Pressure half time, continuity equation, and planimetry all measure what in mitral stenosis assessment?

Pressure half time, continuity equation, and planimetry all measure what in mitral stenosis assessment?

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

Answer: (D)

All three measurements are used to quantify the size of the mitral valve opening, which determines how severely the mitral stenosis limits flow. In practice, the mitral valve area is the key metric for grading severity. Pressure half-time uses the rate at which the diastolic pressure difference between the left atrium and left ventricle declines after opening the valve. A larger orifice (less severe stenosis) allows the gradient to dissipate more quickly, giving a shorter half-time, while a smaller orifice (more severe stenosis) slows that decay. Clinically, this is summarized by the approximate relation MVA ≈ 220 divided by the pressure half-time; a longer half-time implies a smaller valve area. The continuity equation relies on conservation of flow: the volume passing through the left ventricular outflow tract equals the volume passing through the mitral valve. By measuring LVOT area and its velocity-time integral, and dividing by the mitral valve velocity-time integral, you obtain the mitral valve area. This method is grounded in flow mechanics and provides another estimate of how open the valve is. Planimetry is a direct measurement of the actual opening by tracing the mitral valve orifice on an image where the valve is fully open. It gives a direct valve area measurement without relying on flow dynamics or pressure decay, provided the image quality allows an accurate tracing. Because these approaches all estimate the same physical quantity—the mitral valve opening area—they best answer the question of how wide the orifice is. The other choices reflect the pressures that result from stenosis, not the size of the opening itself.

All three measurements are used to quantify the size of the mitral valve opening, which determines how severely the mitral stenosis limits flow. In practice, the mitral valve area is the key metric for grading severity.

Pressure half-time uses the rate at which the diastolic pressure difference between the left atrium and left ventricle declines after opening the valve. A larger orifice (less severe stenosis) allows the gradient to dissipate more quickly, giving a shorter half-time, while a smaller orifice (more severe stenosis) slows that decay. Clinically, this is summarized by the approximate relation MVA ≈ 220 divided by the pressure half-time; a longer half-time implies a smaller valve area.

The continuity equation relies on conservation of flow: the volume passing through the left ventricular outflow tract equals the volume passing through the mitral valve. By measuring LVOT area and its velocity-time integral, and dividing by the mitral valve velocity-time integral, you obtain the mitral valve area. This method is grounded in flow mechanics and provides another estimate of how open the valve is.

Planimetry is a direct measurement of the actual opening by tracing the mitral valve orifice on an image where the valve is fully open. It gives a direct valve area measurement without relying on flow dynamics or pressure decay, provided the image quality allows an accurate tracing.

Because these approaches all estimate the same physical quantity—the mitral valve opening area—they best answer the question of how wide the orifice is. The other choices reflect the pressures that result from stenosis, not the size of the opening itself.