The results of this study indicate that in STEMI patients with suitable echocardiographic image quality, both BPS and RTTP methods for evaluation of LVEF relate well with 3D LV full volume method. RTTP showed a significant better correlation with the reference method than BPS for the calculation of LVEF. Our study compared data from BPS and RTTP with 3D echocardiography, as the reference method. Other studies compared RTTP with cardiac MRI and achieved similar results.[15,16] For LV volumes quantification, both methods showed strong correlation with 3D full volumes. However, in our study, RTTP seemed to overestimate EDV and ESV when comparing with 3D full volume. 3D full volume seems to underestimate LV volume in comparison with cardiac MRI, and the study by Malm et al. showed that RTTP, unlike BPS, did not lead to LV volume underestimation, when compared with cardiac MRI. These data may contribute to explain our results. Nevertheless, these findings contrast with the results from the study by Nucifora et al., which showed that both BPS and RTTP underestimated volumes in comparison with cardiac MRI.
Our results also highlights the value of RTTP for LV function evaluation in the specific scenario of myocardial infarction. In fact, this particular setting may have helped the RTTP method excel in view of BPS method because of the high prevalence of extensive wall motion abnormalities in our population. The inclusion of an additional plane (apical long-axis), which displays infero-lateral LV wall and anterior septum (the most frequently involved LV walls in patients with myocardial infarction) may help explain the greater correlation of RTTP with the 3D methodology. RTTP showed greater correlation with 3D echocardiography for EF evaluation in all MI subsets. However, the difference between r coefficients was not statistically significant. It could be hypothesized if, with a greater sample, statistical significance would be attained.
Some studies have shown that 3D-echocardiography has higher reproducibility than 2D-echocardiography.[9,17,18] In our study, inter-operator agreement was good for BPS and RTTP, for both EF and volumes quantification. Reliability of EF measurement by RTTP was higher than EF measured by BPS. However, difference between ICC was not significant. It may be hypothesized if with a greater sample, RTTP would attain significant difference. The better ICC of RTTP may be explained by the intrinsic characteristics of image acquisition and processing with this method, as they are more automatic and less operator dependent, which may lead to more reliability between evaluations. Our results are in consonance with similar studies.[7,15,16]
RTTP method has some intuitive advantages for EF calculation in comparison to BPS. Those are the use of the same cardiac cycle, less susceptibility to LV foreshortening, reduced acquisition time (the transducer is not moved to acquire different planes) and the acquisition of an additional view, which may increase its diagnostic accuracy (especially in myocardial infarction setting). The additional value of long-axis plane has already been addressed in some studies.[6,8] These studies have shown that using apical long-axis plane over apical 2-chamber improved feasibility, accuracy and reproducibility of LV volume and EF calculation by BPS. The information from the 3 planes altogether accomplished by RTTP may contribute to support its stronger correlation with 3D echocardiography for EF calculation.
This study contributes to the validation of RTTP’s accuracy and reproducibility compared with 2D-echocardiography, even though the reference method was not MRI. RTTP is known to be inferior to 3D-echocardiography. However, RTTP also has some advantages facing 3D-echocardiography, such as not requiring a full 3D dataset over consecutive heart beats during breath-hold. This leads to faster acquisition time, less patient and operator dependency, and simpler processing (less frame-rate dependent). These characteristics are supported by good correlation with 3D-echocardiography.
The sample study is small but in line with similar studies. Despite that fact it was possible to achieve statistical significance in the accuracy analysis. However, neither a hypothetic better performance for EF measurement by RTTP in anterior MI subset, nor a better inter-operator agreement for RTTP could be confirmed possibly due to the small sample. The extrapolation of the data should be confirmed in larger-scale studies or meta-analysis.
Our study did not include assessment of intra-operator agreement and measurement of 3D full volume was only made once by patient. However, inter-operator agreement was consistent for 2D and Real-time Triplane echocardiography.
This study does not have MRI data. Nevertheless, the chosen reference method (3D full volume echocardiography) has, according to published data, good correlation with MRI.[9–11]