9.3 Mitral Stenosis: Planimetry, Gradients, Pressure Half-Time, and Suitability
Key Takeaways
- Rheumatic MS is characterized by commissural fusion, leaflet-tip disease, doming, and subvalvular shortening, whereas degenerative MS usually begins in the calcified annulus and basal leaflets.
- Planimetry traces the smallest true orifice at the leaflet tips; 3-D MPR improves alignment for eccentric or irregular openings, but gain and calcium still limit edges.
- Mean gradient must be reported with heart rate and rhythm, while PHT-derived MVA = 220/PHT is limited by chamber compliance, other regurgitation, tachycardia, and recent PBMV.
- PBMV suitability integrates commissural fusion, leaflet mobility and calcification, subvalvular disease, MR severity, and LA/LAA thrombus rather than valve area alone.
Confirm the cause of obstruction
Mitral stenosis, or MS, is impaired diastolic flow from LA to LV through a narrowed mitral orifice. Rheumatic MS typically produces commissural fusion, leaflet-edge thickening, restricted posterior-leaflet motion, anterior-leaflet doming, and chordal thickening, shortening, or fusion. Parasternal short axis may show the central oval fish-mouth orifice. Degenerative MS begins with extensive mitral annular calcification that extends into the basal leaflets; it often lacks commissural fusion and creates a tunnel-like, irregular orifice. Congenital abnormalities, prior repair, radiation, tumor, and high-flow mimics require different assumptions. Confirm morphology before applying a rheumatic formula or intervention score.
A comprehensive study records leaflet mobility and calcification, commissures, subvalvular disease, MR and other valve lesions, LA size, spontaneous contrast or thrombus when visible, pulmonary pressure, RV size and function, TR, heart rate, rhythm, and symptoms or hemodynamic setting. Mean gradient and pressure half-time describe flow consequences; planimetry measures anatomic area. Agreement strengthens the grade, while disagreement should trigger a search for altered flow, compliance, rhythm, or measurement plane.
Planimeter the smallest true orifice
Direct planimetry is the preferred anatomic method for rheumatic MS when image quality is adequate. From parasternal short axis, begin below the valve in the subvalvular funnel, then tilt toward the LV side of the leaflet tips until the smallest opening is seen. Zoom without losing orientation, use the diastolic frame with maximal opening, and trace the inner blood-tissue interface rather than the bright outer border. Excessive gain blooms the leaflets inward and underestimates area; insufficient gain creates dropout and overestimates it. A plane above or below the tips generally traces a larger, false orifice.
Three-dimensional acquisition with multiplanar reconstruction can align a cut plane parallel to an eccentric or irregular orifice at the tips and is more reproducible than unguided 2-D planimetry. Verify the crosshair in two orthogonal long-axis planes and trace from the ventricular perspective. Heavy calcium and acoustic shadowing may still obscure the true edge. Do not trace color flow area as anatomic MVA, and do not force a contour through missing data. Save the source plane and traced frame for review.
Measure hemodynamics with their conditions attached
Use CW Doppler from the apical window aligned coaxially with transmitral inflow. Trace the dense modal envelope through diastole to obtain the mean gradient; a peak gradient alone does not grade MS. Record the heart rate and rhythm with the value. At a heart rate of 60–80 beats/min, current ASE rheumatic guidance organizes severity as follows:
| Rheumatic-MS parameter | Progressive/mild | Moderate | Severe |
|---|---|---|---|
| Mitral valve area | >2.5 cm² | 1.6–2.5 cm² | ≤1.5 cm² |
| Pressure half-time | <100 ms | 100–149 ms | ≥150 ms |
| Mean gradient | <5 mm Hg | 5–9 mm Hg | ≥10 mm Hg |
| Systolic pulmonary artery pressure | <30 mm Hg | 30–49 mm Hg | ≥50 mm Hg |
These categories are integrated, not four independent diagnoses. Mean gradient rises with tachycardia, increased stroke volume, pregnancy, anemia, fever, exercise, and significant MR; it can look deceptively low with low output. Diastolic filling time and E/A fusion change the envelope. In AF, average multiple protocol-defined beats—commonly at least five—with representative cycle lengths, and never use a postectopic beat simply because it is tall. A pulmonary-pressure estimate is supportive only when the TR signal and right-atrial-pressure estimate are valid.
Pressure half-time, or PHT, is the time for the early transmitral pressure gradient to fall to half its peak. Because gradient is proportional to velocity squared, half-gradient occurs when velocity falls to about 0.7 of peak, not half the velocity. For a clean linear slope, MVA = 220/PHT. If PHT is 220 ms, the estimated MVA is 1.0 cm². With a biphasic decay, trace the slower mid-diastolic slope rather than the initial steep component according to the guideline method.
PHT estimates a functional area from LA-LV pressure decay and is changed by more than the valve. Altered LA or LV compliance, elevated LV diastolic pressure, LV hypertrophy, concurrent AR, LA fibrosis, significant MR, and immediate post-balloon changes can produce discordance. Tachycardia and fused waves can prevent a valid slope. PHT can underestimate area with extensive subvalvular disease and is misleading immediately after percutaneous balloon mitral valvuloplasty, or PBMV.
Assess suitability, not just area
PBMV works by splitting fused rheumatic commissures, so morphology determines whether a numeric area is actionable. Document leaflet thickness and mobility, symmetry and degree of commissural fusion, commissural and leaflet calcification, and subvalvular thickening or fusion. Also define MR severity and examine the LA body and appendage for thrombus with TEE when intervention is planned. Moderate-to-severe MR and LA or LAA thrombus argue against immediate PBMV; heavily calcified leaflets, severe or asymmetric commissural calcification, and extensive subvalvular disease predict poorer results and greater tear or MR risk. Scoring systems support but do not replace heart-team judgment.
Measure baseline MVA and gradient, then identify associated aortic disease, TR, pulmonary hypertension, and RV dysfunction that may affect the treatment strategy. Degenerative calcific MS is not a fused-commissure lesion and should not be assumed suitable for balloon splitting.
When a patient has an MVA of 1.2 cm² by high-quality planimetry but a mean gradient of only 6 mm Hg during low output, neither value should be discarded. Report anatomy, flow state, rhythm, and consequences, and integrate multiple methods. Conversely, a gradient of 12 mm Hg at a heart rate of 125 beats/min does not prove severe anatomic stenosis. Reacquire under stable conditions when possible, compare the best-quality primary data, and use exercise or further imaging when symptoms and resting findings remain discordant under physician direction.
Every transmitral gradient needs a heart rate
Mean gradient is flow and diastolic-time dependent. Report rhythm and heart rate, average representative beats when irregular, and interpret the result with planimetered area, morphology, loading, and pulmonary consequences.
A stable rheumatic-MS tracing has a clean pressure half-time of 220 ms. What mitral valve area does the standard PHT equation estimate?
A patient with rheumatic morphology has a mean mitral gradient of 12 mm Hg at a heart rate of 125 beats/min, while careful 3-D-guided planimetry gives an MVA of 1.8 cm². What is the best response?