First-Trimester Ultrasound: A Comprehensive Guide

11. The Fetal Heart in Early Pregnancy

Edgar Hernandez-Andrade  and Manasi S. Patwardhan2

(1)

Division of Maternal Fetal Medicine, Department of Obstetrics and Gynecology, Hutzel Women Hospital, 3990 John R, 4 Brush North, Detroit, MI 48201, USA

(2)

Division of Maternal Fetal Medicine, Department of Obstetrics and Gynecology, Wayne State University, Detroit, MI, USA

Edgar Hernandez-Andrade

Email: ehernand@med.wayne.edu

Keywords

Fetal heartFetal cardiac defectsFetal cardiac ultrasound evaluationIncreased nuchal translucencyTricuspid regurgitationReversed A wave in the ductus venosusAberrant right subclavian arteryAbnormal cardiac axisHydropsMonochorionic twinsTransvaginal ultrasoundTransabdominal ultrasoundColor directional DopplerSpatiotemporal image correlationFour-chamber viewOutflow tracts

Introduction

Congenital heart defects (CHD) are the most common fetal structural anomalies, either in isolation or in association with other fetal anatomical defects [12]. CHD is strongly associated with chromosomal anomalies and genetic syndromes and can significantly change the clinical surveillance plan and perinatal outcome of affected fetuses [37]. Most cardiac defects can be detected early in pregnancy, while some may present later in gestation. The prevalence of major cardiac defects reported varies in literature from 3 to 12 per 1000 pregnancies [89]. This variation is mainly due to the number of minor defects included across different studies [10]. In the pre-echocardiography era, reported incidences ranged from 5 to 8 per 1000 live births. Better imaging techniques and technology have enabled more accurate detection of minor cardiac defects; thus, current estimates range from 8 to 12 per 1000 live births, with some minor geographic variations in the types of congenital heart disease [1].

Basic Description of Cardiac Development1

Formation of the fetal heart begins at around 23–25 days of gestation when the embryo is 2 mm long and it is completed at approximately the 46th day, when most of the cardiac structures are already formed, at an embryonic length of 17 mm. Some structures, such as the atrioventricular septum, can complete their development later in pregnancy. The fetal heart starts contracting at approximately 23 days of gestation. Four main processes occur during the development of the fetal heart: (1) formation of the cardiac tube, (2) looping of the heart, (3) formation of the cono-truncus, and (4) septation. In each of these processes, specific cardiac defects can originate [1113].

At 23–25 days of gestation (2-mm embryo), clusters of angiogenic cells, called blood islands, create a vascular plexus in the anterior segment of the embryo. These clusters generate two primitive cardiac tubes which will later fuse, forming the bulboventricular tube; the primitive ventricles and the outflow tracts originate from this structure. At this stage, the aortic sac and aortic arches begin to develop, and the process of cardiac looping is initiated through bending of the cardiac tube towards the anterior and right parts of the embryo. One of the main cardiac defects originating at this stage is transposition of the great arteries.

On gestational day 28 (3-mm embryo), the early embryonic ventricle originates from the diverticula located near the left ventrolateral border of the cardiac tube. These diverticula penetrate the myocardium, increasing its thickness and creating multiple trabeculae which form the primitive left ventricle. The bulbus cordis splits into three sections: the proximal third forms the primitive right ventricle; the middle third forms the conus cordis and the outflow portions of the ventricles; and the terminal third forms the aortic and pulmonary roots or primitive truncus arteriosus. The formation of the primitive atria, and the septum primum and septum secundum, as well as the process of septation begins at this stage. Cardiac defects that can develop during this period are single ventricle, double inlet and double outlet right ventricle, atrial septal defects and truncus arteriosus.

On gestational days 29–30 (4- to 5-mm embryo), the sinus venosus and the sinus cordis are formed and the external shape of the heart resembles a 4-chamber structure. Cardiac defects that can occur during this period are: persistent left superior vena cava, Tetralogy of Fallot, and ventricular septal defects.

On gestational days 30–32 (5- to 6-mm embryo), the atrioventricular canal, the pulmonary veins and septation of the truncus arteriosus are formed. Cardiac defects developing during this period are anomalous pulmonary venous return, persistent atrioventricular canal, ventricular septal and aortico-pulmonary defects, and persistent truncus arteriosus.

Formation of the arterial valves begins on gestational day 36 (9-mm embryo), and of the atrioventricular valves on days 39–40 (10- to 12-mm embryo). Cardiac defects occurring during this period are bicuspid arterial valves, absent arterial valves, tricuspid valve atresia, and Ebstein’s anomaly. The development of the aortic arch system is completed at approximately 46 days of gestation (17-mm embryo). Cardiac defects developed during this period are double aortic arch, interrupted aortic arch, right aortic arch, and coarctation of the aorta.

Detection of Fetal Congenital Defects

One of the most important contributions of ultrasound (US) in obstetrics is the identification of fetal structural anomalies [1417]. Although the sensitivity of ultrasound as an imaging technique is completely dependent on the operator’s experience and technical skills, other factors such as demographics of the population, gestational age at examination, type of ultrasound equipment, and number of ultrasound scans performed during pregnancy can modify the detection rate of fetal congenital anomalies.

The systematic evaluation of the fetal heart in the mid trimester of pregnancy was first proposed by Allan et al. [1820] during the early 1980s. Prior to this period, the fetal heart was visualized only in very specific high-risk conditions and towards the end of pregnancy [2122]. The main limitations were the poor image resolution of the ultrasound systems, the lack of standardization for fetal evaluation, and the lack of or reduced experience in prenatal diagnosis of congenital heart defects. During the last 30 years, technological advancements in ultrasound systems and most importantly, adequate training of operators and the proposal of standard protocols for fetal evaluation have greatly increased the detection rate of all fetal anomalies, including those in the fetal heart [2325]. Various ultrasound organizations have proposed guidelines for systematic evaluation of the fetal heart and standards for achieving an adequate detection rate [2627]. The optimal period in pregnancy for evaluation of the fetal heart is between 22 and 24 weeks of gestation [28] and that for an early cardiac examination is between 11 and 13 + 6 weeks of gestation [2930]. Still, some fetal cardiac anomalies can present in later gestation [3133]. Technical advances in high-frequency ultrasound probes and the complementary use of 3D and 4D ultrasound techniques have also contributed to an increase in our knowledge of cardiac structure, function, and progression of disease in early stages of pregnancy [3436].

Why Do We Have to Scan the Fetal Heart Early in Pregnancy?

The most frequent indications for early fetal cardiac evaluation are: family history or obstetric history of congenital heart defects [3738]; fetuses with abnormal cardiac images during the first trimester scan [39]; indirect markers for fetal congenital heart defects such as: increased nuchal translucency [4042], abnormal flow in the ductus venous [4346], tricuspid regurgitation [47], cystic hygroma [4849], and fetuses presenting with any other structural defect [5051]. Monochorionic twin pregnancies [52] and pregnancies by assisted reproductive techniques [53] may also benefit from an early cardiac examination as these pregnancies have a higher risk of congenital heart defects (Table 11.1). Cardiac anomalies that can be treated in utero such as aortic stenosis may benefit from an early cardiac examination [54]. In families with a previous history of congenital heart disease, a normal cardiac examination can provide reassurance and reduce the stress and anxiety of their past experience [55].

Table 11.1

Risk factors associated with the presence of congenital heart defects (CHD)

Indication

Association with cardiac defects (%)

Other structural anomalies [103]

21

Increased nuchal translucency [104]

7

Tricuspid regurgitation [47]

5.1

Previous history of CHD [37]

8.7

Abnormal ductus venosus [105]

7.5

Monochorionic twins [52]

5.5 (9.3 in cases with TTS)

Aberrant right subclavian artery [75]

5.1

Assisted reproductive techniques [53]

4.3

Consanguinity [106]

4.4

What Constitutes a Normal Early Fetal Cardiac Examination?

Demonstration of normal situs, cardiac connections, atrioventricular junction, right- and left-sided symmetry and septo-aortic continuity are constituents of a normal early cardiac examination [56]. However, in order to conclude that the fetal heart appears normal, the following parameters should be evaluated.

Heart-to-Chest Ratio

Although the heart size continues to increase with gestational age [57], the mean heart-to-chest area ratio of 0.20 + −0.04 is constantly maintained between 11 and 14 weeks [58].

Cardiac Axis

The complex process of cardiac looping during embryonic development is demonstrated by the cardiac axis being fairly midline at 8 weeks and then gradually levo-rotating by 12 weeks after which it stabilizes at the end of the first trimester [59]. Fetuses with cardiac defects might show an abnormal deviation of the cardiac axis in relation to gestational age [60]. Mc Brien et al. [59] studied the normal changes in the fetal cardiac axis between 8 and 15 weeks of gestation and reported that the cardiac axis is orientated more to the midline of the thorax in early gestation, and then rotates to the left with advancing gestation. The authors noted that the cardiac axis changed from 39° at 11 weeks to 50° at 14 weeks. Sinskovskaya et al. [60] reported a normal variation in the cardiac axis from 34.5° at 11 weeks to 56.8° at 13 + 6 weeks of gestation, and that an abnormal cardiac axis in early gestation can be associated with coarctation of the aorta, Ebstein’s anomaly, transposition of the great vessels and heterotaxy. The same group recently showed that 74.1 % of fetuses with confirmed congenital heart defects had an abnormal cardiac axis when evaluated between 11 and 14 + 6 weeks/days of gestation [61].

Cardiac Planes (Table 11.2)

Table 11.2

Visualization of fetal cardiac structures during the early ultrasound fetal cardiac examination at 11–13 + 6 weeks of gestation

 

10 weeks

11 weeks

12 weeks

13 weeks

13 + 6 weeks

4-chamber view

Yes

Yes

Yes

Yes

Yes

Outflow tracts

No

No

Yes

Yes

Yes

Aortic and ductal arch

No

No

Yes

Yes

Yes

Superior and inferior venae cavae

No

No

Yes

Yes

Yes

Pulmonary veins

No

No

No

Yes

Yes

Marques Carvalho et al. [62] explored the feasibility of obtaining the 4-chamber view and outflow tracts with transvaginal ultrasound in early pregnancy. The authors obtained the three planes in 37 % of fetuses at 11 weeks of gestation, and in 85 % of fetuses at 12 weeks of gestation. At 14 weeks, the three planes were obtained in 100 % of fetuses. The required time for examination at 14 weeks did not exceed 20 min. The authors concluded that after a crown-to-rump length of 64 mm, obtaining these three cardiac planes was completely feasible.

Carvalho et al. [56] suggested that the routine examination of the fetal heart at 11–13 + 6 weeks should include the following: the visceral situs solitus, cardiac position (axis), normal and symmetric 4-chamber view, two separate atrioventricular valves, normal aortic and pulmonary outflow tracts, two great arteries of similar size, and evidence of aortic and ductal arches. The authors mentioned that septal defects cannot be completely excluded, and that evolving cardiac lesions might not be visible in early pregnancy. Krapp et al. [63] reported that during the 11–13 + 6 week scan, the 4-chamber view could be visualized in 96 % of fetuses, the left ventricular outflow tract in 97 %, the 3-vessel view in 98 %, and the aortic arch in 72 % of fetuses, whereas the pulmonary veins were observed in 23 % of cases. Yagel et al. [64] proposed the following planes for fetal heart examination: upper abdomen, 4-chamber view, 5-chamber view, bifurcation of the pulmonary artery, 3-vessel and trachea, and the short axis of the right ventricle. The transvaginal route was suggested to be better than transabdominal ultrasound for detailed examination of the fetal heart. The authors reported that all proposed cardiac planes were obtained in 98 % of fetuses at 11–12 weeks, and in 100 % of fetuses at 13–15 weeks of gestation. They reported a 64 % detection rate for CHD when the cardiac examination was performed before 15 weeks of gestation and an extra 17 % detection when the heart was reevaluated at 20–24 weeks, with an overall detection rate of 85 % for CHD. Khalil et al. [65] proposed the following steps for cardiac evaluation in early pregnancy: assessment of the fetal position, orientation of the fetal heart, visualization of the 4-chamber view, assessment of the tricuspid valve and tricuspid regurgitation, visualization of the outflow tracts, and identification of the aortic and pulmonary arches. Abu-Rustum et al. [24] reported the following success rate for visualization of the cardiac structures during an early fetal cardiac scan: 4-chamber view (100 %), presence/absence of tricuspid regurgitation (100 %), crossing of the great vessels (90 %), bifurcation of the pulmonary artery (81 %), 3-vessel view (55 %), aortic arch (76 %), superior and inferior venae cavae (65 %), and ductus venosus (99 %). They also suggested that operators should perform a minimum of 70 fetal heart examinations at 11–13 + 6 weeks to gain reliable experience for obtaining the proposed anatomical planes with an allocated time of up to 10 min for fetal cardiac evaluation.

Operator Experience and Route of Ultrasound Examination

Allan [66] suggested that experience and technological resources are the main factors associated with differences in the detection rate of CHD, when transvaginal and transabdominal ultrasound examinations are compared. She suggested that the success of transabdominal examination can be attributed to the participation of a pediatric cardiologist in the scanning process, whereas transvaginal studies are mainly performed by obstetricians with limited experience in cardiac scanning. She concluded that it is not enough to only obtain the cardiac planes, but to also have the proper knowledge to interpret the images; and that another important factor for improving the detection of cardiac anomalies is the development of technical skills to improve the scanning plane, either by adjusting the position of the US probe or by changing the position of the mother [66]. Tegnander et al. [67] evaluated the detection of fetal cardiac anomalies by comparing operators with different levels of experience. Sonographers with previous experience of more than 2000 examinations had a 52 % detection rate of CHD as compared with a 32.5 % detection rate of operators previously performing fewer than 2000 cardiac examinations. This difference remained unchanged between the two groups of sonographers when detection of isolated CHD, or CHD with associated anomalies was analyzed. The authors concluded that it is necessary to become proficient in the visualization and interpretation of the 4-chamber view and of the left and right ventricular outflows before obtaining other anatomical cardiac planes. They suggested that, despite using a state-of-the art ultrasound system and/or the combination of different ultrasound techniques, operator experience still remains the key factor in improving the detection rate of CHD.

Well-trained operators can achieve a good detection rate of CHD early in pregnancy. Hartge et al. [68] studied a group of 3521 pregnant women presenting with 77 (2.1 %) fetuses with CHD. The ultrasound scans were performed by highly trained operators, using state-of-the art ultrasound systems with high frequency transvaginal probes. They reported 85.7 % detection rate of cardiac anomalies at 11–13 + 6 weeks of gestation. The authors mentioned that, in 64.2 % of cases, only the transabdominal route for ultrasound evaluation was needed and, in the remaining 35.8 % of patients, both transabdominal and transvaginal routes were used. The authors reported that conditions such as coarctation of the aorta, hypoplastic left heart resulting from aortic stenosis, and Tetralogy of Fallot might not be identified early in pregnancy. They concluded that well trained operators and high technology US systems are necessary to achieve a high detection rate of CHD in early pregnancy.

Rasiah et al. [69] performed a systematic review of the diagnostic performance of fetal echocardiography in the first trimester of pregnancy. They identified ten studies done in tertiary centers with good quality control that met the inclusion criteria. They reported a combined sensitivity of 85 % (95 % CI, 78–90 %) and specificity of 99 % (95 % CI, 98–100 %), positive likelihood ratio (LR) of 59.6 (95 % CI, 26.5–133.6), and negative LR of 0.25 (95 % CI, 0.1–0.6) for identification of congenital heart defects. The authors mentioned that, although transvaginal ultrasound is thought to be a better modality for visualization of the fetal heart, the training and experience of the operators and high quality US systems can lead to similar detection rates using transabdominal ultrasound.

When Is the Optimal Time to Perform Early Fetal Cardiac Evaluation?

Carvalho et al. [56] suggested, aside from operator experience, gestational age at examination is an important factor associated with a successful evaluation of the fetal heart. Haak et al. [70] reported that at 11 weeks successful evaluation of the heart can be achieved in about 20 % of fetuses, whereas at 13 weeks of gestation the success rate for fetal cardiac evaluation increases to 92 %.

Smrcek et al. [71] studied fetuses from 10 to 15 weeks of gestation to evaluate the following cardiac planes: 4-chamber view, 3-vessel view, origin and crossing of the great arteries, aortic and ductal arches, superior and inferior venae cavae, and at least two pulmonary veins. They were able to identify all structures at 10 weeks of gestation, except for the superior and inferior vena cava, which were visualized at 11 weeks. The pulmonary veins were observed in 80 % of fetuses between 12 and 14 weeks, and in 100 % of fetuses at 15 weeks of gestation. The authors reported an increment in the detection rate of cardiac defects, from 67 % at 10 weeks to 100 % at 15 weeks of gestation. They mentioned that, between 10 and 13 weeks, the transvaginal route for ultrasound examination was better than the transabdominal route; that, between 12 and 14 weeks of gestation, both transabdominal and transvaginal ultrasound had a similar detection rate; and from 15 weeks of gestation onward, the transabdominal route was better. The authors mentioned that complementary use of color directional Doppler and power Doppler, and not limiting the scanning time, can improve the optimal visualization of the fetal heart.

Vimpelli et al. [72] evaluated the feasibility of performing the cardiac examination at different weeks during the first trimester of pregnancy. The authors aimed to obtain the following planes: 4-chamber, longitudinal views of the aorta and pulmonary trunks, crossing of the great arteries, and aortic and ductal arches. The authors reported that visualization of all structures varied from 43 % at 11 weeks to 62 % at 13 + 6 weeks. The 4-chamber view was obtained in 74 % of cases at 13 + 6 weeks. McAuliffe et al. [73] evaluated a high-risk group of 160 women, defined by previous history of congenital heart disease, increased nuchal translucency, or the presence of a non-cardiac malformation during the nuchal scan. The authors evaluated the following cardiac parameters: 4-chamber view, symmetry of the cardiac chambers, atrioventricular valves, outflow tracts, crossing of the great arteries, and, when possible, the ductal and aortic arches. The mean gestational age at examination was 13.5 weeks, and the prevalence of cardiac defects was 12.5 % (n = 20). The 4-chamber view was seen in 100 % of fetuses, the tricuspid and mitral valves in 96 %, the outflow tracts in 95 %, the aortic and ductal arches in 45 %, and the pulmonary veins in 16 %. From 20 fetuses with CHD, 14 (70 %) were identified during the first trimester scan; the authors reported a specificity of 98 %, a positive predictive value (PPV) of 87.5 % and a negative predictive value (NPV) of 96 %.

Indirect Markers for Early Fetal Cardiac Evaluation

Borrell et al. [43] analyzed the contribution of increased nuchal translucency, tricuspid regurgitation, and reversed A wave in the ductus venosus in the identification of fetal cardiac defects in chromosomally normal fetuses. They reported that, among fetuses identified at 11–14 weeks with congenital heart disease, 40 % also had increased nuchal translucency, and 39 % had reversed A wave in the ductus venosus.

Clur et al. [74] reported that increased nuchal translucency, abnormal ductus venosus, and tricuspid regurgitation were the most frequent extra-cardiac ultrasound findings related with congenital heart disease. They showed that fetuses with normal chromosomes, but with increased nuchal translucency and reversed A wave in the ductus venosus, had an 83 % prevalence of cardiac defects. The authors also proposed that analysis of the pulsatility index of the ductus venosus, instead of presence/absence of atrial flow, might increase to 70 % the detection rate of fetal cardiac anomalies.

Pereira et al. [47] studied 85 euploid fetuses with major congenital heart defects and found an increased nuchal translucency (>95th percentile) in 35.3 %, tricuspid regurgitation in 32.9 %, and reversed A wave in the ductus venosus in 28.2 % of fetuses during first trimester ultrasound screening. In fact, any one of these markers was identified in 57.6 % of fetuses with cardiac defects and in 8 % of structurally normal fetuses. They concluded that these three markers improved the performance of screening for congenital heart defects in the first trimester.

Rembouskos et al. [75] suggested an association between aberrant right subclavian artery (ARSA) and fetal cardiac defects. The authors studied 4566 fetuses and identified 89 fetuses with ARSA, of which 12 fetuses had a chromosomal anomaly. The prevalence of fetal cardiac defects in chromosomally normal fetuses with ARSA was 4/77 (5.1 %), including Tetralogy of Fallot (n = 1), aberrant umbilical vein (n = 1) and tricuspid atresia (n = 2). The authors suggested that early fetal echocardiography is indicated in the presence of ARSA.

Sinkovskaya et al. [6061] evaluated the performance of cardiac axis measurement in early gestation for detection of major fetal cardiac defects. They examined the cardiac axis between 11 and 14 + 6 weeks in fetuses with confirmed congenital heart defects across three tertiary centers. They documented an extreme left or right deviation of the cardiac axis in 74.1 % of fetuses with congenital heart defects. In their study the cardiac axis performed better than enlarged nuchal translucency, tricuspid regurgitation, or reversed A wave in the ductus venosus, alone or combined, in detecting major fetal cardiac defects.

Clinical Application: Imaging the Fetal Heart in Early Pregnancy, Practical Recommendations

It is necessary for the operator to adjust the settings of the ultrasound system prior to a fetal cardiac examination. Even though this is an individual process, some basic principles might contribute to improved image quality.

Frequency and Depth

High-frequency transducers are a better option if the fetal heart is located close to the ultrasound probe. Transvaginal high-frequency ultrasound probes emitting at 9–12 MHz might be preferable at 11–12 weeks of gestation when the fetus is located close to the probe, whereas probes emitting at 5–9 MHz might be preferred at 12–13 weeks of gestation when the fetus is located away from the transducer. Transabdominal examination might be better with a linear 9-MHz probe if the fetus is located close to the maternal abdominal wall; if not, a 2- to 5- or 4- to 6-MHz probe might provide better ultrasound images. During B-mode, system settings should be optimized to obtain images with a high frame rate, increased contrast and high resolution along with the use of low persistence, a single acoustic focal zone and a relatively narrow image field. Depth adjustment and magnification should be employed when possible. Harmonic imaging can also be used to improve image quality and particularly for patients with increased maternal abdominal wall thickness.

Identification of the Scanning Planes

Transvaginal ultrasound might provide adequate images when performed between 11 and 12 weeks of gestation and when the fetus is in an optimal position. In some cases the required planes might not be immediately acquired, as the possibility of modifying the position of the uterus and the fetus and manipulating the ultrasound probe is limited. A prolonged transvaginal examination might be uncomfortable. In patients with increased body mass index, or with previous cesarean section or abdominal surgery, the transvaginal route for fetal cardiac examination should be preferred. Transabdominal examination from 13 weeks onwards offers the possibility to freely manipulate the ultrasound probe, and to change the position of the patient and of the scanning bed to acquire the fetal cardiac planes. The scanning time can also be prolonged.

A cross sectional plane of the fetal thorax with the heart in an apical projection and the fetal spine in the lower part of the ultrasound screen is the optimal image for cardiac examination. The 4-chamber view, 5-chamber view, crossing of the big arteries, and 3-vessel view can be obtained from this projection by performing a slow sweep towards the fetal head and maintaining cross sectional images of the studied planes (Fig. 11.1). The two outflow tracts can be visualized by rotating the ultrasound probe clockwise or anticlockwise from the 4-chamber view (Fig. 11.2). By rotating the probe 90° from the 4-chamber view, a sagittal plane of the thorax is obtained, and by gently moving the ultrasound probe from side to side, the aortic and ductal arches, and inferior and superior vena cava can be observed (Fig. 11.3). Color directional Doppler might be helpful in assessing the integrity of the interventricular septum, to visualize the crossing of the great arteries, and to document the direction of flow in the aortic arch (Fig. 11.4). Spectral Doppler is probably not necessary at this stage unless evaluation of the fetal cardiac function is necessary.

A328333_1_En_11_Fig1_HTML.jpg

Fig. 11.1

Cross-sectional image of the fetal heart at the level of the 4-chamber view at 13 + 5 weeks /days of gestation. (a) 4-chamber view. (b) Highlighted anatomical structures: LA left atrium, LVleft ventricle, RAright atrium, RV right ventricle. Note the pulmonary veins reaching the left atrium. (c) Heart-to-thorax ratio. (d) Cardiac axis

A328333_1_En_11_Fig2_HTML.jpg

Fig. 11.2

Outflow tracts and 3-vessel view. (a) Left outflow tract and aorta (LA left atrium, RV right ventricle). (b) Right outflow tract and pulmonary valve obtained from a short axis. (c) 3-vessel view. (d) Slightly oblique plane from the 3-vessel view to obtain the pulmonary valve

A328333_1_En_11_Fig3_HTML.jpg

Fig. 11.3

Sagittal images. (a) Aortic arch and descending aorta. (b) Pulmonary artery and ductal arch (RV right ventricle). (c) Ductal arch and descending aorta. (d) Inferior and superior venae cavae

A328333_1_En_11_Fig4_HTML.jpg

Fig. 11.4

High-definition color directional Doppler. (a) Cross-sectional view of the fetal heart and interventricular septum (LA left atrium, LV left ventricle, RA right atrium, RV right ventricle). (b) Joint of the aorta and pulmonary artery with blood flow moving in the same direction. (c) Ductal arch and descending aorta. (d) Inferior and superior venae cavae

Clinical Application: Detection of Cardiac Anomalies

There is a great variation in the detection rate of congenital heart disease due to non-modifiable factors, such as: the prevalence of the disease, the presence of high-risk ultrasound markers, the type of CHD and some modifiable factors, such as: the population screened, gestational age selected at scanning, operator experience and ultrasound system and techniques used (Table 11.3).

Table 11.3

Studies on the diagnostic capacity of early ultrasound for the identification of congenital heart disease

Study

Total (n)

Scan route

GA (weeks)

Prevalence of CHD (n[%])

Early detection (n[%])

Hernadi and Torocsik [107]

3991

TA, TV

11–14

1 (0.02)

D’Ottavio et al. [108]

4078

TV

13–14

12 (0.29)

3 (25.0)

Bilardo et al. [109]

1690

TA

10–14

4 (0.23)

Hafner et al. [110]

4233

TA

10–14

14 (0.33)

1 (7.1)

Hyett et al. [41]

29,154

TA

10–14

43 (0.15)

1 (2.3)

Schwarzler et al. [111]

4523

TA

10–14

9 (0.20)

Mavrides et al. [112]

7339

TA

10–14

24 (0.33)

4 (16.7)

Michailidis and Economides [113]

6650

TA, TV

10–14

9 (0.14)

2 (22.2)

Orvos et al. [114]

4309

TV

10–13

32 (0.74)

Taipale et al. [115]

4789

TV

10–16

18 (0.38)

1 (5.6)

Chen et al. [116]

1609

TA, TV

12–14

7 (0.44)

4 (57.1)

Bahado Singh et al. [42]

8167

TA

10–14

6 (0.07)

Bruns et al. [117]

3664

?

11–14

9 (0.25)

Becker and Wegner [29]

3094

TA, TV

11–14

11 (0.36)

6 (54.5)a

Cedergren and Selbing [118]

2708

TA

11–14

3 (0.11)

Dane et al. [119]

1290

TA

11–14

1 (0.08)

Westin et al. [81]

16,260

TA

12–14

29 (0.18)

Muller et al. [120]

4144

TA

10–14

13 (0.31)

Chen et al. [121]

7642

TA

10–14

19 (0.25)

7 (36.8)

Oztekin et al. [122]

1805

TA

11–14

2 (0.11)

Hildebrand et al. [79]

21,189

?

11–14

62 (0.29)

0

Syngelaki et al. [80]

44,859

TA, TV

11–13

106 (0.24)

36 (34)

Volpe et al. [76]

4445

TA, TV

11–14

28 (0.63)

23 (82.1)

Grande et al. [123]

13,723

TA, TV

11-14

44 (0.32)

25 (56.8)

Hartge et al. [68]

3521

TA, TV

11–13 + 6

77 (2.1)

66 (85.7)

Iliescu et al. [77]

5472

TA, TV

12–13 + 6

30 (0.54)

27 (90)

Persico et al. [83]

886

TA

11–13

100 (11.2)

96 (96)

Eleftheriades et al. [82]

3774

TA

11–13 + 6

29 (0.77)

13 (44.8)

Volpe et al. [100]

870

TA

11–14

62 (0.17)

56 (90.3)

Rossi et al. [78] (systematic review)

78,002

TA, TV

11–14

418 (0.53)

118/224b (53)

GA gestational age, TA transabdominal, TV transvaginal

aOnly major cardiac defects included

bFetal echocardiography performed in 224

Low-Risk Population

Volpe 2011 et al. [76] studied 4445 low risk fetuses with a 0.9 % prevalence of cardiac defects (n = 42), 28 major and 14 minor. A total of 39 cases were identified prenatally, 29 (69 %) during the first-trimester scan and 10 (23.8 %) in later stages of pregnancy. The authors mentioned that increased nuchal translucency, tricuspid regurgitation and reversed A wave in the ductus venosus were associated with a higher prevalence of fetal cardiac defects. The presence of these ultrasound markers should be considered an indication for targeted fetal cardiac evaluation. The authors reported that an abnormal 4-chamber view had a 50 % detection rate for major cardiac defects (Figs. 11.5 and 11.6).

A328333_1_En_11_Fig5_HTML.jpg

Fig. 11.5

Abnormal 4-chamber view; dilatation of the right atrium due to tricuspid insufficiency

A328333_1_En_11_Fig6_HTML.jpg

Fig. 11.6

Abnormal 4-chamber view; atrioventricular septal canal (power Doppler ultrasound)

Iliescu et al. [77] evaluated 5472 unselected patients and reported a prevalence of cardiac defects of 0.54 % (n = 30). Early examination of the fetal heart detected 40.6 % of congenital heart defects, 75 % of them major. The authors mentioned that 89 % of minor cardiac defects were detected in late stages of pregnancy. The authors confirmed that increased nuchal translucency had a strong association with fetal cardiac defects; 8.68 % of fetuses with increased nuchal translucency had major cardiac anomalies, and 96 % of them were detected during the first trimester cardiac scan. First trimester echocardiography was able to similarly identify major CDH in fetuses with increased or normal nuchal translucency. The authors reported that the time required for first trimester examination ranged from 18 to 52 min (median, 34 min).

Rossi and Prefumo [78] performed a systematic review of the evaluation of the fetal heart in the first trimester of pregnancy in a low risk population. The overall diagnostic performance at 11–14 weeks for detection of congenital heart defects was 48 % (210/418). The authors mentioned that the addition of Doppler ultrasound did not improve the detection of CHD. They also mentioned that targeted echocardiography in high risk pregnancies was able to identify 53 % of cardiac anomalies, and that an apparently normal fetal cardiac examination at 11–14 weeks does not exclude a cardiac defect.

Hildebrand et al. [79] evaluated a large group of 21,189 unselected pregnant women in Southern Sweden where ultrasound scans were performed by trained midwives. No congenital heart anomalies were detected during the first-trimester scan, and only 5.3 % of congenital heart defects were identified in the second-trimester ultrasound scan. The authors suggested that the operators’ lack of experience and non-actualized US systems greatly contributed to the reduced detection rate found in this study.

Syngelaki et al. [80] studied nearly 45,000 patients at 11 and 13 + 6 weeks of gestation and reported an overall detection rate of cardiac anomalies of 34 %; in particular, they found a 50 % detection rate of hypoplastic left heart (Fig. 11.7), transposition of the great arteries, and double outlet right ventricle; a 33 % detection rate of coarctation of the aorta, Tetralogy of Fallot and atrioventricular septal defects; and no acceptable detection rate for ventricular septal defects, Ebstein’s anomaly, aortic and pulmonary stenosis, tricuspid atresia, and cardiac tumors.

A328333_1_En_11_Fig7_HTML.jpg

Fig. 11.7

Abnormal 4-chamber view; asymmetric size of the ventricles early manifestation of a hypoplastic left ventricle

Westin et al. [81], in a large multicenter study, also from Sweden, compared the detection rate of cardiac anomalies during the routine fetal examinations, performed between 12 and 18 weeks of gestation. The authors reported an 11 % detection rate at 12 weeks and a 15 % detection rate at 18 weeks. The authors mentioned that, using 3.5 mm as a fixed cut-off value for defining an increased nuchal translucency, the detection rate of cardiac defects can be significantly reduced. They also mentioned that differences in operator expertise can be responsible for the low detection rate found in this study.

Eleftheriades et al. [82] studied 3774 fetuses with a prevalence of congenital heart anomalies of 0.77 % (n = 29) and reported that evaluation of the fetal heart in the first trimester of pregnancy allowed for the diagnosis of almost 45 % of the total number of cardiac defects; 48 % were diagnosed during the 20- to 24-week ultrasound scan, and the remaining 7 % later in pregnancy. The authors also showed a significant association between major cardiac defects and increased nuchal translucency and suggested that the evaluation of the 4-chamber view should be considered as part of the routine fetal examination at 11–13 + 6 weeks of gestation.

High-Risk Population

Persico et al. [83] evaluated the fetal heart in 855 pregnant women undergoing chorionic villus sampling due to the presence of ultrasound markers or altered maternal biochemical markers of fetal chromosomal anomalies. They reported 100 cases in which a cardiac defect was suspected (54 % major and 46 % minor). The authors reported a 93.1 % detection rate of cardiac anomalies using transabdominal ultrasound and a high association between congenital heart defects and increased nuchal translucency and tricuspid regurgitation.

Carvalho et al. [84] reported the diagnostic performance of targeted cardiac examination at the end of the first and early second trimesters of pregnancy in 230 high-risk women. Indications for fetal cardiac evaluation were: increased NT, family history of congenital heart disease, and abnormal findings during the routine US scan. They considered a normal US examination when the following structures were visualized: visceral situs solitus, normal cardiac position, normal 4-chamber view, two separate atrioventricular valves, normal aortic and pulmonary outflow tracts, two great arteries of similar size, and visualization of the aortic and ductal arches. The ultrasound scans were mainly performed transabdominally. The authors reported 199 normal and 21 abnormal cardiac evaluations; it was not possible to adequately visualize the heart in ten fetuses. From the 199 normal scans, perinatal results were available in 188 cases, and four of them had a cardiac defect (three ventricular septal defects and one pulmonary stenosis) (Fig. 11.8). From the 21 abnormal scans, 12 fetuses had a major and 2 fetuses a minor cardiac defect. The authors reported a 96 % diagnostic accuracy of early fetal echocardiography in high-risk pregnancies, and a high association between increased nuchal translucency, chromosomal anomalies and cardiac defects.

A328333_1_En_11_Fig8_HTML.jpg

Fig. 11.8

Abnormal 4-chamber view; severely small right ventricle and increased thickness of the left ventricular walls

Becker et al. [29] evaluated 3094 fetuses, referred secondary to an abnormal US examination, or to an increased nuchal translucency and reported a 2.8 % prevalence of CHD (n = 86), 84.2 % of them detected during the first-trimester fetal cardiac evaluation. The cardiac evaluation included the visualization of the 4-chamber view, outflow tracts and pulmonary and aortic valves. They reported that fetuses with increased nuchal translucency (>2.5 mm) had a prevalence of heart defects of 9.8 %, whereas fetuses with a normal nuchal translucency (<2.5 mm) had a prevalence of heart defects of 0.3 %.

Smrcek et al. [85] studied 2165 fetuses from low and high risk populations using the combination of 2-D ultrasound image and color directional Doppler. They reported a detection rate for congenital heart defects of 63.0 % (29/46); nine more fetuses (19.5 %) were diagnosed during the second-trimester ultrasound scan. Fetuses with an abnormal cardiac examination had a prevalence of chromosomal anomalies of 65.8 %; a prevalence of abnormal ductus venosus of 51.2 %; and a prevalence of increased nuchal translucency of 32.2 %. The authors mentioned that cardiac defects that tend to progress, such as myocardial hypertrophy, ventricular hypoplasia, fiboelastosis, and coarctation of the aorta, might not be identified at 11–14 weeks.

Improved Detection by Adding Other Ultrasound Findings

Axt-Fliedner et al. [54] reported a case of a normal 4-chamber view at 11 + 3 weeks of gestation with color Doppler indicating increased velocities across the aortic valve. Doppler interrogation across the atrio-ventricular valves and pulmonary outflow was normal. A follow-up ultrasound at 16 + 6 weeks/days demonstrated a hypoplastic left heart with no color flow across the mitral and aortic valve.

Bhat et al. [86] compared diagnosis of fetal Tetralogy of Fallot made before (Group 1) and after (Group 2) 17 weeks of gestation. The main findings increasing the suspicion of Tetralogy of Fallot during early fetal cardiac examination were a more levo rotated 4-chamber view, the presence of ventricular septal defect, overriding aorta, and discrepancy in the size of the great arteries. The authors were able to obtain most of these images early in pregnancy. There were seven out of ten fetuses in Group 1 with pulmonary stenosis and antegrade flow through the ductus arteriosus. Other cardiac anomalies such as interrupted inferior vena cava, bilateral superior vena cava, atrioventricular septal defect, and atrial bigeminy were also documented during the early ultrasound scan. Color Doppler ultrasound contributed to the identification of the outflow tracts. Transabdominal scanning was considered adequate in about 50 % of early ultrasound examinations.

Baschat et al. [87] evaluated four fetuses that were referred for increased nuchal translucency and bradycardia. Fetal heart block was diagnosed using M-mode ultrasound, and a congenital heart defect was present in all four fetuses; three out of four fetuses were confirmed to have heterotaxy on autopsy. Sciarrone et al. [88] identified complex congenital heart defects in two euploid fetuses with increased nuchal translucency and fetal bradycardia during early ultrasound examination.

Lafouge et al. [89] reported a right aortic arch and ductus arteriosus in the first trimester identified by the presence of a mirror image-like appearance of the main vessels in a 3-vessel trachea view.

Prefumo et al. [90] reported two cases of cardiac diverticula with large pericardial effusions. Color flow and Doppler demonstrated bidirectional flow into a saccular dilatation at the ventricular apex filling the pericardial space in both cases.

Complementary Ultrasound Techniques

Fundamental 2D imaging is the cornerstone for fetal cardiac evaluation; color Doppler and M-mode ultrasound might improve the diagnosis of septal defects and cardiac arrhythmias [8791]. Four-dimensional (4D)-ultrasound and STIC (Fig. 11.9) can by applied for off-line evaluation of the fetal heart either by the same or by different experts to confirm/exclude congenital heart defects [92].

A328333_1_En_11_Fig9_HTML.jpg

Fig. 11.9

Spatiotemporal imaging correlation (STIC) at 14 weeks of gestation. From a sagittal plane where the ductal arch and descending aorta can be visualized, seven cross-sectional planes are generated using tomographic ultrasound imaging (TUI)

A328333_1_En_11_Fig10_HTML.jpg

Fig. 11.10

Abnormal outflow tracts: truncus arteriosus

Spatiotemporal Imaging Correlation

Bennasar et al. [93] evaluated the reproducibility in evaluating STIC volumes at 11–15 weeks of gestation for identification of congenital heart defects. The authors used transvaginal ultrasound, combining color directional Doppler and gray-scale images. The structures evaluated in the STIC volume were 4-chamber view, crossing of the great vessels, left and right cardiac outflows, and 3-vessel view. They reported excellent agreement in the visualization of the 4-chamber view and outflow tracts. The same authors also reported that STIC volumes in early pregnancy allowed correct identification of 95 % of fetuses with suspected cardiac anomalies [94].

Espinoza et al. [34] obtained STIC volumes from 16 normal fetuses and 71 fetuses with congenital heart defects. The STIC volumes were evaluated by operators blinded to the clinical diagnosis. The results showed 79 % sensitivity and 90 % specificity for identification of fetal cardiac defects. The authors concluded that acquisition of cardiac STIC volumes and evaluation by an expert in fetal heart can be used to confirm/exclude the presence of a cardiac defect.

Lima et al. [95] explored the combined value of color Doppler ultrasound and STIC volume analysis in the identification of the basic planes for first trimester fetal cardiac examination. The authors reported that this combination allowed identification of most of fetal cardiac planes in 90.6 % of women in STIC volumes obtained either transabdominally or transvaginally. Tudorache et al. [91] also reported excellent reproducibility in obtaining STIC volumes for identification of fetal cardiac structures in early pregnancy.

Turan et al. [96] studied STIC volumes for evaluation of the fetal heart in the first trimester of pregnancy. The authors suggested that good-quality volumes should have the fetal spine clearly seen and minimal or no motion observed in the sagittal view of the multiplanar display of the fetal heart. They were able to visualize the following structures: 4-chamber view, descending aorta, heart size, cardiac axis, two equal size atria and ventricles, two opening atrioventricular valves, two great arteries, crossing and adequate size of the two great arteries, and presence of the aortic and ductal arches with forward flow in both. They reported that the 4-chamber view was obtained in all cases, and the remaining parameters in 85 % of fetuses. Transabdominal ultrasound examination was successful in 92 % of fetuses in obtaining good quality STIC volumes.

Viñals et al. [92] reported the acquisition of STIC volumes in the first trimester of pregnancy and interpretation by an experienced operator located remotely from the acquisition site. They showed that 71 % (35/49) of STIC volumes were obtained within a 20-min period, and a good agreement between operators for identification of fetal cardiac structures was achieved.

Evaluation of the Cardiac Function in Early Pregnancy

The evaluation of the fetal cardiac function in early pregnancies might be a complementary method for improving the identification of congenital heart defects. Clur et al. [74] studied changes in the cardiac function throughout gestation in fetuses with increased nuchal translucency. They evaluated the E and A peak velocities of the Doppler waveform of the ventricular filling, the E/A ratio, outflow velocities, stroke volume, and cardiac output. The authors reported discrepancies in cardiac function parameters between the two cardiac ventricles with a predominant function of the right ventricle. Ninno et al. [97] reported the evaluation of the tricuspid valve during the 11–13 + 6 week scan and showed an increment in the E velocity and in the E/A ratios, and mild changes in the A velocity as gestation progresses.

Rozmus-Warcholinska et al. [58] reported normal values for fetal cardiac function parameters between 11 and 13 + 6 weeks of gestation. The authors showed a mild difference in the Tei index (MPI, or myocardial performance index) between the left and right ventricles, and stable values of the Tei index during that period. There was an increment in the E/A ratio and in the E velocity but no changes in the Avelocity during the same gestational period.

Turan et al. [98] reported a high association between abnormal fetal cardiac function parameters in early pregnancy and maternal hyperglycemia in women with pregestational diabetes. The authors showed reduced left E/A ratio, prolongation of the isovolumetric relaxation time in both ventricles, reduction in the isovolumetric contraction time in the left ventricle, and prolonged MPI in the two ventricles.

Do We Have to Evaluate All Patients at 11–13 + 6 Weeks?

Gardiner [99] suggested caution in proposing an extended cardiac examination in the first trimester of pregnancy due to the risk of false-positive cases in which parents might decide to terminate the pregnancy in a structurally normal fetus. The author mentioned that, based on morphologic information provided by high-resolution episcopic microscopy (HREM), growth of the atrioventricular septum occurs later in the first trimester of pregnancy, and offset of the mitral and tricuspid valves might not be visualized before 14 weeks of gestation in a structurally normal fetus. The author concluded that there is a high risk of incorrect diagnoses of atrioventricular septal defects in early pregnancy. Volpe et al. [100] evaluated the contribution of the first- and second-trimester echocardiography in the diagnosis of CHD and reported that a considerable proportion of cases, considered as normal in the first trimester examination, might develop cardiac defects at later stages of pregnancy (Table 11.4). Similarly, they reported that a considerable percentage of fetuses with an abnormal cardiac examination might actually have a structurally normal heart.

Table 11.4

Congenital heart defects that can be identified during the early ultrasound fetal cardiac examination at 11–13 + 6 weeks of gestation

Cardiac defects that can be detected

Transposition of the great arteries; double outlet right ventricle; hypoplastic left heart

Cardiac defects that might be detected

Coarctation of the aorta

Tetralogy of Fallot

Canal AV or atrioventricular septal defects

Truncus arteriosus (Fig. 11.10)

Cardiac defects unlikely to be detected

Ventricular septal defects

Ebstein’s anomaly

Mild aortic and pulmonary stenosis

Cardiac tumors

Myocardial hypertrophy

Fibroelastosis

Abnormal pulmonary venous return

Safety

Guidelines of the International Society of Ultrasound in Obstetrics and Gynecology (ISUOG, 2011) recommend keeping the thermal index (TI) < 1.0 during Doppler examination at 11–13 + 6 weeks. They suggest that the main reason for advocating the principle of ALARA (As Low As Reasonably Achievable) in the first trimester of pregnancy is the unknown effect of Doppler ultrasound during embryogenesis [101]. Nemescu et al. [102] assessed the safety of first trimester fetal echocardiography by measuring the TI and mechanical index (MI) generated during 399 examinations. Although there was an increase in TI values from B mode to color flow to power Doppler studies, these values were always lower than 0.5. Satisfactory Doppler images were obtained with these settings.

Teaching Points

·               Early evaluation of the fetal heart as a screening or indicated procedure should be considered based on the availability of technological resources and on the experience of operators.

·               Experience and training are the most important factors for early identification of fetal cardiac defects; highly trained operators achieve a better detection rate.

·               Increased nuchal translucency, tricuspid regurgitation, reversed A wave in the ductus venosus, aberrant right subclavian artery, abnormal cardiac axis, hydrops, monochorionic twins, pregnancies from assisted reproductive techniques, and any other fetal structural defect are indications for early fetal cardiac ultrasound evaluation.

·               Before 12 weeks of gestation transvaginal ultrasound provides adequate images for cardiac examination; from 13 weeks onwards, transabdominal ultrasound also provides reliable cardiac images.

·               The 4-chamber and outflow tracts views are the most important ultrasound images to achieve a good detection of congenital heart defects.

·               The 4-chamber view and outflow tracts can be identified from 12 weeks of gestation in almost all fetuses. The majority of cardiac planes of the basic and extended fetal cardiac evaluations can be obtained from 13 weeks of pregnancy.

·               Additional US techniques such as color directional Doppler and STIC (spatiotemporal image correlation) can contribute in improving the detection rate of congenital heart defects in early pregnancy.

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Footnotes

1

See also Chap. 4.