Speckle-tracking RV free wall strain
RV lateral free wall strain had the best accuracy among the four echocardiographic parameters. It consistently outperformed other parameters in identifying different levels of RV systolic dysfunction and was most accurate with severe RV systolic dysfunction. We identified cutoff levels of lateral RV free wall strain of <23.5% and <20.5 % that accurately detects for moderately and severely reduced RV systolic function, respectively. Although the RV free wall strain technically measures more of the longitudinal deformation of the RV myocardium, it has been validated as a global function parameter in a variety of diseases with promising results and predicting prognosis . Compared to LV, base-to-apex shortening plays a more important role in RV systolic function due to its distinct muscle fiber architecture. This also partially explained the superiority of longitudinal RV strain in assessing RV systolic function. In addition, speckle-tracking RV strain also has the unique advantage of being angle-independent, and able to measure the intrinsic myocardium deformation. An issue of using RV strain is the different reference values generated by the software package from different vendors; one should be cautious when comparing RV strain data from different studies. The ease of performance for sonographers comparing all four modalities in descending order are TAPSE, S’, FAC and RV strain. Theoretically, RV myocardial strain should be superior to localized velocity measurements such as S’. Our study demonstrates strain is superior to other echo parameters as compared with Cardiac MRI as the standard.
In conclusion, conventional one-dimensional echocardiographic parameters, such as S’ and TAPSE, were well-validated and have the advantage of simplicity, reproducibility and are less dependent on image quality. However, either TAPSE or S’ in our study were not as good as reported in prior RV dysfunction studies. The 2-dimensional parameters, RV FAC and RV free wall strain were superior in accuracy. The ease of performance for sonographers comparing all four modalities in descending order are TAPSE, S’, FAC and RV strain.
Considering the availability, reproducibility, accuracy and the correlation to prognosis, our results suggested that RV free wall strain is the preferred choice for RV functional assessment among the four echocardiographic parameters.
As a final comment, the AUC of all four parameters improved with worsening RV dysfunction, which reflects the challenge in detecting mild to moderate RV dysfunction in clinical practice. Despite the relatively good AUC data, all the four echocardiographic parameters only had modest correlations with CMR RVEF. This implied a substantial limitation on 1- or 2-dimensional assessment of RV systolic function. In clinical practice, these parameters can serve as surrogates of RV dysfunction concerning their availability and relatively low costs. However, when accurate assessment of RV systolic function is warranted, 3-dimensional tools like cardiac MRI should be the preferred choice when it’s available.