15.8: Mitral Stenosis I: Introduction

Mitral Valve Stenosis (MVS) is a heart condition where the mitral valve narrows, impeding blood circulation from the left atrium to the left ventricle. The etiology and pathophysiology of this condition are multifaceted, leading to a cascade of cardiovascular complications.

Causes of Mitral Valve Stenosis

1. Rheumatic Heart Disease: It is the main cause of mitral valve stenosis, particularly in developing nations. This condition arises from rheumatic fever, an inflammatory illness resulting from inadequately treated or untreated streptococcal infections like strep throat or scarlet fever.
2. Congenital Factors: In some individuals, MVS is congenital, meaning the condition is present at birth due to malformations of the mitral valve structure.
3. Autoimmune Disorders: Systemic diseases such as rheumatoid arthritis and systemic lupus erythematosus can contribute to the development of MVS.
4. Radiation exposure: Patients who have undergone radiation therapy in the past are at higher risk of radiation exposure, especially in the chest area, and may be at risk of developing MVS.
5. Age-related Changes: In older adults, severe mitral annular calcification can also lead to stenosis.

Pathophysiology of Mitral Valve Stenosis

1. Structural Changes in the Valve: Rheumatic infective endocarditis leads to scarring of the mitral valve leaflets and chordae tendineae. It also results in contractures and adhesions, particularly around the commissures. These deformities distort the valve, causing it to acquire a "fish mouth" shape due to the thickening and shortening of its structures.
2. Impaired Blood Flow: The structural alterations in the mitral valve obstruct blood flow between the left atrium and ventricle during diastole, leading to a significant pressure differential between these chambers.
3. Pressure and Volume Changes: The obstruction causes increased pressure and volume in the left atrium, leading to elevated pulmonary vasculature pressure and the risk of atrial fibrillation.
4. Left Atrial Hypertrophy and Dilation: The left atrium struggles to push blood into the left ventricle, causing a higher residual blood volume in the atrium. Over time, this leads to left atrial hypertrophy and dilation.
5. Reduced Cardiac Output: The decreased flow into the left ventricle results in reduced ventricular filling and, as a result, a decrease in cardiac output.
6. Pulmonary and Right Ventricular Effects: The failure of the stenotic valve to protect the pulmonary veins from blood backflow from the atrium leads to pulmonary circulation congestion, placing excessive strain on the right ventricle. It can lead to right ventricular hypertrophy and eventual failure.
7. Exacerbation by Increased Heart Rate: An increased heart rate shortens the diastolic phase, decreasing the time for forward blood flow and causing more blood to back up into the pulmonary veins. It further reduces cardiac output and increases pulmonary pressures.