Valvular heart disease

The proper functioning of the atrioventricular valves depends on the integrity of the valve annulus, the leaflets, the chordae tendineae and the papillary muscles. Malfunction of one or more components will adversely affect the performance of the valve. The semilunar valves allow blood to leave the ventricle during systole and prevent its regurgitation during diastole. The intrinsic shape of the valve allows this and disruption of the leaflets or the annulus can affect valve function. In the normal state a heart valve presents no resistance to forward flow but prevents regurgitation into the chamber proximal to it (Figs 48.6 and 48.7).

Mitral valve disease

Mitral stenosis

Apart from rare congenital anomalies which present in infancy, mitral stenosis is a consequence of rheumatic fever (Figs 48.8 and 48.9). During the healing phase of acute rheumatic fever, the valve leaflets become adherent to each other at their free border so that the commissures become obliterated. This narrows the valve orifice and further obstruction ensues when the cusps become thickened and stiff. There may be a degree of regurgitation if the valve is unable to close during systole. This is the most common inflammatory disease affecting the heart valves world-wide, but the incidence has fallen over the last few decades probably as a result of a combination of improved housing, early treatment of streptococcal infections with antibiotics and possibly a change in the virulence of the organism. The acute condition affects all parts of the heart but the major residual haemodynamic effects are the result of involvement of the valves. The mitral valve is most frequently involved with the aortic, tricuspid and pulmonary valves affected less often. The characteristic pathological finding in chronic rheumatic valve disease is thickened valve cusps with fused leaflets and fused chordae.

Haemodynamics. The passage of blood is obstructed from the left atrium to the left ventricle and the pressure in the left atrium rises. The pressure in the pulmonary veins and capillaries rises and, if it exceeds the oncotic pressure, there is acute pulmonary oedema. With time, the lungs are protected against pulmonary oedema by contraction of proximal pulmonary arterioles, but this leads to an increased demand on the right ventricle which ultimately fails. Raised systemic venous pressure leads to peripheral oedema.

A serious complication of mitral stenosis is the development of atrial fibrillation. This may herald the onset of symptoms and the enlargement of the left atrium may predispose to the formation of thrombus. Infective endocarditis is a further hazard (Fig. 48.10).

Clinical features. There may be signs of right heart failure and the pulse may be irregular if atrial fibrillation has occurred. The heart sounds may reveal an opening snap if the valve is still pliable and in pure mitral stenosis, a low rumbling diastolic murmur will be heard. The pulmonary component of the second heart sound may be loud depending on the severity of the pulmonary hypertension.

Investigation. Chest radiography. There is a small aortic outline and a prominent pulmonary artery. The left atrium enlarges (sometimes to an enormous degree) and the right ventricle also appears enlarged. The left ventricle is spared if there is no aortic valve disease and is of normal size or small (Figs 48.11 and 48.12).

Electrocardiography (ECG). The right ventricular hypertrophy results in tall QRS complexes in the right ventricular leads (combined height of Q and R>30 mm in leads V1-V3). There may also be a characteristic notched P wave (P mitrale) if sinus rhythm is present. In long-standing mitral stenosis there is usually atrial fibrillation and no P waves are seen.

Indications for surgery. Surgery is indicated for severe symptoms which are usually present if the pressure difference across the valve (during diastole) is 10 mmHg or more. Surgery is also indicated to protect the patient's future under certain circumstances, even if the patient is uncomplaining. Prognosis is determined by the severity of the stenosis, the size of the atrium, the onset of atrial fibrillation, rising pulmonary artery pressure and the unpredictable risk of embolism from a large fibrillating atrium. The operation carries a low risk, particularly if the valve can be conserved rather than replaced; there is a high prospect of success and improved prognosis thereafter.

Surgery is best avoided during pregnancy but may be necessary if the heart cannot meet the extra demands placed on it. Other valves may be affected and their relative importance to the patient's condition must be assessed. Age is not a contraindication but the risks from surgery increase with age. A pliant, mobile valve may benefit from balloon valvotomy but restenosis is likely. Stiff, calcified valves require replacement.

Mitral regurgitation

Any pathology affecting the integrity of the valve apparatus (annulus, leaflets, chordae tendineae and papillary muscles) will lead to mitral regurgitation. There are many causes of regurgitation but they can be broadly classified into four headings:

1. degenerative (floppy valve - myxomatous degeneration of the leaflets);

2. ischaemic (papillary muscle rupture);

3. rheumatic (stiffened leaflets unable to coapt);

4. endocarditis (leaflet destruction by the infective process).

Mild degrees of regurgitation are well tolerated and even severe regurgitation which has slowly progressed may cause little disability (Fig. 48.13). The ventricle ejects into a large compliant left atrium and the pulmonary capillary pressure may be little affected. There is a pansystolic murmur over the apex, but there may be no other clinical signs if the process has progressed slowly and the left ventricle has adapted to the volume load placed on it. In contrast, acute mitral regurgitation is not well tolerated because the atrium is small and it may be associated with left ventricular ischaemia (for example, with papillary muscle rupture). There may then be clinical and radiological evidence of acute pulmonary oedema.

Investigations. Electrocardiography. This does not really contribute to the diagnosis although there may be left ventricular hypertrophy (Fig. 48.14).

Chest radiography. There may be cardiomegaly and plethoric lung fields (Fig. 48.15).

Echocardiography. This will confirm the diagnosis and assess the degree of regurgitation.

Indications for operation. Patients with similar haemodynamics may have very different symptoms. Definite indications include severe symptoms, increasing pulmonary hypertension and uncontrolled endocarditis. Even in an asymptomatic patient it may be important to operate to protect the future if the left ventricle is beginning to dilate. The aim is to conserve the valve but, if it cannot be made competent by surgical valvuloplasty, replacement is necessary.

Mitral valve operations

Closed mitral valvotomy

This procedure was the first commonly performed valve operation which effectively and reproducibly relieved the obstruction of mitral stenosis. The heart is approached through a left thoracotomy, and purse-string sutures are placed at the apex of the left ventricle and in the left atrial appendage. A finger is introduced into the left atrial appendage and the mitral valve is assessed by direct palpation. A special dilator (Tubbs) is inserted through the left ventricular apex and across the mitral valve (Fig. 48.16). The dilator is opened and the fused commissures are split. Some regurgitation may occur and the process may have to be repeated after 10-15 years. For the best results, the valve should be pliant, judged clinically by its loud first sound and opening snap; the characteristics of the valve are now ascertained by two-dimensional echocardiography. In experienced hands, the mortality rate is less than 1 per cent. It is uncommonly performed at present as similar results can be achieved with percutaneous balloon valvotomy (Fig. 48.17).

Open repair

The current preference is to perform an open valvotomy with cardiopulmonary bypass under direct vision. This allows more accurate division of the commissures. In regurgitation, the valve can be repaired with a variety of techniques depending on the underlying pathology. Annular dilatation may be corrected by the use of an annuloplasty ring (Fig. 48.18). Leaflet destruction can be repaired with autologous pericardium and redundant tissue can be excised with direct repair to ensure leaflet apposition. Chordae can also be reconstructed. There is a trend to try and preserve the patient's native valve but if the valve is irreparable then it requires replacement.

Valve replacement

Valve replacement has undergone many modifications since it was introduced in the 1950s. There are two basic categories of replacement valve: biological and mechanical.

Biological valves. The most commonly used valve is the glutaraldehyde-preserved porcine valve, mounted on a sewing ring and frame (Carpentier). It has very similar haemodynamics to a human valve but it degenerates with time. Its main advantage is that it is not thrombogenic and therefore anticoagulants are not required. Its limited lifespan and nonthrombogenicity make it suitable for elderly patients. Other indications include women of child-bearing age and those in whom warfarin is contraindicated; however, a further valve replacement will become necessary within 10-15 years. Human valves (homograft) may be used particularly in the aortic position in young patients. There is an increasing trend to remove the native pulmonary valve and place it in the aortic position, using a homograft to replace the pulmonary valve (Ross). This operation is technically difficult and involves two valve operations (aortic and pulmonary) but the results are impressive with a low valve degeneration rate.

Mechanical valves. There are three commonly used designs: the cage and ball, the tilting disc and the bileaflet (Fig. 48.19). They are composed of a sewing ring and moving component(s) and have the advantage of durability. The main disadvantage is that the components of the valve are thrombogenic and therefore the patient requires systemic anti- coagulation, usually with warfarin. This subjects the patients to a lifetime of blood tests, medication and the constant threat of haemorrhagic complications (intracerebral, epistaxis, gastrointestinal bleed). All patients with prosthetic valves are at risk of developing endocarditis.

Results of treatment

The operative mortality rate for elective mitral valve replacement is about 5 per cent (Fig. 48.20). This depends largely on the state of the myocardium and the general condition (including age) of the patient. Any associated pathology such as endocarditis or ischaemic heart disease increases the risk.

The aortic valve

Aortic valve disease

  The normal aortic valve has three cusps corresponding to the sinuses of Valsalva, and named according to the relationships of the coronary orifices - right, left and noncoronary. Its surgical anatomy is challenging as it sits in the middle of the heart surrounded by the neighbouring three cardiac chambers: the right atrium (RA) and right ventricular (RV) outflow and the left atrium. The anterior leaflet of the mitral with the conducting tissue lies in continuity with the aortic valve annulus.

Stenosis

In young patients, stenosis is almost always congenital. In middle age, pathology is usually extensive calcification in a congenitally bicuspid valve. Senile stenosis is a result of thickening and calcification of the valve cusps but with no commissural fusion (unlike the appearances in rheumatic stenosis) (Figs 48.21-48.23). The left ventricle hypertrophies to overcome the stenosis but eventually the ventricular muscle fails. Patients are often asymptomatic until decompensation occurs. Dyspnoea, angina and exercise syncope are common complaints. There is an ejection systolic murmur over the aortic area radiating to the carotids. The pulse is slow rising in character and the apex beat may be displaced.

Investigations.

Chest radiography. There is cardiomegaly in the advanced case and poststenotic dilatation of the aorta (Fig. 48.23).
Electrocardiography. There is left ventricular hypertrophy with tall R waves in the lateral leads and sometime a strain pattern' (ST depression in the lateral leads).
Echocardiography. This confirms the diagnosis and estimates the gradient.
Coronary angiography is often undertaken to exclude concurrent coronary artery disease and a direct measurement of the pressure gradient (the peak systolic difference between the left ventricle and the aorta) across the valve may be obtained.

Indications for operation. Operation is indicated for symptoms. In asymptomatic patients the stenosis should be relieved before irretrievable left ventricular failure occurs. The natural history is poor with a median survival of less than 2 years once symptoms occur. The patient is at risk of sudden death related to the severity of the stenosis. An estimated or actual gradient of over 60 mmHg is sufficient indication for replacement, but it should be remembered that, as the left ventricular function deteriorates, the stroke volume falls and the measurable gradient becomes less.

Aortic regurgitation

This may be caused by a number of conditions which disrupt the integrity of the aortic valve by affecting the cusps or their ability to coapt (Figs 48.25 and 48.26). Marfan's syndrome causes dilatation of the aortic root thus preventing closure of the valve. Other causes include rheumatic fever, connective tissue disorders, aortic dissection, tertiary syphilis and endocarditis. The increased stroke volume results in left ventricular dilatation. The pulse is large volume and collapsing in character. Slowly progressive regurgitation may be well tolerated for years but the patient may complain of progressive dyspnoea on exertion and angina. Up to 70 per cent of the ejection fraction may return to the left ventricle in aortic regurgitation.

Investigations.

Chest radiography. The disease may be severe without overall increase in the cardiac dimensions and increasing size is an indication that the left ventricle is dilating.

Electrocardiography. There are enlarged R waves in the lateral chest leads denoting left ventricular hypertrophy and a strain' pattern (ST depression) but the rhythm is normally regular.

Echocardiography with a Doppler probe will confirm the regurgitation.

Coronary angiography may be required if coexistent ischaemic heart disease is suspected.

Indications for operation. Minor degrees of aortic regurgitation are well tolerated but if the ventricle deteriorates and dilates it may be too late to retrieve the situation. The end- systolic dimension, as measured by echocardiography, is often the best serial measure of worsening left ventricular dilatation and a figure of over 5.5 cmHg indicates severe pathology warranting valve replacement. Patients with severe symptoms or worsening left ventricular dilatation are candidates for surgery.

Aortic valve surgery

Unlike mitral valve surgery, there are few occasions where the aortic valve can be repaired and usually the valve requires replacement. This is performed through a median sternotomy on cardiopulmonary bypass. The aorta is cross- clamped and opened proximally to reveal the diseased valve. Cardioplegic solution is infused into the coronary arteries to arrest the heart in diastole. The valve is then excised leaving the annulus in situ but removing as much calcific debris as possible. The replacement valve is then sutured into position at the level of the native annulus and the aortotomy is closed. The heart is de-aired and the cross-clamp released, thus reperfusing the myocardium.

Results of treatment

The operative mortality rate for elective aortic valve surgery is less than 5 per cent, but emergency surgery, surgery for endocarditis or surgery in older patients results in a higher operative mortality rate (Fig. 48.27).

Tricuspid valve

Tricuspid valve disease

This valve is rarely involved in isolation by a disease process (Fig. 48.28). In rheumatic fever, the aortic and mitral valves are usually affected as well, with stenosis more common than regurgitation. The carcinoid syndrome may produce isolated stenosis.

Isolated tricuspid regurgitation is almost exclusively caused by endocarditis in drug addicts who inject intravenously. There is characteristic venous pulsation in the neck and systolic pulsation of the liver, leading to abdominal pain and ascites.

It may be possible to perform a valvotomy for stenosis but this usually leads to severe incompetence. In these cases it is necessary to replace the valve. For regurgitation there are numerous ways to perform valvuloplasty, all of which seem to produce reasonable results. The mortality from tricuspid valve surgery is high, largely as a result of the associated pathology from other valve lesions.

Pulmonary valvular disease

Acquired pulmonary valve disease is rare and usually results from the carcinoid syndrome or rheumatic fever. In both diseases, other valve lesions usually dominate the clinical picture. Pulmonary valvotomy is usually feasible for stenosis. Replacement is almost never performed.

Prosthetic valve

  Prosthetic valve disease

  There is now a large cohort of patients who are long-term survivors after prosthetic valve surgery and a number of problems and complications can occur. Some of these problems may be technical and related to the valve itself and others are the result of valve replacement in general (Fig.48.29).

Valve failure. From about 7 years after implantation, cases begin to come back for reoperation with increasing frequency. The deterioration results in stenosis, incompetence or both. This usually progresses slowly, allowing planned replacement in most cases (Fig. 48.30).

Failure of a mechanical prosthesis can be sudden and catastrophic, resulting in a rapid demise.

Thromboembolism. This is always a risk with foreign material in the circulation (Fig. 48.31). The risk is low with the biological valves and anticoagulation is unnecessary. This makes this type of valve suitable for elderly patients. Anticoagulation is mandatory for mechanical valves and this results in frequent blood tests and the associated bleeding problems.

Paravalvular leak. This is usually a technical problem resulting in a leak between the valve ring and the native annulus (Fig. 48.32). It may also be the result of infection. The leak can cause haemolytic anaemia or haemodynamic compromise and the valve may need replacement.

Endocarditis is a serious complication. All patients must be made aware of this potential complication and must have prophylactic antibiotics for any type of surgical or dental procedure. There are marked systemic symptoms and the infective process may progress rapidly to destroy the native valve annulus, leading to abscess formation.

The mortality rate from this condition is very high (>50 per cent) even with antibiotics, and early surgery to remove the infected prosthesis is recommended. Aggressive surgical therapy using a homograft wherever possible has reduced the mortality rate to less than 20 per cent. Management should be a joint approach with involvement of the surgeon, physician and microbiologist.

Infective endocarditis

Endocarditis of a heart valve occurs when a suitable organism is exposed to a vulnerable intracardiac site. Most commonly, this is the patient's own abnormal valve or a valve replacement. Rarely it can occur in an intracardiac shunt (ventricular septal defect or patent ductus arteriosus). The bloodstream is often exposed to transient bacteraemias, particularly during dental treatment, but any microorganism, except viruses, can lead to endocarditis.

The most common organisms are:

Streptococcus viridians;

· staphylococci;

· enterococci.

Endocarditis seems to become established in regions of turbulent flow in the heart. Fibrinous deposits containing platelets and the organisms develop to form characteristic vegetations. These may invade the surrounding tissue and destroy it, leading to valve incompetence and abscess formation (Fig. 48.33). Embolic debris may become lodged in the peripheries causing a variety of clinical features.

Presentation. There is often an influenza-type illness with generalised pain. The symptoms may fluctuate over several weeks, but once the endocarditis begins to destroy tissue then the patient's condition may markedly worsen. An important part of the history is the presence of an underlying congenital or valvular anomaly. Anaemia may be present together with splinter haemorrhages and tender nodules (Osler's nodes) in the finger pulps. A detailed examination of the cardiovascular system should note any murmurs or change of murmur from those heard previously. Splenomegaly may occur and retinal emboli should be specifically excluded. Daily examination is mandatory to detect any deterioration in the patient's condition.

Blood cultures are taken from up to six different sites before antibiotics are given. Once an organism is grown, the antibiotics can be tailored to the organism isolated. About 80 per cent of blood cultures will grow an organism in this condition. The chest radiograph is often normal but the cardiac outline may enlarge if valve regurgitation is present and metastatic lung abscesses may occur. The EGG may show a lengthened P-R interval or degrees of heart block if an aortic root abscess has formed. Echocardiography is an important investigation because it will demonstrate the motion of the heart, the state of the valves and any vegetations present. Serial echocardiograms will monitor response to treatment.

In spite of the introduction of antibiotics, the 1-year mortality rate of this condition is 25-3 0 per cent. Cure is often possible if a sensitive organism is present and treatment started early. A delay in the diagnosis, inadequate treatment, prosthetic valve endocarditis and resistant organisms all reduce the likelihood of cure. Urgent surgery may be necessary if the haemodynamic state deteriorates while infection is still present. If the patient is haemodynamically stable, he or she needs 6 weeks of intravenous antibiotics. Indications for surgical intervention are:

· an important mechanical lesion that can be corrected (regurgitant valve or acquired shunt);

· development of an abscess resulting in heart block;

· uncontrolled infection in spite of seemingly adequate antibiotic regimens.