| Research Purpose and SignificanceCurrently，about5‰-10‰of newborns suffer from the disease of congenitalcardiovascular malformations. The morbidity rates of congenital cardiovascularmalformations are higher than any other congenital malformations, which lead to abortion,fetal death in uterus, and main reason of infant death. Vena cava is one of the mostimportant veins in the cardiac system. The system of right heart is the dominant part in thefetal heart development. It has been reported that adult cavity hemodynamics is closelyrelated to the right heart function. However, there are few of studies focus on theevaluation of fetal heart function, especially on the right heart function. Owing to thecomplex structure of the fetal right heart, the effective evaluation method of fetal rightheart function has yet to be developed. Therefore, it is necessary to develop a neweffective evaluation method, which holds great potential for improving the diagnosis ofcongenital cardiovascular malformations and improving the quality of life by earlyintervention.Vena cava are the major veins connected to the right heart. It has been shown thatvena cava hemodynamics are closely related to the right heart function in adults.Numerous studies have also been conducted in fetus on the hemodynamic changes of the inferior vena cava. While superior vena cava hemodynamics in fetus and its applicationsin assessing right heart function has less been investigated.The aim of this study was to evaluate the morphological characterization andhemodynamics of superior vena cava (SVC) and inferior vena cava (IVC) in normal fetusin late pregnancy by using ultrasound. The changes of the vena cavaDopplerwaveformswith gestational week and theirvaluein assessing the right ventricular systolicand diastolic function were also investigated in order to develop new parameters forevaluation of the fetal right heart function.Materials and methods1. PatientsTwo hundred normal singleton pregnancies between20and40weeks of gestationfrom our out-patient department were included. They were divided into5groups (20～24w,24+1～28w,28+1～32w,32+1～36w，36+1～40w) with40cases for each group.200cases of normal singleton pregnant women were examined by ultrasound. The selectedpregnant womenwerein good health, not addicted to alcohol, with no previous history ofhypertension, diabetes and heart, liver, kidney disease history and so on. There was nofetal malformations in these women. All the pregnant women have been informed and allagreed to conduct the study.2. Methods2.1Instrument and preparations: Siemens Acuson Sequoia512was adopted with thetransducer of6C2-S and the frequency was4.0～6.0MHz with harmonic imaging. Thepregnant women were told to empty the bladder before the ultrasound examination. Asupine position was adopted. Routine obstetric ultrasound sound was performed toexclude fetal abnormalities. Only the women with qualified fetal images were included.2.2Fetal right heart echocardiography: Fetal abdominaltransverse view was firstrecorded and the organ orientation was determined. Color Doppler was initiated to displaythe tricuspid flow and the Doppler spectra of the tricuspid flow was recorded and analyzed from the apical four chamber view. Then tissue Doppler was initiated to record thetricuspid annular velocities. The tissue velocities during early and late diastole (Ea, Aa)were measured and Ea/Aa ratio was calculated. The Doppler angle was kept less than20degree.2.3Vena cava ultrasound examination: Long axis view of the fetus was displayed andthe long axis view of the superior and inferior vena cava was fully demonstrated. Thediameters (d) and the measurable length (l) of the superior and inferior vena cava weremeasured at the0.5-1.0cm distal to its junction with the right atrium. The Doppler samplevolume (2-4mm) was put in the middle of the vessels and the spectral Doppler of the venacava was recorded. The S wave, D wave and A wave during ventricular systole, diastoleand atrial systole were measured and averaged for three consecutive cardiac cycles. Theexamination time was kept less than20minute. The imaging recording and measurementswere done by one observer.3. Data analysisAll data were analyzedusing SPSS19.0statistics software. Quantitative data wereexpressed as mean+/-SD. Paired t-test and was performed to compare the differences ofthe parameters between groups. Correlations of the parameters between groups wereanalyzed using Spearman method. P＜0.05was considered statistically significance.Results1. The diameters and the measurable length of the superior and inferior vena cava wereincreased with gestational age in normal fetus and significant difference was noticedamong different groups (P＜0.01).2. Tri-phasic Doppler waveform was seen in normal fetal superior vena cava: S waveduring ventricular systole, D wave during ventricular diastole and A wave due to atrialcontraction. The velocities of all these three waves increased with gestational week (P＜0.05). The velocities were significantly increased after28gestational week compared withthose before28gestational week (P＜0.05).No significant difference was seen in these velocities between the groups of20～24week and24+1～28week. Significant differencewas seen among the groups of24+1～28week,28+1～32week and32+1～36week, whereno significant difference was seen in these parameters between the groups of32+1～36week and36+1～40week.3. Similar SVC Doppler spectra was seen in IVC, but with higher flow velocities.4. Tricuspid E wave flow velocity was lower than A wave flow velocity in normalmid-late gestation. E wave flow velocity increased with gestational age(r=0.514，P＜0.01), while no significant difference was seen in A wave flow velocity, which resulted inincreased E/A ratio with gestational age. E/A ratio correlated significantly with gestationalage(r=0.647，P＜0.01).5. Tissue Doppler showed that fetal tricuspid annular Ea/Aa increased with gestationalage(r=0.560，P＜0.01), and close to1near the late gestational age.6. Significant correlations were observed between superior vena cava D wave velocityand tricuspid E, Ea wave flow velocity (r=0.402, r=0.240, P＜0.01), between superiorvena cava A wave velocity and tricuspid A wave flow velocity (r=0.315, P＜0.01), andbetween superior vena cava D/A and tricuspid E/A ratio (r=0.228, P＜0.01). Significantcorrelations were observed between inferior vena cava D wave velocity and tricuspid E,Ea wave flow velocity (r=0.333, r=0.233, P＜0.01), between superior vena cava Awave velocity and tricuspid A wave flow velocity (r=0.358, P＜0.01), and betweensuperior vena cava D/A and tricuspid E/Aratio (r=0.398, P＜0.01).Conclusions1. In normal fetus, the diameters and the measurable length of the superior and inferiorvena cava were increased with gestational age; Superior vena cava flow velocities changeregularly with gestational age, that is: the flow velocities was lower before28weekgestational age, and a dramatic rise of the flow velocities was seen between28and36week gestational age.2. E wave flow velocity increased with gestational age, while no significant difference was seen in A wave flow velocity, which resulted in increased E/A ratio with gestationalage. E/A ratio correlated significantly with gestational age, indicating a non-maturedventricular diastolic function in fetus.3. Fetal tricuspid annular Ea/Aa is kept less than1and increases with gestational age,which is close to1near the late gestational age.4. Significant correlation is seen between the tricuspid A wave flow velocity and thetricuspid annular Aa velocity, between the tricuspid E wave flow velocity and th tricuspidannular Ea velocity.5. Significant correlations were observed between superior vena cava D wave velocityand tricuspid E, Ea wave flow velocity (r=0.402, r=0.240, P＜0.01), between superiorvena cava D/A and tricuspid E/A ratio (r=0.228, P＜0.01). Significant correlations wereobserved between inferior vena cava D wave velocity and tricuspid E, Ea wave flowvelocity (r=0.333, r=0.233, P＜0.01), between inferior vena cava D/Aand tricuspid E/Aratio (r=0.398, P＜0.01). This shows that fetal venous flow parameters can be used toevaluate the right ventricular diastolic function. |
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