Our 13th Pathology Spotlight features a heart with mitral valve disease.
The specimen is a horizontal cut through a heart showing the thick muscular wall of the left ventricle enclosing the lower end of a prosthetic mitral valve which has been stitched into position to replace a diseased one. The mitral valve is the valve that controls the flow of blood from the left atrium to the left ventricle and lies between the two chambers. The left ventricle develops the highest blood pressure in the body when it pumps blood out of the heart to the whole body. As the ventricle pumps, the valve closes to prevent back-flow allowing blood to be ejected through the aorta, and so the valve is regularly under very high pressure and is liable to damage. Mitral valve disease (stenosis) occurs when valve gets damaged and becomes scarred. As a result it cannot open as widely as it should and blood flow from the left atrium to ventricle is restricted, reducing cardiac output and causing light-headedness and tiredness. In addition the left atrium swells as pressure builds up, and this back pressure causes fluid to collect in the lungs (pulmonary oedema), which results in breathlessness. Under these conditions a valve replacement is a possibility.
This replacement valve is of the ‘ball and cage’ type and is called a Starr-Edwards valve similar to the one in the image below.
It has a relatively simple action :-
1) when pressure is high during atrial contraction, the ball is pushed to the bottom of the cage, opening the aperture and allowing blood to flow down into the ventricle
2) When ventricular contraction occurs and the pressure increase in the ventricle, this drives the ball back up into the aperture preventing back-flow of blood.
In adults, mitral stenosis occurs most commonly in those who have had an infection with a common throat bacterium called Streptococcus. In some people the body’s response to the infection leads on to rheumatic fever, an illness which may cause permanent damage to the mitral valve –rheumatic heart disease. This has been decreasing in developed countries since the early 20th century but remains a significant health problem in developing countries with an estimated 250,000 new cases annually worldwide.