Biology – The heart | e-Consult

Mitral valve stenosis, the narrowing of the mitral valve, significantly impacts the cardiac cycle. The primary effect is a restriction in blood flow from the left atrium to the left ventricle during diastole. This restriction leads to a number of consequences:

Diastole: The stenotic valve restricts blood flow, resulting in a prolongation of diastole. The left atrium fills more slowly, and the pressure in the left atrium rises. The mitral valve opens later and only to a smaller degree, meaning less blood flows into the left ventricle during diastole. This increased atrial pressure can also lead to pulmonary congestion.

Systole: The pressure gradient between the left atrium and left ventricle is reduced. While the aortic valve still opens when ventricular pressure exceeds aortic pressure, the reduced filling during diastole means the left ventricle has less blood available for ejection. The ejection fraction (the percentage of blood ejected with each contraction) is likely to be reduced.

Pressures: The pressure in the left atrium is elevated during diastole. The pressure in the left ventricle may also be elevated, particularly during diastole, due to the increased volume. The pressure in the aorta may be relatively normal, although it could be affected if the heart is working harder to compensate for the reduced cardiac output.

Consequences for Cardiac Output: The reduced filling of the left ventricle during diastole leads to a decreased cardiac output. The heart has to work harder to generate the necessary pressure to overcome the resistance in the stenotic valve. This can lead to symptoms such as shortness of breath, fatigue, and swelling in the legs (edema). Over time, the heart may enlarge (left atrial enlargement) as it attempts to compensate for the reduced filling, further impacting its efficiency.