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 Table of Contents  
REVIEW ARTICLE
Year : 2020  |  Volume : 4  |  Issue : 2  |  Page : 184-192

Fetal Echo: Application of Four Chamber View and Additional Views in Obstetrics Anomaly Scan and Third Trimester Low-Risk Pregnancy


Department of Radio-Diagnosis, SSIMS, Bhilai, Chhattisgarh, India

Date of Submission16-Nov-2019
Date of Acceptance28-Mar-2020
Date of Web Publication19-Aug-2020

Correspondence Address:
Dr. Rajendra Kumar Diwakar
Department of Radio-Diagnosis, SSIMS, Junwani, Durg, Bhilai - 490 020, Chhattisgarh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jiae.jiae_51_19

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  Abstract 

This article presents a step-wise process to evaluate fetal cardiac anatomy by the radiologist and the pediatric cardiologist, to become more familiar while assessing the four chamber view including the views for the outflow tracts. The additional views include bicaval view, three-vessel view (3VV), three- vessel trachea view (3VT), and aortic arch view. M-mode, color flow mapping and pulse Doppler ultrasound are useful to evaluate cardiac anatomy and function. If the heart does not look normal, the patient should be referred to dedicated fetal echo centre for detailed evaluation. Ductus venosus Doppler, cardiovascular profile score and visualization of thymus in 3-vessel view have also been described in brief.

Keywords: Anomaly scan, congenital heart disease, fetal echo, four-chamber view of heart, low risk pregnancy, prenatal diagnosis


How to cite this article:
Diwakar RK, Dwivedi MK, Bhende V. Fetal Echo: Application of Four Chamber View and Additional Views in Obstetrics Anomaly Scan and Third Trimester Low-Risk Pregnancy. J Indian Acad Echocardiogr Cardiovasc Imaging 2020;4:184-92

How to cite this URL:
Diwakar RK, Dwivedi MK, Bhende V. Fetal Echo: Application of Four Chamber View and Additional Views in Obstetrics Anomaly Scan and Third Trimester Low-Risk Pregnancy. J Indian Acad Echocardiogr Cardiovasc Imaging [serial online] 2020 [cited 2020 Oct 27];4:184-92. Available from: https://www.jiaecho.org/text.asp?2020/4/2/184/292632


  Introduction Top


The sonologists engaged in obstetric sonography can improve the capability of the evaluation of fetal heart by echocardiography by learning the systematic approach to study the fetal heart anatomy on 4-chamber (4-CH) view and additional views during the routine anomaly scan using the application of guidelines provided by the American Institute of Ultrasound in Medicine [1] and International Society of Ultrasound in Obstetrics and Gynecology.[2] This study was conducted on 100 patients over 3 months during anomaly scan and in third trimester obstetric scan using Siemens Juniper ultrasound equipment with 3.5 MHz convex probe and 12 MHz linear probe with fetal echo software application, color flow study, and pulse echo Doppler and GE V5 ultrasound machine having 3 MHz convex probe and 12 MHz linear probe. Cine clips were recorded for subsequent evaluation. This study includes in brief the M-mode examination and flow velocity measurements.

Fetal echocardiography is a time-consuming procedure that requires skilled investigators; hence, it is not a part of routine antenatal screening. Therefore, cardiac abnormalities are frequently missed in routine obstetric ultrasound. Fetal echocardiography is mostly reserved for high-risk pregnant women. Medical society guidelines now mandate evaluation of the 4-CH view of the heart and cardiac outflow tracts in all second and third trimester obstetric scans. It is expected that early diagnosis of heart lesion in the fetus might help in the subsequent appropriate management of the newborn in the tertiary care center after delivery. The value of this investigation will vary with the availability of neonatal care in the society.

In India, <10% of neonates with critical cardiac lesion undergo operative treatment.[3] Prenatal diagnosis is expected to make a positive impact on the clinical outcome of fetuses.[4] Prenatal diagnosis of congenital heart disease (CHD) helps family in making a decision regarding the outcome of pregnancy, including termination. In one of the European registries, termination of pregnancy was done in 6.6% after fetal cardiac diagnosis. It increased to 12%–23% when a serious heart defect was diagnosed.[5] In the U. K., between 1993 and 1995, half of the pregnancies affected by fetus cardiac defects resulted in termination.[6] Earlier detection is usually associated with a higher termination rate than the diagnosis made later in the gestation.

The optimal timing for a single scan is 18–20 weeks' gestation.[1] Prenatal detection rate of CHD is only 30%–50% in developed countries.[7],[8] The detection of CHD with 4-CH view is 55%–65% which jumps to 80%–84% if outflow tract assessment is included.[1],[2],[9] Some centers report up to 20% of total neonatal admissions due to underlying cardiac defects having had fetal cardiac diagnosis.[10]

Incidence

CHDs are one of the most common forms of congenital anomalies found in humans. The approximate incidence of CHD is about 6 in 1,000 live births and about 8–10 in 1,000 pregnancies.[11] CHDs are responsible for about 40% of perinatal deaths [12] of which more than 20% of deaths occur in the first year of life.[13] Earlier studies have emphasized the importance of routine fetal screening for CHD.[14],[15],[16]

Technical factors include the use of higher frequency probes. Cross-sectional gray-scale imaging with high frame rate, high resolution and increased contrast, zoom, and cine loop help in identifying the abnormalities. Although the use of color flow Doppler is not considered mandatory in these guidelines, it may improve detection rates of major CHD in low-risk pregnancies.[17],[18]

The reasons for failed detection of CHD on the level 2 ultrasound include failure of recognition of CHD, non-identification of outflow tracts/inadequate visualization of the heart, operator error, available equipment, and personnel training, and technical challengers, for example, maternal habitus, late gestational age, and multiple pregnancy. In approximately one-third of cases, the cardiac examination was postponed by 15–20 min due to an unfavorable fetal lie (anterior spine).[2]

Indications for fetal echocardiography based on a variety of parental and fetal risk factors for CHD have been described by Small and Copel.[19]

Four chamber view of fetal heart

4-CH view is the most important plane which enables evaluation of the main cardiac structures, the position, the size, the cardiac axis, the contractility, and the rhythm of the heart. In normal levocardia, 2/3 of the heart is left-sided with the axis pointing to the left. The cardiac axis is at 45+/-20° and abnormal axis is associated with chromosomal anomaly, abnormal displacement of the heart (diaphragmatic hernia or space-occupying lesion), and many CHD, especially in conotruncal anomalies and univentricular heart.[20]

Complete cardiac examination encompasses scanning of the fetal heart from side to side and from top to bottom. Reference plane terms are named 4-CH, long- and short-axis views. Sonographic technique includes performing a transverse sweep with cephalad movement of the transducer from fetal abdomen through the 4-CH view and towards the upper mediastinum provides the various views, i.e., left ventricular outflow tract (LVOT), right ventricular outflow tract (RVOT), 3 vessel view (3VV), and 3 vessel trachea view (3VT).[21]

The right ventricle is identified by the presence of moderator band (also known as the septomarginal trabecula) seen at the ventricular apex to connect the interventricular septum (IVS) to the anterior papillary muscle [Figure 1]. The left ventricle has a smooth interior contour and no septal valve attachment. The right ventricle is the anterior ventricle closest to the chest wall. The ventricles should be symmetric in size in the midtrimester scan. The width of the right ventricle can be 1.3 times that of the left ventricle by term.[22],[23],[24] Both ventricles should be apex-forming. The width of the ventricles is measured at the level of atrio-ventricular (AV) valves [Figure 2]. The internal diameter of left and right ventricle in diastole and systole can be measured in M-mode also [Figure 3]. The right atrium receives the systemic veins, superior vena cava (SVC) and inferior vena cava, but they are not visible in the 4-CH view. Bicaval view demonstrates this clearly. However, the left atrium is identified by its drainage of the pulmonary veins which are visible on the 4-CH view. The atria should be similar in size. The foramen ovale flap moves from right atrium into the left atrium with flow toward the left atrium [Figure 4].
Figure 1: Normal four chamber view of heart shows moderator band in right ventricle and relatively smooth left ventricle, chamber symmetry, drop out at membranous interventricular septum; (arrow). RA: Right atrium, LA: Left atrium, RV: Right ventricle, LV: Left atrium, IVS: Interventricular septum

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Figure 2: Measurement of ventricular size at the level of AV valves (34 weeks GA), LV: Left ventricle (86 mm), RV: Right ventricle (94 mm), Crux (arrow)

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Figure 3: Measurement of left ventricular internal diameter in systole and diastole in M-mode (36 weeks GA). RV: Right ventricle, LV: Left ventricle, IVS: Interventricular septum

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Figure 4: Color flow within cardiac chambers with flow across foramen ovale from right atrium to left atrium, and intact interventricular septum, No ventricular septal defect in 38 weeks pregnancy. LA: Left atrium, LV: Left ventricle, RA: Right atrium, RV: Right ventricle, FO: Fossa ovalis, TR: Tricuspid regurgitation

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Situs

The first step in the assessment of the cardiac position and situs is to identify the fetal position and the transducer orientation.[25] To determine situs, the orientation of the fetal head and spine is to be checked. If the fetus is in cephalic presentation with its spine to the maternal left, then the fetal right side is “up,” i.e., closest to the maternal abdominal wall, so the cardiac apex should point down, and the stomach should be down or left as well. This is described as situs solitus. The cardiac apex and stomach on the right and the liver on the left is described as solitus inversus or mirror-image dextrocardia.

Heart position

The normal heart is situated in the midline apex directed left. A line that bisects the chest from spine to sternum should pass through the left atrium and right ventricle [Figure 5].
Figure 5: A line bisecting the chest from spine to sternum passes through the left atrium and right ventricle

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Cardiac axis

In the second and third trimesters, the axis normally ranges from 30° to 45° [Figure 6]. In the first trimester, the range is 34.5° to 56.8°.[26] An abnormal cardiac axis in the first trimester at the time of nuchal translucency measurement is an effective tool for the detection of CHD.
Figure 6: The cardiac axis is the angle (beta) between a line bisecting the fetal chest from spine to sternum and a line drawn along the plane of the interventricular septum, normal 30 -45 degrees

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Size

The heart should occupy approximately one-third of the chest. Heart area to chest area ratio should be ~33%. The ratio of heart circumference to chest circumference should be ~50%[27] [Figure 7].
Figure 7: Ratio of circumference of heart to chest circumference (Normal ~50%)

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Squeeze

The term squeeze refers to the ventricular contraction and can be assessed only on cine clips. Right ventricle and left ventricle wall thickness and chamber contractility should be comparable. Nomograms are available for heart size, ventricular diameter, and wall thickness.[28]

Septum appearance

The ventricular septum is about twice the length of the atrial septum [Figure 8]. The ventricular septum thins from muscular to membranous near crux of the heart and should not be misinterpreted as a ventricular septal defect [Figure 1]. The crux is formed at point where the lower part of the atrial septum meets the upper part of the ventricular septum and where the AV valves insert. The septum is best seen when the angle of insonation is perpendicular to it. Small septal defects (1–2 mm) can be very difficult to confirm. However, in most of the cases, these may even undergo spontaneous closure in utero.[29]
Figure 8: Measurement of length of Interventricular septum and atrial septum. LA: Left atrium, LV: Left ventricle, RA: Right atrium, RV: Right ventricle, IVS: Interventricular septum

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Atrioventricular valve offset

The tricuspid valve (TV) is part of the right ventricle, and it is more apically placed, located a millimeter closer to the apex of the heart than the mitral valve (MV) [Figure 9] and has septal leaflet attached to the IVS. The MV is part of the left ventricle and does not have a septal leaflet. Abnormal alignment of the atrioventricular valves can be a key sonographic finding for cardiac anomalies such as atrioventricular septal defect.
Figure 9: Atrioventricular offset showing tricuspid valve located nearer to cardiac apex than the mitral valve and the cardiac apex is formed by both the ventricles. TV: Tricuspid valve, MV: Mitral valve

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  Rate and Rhythm Top


Cardiac rate and rhythm can be documented using M-mode or pulsed Doppler imaging. For M-mode imaging, the beam is directed through one atrium and one ventricle to evaluate atrioventricular conduction [Figure 10].
Figure 10: Sample volume passing through right atrium and left ventricle showing 1:1 conduction with normal rhythm and atrio-ventricular conduction

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Outflow tract views

The outflow tract view (five-chamber view), can be obtained from the 4-CH by sliding the transducer to the fetal head that enables the identification of the origin of the great arteries.

Examination of outflow tracts reveals that the great vessels are approximately equal in size and cross each other at right angles from their origin as they exit from the respective ventricles (normal cross-over). LVOT [Figure 11] and RVOT [Figure 12] views can be obtained by sliding the transducer toward fetal head from the 4-CH view. Alternatively, the rotational technique may be used by rotating the transducer toward right fetal shoulder. An angulation between left ventricular (LV) and LVOT is normally observed [Figure 13]. Head and neck vessels arise from the apex of aortic arch [Figure 14].
Figure 11: Left ventricle outflow tract, Valve: Aortic valve, LV: Left Ventricle, IVS: Interventricular Septum

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Figure 12: Right ventricle outflow tract, RV: Right ventricle, AO: Aorta, SVC: Superior vena cava, SP: Spine, Valve: Pulmonary valve

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Figure 13: Normal angulation between left ventricle and left ventricular outflow tract

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Figure 14: Aortic arch view showing three head neck vessels (HNV) arising from the arch. DAO: Descending aorta

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Complex fetal cardiac scan

Additional views are required to evaluate complex fetal cardiac scan are aortic arch view, the bicaval view [Figure 15], 3VV (3-Vessel) view, 3V T (3-Vessel Trachea) view [Figure 16], and diaphragmatic integrity.
Figure 15: Right parasagittal bicaval view shows entry of inferior vena cava and superior vena cava into right atrium. RA: Right atrium

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Figure 16: 3-vessel trachea view showing from left to right pulmonary artery, aorta, superior vena cava, descending aorta, and trachea

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The 3V view is obtained from the 4-CH view by moving the transducer in the direction of the upper fetal and the pulmonary trunk, the arch with aortic isthmus and SVC can be visualized.[30] From left to right, the vessels are the pulmonary artery, the aorta, and the SVC. The relative diameter decrease from left to right, with the pulmonary artery being larger than the aorta and the aorta larger than the SVC [Figure 17]. Certain abnormalities may have a normal 4-CH view but may have an abnormal 3VV. In 3VT view, the trachea is identified as a hyperechogenic ring surrounding a small fluid-filled space.
Figure 17: (a) Pulmonary artery dividing into right pulmonary artery coursing round behind aorta, and the left pulmonary artery. (b) Color flow image of pulmonary artery division

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In 3-VT, the ductal and aortic arches are positioned to the left of trachea and form a “V” shape as they both join the descending aorta [31] [Figure 18]. Integrity of diaphragm should be demonstrated at the time when longitudinal views of fetal spine are obtained or using the cine clips.
Figure 18: Ductal and aortic arch form a “V” when they join descending aorta

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Real-time directed M-mode echocardiography is a useful addition to cross-sectional imaging in the evaluation of fetal ventricular cavity dimension and wall thickness or valve and wall motion as well as cardiac arrthythmias.[32]

Pulse-Doppler ultrasonography demonstrates the direction and characteristics of the blood flow within the fetal heart and the great vessels, and allows the qualitative and quantitative definition of flow disturbances such as those that occur with valvular stenotic or regurgitant lesions. As is our practice after birth, pulse-wave Doppler ultrasonography can also be used as a form of flow mapping or “intracardiac stesthoscope.”[33]

The flow measurements in the normal fetal heart described by Reed et al.[34] are shown as follows:

Figure 19: Normal peak velocity across mitral valve 39.2 cm/s

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Normal flow velocity in the left ventricular outflow tract just beyond the aortic valve is 100 cm/s [Figure 20].
Figure 20: Normal flow velocity across aortic valve 105 cm/s

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The checklist for 4-CH view and outflow tract is summarized in [Table 1].[1]
Table 1: Checklist for 4-chamber view and outflow tracts

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The detection of anomalies in 4-CH view and Color Doppler and 3-vessel trachea view is summarized in [Table 2].[35]
Table 2: Detection of anomalies in 4-chamber view and 3-vessel trachea view

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Tricuspid regurgitation

The E-wave/A-wave ratio is shown in [Figure 21]. Both the E and A inflow velocities have been used to assess the ventricular diastolic function increase in fetuses. The E/A ratio increases from 0.5 in late second trimester to 0.8-0.9 in late pregnancy.[36] They increase with advancing gestation and almost equalize at birth.
Figure 21: E-wave and A-wave inflow velocity peaks through the tricuspid valve. No evidence of tricuspid regurgitation

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Thymic-thoracic ratio

The thymus can be visualized in the front of the three vessels as a less echogenic structure [Figure 22], which is important to detect defects associated with the 22q11.2 deletion syndrome, facial abnormalities, absent or hypoplastic thymus, and hypocalcemia.[37] The measurement of the thymic-thoracic ratio (T-T ratio) is a feasible and useful tool in fetuses with cardiac defects [Figure 23].[38]
Figure 22: Transverse dimension of thymus visualized in front of 3-vessels

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Figure 23: Normal thymic-thorax ratio of 1: 3, L: Lung, Sp: Spine

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  Ductus Venosus Doppler Top


The flow velocity waveform (FVW) of ductus venosus (DV) displays a continuous forward flow throughout the cardiac cycle [Figure 24]. The typical biphasic FVW of two surges of velocity peaks, the first corresponding to ventricular systole (S wave) and the second to ventricular diastole (D wave). These are followed by a reduction in velocity during the atrial systole (A wave). The FVW of the DA does not have a reversed flow during atrial contraction in normal conditions. The mean peak velocity in the DA increases from 65 cm/s in week 18 to 75 cm/s near term.[39] Kiserud[40] reported decreased blood flow during atrial contraction in 63% of the fetuses with cardiac defects more commonly associated with anomalies of the ventricular inlet or outlet than isolated septal defects. Baez et al.[41] found an important link between venous Doppler changes in the ductus venosus and hydrops in fetuses with CHD.
Figure 24: Ductus venosus flow velocity waveform at 24 weeks gestation

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Cardiovascular profile score

Fetal CHF may be assessed by the cardiovascular profile (CVP) score.[42] The maximum score is 10 points, and the minimum is 0. Hydrops, Heart size (HA/CA), cardiac function (Normal MV and TV, LV or right ventricular) shortening fraction), arterial umbilical Doppler, and venous Doppler are five categories to detect abnormal finding. A CVP score of <7/10 may warrant closer fetal surveillance. Decrease in CVP score with the development of hydrops, severe cardiomegaly or arterial Doppler abnormalities suggest impending fetal compromise in the fetus with CHD.


  Conclusion Top


The sonologist using a systemic approach to evaluate fetal heart can identify the normal versus abnormal. If the heart does not look normal, the patient is referred for expert evaluation. Once an abnormality is confirmed, a personalized pregnancy management plan can be developed depending on the nature of the lesion and the desires of the family. CHD may be isolated, but it may indicate aneuploidy or a syndrome. When isolated the prognosis is determined by the exact nature of the abnormalities. Aneuploidy and other abnormalities determine the prognosis when present with CHD.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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Chaoui R, Kalache KD, Heling KS, Tennstedt C, Bommer C, Körner H. Absent or hypoplastic thymus on ultrasound: A marker for deletion 22q11.2 in fetal cardiac defects. Ultrasound Obstet Gynecol 2002;20:546-52.  Back to cited text no. 37
    
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Bataeva R, Bellsham-Revell H, Zidere V, Allan LD. Reliability of fetal thymus measurement in prediction of 22q11.2 deletion: A retrospective study using four-dimensional spatiotemporal image correlation volumes. Ultrasound Obstet Gynecol 2013;41:172-6.  Back to cited text no. 38
    
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Kiserud T, Eik-Nes SH, Blaas H-GK, Hellevik LR. Ultrasonographic velocimetry of the fetal ductus venosus. Lancet 1991;388:1412-14.  Back to cited text no. 39
    
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Kiserud T, Eik-Nes SH, Hellevik LR, Blass H-G. Ductus venosus blood velocity changes in fetal cardiac disease. J Matern Fetal Invest 1993;3:15020.  Back to cited text no. 40
    
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Baez E, Steinhard J, Huber J, Vetter M, Hackeloer BJ, Hecher K. Ductus venosus blood flow velocity waveforms as a predictor for fetal outcome in isolated congenital heart disease. Fetal Diagn Ther 2005;20:383-9.  Back to cited text no. 41
    
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13], [Figure 14], [Figure 15], [Figure 16], [Figure 17], [Figure 18], [Figure 19], [Figure 20], [Figure 21], [Figure 22], [Figure 23], [Figure 24]
 
 
    Tables

  [Table 1], [Table 2]



 

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  In this article
Abstract
Introduction
Rate and Rhythm
Ductus Venosus D...
Conclusion
References
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