Purpose of the Four-Chamber View

In Part I, we explored the foundational aspects of the four-chamber view, emphasizing its role in prenatal ultrasonography. With that understanding, we now delve deeper into its practical applications and advanced evaluation techniques in Part II. The four-chamber view remains pivotal for obstetricians and sonographers as it provides a comprehensive assessment of fetal cardiac health. This essential perspective allows for detailed scrutiny of the fetal heart’s chambers and valves, empowering healthcare providers to discern potential congenital heart defects early in gestation. As we progress through this section, we will examine the methodologies used to interpret these ultrasound images, enhancing our ability to identify anomalies and improve outcomes through early intervention.

Cardiac Measurements⁷

Heart size: Should occupy 1/3rd to 1/2 of the thoracic cavity.
Width of the heart at AV valves: Corresponds with gestational age in weeks.
Cardiothoracic (C/T) circumference ratio: Remains constant throughout gestation at 0.45–0.5.
Ventricular Contractility: Should be equal.
Normal Heart Rate: 120–160 beats per minute.

The four-chamber view can detect approximately 64% of congenital cardiac anomalies, making it an indispensable tool in prenatal assessments¹.

Figure 1¹

1. Ventricular Septal Defects (VSDs):
- These defects involve a hole between the heart's left and right ventricles.
- They cause abnormal blood flow and can result in chamber enlargement.

Classification by Anatomic Location⁷:

Perimembranous VSD – Most common in neonates (~80%).
Muscular VSD – Accounts for 5–20% of neonatal VSDs, but more common prenatally (~80–90%).
Inlet VSD – 5–8% of cases.

Outlet VSD – 5% of cases.

Type of VSD	Detection Method	Key Features
Muscular VSD	Best detected in lateral chamber view	Often bidirectional (Figure 2b); difficult to visualize on grayscale
Perimembranous VSD	Five-chamber view	Visualized as discontinuity between the ventricular septum and medial wall of the ascending aorta
Small Muscular VSDs	Color Doppler Imaging	Rarely diagnosed on grayscale imaging
Apical View Consideration	Echogenic borders	Dropout artifact may falsely mimic VSD

Figure 2

Figure 2b¹⁴

2. Atrioventricular Septal Defects (AVSDs):
- AVSDs are characterized by malformations involving the atrial and ventricular chambers and their associated valves.
- They often appear in association with genetic disorders like Down syndrome.
- In the four-chamber view, the presence of a single atrioventricular valve instead of two distinct valves aids in the identification of AVSDs.

Incidence & Detection⁷

AVSDs represent 4–7.4% of congenital heart diseases in infants.
18% of prenatally detected CHDs are AVSDs.
Best detected in: Apical Four-Chamber View

Types of AVSD⁷


Complete AVSD	Includes ASD1, VSD, and a common AV valve with five leaflets. (Figure 3)
Partial AVSD	Includes ASD1 and a cleft mitral valve, but separate AV valves attach at the same level.
Transitional AVSD	Type of partial AVSD with two distinct AV annuli, a large atrial septal defect, and a small VSD.
Balanced vs. Unbalanced AVSD	Unbalanced AVSD occurs when AV connections predominantly drain into one ventricle, leading to ventricular disproportion (often seen in Heterotaxy Syndrome).

Atrioventricular Length Ratio (AVL Ratio)⁷

AVL Ratio > 0.6 detects AVSD with 83% accuracy and a false-positive rate of 5.7%.
Figure 3

3. Hypoplastic Heart Syndromes:
- Hypoplastic Left Heart Syndrome (HLHS) and Hypoplastic Right Heart Syndrome (HRHS) involve underdevelopment of one side of the heart.
- This results in smaller, less developed ventricles, leading to impaired blood circulation.
- The underdeveloped structures are readily apparent in the four-chamber view.

Figure 4

4. Persistent Truncus Arteriosus:
- This condition is identified by the presence of a single blood vessel over both ventricles, instead of separate aorta and pulmonary artery.
- It is noticeable due to the lack of separation, causing altered blood flow patterns visible in the echocardiographic image.

5. Echogenic Intracardiac Foci (EIF):
- EIFs appear as bright spots within the heart chambers.
- While generally benign, they require further evaluation if other anomalies or markers are present.

6. Valve Abnormalities:
When evaluating the fetal heart using the four-chamber view, abnormalities in valve function and structure can manifest in several ways:

- Stenosis: Narrowing of the valve opening, which restricts blood flow and increases pressure in the heart chambers.
- Regurgitation: Leakage of blood backward through the valve, leading to inefficient circulation and possible heart enlargement.
- Atresia: Absence or underdevelopment of a valve, severely impeding blood flow.

The four-chamber view allows for the visualization of the size, movement, and functionality of the heart valves. During an ultrasound:

- Flow Patterns: Doppler techniques can assess blood flow velocity and direction across the valves.
- Valve Morphology: Visual inspection can reveal thickening, calcification, or unusual movement of valve leaflets.
- Chamber Size: Disproportions in atrial or ventricular sizes can indicate compensatory changes due to valve dysfunction.

Anomalies Not Readily Visible in the Four-Chamber View

In the study of heart anomalies, the four-chamber view is a fundamental imaging technique that provides a detailed look at the heart's atria and ventricles. However, while this view is quite informative, it does not always reveal certain complex heart anomalies (Figure 5). For instance, in the case of transposition of the great arteries, where the positions of the aorta and pulmonary artery are reversed, the condition may remain hidden because this detail lies beyond the scope of the four-chamber perspective. Similarly, intricate conditions such as tetralogy of Fallot, which involves multiple structural heart defects, and aortic coarctation, a narrowing of the aorta, may not be easily detected with this view alone. These conditions often require additional imaging techniques to identify and understand the full extent of the abnormalities. Therefore, while the four-chamber view is a vital tool in fetal echocardiography, it's important to complement it with other diagnostic methods to ensure a comprehensive evaluation of the heart's health.

Figure 5

*Special Case: Congenital Corrected Transposition of the Great Arteries (cc-TGA) (Figure 6)
- Description: A rare form where the ventricular inversion allows for correct alignment of the aorta and pulmonary artery despite the ventricular reversal.
- Clinical Implications: Often asymptomatic initially. It may not require immediate surgery, but it may develop complications over time.

Figure 6

Key Morphologic Markers in Four-Chamber View for Diagnosing Heart Defects

In the assessment of congenital heart defects, the four-chamber view serves as a critical window into the structure and function of the fetal heart. Within this view, certain morphologic markers act as internal “birthmarks”—consistent, recognizable features that indicate normal development. By becoming familiar with these key markers, clinicians can use them as reliable landmarks to quickly spot abnormalities. When one or more of these markers appear altered or displaced, it often signals that an embryological error has occurred. Understanding what is normal in the four-chamber view—such as the symmetry of the atria and ventricles, the alignment of the atrioventricular valves, and the integrity of the septa—provides a strong foundation for identifying deviations that may indicate congenital heart defects. This introduction sets the stage for a deeper dive into how these markers guide accurate and early diagnosis.

Causes of Dilated Azygos Vein in a Fetus²

Interrupted Inferior Vena Cava (IVC) (Figure 7)
- Blood from the lower body is rerouted through the azygos vein due to failure of the IVC to connect properly.
- Commonly associated with:
  - Atrial isomerism (malformation of the atria)
  - Polysplenia syndrome (multiple small spleens, often linked with other visceral and cardiac anomalies)
Congenital Heart Disease
- Various cardiac anomalies can contribute to altered venous return and increased pressure in the azygos system.
- Examples include:
  - Atrial septal defect (ASD)
  - Complex congenital heart defects
Right Heart Strain or Pressure Overload
- Increased pressure in the right atrium or ventricle can result in backpressure into systemic veins.
- Often due to:
  - Tricuspid valve insufficiency
  - Pulmonary hypertension
Portal Hypertension
- Elevated pressure in the portal venous system can lead to collateral circulation through the azygos vein.
- May result from liver pathology or vascular abnormalities.
Other Potential Causes
- Congenital Superior Vena Cava (SVC) Interruption
- Constrictive Pericarditis
- Pericardial Effusion

Figure 7

Significance of the Absence of the Moderator Band in the Fetal Right Ventricle

Implications of Absence
- May indicate congenital abnormalities, particularly:
  - Double-Chambered Right Ventricle (DCRV)
  - Other forms of Congenital Heart Disease (CHD)
Double-Chambered Right Ventricle (DCRV)⁴
- Right ventricle is abnormally divided into two chambers.
- Often caused by hypertrophied moderator band or other abnormal muscle bundles.
- Commonly associated with:
  - Ventricular Septal Defect (VSD)
  - Pulmonary valve stenosis
  - Other structural malformations
Other Congenital Heart Diseases (CHD)
- Absence or abnormal appearance of the moderator band may occur in:
  - Transposition of the Great Arteries (TGA)³
    - Great arteries arise from the wrong ventricles dTGA
    - Ventricles switch places (Right ventricle-left atrium & Left ventricle-right atrium) ccTGA
Ventricular Septal Defect (VSD)⁵
- A frequent finding alongside absence of the moderator band.
- Indicates abnormal development of the right ventricle.

Reasons for Displacement of Pulmonary Veins⁶

1. Total Anomalous Pulmonary Venous Return (TAPVR)

Definition:

All (4) pulmonary veins drain into the right atrium or systemic veins instead of the left atrium.

Indications in Fetuses:

Lack of Visualization:
- Pulmonary veins not seen entering the left atrium on fetal echocardiogram.
Other Abnormalities:
- Abnormal Coumadin ridge.
- Abnormal post-left atrium (post-LA) index.
Right Heart Dominance:
- Enlarged right heart due to increased blood flow.
Abnormal Chamber Dimensions:
- Asymmetric ventricular chamber sizes.

2. Partial Anomalous Pulmonary Venous Return (PAPVR) (Figure 8)

Definition:

Some (1-3) pulmonary veins drain into the right atrium or systemic veins.
Similar to TAPVR:
- Abnormal pulmonary vein connections.
- Lack of visualization of some pulmonary veins entering the left atrium.
Associated Atrial Septal Defect (ASD):
- Often associated with sinus venosus type ASD.
Figure 8

Causes of Abnormal Heart Positioning: A Visual Overview⁷

Cardiac Position	Associations
Dextrocardia (Right Chest, Right Axis)	More commonly associated with Situs inversus and Congenital Corrected Transposition
Dextrocardia (Right Chest, Left Axis Deviation)	Often linked with extrinsic factors like left diaphragmatic hernia, lung mass, pleural effusion, or scimitar syndrome (agenesis/hypoplasia of the right lung)
Mesocardia	Frequently associated with abnormal ventriculoarterial connections (e.g., transposition of great arteries, Double Outlet Right Ventricle)
Levocardia (Left Axis Deviation)⁸	Linked to severe congenital heart defects—such as VSD, atrioventricular canal defects, and pulmonary outflow tract anomalies—with left axis deviation on sonography serving as a potential indicator, especially for conotruncal abnormalities.
Levoposition	Noted in conditions such as right-sided space-occupying lesions or left lung agenesis/hypoplasia

Fetal Heart Size Deviations in 4CV: Diagnostic Clues and Causes

Cardiomyopathies⁷

Definition: A disease of the myocardium associated with abnormal cardiac function.

Types of Cardiomyopathies

Dilated Cardiomyopathy (DCM)
- Characterized by enlarged heart with dilated chambers and decreased contractility.
- Clinical Features:
  - Impaired ventricular function.
  - Possible pericardial effusion.
Hypertrophic Cardiomyopathy (HCM)
- Enlarged heart with ventricular wall hypertrophy.
- May reduce ventricular lumen.
- Common association: Maternal diabetes mellitus.
Endocardial Fibroelastosis (EFE)⁹
Rare but serious congenital cardiac disorder characterized by a diffuse or localized thickening of the endocardial lining of the heart chambers. This condition is caused by the excessive deposition of collagen and elastin, resulting in a stiff and non-compliant heart muscle. EFE can develop in isolation (primary) or in association with other structural cardiac anomalies (secondary), and may progress to heart failure in utero.

Pathophysiology⁹

The abnormal endocardial thickening seen in EFE disrupts the heart’s normal ability to contract and relax efficiently. This impaired compliance especially affects diastolic function, limiting ventricular filling and reducing cardiac output. Over time, this can lead to ventricular hypertrophy and congestive heart failure.

Key Clinical Features of EFE¹⁰

Feature	Description
Endocardial Thickening	Increased echogenicity on fetal echocardiography due to fibrous deposition
Ventricular Hypertrophy	Enlargement of one or both ventricles in response to stiffened walls
Diastolic Dysfunction	Impaired relaxation and filling of the ventricles
Congestive Heart Failure	Final common pathway; may present with hydrops fetalis or intrauterine demise

Etiology and Associated Conditions¹⁰

The precise cause of EFE is often unclear. It may occur as:

Primary EFE: Occurs without structural heart disease, potentially due to intrinsic myocardial pathology.
Secondary EFE: Occurs in response to other cardiac conditions such as:
- Aortic stenosis
- Coarctation of the aorta
- Anomalous coronary arteries
Other Contributing Factors:
- Intrauterine infections (e.g., mumps, coxsackievirus, parvovirus B19)
- Autoimmune disorders, especially maternal anti-Ro/SSA antibodies
- Metabolic storage diseases such as Pompe or Barth syndrome
Prenatal Diagnosis
Fetal echocardiography is the primary imaging modality for diagnosing EFE in utero. Sonographic findings include:
- Increased echogenicity of the endocardium (seen as a bright, thickened inner cardiac lining)
- Chamber enlargement, particularly affecting the left ventricle
- Signs of diastolic dysfunction, such as reduced ventricular filling
- In severe cases, hydrops fetalis may be evident

(*Line Chart Visual Aid of Progression of EFE)

Trigger (infection, genetics, structural defect)

↓

Endocardial injury → Collagen/elastin buildup

↓

Endocardial thickening (EFE)

↓

Ventricular stiffness and hypertrophy

↓

Impaired filling (diastolic dysfunction)

↓

Reduced cardiac output → Heart failure

↓

Possible fetal hydrops or demise

Fetal Heart Tumors⁷

Definition: Abnormal cardiac masses, commonly benign tumors detected during prenatal ultrasound on the 4-chamber view.

Types of Fetal Heart Tumors

Tumor Type	Prevalence	Ultrasound Features	Associated Conditions
Rhabdomyomas	80–90% of fetal heart tumors	Oval or circular well-defined echogenic mass	Commonly linked to tuberous sclerosis
Teratoma	Rare	Multi-cystic or solid mass	May be extracardiac
Fibroma	Rare	Well-defined hyperechoic mass	Can obstruct ventricular outflow
Myxoma	Rare	Often mobile mass	May cause valve dysfunction
Hamartoma	Rare	Disorganized tissue growth	May involve ventricular walls
Rhabdomyosarcoma	Rare	Invasive mass	Can affect multiple cardiac structures

Common Locations of Rhabdomyomas

Interventricular septum
Ventricular walls
Atria

Fetal Pericardial Effusion¹¹

Category	Key Information
Definition	Accumulation of fluid in the fetal pericardial sac
Normal Finding	Thin rim <3 mm after 20 weeks gestation (Figure 9)
Pathological Effusion	Fluid >2 mm; may signal hydrops or cardiac pathology

Figure 9

Potential Causes¹³

Etiology	Details
Nonimmune Hydrops Fetalis	Generalized fetal edema, includes pericardial fluid
Fetal Hemolytic Disease	Maternal alloimmunization → anemia → heart failure
Structural Heart Defects	May impair venous return or increase cardiac pressures
Chromosomal Abnormalities	Trisomy 21, 18, 13 commonly associated
Infections	CMV, Parvovirus B19, Rubella, Coxsackievirus
Immunopathies	Maternal lupus, other autoimmune diseases
Fetal Anemia	Can lead to high-output cardiac failure and effusion

Isolated Fetal Pericardial Effusion (IFPE)¹¹

Aspect	Detail
Definition	Effusion without other anomalies or signs of hydrops
Prognosis	Often favorable, but evaluate for genetic anomalies
Surveillance	Serial ultrasounds to monitor for changes

Evaluation Tools¹¹

Modality/Test	Purpose
Ultrasound	Measure fluid; assess for hydrops and cardiac motion
Fetal Echocardiogram	Evaluate structural defects or cardiac dysfunction
Maternal Serum Screening	Rule out TORCH infections
Genetic Testing	Check for chromosomal abnormalities

Management Options¹¹

Approach	Indication
Monitoring	Small, isolated effusions with no progression
Fetal Pericardiocentesis	Large effusion with signs of tamponade or cardiac compromise
Medical Therapy	Treat infections or immune-mediated causes
Delivery Planning	Multidisciplinary coordination for significant patholog

Complementary Imaging Techniques

An abnormal finding in the four-chamber view warrants further investigation with advanced imaging. Because this standard view cannot detect all congenital heart defects—especially those involving the outflow tracts or great vessels—additional techniques are essential for a complete evaluation:

Outflow Tract Views: These assess the right and left ventricular outflow tracts, helping to identify conditions like transposition of the great arteries (TGA), double outlet right ventricle (DORV), and truncus arteriosus.
Three-Vessel and Tracheal View: Offers a cross-sectional view of the great vessels and their relationship to the trachea. It is instrumental in diagnosing conotruncal anomalies, vascular rings, or size discrepancies among the vessels.
Doppler Echocardiography: Evaluates the direction, speed, and quality of blood flow. It provides valuable information for diagnosing stenosis, regurgitation, or interrupted aortic arch.
Advanced Imaging (3D/4D Echocardiography, Fetal MRI): These modalities provide enhanced spatial and functional detail, particularly in complex or inconclusive cases. Fetal MRI is especially helpful for extracardiac evaluation or when ultrasound windows are limited.

Conclusion

While the four-chamber view remains a foundational tool in fetal cardiac screening, it is only one part of a larger diagnostic process. When abnormalities are suspected, the integration of complementary imaging techniques allows for a more precise characterization of cardiac anatomy and function. This layered approach supports earlier intervention planning, multidisciplinary care coordination, and improved outcomes for both the fetus and family.

Part II Advanced Diagnostics: Identifying Congenital Heart Defects Using the 4-Chamber View

Mastering Four-Chamber Fetal Heart Analysis