Clinical background
Mitral stenosis is assessed primarily by echocardiography, and the central question is whether the valve area is small enough to warrant intervention. Planimetry of the mitral orifice in the parasternal short-axis view is the reference method, but it requires good image quality and an experienced operator. When planimetry is not feasible — for example with heavy calcification or a poor acoustic window — the pressure half-time (PHT) becomes an important adjunct. PHT is measured with continuous-wave Doppler across the mitral valve and reflects the rate at which the diastolic pressure difference across the valve halves. The method is simple to perform and requires no geometric assumption about the shape of the valve orifice, but it rests on an empirical relationship that is sensitive to several factors unrelated to the valve area itself.
Calculating the mitral valve area
The mitral valve area is estimated with the formula:
where MVA is given in cm² and PHT in milliseconds. The constant 220 is empirically derived and rests on the assumption that the pressure decay across a stenotic mitral valve follows an exponential course, and that the relationship between PHT and valve area is approximately reciprocal in rheumatic mitral stenosis with normal left ventricular and atrial compliance.
The derivation study is Hatle et al. (1979), which measured PHT with Doppler ultrasound in 40 healthy subjects, 17 patients with mitral regurgitation, 32 with mitral stenosis and 12 with combined stenosis and regurgitation [1]. In healthy subjects PHT was 20 to 60 ms, in patients with isolated mitral regurgitation 35 to 80 ms, and in patients with mitral stenosis 90 to 383 ms. In 25 cases of mitral stenosis and seven with a combined lesion, PHT was related to valve area calculated from catheter data, and a reciprocal relationship was identified. PHT was not appreciably affected by exertion or by repeated measurements, which suggested that the method was relatively independent of flow across the valve. It was from this work that the constant 220 was established, and it has survived in guidelines and textbooks ever since, despite resting on a limited patient series from the late 1970s.
Interpretation in practice
The mitral valve area estimated from PHT is interpreted against the established grades of mitral stenosis:
| Valve area (cm²) | Severity | Clinical action |
|---|---|---|
| > 1.5 | Non-significant stenosis | Follow-up, no intervention |
| 1.0 to 1.5 | Moderate stenosis | Assess symptoms, consider exercise testing where there is doubt |
| ≤ 1.0 | Severe stenosis | Referral for intervention, assess valve morphology for balloon valvuloplasty versus surgery |
A PHT of 220 ms gives an estimated valve area of 1.0 cm², which is the threshold for severe mitral stenosis. A PHT of 150 ms corresponds to approximately 1.5 cm². These thresholds are not sharp, however, and the results must always be interpreted together with the mean gradient across the valve, the pulmonary artery systolic pressure and the patient's symptoms. Where the findings are discordant — for example a low PHT but a high gradient — one should suspect that the PHT is misleading and not rely on the single value.
Validation and performance
Several studies have compared the PHT method with other approaches. Rifkin et al. compared PISA, PHT and planimetry against the Gorlin formula at cardiac catheterisation in 48 patients with mitral stenosis [2]. The correlation between Gorlin and PHT was 0.78, compared with 0.88 for PISA and 0.72 for planimetry. PHT was thus no worse than planimetry in this cohort, but nor was it superior.
The most important limitation of the PHT method has been demonstrated by Li et al., who studied 244 patients with rheumatic mitral stenosis and compared several estimation methods against the 3D valve area measured with transoesophageal echocardiography (TEE 3DMVA) as the gold standard [3]. Concordance between PHT and TEE 3DMVA was significantly poorer in patients with abnormal net atrioventricular compliance (Cn ≤ 4 mL/mmHg) than in those with normal Cn. The deviation was statistically significant only for PHT, not for planimetry or the continuity equation. The reason is mechanical: at low compliance the pressure across the valve falls more rapidly, PHT is shortened and the valve area is overestimated. The authors found that the combination of a planimetered MVA ≤ 1.5 cm² and a PHT ≤ 130 ms had a specificity of 98.5% (validated at 93% in a separate cohort) for identifying abnormal Cn, meaning that in such cases the PHT is directly misleading.
A recent review by Pala et al. confirms that PHT and mean gradient are markedly load-dependent and can misclassify severity in tachycardia, atrial fibrillation or reduced cardiac output [4]. The review stresses that no single parameter is reliable and that a multiparametric approach is necessary.
Limitations
The PHT method rests on the assumption that the pressure decay across the valve is determined solely by the degree of anatomical stenosis. This does not hold in several clinically important situations:
Immediately after balloon valvuloplasty the PHT is unreliable. Acute changes in atrial and left ventricular compliance together with rapid haemodynamic shifts mean that the empirical constant 220 does not apply, and the method should not be used to assess the procedural result.
In significant aortic regurgitation the left ventricle fills rapidly during diastole, which shortens the pressure decay across the mitral valve and gives a falsely short PHT with consequent overestimation of the valve area.
An atrial septal defect creates a low-pressure decompression of the left atrium, which alters the pressure gradient across the mitral valve independently of valve area.
Abnormal compliance of the left ventricle or atrium, as in hypertrophy, restrictive filling or after myocardial infarction, affects the PHT independently of the degree of stenosis. Li et al. showed that this is the single most important source of error in PHT measurement, and that it should be suspected when planimetry shows an MVA ≤ 1.5 cm² but the PHT is inexplicably short (≤ 130 ms) [3].
Tachycardia and atrial fibrillation hamper the measurement, since diastole is shortened and the pressure curve does not have time to reach a stable decay. With irregular RR intervals the measurement should be made over several consecutive beats and the mean used.
Finally, the method applies to rheumatic mitral stenosis. In degenerative mitral stenosis caused by mitral annular calcification the geometry of the valve orifice is different, and the empirical relationship underlying the constant 220 has not been validated in this population.
References
- Hatle L, Angelsen B, Tromsdal A. Noninvasive assessment of atrioventricular pressure half-time by Doppler ultrasound. Circulation. 1979;60(5):1096–104. PMID: 487543
- Rifkin RD, Harper K, Tighe D. Comparison of proximal isovelocity surface area method with pressure half-time and planimetry in evaluation of mitral stenosis. J Am Coll Cardiol. 1995;26(2):458–65. PMID: 7608451
- Li T, Leow R, Chan MW et al. Impact of Net Atrioventricular Compliance on Mitral Valve Area Assessment. Diagnostics (Basel). 2024;14(15):1595. PMID: 39125471
- Pala B, Piscione M, Gaudio D et al. Mitral Stenosis in the Multimodality Imaging Era: Pitfalls, Stress Echocardiography, and Integrated Therapeutic Assessment. Diagnostics (Basel). 2026;16(14):2285. PMID: 42510148
