Mitral stenosis pressure half-time
MS PHT · CW Doppler of mitral inflow; PHT is the time for the peak gradient to halve, i.e. for velocity to fall to Vmax/√2
Normal range & thresholds
MVA = 220 / PHT (Hatle’s empirical constant).[43]
PHT = 0.29 × deceleration time, so the same information can be read off the DT (card 36).
| PHT | Implied MVA | Severity |
|---|---|---|
| <100 ms | >2.2 cm² | Mild or none |
| 100–150 ms | 1.5–2.2 cm² | Mild–moderate |
| ≥150 ms | ≤1.5 cm² | Severe |
| ≥220 ms | ≤1.0 cm² | Very severe |
Pathophysiology
After the mitral valve opens, the atrioventricular pressure gradient decays at a rate determined by the orifice area and by the combined compliance of the left atrium and left ventricle. A narrow orifice sustains the gradient and lengthens the half-time. The dependence on compliance is not a nuisance detail — it is the reason the method fails wherever compliance is abnormal: in the stiff ventricle of the elderly or hypertensive patient, in significant aortic regurgitation (which fills the ventricle from the other side), and in the first hours after balloon valvuloplasty, when atrial and ventricular compliance change abruptly while the orifice does not.[5,43]
Raised by
- More severe mitral stenosis (the intended signal)
- Significant aortic regurgitation — the AR jet raises LV diastolic pressure, flattens the transmitral gradient decay, and lengthens PHT: a falsely small calculated valve area
- Reduced LV compliance — elderly, hypertensive, hypertrophied, restrictive ventricles
- Bradycardia; first-degree AV block
- Elevated LV end-diastolic pressure of any cause
Lowered by
- Atrial septal defect — the left atrium decompresses into the right, the gradient falls quickly, PHT shortens, and the valve area is overestimated (relevant in Lutembacher syndrome and after transseptal puncture)
- Immediately after balloon valvuloplasty — PHT shortens more than the true area increase, and the guideline advises against using it for 24–72 hours[5]
- Tachycardia; high cardiac output states; increased LA compliance (a very large, floppy atrium)
- Significant mitral regurgitation coexisting with stenosis
Technique & pitfalls
- Use continuous-wave Doppler, well aligned with inflow; sweep speed 100 mm/s.
- Draw the tangent along the mid-diastolic slope. In many rheumatic valves the descent is bilinear — steep early, then flatter; use the flatter mid-diastolic portion, not the initial segment.
- In atrial fibrillation, average 5–10 cycles and avoid beats after short or very long cycles.
- Always cross-check against planimetry. When the two disagree, planimetry — ideally 3D TOE — is the more reliable.
- State the heart rate and the rhythm with the value.
- Report the reasons for any expected inaccuracy (aortic regurgitation, recent valvuloplasty, tachycardia) rather than silently reporting the number.
Pseudo-change & artefact
- Aortic regurgitation (lengthens PHT → overestimates severity) — the classic pitfall.
- Recent balloon valvuloplasty (shortens PHT → overestimates the result achieved).[5]
- Atrial septal defect (shortens).
- Abnormal LV compliance in the elderly or hypertensive (lengthens).
- Tachycardia, arrhythmia, first-degree AV block.
- Choosing the wrong segment of a bilinear descent — a purely observer-dependent error that can move the calculated area by more than 0.3 cm².
Treatment thresholds
- PHT ≥150 ms (MVA ≤1.5 cm²) = severe mitral stenosis, and severity is the anatomical precondition for every intervention decision in card 34 — balloon valvuloplasty for suitable anatomy (class I when symptomatic), surgery otherwise.[6,7]
- Post-valvuloplasty assessment: PHT is explicitly not to be used in the first 24–72 hours; judge the immediate result by planimetry and by the mean gradient instead.[5]
- Prosthetic mitral valves: a prolonged PHT with a raised mean gradient suggests obstruction; the Doppler velocity index and TOE settle it.[20,21]
- Because PHT can be so easily distorted, no intervention should rest on PHT alone — the guideline expects planimetry and gradient to agree with it.
Next step
- Next: planimetry at the leaflet tips (2D and, where available, 3D TOE) and the mean gradient with the heart rate.
- Then: Wilkins score, commissural calcification and mitral regurgitation severity to decide balloon versus surgery.[45]
- Then: TOE to exclude left atrial appendage thrombus before valvuloplasty.
- Then: exercise echocardiography if symptoms and resting numbers disagree; then Heart Team.
Drugs
- Rate-limiting agents (beta-blockers, verapamil, diltiazem, digoxin) lengthen diastole and reduce the gradient — note that they also alter PHT, so serial comparisons should be made at similar heart rates.
- Diuretics relieve congestion.
- Vitamin K antagonists for atrial fibrillation; DOACs are not established in rheumatic mitral stenosis.[40]
- No drug changes the orifice.
Reversibility
PHT falls immediately after balloon valvuloplasty or commissurotomy, though the earliest measurements overstate the improvement for the compliance reasons above. Untreated, PHT lengthens slowly as the valve restenoses, at roughly the same 0.1 cm² per year loss of area. There is no pharmacological reversibility.[5,45]