Novel Technique for the Measurement of Fetal Right Modified Myocardial Performance Index Using Synchronized Images of Right Ventricular Inflow and Outflow and Clinical Application to Twin‐to‐Twin Transfusion Syndrome

OBJECTIVE: To evaluate the reproducibility of the fetal right modified myocardial performance index (Mod-MPI) obtained by synchronizing the inflow and outflow images of the right ventricle (RV) and to evaluate its feasibility through clinical application to twin-to-twin transfusion syndrome (TTTS). METHODS: We prospectively evaluated 77 normal fetuses. Two experienced operators individually measured the right Mod-MPI using two different methods: (1) separate recording of the RV inflow and outflow using pulsed-wave Doppler (conventional method) and (2) synchronization of RV inflow and outflow images using the MPI + ™ function based on the closure click of the pulmonary valve (new method). To evaluate the clinical utility of the new method, we measured the right Mod-MPI in 33 TTTS fetuses using the new method before and after the fetoscopic laser coagulation (FLC). RESULTS: There was no statistical difference in Mod-MPI values between the two methods (p = .242). For both operators, the intra- and interoperator reproducibility of Mod-MPI was high with both methods (ICCs >0.950). Among the components of Mod-MPI measured using the new method, ejection time showed the highest reproducibility, whereas isovolumetric relaxation time demonstrated the lowest reproducibility. In TTTS fetuses, the Mod-MPI significantly decreased after FLC in recipients, and there was no difference in MPI values before and after FLC in donors. CONCLUSION: Right Mod-MPI measurement after the synchronization of RV inflow and outflow images is a reliable technique for evaluating fetal right cardiac function. This novel method can also independently evaluate the systolic and diastolic functions of the right heart.