Valve Pathology PDF

Valve pathology Valvular heart disease can be congenital (born with the problem) or acquired (resulting from illness after birth) Incompetent valve: Insufficiency results from failure of a valve to close completely, thereby allowing regurgitation (backflow) of blood. Stenotic valve: Stenosis is the...

Valve pathology Valvular heart disease can be congenital (born with the problem) or acquired (resulting from illness after birth) Incompetent valve: Insufficiency results from failure of a valve to close completely, thereby allowing regurgitation (backflow) of blood. Stenotic valve: Stenosis is the failure of a valve to open completely, obstructing forward flow. Stenotic and incompetent Turbulent flow through diseased valves typically produces abnormal heart sounds called murmurs. Bicuspid aortic valve 1% of population has a congenital bicuspid valve Aortic valve is replaced by complete fibrous tissue or unicommissural Aortic valve stenosis Aortic valve incompetence Intrinsic abnormality (like endocarditis) or dilatation of aortic root (idiopathic/ Marfan`s syndrome) due to accumulation of mucus in the wall of aorta Mitral valve incompetence Floppy mitral valve where the cusps are larger than normal, dome shaped and the chordae tendinae are elongated Rheumatic valvular disease Rheumatic fever is an acute, immunologically mediated, multisystem inflammatory disease that occurs after group A β-hemolytic streptococcal throat or skin infections Rheumatic heart disease is the cardiac manifestation of rheumatic fever. It is associated with inflammation of all parts of the heart (pan carditis), but valvular inflammation and scarring produce the most important clinical features. The valvular disease principally takes the form of deforming fibrotic mitral stenosis; indeed rheumatic heart disease is essentially the only cause of acquired mitral stenosis. The incidence of rheumatic fever has declined remarkably in many parts of the Western world over the past several decades due to a combination of improved socioeconomic conditions, rapid diagnosis and treatment of streptococcal pharyngitis, and a decline in the virulence of many strains of group A streptococci. Nevertheless, in developing countries and economically depressed urban areas in the United States, rheumatic fever and rheumatic heart disease remain important public health problems. Pathogenesis Acute rheumatic fever is a hypersensitivity reaction classically attributed to antibodies directed against group A streptococcal molecules that cross-react with host myocardial antigens Antibodies against M proteins of certain streptococcal strains bind to proteins in the myocardium and cardiac valves and cause injury through the activation of complement and Fc receptor–bearing cells The characteristic 2- to 3-week delay in symptom onset after infection is explained by the time needed to generate an immune response; streptococci are completely absent from the lesions. Since only a small minority of infected patients develop rheumatic fever (estimated at 3%), genetic susceptibility to the development of the cross-reactive immune responses is likely in those affected. The deforming fibrotic lesions are the predictable consequence of healing and scarring associated with the resolution of the acute inflammation. Acute rheumatic fever is characterized by discrete inflammatory foci called Aschoff bodies; these are collections of lymphocytes (primarily T cells), scattered plasma cells, and plump activated macrophages called Anitschkow cells associated with zones of fibrinoid necrosis. Rheumatic fever is said to cause pancarditis, The pericardium may exhibit a fibrinous exudate, which generally resolves without sequelae. The myocardial involvement—myocarditis—takes the form of scattered Aschoff bodies within the interstitial connective tissue. Valve involvement results in fibrinoid necrosis and fibrin deposition along the lines of closure forming 1- to 2-mm vegetations—verrucae—that cause little disturbance in cardiac function. Chronic rheumatic heart disease is characterized by organization of acute inflammation and subsequent scarring. Aschoff bodies are replaced by fibrous scar so that these lesions are rarely seen in chronic disease. Most characteristically, valve cusps and leaflets become permanently thickened and retracted. Classically, the mitral valves exhibit leaflet thickening, commissural fusion and shortening, and thickening and fusion of the chordae tendineae Fibrous bridging across the valvular commissures and calcification create “fishmouth” or “buttonhole” stenosis The most important functional consequence of rheumatic heart disease is valvular stenosis and regurgitation; stenosis tends to predominate. The mitral valve alone is involved in 70% of cases, and combined mitral and aortic disease in seen in another 25%; the tricuspid valve is less frequently involved; and the pulmonic valve almost always escapes injury. With tight mitral stenosis, the left atrium progressively dilates owing to pressure overload, precipitating atrial fibrillations, and formation of large mural thrombi is common. Long-standing passive venous congestion gives rise to pulmonary vascular and parenchymal changes typical of left-sided heart failure. In time, this leads to right ventricular hypertrophy and failure. With pure mitral stenosis, the left ventricle generally is normal. Clinical features Acute rheumatic fever occurs most often in children; the principal clinical manifestation is carditis Symptoms in all age groups typically begin 2 to 3 weeks after streptococcal infection and are heralded by fever and migratory polyarthritis—one large joint after another becomes painful and swollen for a period of days, followed by spontaneous resolution with no residual disability. Although cultures are negative for streptococci at the time of symptom onset, serum titers of antibodies against one or more streptococcal antigens (e.g., streptolysin O or DNAase) usually are elevated. The diagnosis of acute rheumatic fever is made based on serologic evidence of previous streptococcal infection in conjunction with two or more of the Jones criteria: (1)carditis; (2) migratory polyarthritis of large joints; (3) subcutaneous nodules; (4) erythematous annular rash (erythema marginatum) in the skin; and (5) Sydenham chorea, a neurologic disorder characterized by involuntary purposeless, rapid movements. Minor criteria such as fever, arthralgias, EKG changes, or elevated acute phase reactants also can help support the diagnosis. Infective endocarditis This is an inflammatory condition affecting the endocardium particularly on the heart valves It leads to the development of large, friable, vegetation on the heart valves, fragments of these thrombi split from the main mass, embolize around blood stream, and may impact in distant vessels causing infarction and spread of infection Acute IE occur on previous normal valves, this form is destructive with fatal results The patient is feverish and becomes rapidly ill, the classic organism is staphylococcus aureus, usually in intravenous drug abusers because the inject dirty drug solutions affecting right sided valves Subacute IE is a slow disease that occur on top of diseased valves by rheumatic heart disease or prosthetic The organism is the less virulent streptococcus viridans, the vegetations are smaller, firmer and embolization less common Morphology The vegetations are usually 0.5-1 cm in subacute IE and 1-2 cm in acute IE The vegetation may be single or form a confluent valve-destroying mass In acute IE perforation of valve cusp may be seen or infiltration of the myocardium with abscess formation The vegetations are on the upper aspect of tricuspid and mitral valves and on the ventricular surface of pulmonary and aortic valves Consequences Embolus formation: may travel along coronary artery or systemic circulation, after impaction, infection weakens the wall of the vessel, leading to a weak dilated artery (mycotic aneurysm) Valve perforation and destruction leading to spread of infection into the myocardium which may lead to heart failure Immune complex tissue injury which may cause glomerulonephritis in kidney, vasculitis of skin or arthralgia in joints Book chapter 3 pages 30-33