Quantitative Assessment Of Ventricular Longitudinal Function In Fetuses Using Velocity Vector Imaging

Background:Assessment of fetal cardiac function is one of the most important issues.Investigating the relationship between cardiac function and gestational age is not only helpful for evaluating fetal development,but also necessary for taking care of the high-risk fetuses. But conventional M-mode or 2-D mode techniques for cardiac function assessment are technically difficult,load-dependent,and only provide information on global ventricular function.Velocity vector imaging(VVI) is a novel technique for regional assessment of myocardial mechanics. VVI is a Doppler-independent method that uses a combination of speckle tracking technique and complex geometric analysis to follow the myocardial motion through the cardiac cycle for measurement of myocardial velocity,strain,and strain rate.Few studies of VVI in fetal hearts have yet been reported.Objective:The purpose of this study was to investigate the clinical value of VVI in the assessment of normal fetal regional myocardial performance.Discuss differences between left and right ventricular function in normal fetuses and investigate the relationship between cardiac function and gestational age through detecting regional myocardial mechanics in systole and diastole.Methods:All pregnant women referred for routin prenatal ultrasound examination at the second Xiangya Hospital between March 2005 and January 2007 with structurally normal and appropriate-for-gestational-age(assessed by last menstrual period(LMP) date) fetuses were considered for study enrollment.Fetuses with congenital malformations,arrhythmias,or of inappropriate size for gestational age,or the fetuses of mothers with systemic diseases,such as maternal hypertension and diabetes mellitus,were excluded.One hundred and seventy singleton fetuses were examined.Maternal age ranged from 20 to 41 years(mean,28.3±3.6 years).All fetuses were followed-up for one year after birth and proven to be healthy.The study protocol was approved by the hospital committee on human rights.Written informed consent was obtained from each mother before examination.Gestational ages ranged from 18⁺⁰to 40⁺¹ weeks(mean,29.9±5.9 weeks).Gestational age was calculated using the biparietal diameter, head circumference,abdominal circumference,and femur length,and correlated with LMP gestational age.All fetuses were divided into five groups according to their gestational age:18⁺⁰-23⁺⁶ week group(n=34), 24⁺⁰-27⁺⁶ week group(n=35) 28⁺⁰-31⁺⁶ week group(n=32),32⁺⁰-35⁺⁶ week group(n=36),and 36⁺⁰-40⁺¹ week group(n=33).Systolic peak velocity,strain,strain rate and diastolic peak velocity, strain rate in both left and right ventricles were assessed using VVI software. Results:Dynamic 4-chamber views of 170 normal fetuses were collected.151 fetuses were analyzed successfully,whereas 19 fetuses can not been analyzed as a result of fetal movement in 4 fetuses and inaccurate tracking of subendocardium in 15 fetuses(89%feasibility).Normal systolic and diastolic values for tissue velocity,strain,and strain rate were established.Tissue velocity gradually decreased from the basal segment to the apical segment(P＜0.01),whereas strain and strain rate were stable among all segments in every group in both ventricles (P＞0.05).Tissue velocity increased with advancing gestational age (P＜0.05),whereas strain and strain rate were stable throughout gestation (P＞0.05).The values of velocity,strain and strain rate in right ventricle were obvious higher than that in the corresponding segment in left ventricle(P＜0.05).Conclusion:Fetal myocardial velocity,strain,and strain rate measurements are easy to obtain and reproducible.The strain and strain rate are stable throughout gestation which indicates that fetal cardiac function maturation occurs in the second trimester and keep stable in third trimester.The index of contraction and relaxation in right ventricle are higher than that in left ventricle which indicates that right ventricular function is stronger than left ventricular function in fetus.VVI is a novel noninvasive tool to quantitatively and objectively assess regional systolic and diastolic function in fetuses.It provides another useful modality for evaluating fetal cardiac function.