What distinguishes primary mitral regurgitation from secondary mitral regurgitation?

Primary mitral regurgitation is characterized by the dysfunction of the mitral valve itself, often resulting from issues such as degenerative changes, rheumatic disease, or trauma. In this context, primary refers to abnormalities directly affecting the mitral valve structure, causing it to be incapable of closing properly during systole, which leads to backward flow of blood into the left atrium.

Secondary mitral regurgitation, on the other hand, is not primarily due to dysfunctional leaflets or chords but rather occurs due to heart conditions that affect the valve's functioning indirectly. This may include left ventricle (LV) dilation or other forms of structural heart disease that alter the geometry of the heart and impact the functioning of the mitral valve without intrinsic damage to the valve itself.

Thus, understanding the distinction lies in recognizing that primary mitral regurgitation involves direct pathologies affecting the valve, while secondary mitral regurgitation arises from structural heart disease leading to functional impairment of the mitral valve. This is why option D correctly differentiates the two types based on their underlying causes.