**3. Genetic diseases related to cardiac anomalies**

CHD and chromosomal deletion syndrome: (1) DiGeorge syndrome or 22q11microdeletion; (2) Williams-Beuren syndrome, 1p36 deletion syndrome.

CHD associated with single gene disorders: Noonan syndrome and RASopathies, Holt-Oram syndrome, Alagille syndrome, Tuberous sclerosis complex and CHARGE syndrome.

Familial recurrence of congenital heart defects: recurrence risk of 3% for two healthy nonconsanguineous parents with one affected child, risk of recurrence increases to 10% with two affected siblings.

### **3.1 Fetal situs**

Assessment of fetal visceral situs is essential first step in fetal echocardiogram. Evaluating cardiac position and orientation in thoracic cavity and anatomical relationship of abdominal organs is the part of the fetal echocardiogram examination.

Steps for sequential segmental analysis in the fetus are identifying visceral situs, Atrial arrangement, Atrioventricular valves, ventricular arrangement, ventriculoarterial connection, Ventricular outflow tracts and systemic and pulmonary venous connections. First step is Fetal visceral situs (**Figure 2**) for this identify fetal presenting part (cephalic/breech) next step is to determine fetal lie by obtaining sagittal view of fetal spine and compare with the maternal spine after this determine the location of the fetal left side with the regard to maternal abdomen. Bronshtein et al. [6] described a method to determine situs is referred as the right-hand rule for abdominal scan and left-hand rule for transvaginal approach. Palm of the hand corresponds to the face of fetus and sonographer holds the hand according to the side of fetal face; left side of the fetus will be shown by the examiners thumb.

Types of visceral situs are situs solitus, situs inversus and situs ambiguous.

Situs solitus is normal viscerocardiac arrangement where the cardiac apex, stomach and descending Aorta should be located on the fetal left side. Inferior vena cava is located on the right side. Situs inversus is the mirror image arrangement of organs and vessels to situs solitus. Incidence is about 0.01%. There is slight increased risk of CHD and 20% association with Kartagener's syndrome which is autosomal recessive transmission.

#### **Figure 2.**

*Determining the fetal situs in longitudinal lie. (A) Fetus in cephalic presentation with spine close left uterine wall, results right side being anterior and left side posterior. (B) Cephalic with spine close to left uterine wall results left side being anterior and right side posterior. (C) Fetus in breech presentation with spine close to left uterine wall results left side being anterior and right side posterior. (D) Fetus in breech with spine close to right uterine wall results right side being anterior and left side posterior. The corresponding transverse ultrasound planes of the chest and abdomen. Blue arrow indicates fetal stomach, red arrow apex of heart and yellow arrow descending aorta.*

Situs ambiguous, which refers to Viscerocardiac malposition, is commonly associated with complex CHD. Incidence of situs ambiguous is around 1per 10,000 infants [7]. This may be of right or left isomerism or situs ambiguous also known as visceral Heterotaxy syndrome which is very less commonly noted.

Detection of CHD on ultrasound depends on the position and axis of the cardia. Fetal cardiac axis: to determine the axis, obtain the transverse view of the chest at the level of four chamber view plane. A line is drawn from the spine to the anterior chest wall, the cardiac axis is the angle that the interventricular septum makes with this line (**Figure 3A**). Normal angle lies 45° to the left of the midline [8]. It is independent of gestational age. The axis is abnormal when it is >65° and < 25°. Study of Smith et al. [9] showed that >75° of leftward deviation are associated with CHD in 76% of fetuses which include Tetralogy of Fallot, Common arterial trunk, coarctation of aorta and Ebstein anomaly. Double outlet right ventricle, Atrioventricular septal defect and common atrium are more commonly associated with right axis deviation.

Cardiac position: depending upon the position of the heart it can be described as Levocardia Dextrocardia and mesocardia. Ectopia cordis refers when the cardia is outside the chest. As per Abuhamad et al [10] Heart positioned in right chest regardless of its axis it is termed as Dextrocardia, when the heart is placed in right chest with axis pointing to left then it is termed as Dextroposition and when the heart is positioned in right chest with axis pointing toward right side is known as dextroversion. Dextrocardia with axis to right: more commonly associated with Situs inversus, Congenital corrected transposition. Whereas Dextrocardia with left axis deviation is more commonly associated with extrinsic factors (**Figure 3B** and **C**) resulting in shift of heart to right side like Left diaphragmatic hernia, left lung mass, left pleural effusion, agenesis or hypoplasia of the right lung (scimitar syndrome). Mesocardia-Heart located in central chest

**93**

*Fetal Echocardiogram Normal and Abnormal DOI: http://dx.doi.org/10.5772/intechopen.91867*

with cardiac apex pointing toward the midline of the chest usually associated with abnormal ventriculoarterial connections such as transposition of great arteries, Double outlet right ventricle. Bilateral increased lung volume such as laryngeal atresia is also associated with mesocardiac. Levocardia–it is more commonly used term for normal position of heart. Levoposition is noted in Right sided space occupying lesions or agenesis/hypoplasia of left lung. Levocardia with left axis deviation is commonly associated with CHD. Normal heart size should be 1/3rd to 1/2 that of thoracic cavity. The width of heart at AV valves corresponds to gestational age in weeks. Cardiothoracic (C/T) circumference is constant throughout gestation is about 0.45–0.5. Contractility of vetricles should

*(C) Dextrocardia with apex pointing to left due to congenital diaphragmatic hernia.*

*(A) Measuring the cardiac axis. (B) Dextrocardia due to congenital adenomatoid malformation of left lung.* 

be equal. Rhythm normal is 120–160 beats per minute.

**echocardiography**

**Figure 3.**

**4. Optimization of two-dimensional grayscale image in fetal** 

The quality of 2D image is dependent on several factors such as choice of the transducer and presets, the angle of insonation and access to the region of interest and magnification of target region. Routinely two types of transducers are used in fetal echocardiography low frequency range (2–5 MHz) which allows good penetration and acceptable resolution. High frequency range (5–8 MHz) allows for improved resolution but limited penetration. Recently linear transducers are used for first trimester echocardiography as it gives high resolution. Image presets: (1) Harmonic imaging: in harmonic imaging, the reflected harmonic wave has a low amplitude high frequency which results in improved image and contrast with reduced artifacts. (2) Compound imaging allows the transducer to send signals at multiple angles to eliminate artifacts and improves the image resolution. (3) Speckle reduction imaging: weak signals are eliminated and strong signals are enhanced this allows the image to become smoother and reduces artifacts. (4) Focal zones: when imaging the heart chooses one focal zone at the region of interest to obtain better lateral resolution. (5) Dynamic range: narrow dynamic range provide better image as artifacts are eliminated. (6) High frame rate: high frame rate more than 25 frames per second. This can be achieved by narrowing the sector width and

**Figure 3.**

*Advanced Concepts in Endocarditis - 2021*

Situs ambiguous, which refers to Viscerocardiac malposition, is commonly associated with complex CHD. Incidence of situs ambiguous is around 1per 10,000 infants [7]. This may be of right or left isomerism or situs ambiguous also known as

*Determining the fetal situs in longitudinal lie. (A) Fetus in cephalic presentation with spine close left uterine wall, results right side being anterior and left side posterior. (B) Cephalic with spine close to left uterine wall results left side being anterior and right side posterior. (C) Fetus in breech presentation with spine close to left uterine wall results left side being anterior and right side posterior. (D) Fetus in breech with spine close to right uterine wall results right side being anterior and left side posterior. The corresponding transverse ultrasound planes of the chest and abdomen. Blue arrow indicates fetal stomach, red arrow apex of heart and yellow* 

as Levocardia Dextrocardia and mesocardia. Ectopia cordis refers when the cardia is outside the chest. As per Abuhamad et al [10] Heart positioned in right chest regardless of its axis it is termed as Dextrocardia, when the heart is placed in right chest with axis pointing to left then it is termed as Dextroposition and when the heart is positioned in right chest with axis pointing toward right side is known as dextroversion. Dextrocardia with axis to right: more commonly associated with Situs inversus, Congenital corrected transposition. Whereas Dextrocardia with left axis deviation is more commonly associated with extrinsic factors (**Figure 3B** and **C**) resulting in shift of heart to right side like Left diaphragmatic hernia, left lung mass, left pleural effusion, agenesis or hypoplasia of the right lung (scimitar syndrome). Mesocardia-Heart located in central chest

Detection of CHD on ultrasound depends on the position and axis of the cardia. Fetal cardiac axis: to determine the axis, obtain the transverse view of the chest at the level of four chamber view plane. A line is drawn from the spine to the anterior chest wall, the cardiac axis is the angle that the interventricular septum makes with this line (**Figure 3A**). Normal angle lies 45° to the left of the midline [8]. It is independent of gestational age. The axis is abnormal when it is >65° and < 25°. Study of Smith et al. [9] showed that >75° of leftward deviation are associated with CHD in 76% of fetuses which include Tetralogy of Fallot, Common arterial trunk, coarctation of aorta and Ebstein anomaly. Double outlet right ventricle, Atrioventricular septal defect and common atrium are more commonly associated with right axis deviation. Cardiac position: depending upon the position of the heart it can be described

visceral Heterotaxy syndrome which is very less commonly noted.

**92**

**Figure 2.**

*arrow descending aorta.*

*(A) Measuring the cardiac axis. (B) Dextrocardia due to congenital adenomatoid malformation of left lung. (C) Dextrocardia with apex pointing to left due to congenital diaphragmatic hernia.*

with cardiac apex pointing toward the midline of the chest usually associated with abnormal ventriculoarterial connections such as transposition of great arteries, Double outlet right ventricle. Bilateral increased lung volume such as laryngeal atresia is also associated with mesocardiac. Levocardia–it is more commonly used term for normal position of heart. Levoposition is noted in Right sided space occupying lesions or agenesis/hypoplasia of left lung. Levocardia with left axis deviation is commonly associated with CHD. Normal heart size should be 1/3rd to 1/2 that of thoracic cavity. The width of heart at AV valves corresponds to gestational age in weeks. Cardiothoracic (C/T) circumference is constant throughout gestation is about 0.45–0.5. Contractility of vetricles should be equal. Rhythm normal is 120–160 beats per minute.
