Pulmonary capillary wedge pressure (PCWP) is an indirect estimate of which pressure?

• A. Left atrial pressure
• B. Right atrial pressure
• C. Pulmonary artery systolic pressure
• D. Left ventricular end-diastolic pressure

Answer: (C)

Pulmonary capillary wedge pressure is read after a balloon-tipped catheter is advanced into a small branch of the pulmonary artery and the balloon is inflated to occlude flow. With the distal artery wedged, the pressure you see is no longer the forward pressure in the artery but the pressure transmitted back through the pulmonary capillaries and veins to the left side of the heart. That makes the wedge pressure an indirect estimate of left atrial pressure. Since left atrial pressure closely mirrors left-sided filling pressures, clinicians use wedge pressure as a surrogate for left ventricular end-diastolic pressure in many situations, though they are not always identical, especially if there are mitral valve abnormalities or altered LV diastolic function. It is not a measure of right atrial pressure, which is obtained from central venous pressure, nor is it a measurement of pulmonary artery systolic pressure, which reflects the pressure generated by the right ventricle during systole.