The results of our study with a relatively large sample size indicated that MVA measurement by two different 3D-direct and 3D-MPR planimetry methods had consistent results, with moderate to excellent agreement. Overlay MVA measured by the 3D-direct method is less than 3D-MPR, and mitral stenosis severity is overestimated by 3D-direct dominantly at MVA above 1.5 cm2. Our subgroup analysis revealed that although there was a significant correlation between 3D-direct and 3D-MPR in very severe MS (i.e. MVA< 1 cm2), no significant correlation was observed in cases with progressive (moderate) MS (i.e. MVA>1.5 cm2). 3D-MPR is the most accurate method for planimetry and can theoretically produce reliable measurements by delineating the mitral valve orifice. The discrepancy between the 3D- MPR and 3D-direct planimetry methods in moderate MS is mainly due to the limitation of the latter in obtaining appropriate en face plane to evaluate the entire MV in a single view because of its saddle-like shape and relatively pliable leaflets at progressive (moderate) MS. (Fig. 3) In practice, we need to frequently tilt the 3D volume image of MV, so that we can see the entire MV orifice in the patients with progressive MS. So using a single en face plane during 3D-direct planimetry will underestimate MVA significantly.
Considering the higher accuracy of the MPR technique, it seems that in the case of patients with progressive (moderate) MS, it is better to measure the MVA by 3D-MPR method instead of 3D-direct. 3D-MPR is a 3D data set processing that combines image reconstruction and multiplanar cropping to identify the narrowest orifice of the valve (Fig. 3). Recently, Zhong et al., by comparing 3D-direct and 3D-MPR methods in the case of patients with MS demonstrated that while MVA measured by 3D-direct was significantly lower than that obtained by 3D-MPR (12). The underestimation of MVA by 3D-direct was also reported by other studies (13, 15). Our study confirms and extends the findings of previous studies as we compared 3D-direct and MPR techniques in different severities of MS.
MVA measured by 2D-TTE and various 3D-TEE methods had consistent results with moderate to excellent agreement. The MVA measured by 2D method was on average lower than that measured by 3D-MPR method and, in general, 2D method overestimated MS severity. Comparing the three subgroups of MVA (MVA<1 cm2, MVA between 1-1.5 cm2 and MVA>1.5 cm2) measured by 3D-direct, 3D-MPR and 2D methods showed that there is a good agreement between 2D and different 3D methods at MVAs below 1 cm2, moderate agreement at MVA between 1 cm2 and 1.5 cm2, and no agreement at MVA more than 1.5 cm2. Moreover, after determining MVA by 3D methods, patients with MVA> 1.5 cm2 were excluded from planned PTMC.
Traditionally, 2D–TTE is a well-established routine method for MVA measurement in the case of patients with mitral stenosis, which is believed to be unaffected by hemodynamic changes. However, considering that obtaining an optimal perpendicular short-axis plane that crosses the tip of the mitral leaflets is sometimes difficult, the 2D–TTE method is less accurate than the 3D-TEE. Our results demonstrated that there was a significant correlation between MVA measured by 2D-TTE and 3D-TEE methods at MVA less than 1.5 cm2 ,but at MVA above 1.5 cm2 the correlation is non-significant. This results showed that 2D-TTE has acceptable and consistent results and could be used confidently for planning patients with severe MS for PTMC but in the case of patients with discrepancy between clinical and echocardiographic findings, 3D-MPR or 3D-direct could be used for decision making. According to the current guidelines, an accurate determination of MVA is essential for choosing the best therapeutic strategy for MS patients (16).
Our results were supported by the findings of some previous studies (17, 18). Min et al. compared the MVA measured by 2D-TTE and 3D-TEE in 87 patients with MS. Our results were contrary to this essay. They reported more overestimation in the measurement of the MVA by 0.19 ± 0.2 cm2 with 2D-TEE in comparison to 3D-MPR. On the other hand, our study showed that 2D-TTE underestimates MVA compared to 3D-MPR, but overestimates when it is compared to 3D-direct.
Mean MV gradient had no significant correlation with MVA measured by both 2D–TTE and 3D-TEE methods in our study. Likewise, in the study of Najih et al. 42% of patients with severe MS (MVA <1 cm2) had a mean MV gradient <10 mmHg, which suggests the absence of a direct correlation between an MVA <1 cm2 or <1.5 cm2 and a mean MV gradient > 10 mmHg (19). It was notable that even severe MS exists with a mean MV gradient <10 mmHg (19). The 2020 European Society of Cardiology guideline defined the severe MS as an MVA of <1.5 cm2 and a mean MV gradient of >5 mmHg, under a condition in which this gradient is interpreted as a product of the heart rate and the patient having sinus rhythm (20). Consequently, although the mean MV gradient is an important indicator of MS tolerance, it is not a reliable marker of MS severity. This is mostly because of its dependence on several hemodynamic parameters including rhythm, heart rate, cardiac output, and the coexistence of mitral insufficiency (5, 20, 21). Thus, it is suggested that the value of the mean MV gradient should never be interpreted as a single value.
The systolic PAP estimated through echocardiography had a significant inverse correlation with MVA in all measurement methods; therefore, it seems to be better than MG in assessing the severity of mitral valve stenosis.
AF rhythm was found in 44.3% of the patients which warrants anticoagulation.