What causes pulmonary hypertension from moderate to severe MS?

• A. Increased LV Pressure
• B. Elevated LA Pressure transmitted to the pulmonary circulation
• C. LA Dilatation
• D. Systemic Hypertension

Answer: (B)

When mitral stenosis becomes moderate to severe, the valve obstruction raises pressure in the left atrium. That elevated left atrial pressure is transmitted back into the pulmonary veins and capillaries, raising pulmonary capillary hydrostatic pressure and causing pulmonary venous congestion. This passive rise in the pulmonary circulation is what drives pulmonary hypertension. Over time, the pulmonary vasculature can remodel, adding a component of pulmonary hypertension beyond the initial venous pressure, but the starting and primary cause is the elevated left atrial pressure transmitted to the lungs. Systemic hypertension or a primary rise in LV pressure aren’t the driving factors here, and left atrial dilation is more a consequence of the high LA pressure than the cause of the pulmonary hypertension.