Clinical Study Of Myocardial Deformation In Fetus With Twin-twin Transfusion Syndrome

Backgroud:Twin-to-twin transfusion is a severe complication unique to monochorionic twin pregnancies. Although previously known by such terms as feto-fetal transfusion syndrome, autotransfusion syndrome,intrauterine parabiotic syndrome,twin-twin transfusion syndrome (TTTS) is now commonly used. The incidence of TTTS ranges between10%and15%of monochorionic twins. It carries a high risk of fetal death if left untreated(80%-100%) and short-and long-term cardiocirculatory complications.Currently, Quintero’s staging system is quite universally used to describe severity of TTTS and monitor disease. However, it ignores the fundamental cardiovascular elements of the disease and lacks accurative and quantitative assessment of cardiac function in both donors and recipients. Selective fetoscopic laser photocoagulation(SFLP) aiming at interrupting abnormal placental vascular connections has emerged as the optimal treatment for TTTS Fetal cardiac function is an important prognostic factor for fetal outcome after therapy. Velocity vector imaging (VVI) is a novel speckletracking-based technique for analysing myocardial deformation withoutlimitations of Doppler echocradiography. It offers an intuitive analysis of myocardial mechanics.This is achieved via the combination of speckle tracking, mitral annulus motion, tissue-blood border detection, and the periodicity of the cardiac cycle.It has been introduced but not well studied in fetus. As to our aware, there is no report of its use to assess the differences in myocardial mechanics between donor and recipient in TTTS and the impact of SFLP on myocardial defromaton in TTTS.Objective:To manifest the intertwin differences in myocardial deformation analysis using VVI; To elucidate poorly understood mechanisms of cardiovascular compromise in TTTS; To manifest changes in myocardial deformation in donor and recipient using VVI; To assess impacts of SLP on cardiac function in TTTS.To discuss the important clinical value of velocity vector imaging in quantitatively evaluating myocardial deformation of fetus.Methods:The study population consisted of consecutive MCDA twin pregnancies complicated by TTTS and treated by SFLP who referred for fetal echocardiography to the Fetal Heart Program at the Cardiac Center of the Children’s Hospital of Philadelphia from November2007to March2010. The normal group consisted of pregnant women referred for fetal echocardiography to the ultrasound department of the second Hospital of Central South University from2008to2011. Fetuses considered for inclusion in normal control group were normal cardiovascular anatomy and no extracardiac anatomical abnormalities of hemodynamic significance and mothers had normal uteroplacental function. After performing routine OB exam and complete fetal echocardiogram, a digital dynamic zoomed loop of apical four-chamber view incorporating was recorded when there was no fetal movement.This image was stored as DICOM format, transferred to the offline Siemens KinetDx workstation and analysed by Syngo VVI software. Interventricular septum and free wall in both ventricles were divided into basal middle and apical segments, for a total six segments in each ventricle.Cardiac strain and strain rate were automatically calculated and displayed in a six segment model.Results:Donor fetuses showed increased strain and strain rate in LV and decreased strain and strain rate in RV,although only LV-SRs and RV-SRd had statistically meaning, and echocardiography findings were more likely to be normal.In the recipients, strain and strain rate in both ventricles were clearly significant lower than control values.Besides,cardiovascular abnormalities such as cardiac dilation, ventricular hypertrophy,tricuspid/mitral regurgitation and tricuspid/mitral valve single-peak inflow were more common in recipient fetuses.With in one week after SFLP, both ventricular function in donors impaired considerably:decrease in strain and strain rate,new onset of tricuspid regurgitation,mild cardiomegaly and even hydrops.Recipients twin,in contrast, experienced significant improvement in both ventricular strain and strain rate,less frequency of tricuspid regurgitation and tricuspid valve single peak.Conclusion:In TTTS, donor mechanics reflect loading conditions.Donor LV systolic function is hyperdynamic, due to hypovolemia and ejection into a low resistance cerebrovascular circuit while the RV ejects into a high resistance placental circuit. Recipient RV and LV are both globally depressed with systolic and diastolic dysfunction despite normal vascular resistances and presumed volume overload, suggesting intrinsic acquired cardiomyopathy. Myocardial deformational mechanics improve in the recipient but worsen in the donor following SFLP for TTTS. VVI analysis provides insight into myocardial function in TTTS and may be a valuable tool to track progress after SFLP.