Heart valve disease, also known as valvular heart disease, is a condition where the valves of the heart do not function properly thereby affecting the normal circulation through the heart ad great vessels. The normal function of the tricuspid, mitral, aortic and pulmonary valves are discussed further under Heart Valves Function.
There are four heart valves – two atrioventricular valves and two semilunar valves. The atrioventricular valves (AV) lie between the atrium and ventricle – tricuspid valve between the right atrium and ventricle and mitral valve between the left atrium and ventricle. The semilunar valves lie at the junction of the ventricle and great blood vessel that stems from it – pulmonary (pulmonic) valve between the right ventricle and pulmonary artery and aortic valve between the left ventricle and aorta.
Heart valve disease can be of two types :
- Stenosis which is failure of the valve to open completely.
- Insufficiency which is failure of the valve to close completely. This is also known as regurgitation or incompetence.
One or both diseases can affect a valve and only valve may be involved (isolated) or more than one valve (combined). Heart valve diseases may be congenital (present from birth) or acquired (develop during life). While any valve may be involved in valvular disease, the aortic and mitral valves are more frequently affected.
Effects of Heart Valve Disease
Aortic Valve Disease
In both aortic stenosis and aortic insufficiency, the left ventricle fails to empty completely. With stenosis, all the blood cannot leave the ventricle since the valve does not open fully whereas with stenosis some of the blood in the aorta flows back into the ventricle because the valve does not completely close. The cardiac output is therefore decreased due to a reduced stroke volume.
In order to compensate. the muscle of the left ventricular wall increases in size (hypertrophy). This allows the ventricle to push out more blood on each contraction. At the same time the blood volume is increased in order to increase venous return and cardiac output. These compensatory mechanisms cannot sustain the cardiac output indefinitely. Left ventricular failure (left sided heart failure) occurs either due to a progression in the valvular disease or failure of the left ventricle to cope with the increased workload.
Mitral Valve Disease
In mitral stenosis and mitral insufficiency, the left atrium fails to empty completely. Either the blood flows back into the atrium from the ventricle during systole (insufficiency) since the mitral valve does not close fully or all the blood does not pass into the ventricle (stenosis) since the valve does not open completely. Therefore the left ventricle cannot pass out enough blood into the aorta to maintain a normal cardiac output.
Blood backs up in the atrium and pulmonary vessels and even the right ventricle. The pressure in the left atrium increases and the chamber enlarges. This affects the cardiac conduction system and leads to atrial fibrillation which also impairs the normal pumping of blood from the heart. The body compensates by increasing blood volume and further straining the heart. The right ventricle enlarges in an attempt to increase output as a result of the backed up blood.