Pressure half-time method for mitral stenosis grading.
MVA = 220 / PHT (ms). Normal MVA is 4–6 cm². Mild stenosis: 1.5–2.5 cm². Moderate: 1.0–1.5 cm². Severe: < 1.0 cm². The PHT method may be inaccurate immediately after balloon valvuloplasty or with significant aortic regurgitation. Planimetry is the reference standard.