and congenital heart disease

Chapter 38 Valvular and congenital heart disease




Questions


image What are the main clinical effects of cardiac valvular disease?

image What is rheumatic fever?

image What are the most common forms of congenital heart disease?

This chapter considers some diseases associated with abnormal patterns of flow through the heart.




Valvular heart disease


The significance of valvular heart disease is twofold: impairing normal function and increasing the risk of valve infection.


If normal valve function is impaired, there can be narrowing (stenosis), regurgitation (incompetence) or both, depending on the morphological abnormality. Disease of the heart may follow. For example, a stenotic aortic valve requires extra effort on the part of the left ventricle to expel blood (i.e. there is pressure overload). If the aortic valve is incompetent, part of the ejection fraction regurgitates back into the left ventricle, so the ventricle must work harder to maintain cardiac output (i.e. there is volume overload). Pressure or volume overload will lead to left ventricular hypertrophy and ultimately to heart failure. If both are present, the risk of heart failure is compounded. Cardiac valve abnormalities are also associated with sudden unexpected death.


There is also an increased risk of infective endocarditis as any anatomical abnormality makes the valve susceptible to infection by bacteria or other organisms circulating in the blood; infection rarely develops on normal valves. Injury to a mucosal surface can cause bacteria to enter the bloodstream (bacteraemia); for example, mouth commensal bacteria can enter the bloodstream following dental treatment or even brushing the teeth; Streptococcus viridans is the organism most often responsible in these circumstances. On other occasions, the source is intravenous drug abuse with injection of contaminated material. A characteristic feature of infective endocarditis is the formation of vegetations on the valves: irregular deposits of fibrin, platelets and bacteria.



Causes of valvular heart disease


A wide variety of diseases affect the heart valves. Some occur as congenital malformations (see below) while others are acquired.


Rheumatic fever can lead to valvular heart disease (chronic rheumatic heart disease). Rheumatic fever is an autoimmune condition in which inflammation of many organs follows an episode of pharyngitis caused by group A streptococci. It appears that antibodies directed against the streptococci cross-react with normal proteins present in the heart, joints and other tissues. Inflammation of the heart in rheumatic fever is called acute rheumatic carditis. When the valves are involved, vegetations form on them; these are smaller than the vegetations typical of infective endocarditis and do not contain bacteria. Healing occurs with scar formation; the fibrosis can cause stenosis by reducing the valve diameter and/or regurgitation by preventing proper closure of the valve leaflets.


Calcification of the aortic valve often occurs with ageing. Sometimes, the calcified leaflets become so rigid that clinically apparent stenosis occurs (calcific aortic stenosis). Although calcification is often seen in normal valves, it is more common in congenitally bicuspid aortic valves, a common lesion in which the aortic valve is composed of two leaflets instead of three.


The mitral valve can also be affected, leading to mitral regurgitation. Mitral regurgitation can occur in many different circumstances, including dilated valve rings in cardiac failure, papillary muscle dysfunction or rupture following myocardial infarction, and chronic rheumatic heart disease. However, the most common cause of isolated mitral regurgitation is mitral valve prolapse, sometimes called floppy mitral valve, caused by myxoid degeneration of the valve leaflets.

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Jul 3, 2016 | Posted by in MUSCULOSKELETAL MEDICINE | Comments Off on and congenital heart disease

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