or acquired. It may be part of a more complex syndrome such as Fallot's tetralogy. Post-rheumatic valve disease is becoming rarer and degenerative disease is more prominent in an aging population.

Prevalence

Aortic valve disease occurs in 4 of every 1,000 births. There is a male preponderance of 3:1 in pure AS or AR but if there is also mitral valve disease there is a female preponderance. Over age 65, 2 to 3% of people have some degree of aortic stenosis. Aortic sclerosis is usually considered to be the precursor of calcified, degenerative aortic stenosis but sclerosis is rather more common than stenosis.

A congenital bicuspid or even unicuspid valve predisposes to both stenosis and regurgitation. Aortic regurgitation can occur in systemic lupus erythematosis. It may also occur in Marfan's syndrome, Ehlers-Danlos syndrome type IV and Turner's syndrome. AR as a result of advanced syphilis with aortic aneurysm is rarely seen nowadays. Syphilis does not cause aortic stenosis. Aortic dilatation causing AR can also occur with ankylosing spondylitis and Reiter's disease and after Takayasu's disease. It may also occur with Behcet's syndrome.

Symptoms

Symptoms will depend upon the severity of disease. Infants with severe disease present in the 1st few weeks of life with heart failure. They often have other abnormalities too. Older patients may give a history of rheumatic fever or Sydenham's chorea although about 50% of classical rheumatic heart disease has no such history and such a history is not invariably followed by heart disease. There may be a history of other conditions such as Marfan's syndrome. Symptoms are more likely if it is part of a complex.

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.

Both stenosis and regurgitation, if significant, may cause shortness of breath on exertion. Aortic stenosis predisposes to angina and is a reason to auscultate the chest when a patient presents with angina. It can also cause syncope on exertion and even sudden death and so violent exertion should be avoided. Pure AR can also cause angina but less often than pure AS.

Aortic stenosis tends to cause more problems than regurgitation. Symptoms of congenital disease often appear between 10 and 20 years old. The classic triad of chest pain, heart failure and syncope are found in only in 30 to 40% and usually after 50 years old. Fatigue may be the presentation in children. Syncope, especially on exertion, may be from arrhythmia or sudden heart failure with an abrupt decline in cardiac output.

Signs

Techniques of examination are described elsewhere and will not be repeated here. Articles include history and examination, examining the pulse and jugular venous pressure. Remember to look and feel before auscultation. Murmurs and heart sounds in children is a complex topic that is discussed elsewhere.

• Disease of the aortic valve affects the character of the arterial pulse. Examination of the pulse in significant aortic stenosis 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.
• In aortic regurgitation, the pulse pressure will be wide with a sudden collapse of the pulse at the end. The classical Corrigan or "waterhammer pulse" is rarely felt these days as such marked disease is surgically corrected. For similar reasons, signs associated with very high pulse pressure such as the head bobbing with each pulse and pulsus bisferiens are largely of historical interest.
• 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 aortic stenosis 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.
• An abnormal aortic valve can become the site of subacute bacterial endocarditis. Clubbing of fingers takes about 6 weeks to develop. Splinter haemorrhages appear earlier.

Auscultation of the heart is described elsewhere.

• Heart sounds, whether normal or pathological, are caused by turbulent blood flow, laminar flow being silent. Auscultation of the heart involves listening to the heart sounds as well as any murmurs.
• In aortic stenosis, A2 is soft. 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 aneurism 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. An ejection click may be present, especially with bicuspid valves.
• A fourth heart sound indicates left ventricular hypertrophy in severe AS. If the left ventricle dilates and fails, a third heart sound may be heard.
• In aortic regurgitation, S1 is soft and there is an early diastolic murmur, best heard in the aortic area, with the patient sitting forward and in expiration. Both the murmur of regurgitation and the flow murmur from aortic dilatation are not well transmitted to the carotids. If significant regurgitation means that the stroke volume is very high, there will be an ejection flow murmur too.
• In subacute bacterial endocarditis, the only feature may be a change in nature of the murmur.
• Rarely, the aortic valve may collapse and become completely incompetent producing the sound of "a cooing dove". This requires urgent valve replacement.

There are a number of pathologies that can produce murmurs that are or appear to be from the aortic valve.

• Aortic stenosis
• Aortic sclerosis
• Aortic regurgitation
• Subacute bacterial endocarditis
• Dilatation of the root of the aorta that may also lead to a leaking valve.
• Flow murmurs. These are 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.
• Murmurs from mitral valves are not transmitted to the carotids but are heard best at the apex with the patient in the left lateral position and are transmitted to the mid-axillary line.
• 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 left ventricular hypertrophy or left ventricular strain.
• Chest x-ray may show cardiac enlargement, calcification of the aortic ring or evidence of other disease. It is often normal except in advanced disease.
• Echocardiography gives a very good indication of flow, obstruction and incomplete emptying. Doppler studies can indicate speed of ejection and give a very good idea of the degree of stenosis or regurgitation. Two-dimensional Doppler echocardiography is the imaging modality of choice.
• 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 arteriography is also performed in patients over 40 as there is a 50% chance of CHD too. Angina can occur without coronary artery disease¹ but, particularly in the elderly, it is a strong pointer to coronary narrowing² too.
• The risk factors for aortic sclerosis are similar to those for CHD and so similar investigations should be undertaken.³

Non-Drug

Avoid heavy exertion, especially with AS. Educate the patient about the need for prophylaxis against SBE.

Drugs

If there is heart failure due to aortic valve disease it will need to be treated in the usual way. ACE inhibitors can reduce left ventricular mass. In AR, vasodilators should be used with care, if at all.⁴ Failure of medical therapy is an indication for surgery.

Aortic sclerosis and stenosis in the older age group, should be seen as a strong risk for IHD and appropriate steps taken.⁵ Statins may even delay progress of the disease but ACE inhibitors do not.⁶

Surgical

It is possible to replace the diseased valve under cardiopulmonary bypass. As heart valves display very little in terms of tissue antigens it is possible to use xenografts such as pig's valves without fear of rejection. Prosthetic valves are a variation of the original Starr-Edwards valve. It produces a very loud noise that can often be heard across a quiet room and it requires long-term anticoagulation to prevent thrombo-embolism. In pure stenosis it may be possible to dilate the valve. This can be done by balloon inflation at angiography.

Surgery is a major procedure but it should best be undertaken before heart failure becomes established.⁷ Many of the adverse effects will reverse after surgery but if severe, they may persist.⁸

Particularly in adults with aortic stenosis, balloon valvotomy may be undertaken but it is usually as a palliative procedure, especially in those too ill to undergo surgery.⁹

Damaged valves are susceptible to SBE and appropriate precautions must be taken. The risk with disease of old age is rather less than in younger patients but it can occur and precautions should be taken in older patients too.

Calcified AS may produce small systemic emboli. The effect will depend upon where they lodge.

• Aortic valve disease will eventually lead to decompensation with raised end-diastolic pressure, increased pressure in the pulmonary system and congestive heart failure.
• Sudden death occurs in 3 to 5% of patients with AS. Adults with AS have a mortality rate of 9% per year. When symptoms develop, sudden death rises to 15 to 20% per year. Average survival is under 5 years. Patients with angina or syncope survive an average of 3 years. After the development of left ventricular failure, life expectancy is slightly over 1 year.
• After diagnosis of aortic regurgitation those who are asymptomatic with normal left ventricular function have a 5-year survival rate around 75%, falling to 50% at 10 years.
• Sudden death occurs in less than 0.2% of patients per year.
• In asymptomatic patients with left ventricular systolic dysfunction, there is progression to cardiac symptoms in more than 25% per year.
• In symptomatic patients the mortality rate is above 10% per year.
• Functional pathology in patients with AR is related to left ventricular volume overload and eventual myocardial dysfunction.
• Of those who develop the features of angina, syncope or heart failure, the approximate interval from the onset of symptoms to death is 2 years for heart failure, 3 years for syncope, and 5 years for angina.
• Even in the absence of significant obstruction, aortic sclerosis in the elderly is associated with a 50% increase in the risk of death from myocardial infarction.¹⁰
• The prognosis in even mild or moderate stenosis should not be underestimated as the outcome is rather poor.¹¹

Prevention of Subacute Bacterial Endocarditis

Bacteraemia can result in vegetations forming on damaged or abnormal valves. Anything that can cause a transient bacteraemia , including dental surgery, requires antibiotic cover. If in doubt, give cover, as SBE is very difficult to treat and has serious consequences. It makes sense to base the antibiotic on the likely organisms to enter the blood. For dentistry a single 3g of amoxicillin is usually given an hour before surgery. Clindamycin and azithromycin are used in those allergic to penicillin.

Whilst most doctors and dentists are aware of the need for antibiotic cover, body piercing and tattooing are also a risk¹² and their practitioners are unlikely to be so aware. Patients need to be educated about the need for cover for both medical and other procedures.¹³ The matter of prophylaxis has been addressed by a consensus paper¹⁴ in the European Heart Journal.

In view of this, a paper in 2006 from the Working Party of the British Society for Antimicrobial Chemotherapy may seem rather controversial.¹⁵ They reviewed the evidence from the American Heart Association, European Cardiac Society and British Cardiac Society as well as other sources. They also noted a Cochrane review¹⁶ which failed to find any benefit from prophylactic antibiotics before dental surgery in at-risk patients. General dental hygiene appears to be important in those at risk and general background bacteraemia from activites such as cleaning teeth appears to be a greater risk than dental surgery. The working party recomended that the indication for antibiotic prophylaxis for dental treatment should be restricted to patients who have a history of previous endocarditis, or who have had cardiac valve replacement surgery, or those with a surgically constructed systemic or pulmonary shunt or conduit.¹⁵

Enterococci, streptococci and staphylococci can cause endocarditis in procedures other than dentistry. Thee may include endoscopy of the gastrointestinal or respiratory tract, ENT, urology and gynaecology procedures. The article suggests appropriate antibiotics for the various procedures, based on likely relevant flora. They recommend that adequate skin cleaning should be undertaken but antibiotic prophylaxis is unnecessary for cardiac catheterisation and "cosmetic" piercing of ears or nipples.¹⁵

As this is at variance with traditional teaching, it needs to be discussed with the patient before implementation and it is probably best to assume that, if in doubt, give antibiotic. Even "correct use of the appropriate antibiotic" does not have 100% effectiveness.