Diseases of the Endocardium and Valves

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Primary diseases of the non-valvar endocardium are rare
As a long-term result of myocardial infarction that involves the endocardial surface,
the endocardium is damaged and thickened, and may be a predisposing site for mural thrombosis,
although this complication is more frequent in the immediate post-infarctive period.
Similar patchy areas of endocardial thickening can be seen (particularly in the left atrium) where the flow through the mitral valve has been modified by valve disease. A jet of blood squirting through the
incompetent mitral valve during systole can produce a patch of endocardial thickening (jet lesion)
where the jet hits the atrial wall.
Endocardial thickening in the right side of the heart is rare, but may occur in the carcinoid syndrome or in some congenital heart disease, where there is a left-to-right shunt.
Diffuse endocardial thickening in the left heart is seen in two diseases, both of which are rare in the UK, Europe and USA.
In endocardial fibroelastosis the endocardium becomes greatly thickened and replaced by fibroelastic tissue, mainly in the left heart, often extending over the papillary muscles.
This disease occurs in babies and young children, presenting with unexplained heart failure. Its cause is not known.
In endomyocardial fibrosis there is fibrous thickening of the endocardium and the inner myocardium, leading to limitation of cardiac contraction. Occurring particularly in Central Africa, this condition is often associated with peripheral blood eosinophilia; its cause is not known.
Both of the above conditions lead to cardiac failure by restricting contraction of the cardiac chambers during systole; they are sometimes classified as a form of cardiomyopathy (restrictive cardiomyopathy) by clinicians, despite the fact that the primary structural abnormality is endocardial.

The endocardium of the right ventricle shows smooth white thickening in this patient with long-standing carcinoid syndrome.
Inflammatory disorders of heart valves cause vegetations and late scarring Inflammation of the endocardium of heart valves (valvulitis) is an important cause of valve disease, which results either from immune-mediated damage initiating inflammation in the valve cusps (seen in acute rheumatic fever, or from damage due to infection, e.g. in bacterial and fungal endocarditis.

Inflammatory damage to heart valves has two important consequences:
1 Valve collagen is exposed, causing thrombus deposition. The thrombus develops as exophytic nodules or irregular warty growths on the valve leaflets, called vegetations.
2 Inflammation and thrombus formation on the valve causes organization with collagenous scarring. This
causes physical distortion to the valve cusps and renders them mechanically and functionally abnormal.
The valves on the left side of the heart (mitral and aortic) are much more frequently the site of endocarditis and thrombotic vegetation formation than the valves of the right side of the heart (tricuspid and pulmonary); thus, embolic material from valve thrombosis passes into the systemic circulation and produces infarcts in the systemic organs.
The main cause of chronic scarring of valves is rheumatic fever, the incidence of which has decreased in many countries in recent years.

The rheumatic pericarditis and myocarditis that arise in the acute phase usually resolve without long-term ill-effect. However, the damage to the valves heals by progressive fibrosis, with fibrous thickening of the valve leaflets and associated chordae tendineae.
The valve leaflets become thickened, fibrotic and shrunken, often with fusion to their partners, and there is frequent secondary deposition of calcium.
Many patients with chronic scarring of valves give no history of having had rheumatic fever; the non-committal term 'post-inflammatory scarring' is used in such cases.
A thrombotic vegetation on the mitral valve caused by inflammation of the valve.
Some vegetations form on valves as a consequence of hypercoagulability of blood.
In patients who are severely debilitated, for example with widespread metastatic carcinoma or severe chronic infections, small, non-infective, firm, platelet-rich vegetations (marantic vegetations) may form on the heart valves of the left side of the heart.
The reason for this is hypercoagulability of blood caused by an acute phase response, manifest by a very high ESR.
Vegetations may form on the heart valves in SLE (Libman-Sacks endocarditis).
This is related to the presence of high titres of anti-cardiolipin antibodies, which cause platelet aggregation.

The aortic valve leaflets bear pink thrombotic vegetations (marantic vegetations).

Mitral stenosis causes left-sided heart failure and predisposes to atrial thrombosis
Mitral stenosis is caused by post-inflammatory scarring of the valve cusps. A history of rheumatic fever is obtained in only about half of the cases, and a chronic rheumatic aetiology cannot be assumed in all instances.
Valves cusps are thickened and there is fusion of commissures.
Chordae tendineae are thickened and fused, resulting in a funnel-shaped, narrowed valve orifice with a slit-like opening.
Failure of the left atrium to empty through the stenosed valve leads to left atrial hypertrophy and dilatation.
Back pressure causes pulmonary hypertension and pulmonary vascular congestion, which commonly causes haemoptysis.

Left-sided cardiac failure develops.
Atrial fibrillation is a common complication, with resultant development of left atrial thrombosis.
Mitral incompetence leads to left-sided heart failure and has many causes
Regurgitation from the left ventricle back into the atrium is the result of mitral valve incompetence,
the main causes of which are:
post-inflammatory scarring (commonly rheumatic)
papillary muscle dysfunction after infarction
left ventricular dilatation
cusp destruction by infection (infective endocarditis)
floppy mitral valve syndrome.
If the valve is suddenly rendered incompetent (papillary muscle rupture or infective perforation),
severe acute pulmonary oedema develops.
In most cases regurgitation develops slowly and results in left ventricular enlargement
and a giant left atrium (caused by its filling with blood in systole).
Progressive left-sided cardiac failure develops with time.
Mitral valve prolapse (floppy valve syndrome) is now much more common than rheumatic mitral valve disease.
The valve leaflet becomes degenerate, with myxoid degeneration of the central zona fibrosa.
The valve leaflet is soft and bulges upwards into the atrium during systole.
The posterior mitral leaflet is most commonly involved, and mild valve incompetence is the result of the
hypermobility of the leaflet. However, there is a danger of rupture of one of the chordae,
leading to severe valve incompetence.
It is most common in women and usually presents in young adulthood.
In some cases there is a family history.

Aortic valve disease is a cause of sudden cardiac death
The aortic valve is frequently affected by disease resulting either in stenosis or in incompetence.
Aortic stenosis is most commonly due to calcification of a congenital bicuspid aortic valve, post-inflammatory
scarring after rheumatic fever, or senile calcific degeneration.
Isolated fibrosis and calcification of the aortic valve, with no evidence of mitral valve involvement or
evidence of previous rheumatic fever, is the most common valve disease, although its cause is unknown.
The disease is most commonly seen in bicuspid aortic valves, a common congenital malformation,
but can also been seen in originally normal valves with three cusps.
Aortic regurgitation has four main causes:
Retraction of cusps due to post-inflammatory scarring.
Erosion of cusps by inflammation in infective endocarditis.
Retraction of cusps due to senile calcification.
Dilatation of the aortic wall and valve ring caused by inflammatory diseases (e.g. syphilis, ankylosing
spondylitis).

Mixed Stenosis and regurgitation is common.

Aortic valve disease is a cause of sudden cardiac death
The aortic valve is frequently affected by disease resulting either in stenosis or in incompetence.

Disease of the pulmonary and tricuspid valves is uncommon
The valves of the right side of the heart are infrequently involved in disease, but may be damaged by post-inflammatory scarring in rheumatic heart disease.
Endocarditis of the right side of the heart is seen in association with intravenous drug abuse.
For reasons that are as yet unclear, the carcinoid syndrome, caused by excess 5-hydroxytryptamine secretion by tumour, can result in endocardial fibrosis of the right side of the heart and pulmonary stenosis.
Infective endocarditis is caused by infection of heart valves or other areas of endocardium.
Infection of the endocardium, whether on heart valves or elsewhere, is termed 'infective endocarditis'.
There are two broad groups of cases.
In one group, patients are predisposed to infection by a structural abnormality of heart valves or by congenital cardiac defects. The incidence of this pattern has increased in Western countries in recent years, mainly as a result of patients surviving with structurally abnormal hearts and heart valves.
The infective organisms responsible are of low pathogenicity and are derived from normal commensal organisms of skin, mouth, urinary tract and gut.
Organisms that enter the blood in trivialepisodes of bacteraemia become enmeshed in platelet aggregates on the surface of abnormal endocardium, growing to cause persistent infection.
The main underlying abnormalities in this group are congenital bicuspid aortic valves, post-inflammatory scarring, mitral valve prolapse syndrome,and prosthetic valves.
Infection of normal valves accounts for the remaining cases of infective endocarditis.
In contrast to the first group, infection is with pathogenic organisms that directly invade the valve and cause rapid destruction.
This pattern of disease is predisposed by conditions that promote entry of pathogenic organisms into the blood. It is seen in intravenous-drug addicts, after open-heart surgery, and following septicaemia from other causes.

The valves become thick and fibrotic, with fusion of the commissures and heavy calcification.
The thickening and fusion lead to reduction of the valve lumen, so that flow out of the valve is greatly reduced during systole (aortic stenosis).
Furthermore, because the valve leaflets are rigid and fused, they are unable to close completely,
and there is flow of blood back into the left ventricle during diastole(aortic regurgitation).

Infective endocarditis occurs as two main clinical syndromes Following on from the two main groups of cases of infective endocarditis described earlier, there are two main clinical disease patterns.
Acute infective endocarditis is usually due to a virulent organism, Staphylococcus
aureus, and can occur on a previously normal heart valve. The bacteria proliferate in the valve, and cause necrosis, with generation of thrombotic vegetations. The pathogenic bacteria lead to destruction of the valve leaflets, with perforation and acute disturbance of valve function leading to acute cardiac failure. The disease is rapidly progressive and often fatal.

Sub-acute bacterial endocarditis generally occurs on structurally abnormal valves.
The causative organisms are generally poorly virulent (Streptococcus viridans) and proliferate slowly in thrombotic vegetations on the damaged valve surface.
In most cases, they cause very gradual valve destruction, stimulating the formation of thrombus with potential for systemic embolization. Many of the effects of this pattern of infection are through immunological phenomena and generation of cytokines from persisting low-grade inflammation.

The main clinical effects of sub-acute infective endocarditis are:
Small emboli of infected thrombotic material enter the systemic circulation, producing infarcts in many organs, particularly brain, spleen, and kidneys. These necrotic areas may, in turn, become infected by organisms in the occluding thrombus.
Gradual destruction of valve cusps leads to features of valve incompetence with cardiac failure.
Immune complexes against antigens in the infecting organism are trapped in small vessels. They cause skin petechiae and microhaemorrhages seen in the retina and skin, particularly around the finger nails. They also cause a form of glomerulonephritis.
Cytokine generation from low-grade infection leads to systemic features of fever, weight loss and malaise.

The aortic valve cusps are partly destroyed by the large irregular vegetations.
Numerous small vegetations are present on the mitral valve leaflets which are thickened and distorted as a result of rheumatic mitral valve disease.
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