What happens to the left atrium in mitral regurgitation (MR)?

In mitral regurgitation, the left atrium experiences volume overload due to the backflow of blood from the left ventricle during systole. This backflow occurs because the mitral valve does not close properly, allowing some of the blood that should be pumped into the aorta to instead flow back into the left atrium. Over time, this increased volume of blood leads to left atrial dilation, resulting in an enlargement of the left atrium.

As the left atrium enlarges, it can also increase the risk of complications such as atrial fibrillation and thrombus (blood clot) formation due to stasis of blood flow. This enlargement is a significant clinical finding in patients with chronic mitral regurgitation and can have important implications for management and treatment.

The other outcomes, such as a decrease in size, being unchanged, or becoming scarred, do not accurately reflect the physiological processes happening in the left atrium in the context of mitral regurgitation.