Fetal Chest and Cardiovascular System

• Fetal Chest and Cardiovascular System

Objectives

• Describe the normal anatomy of the fetal chest
• Discuss common cardiac defects, tumors, and defects
• Discuss abnormalities of heart rhythm
• Describe normal pulmonary anatomy and defects that can occur

Review Fetal Circulation

• Oxygenated blood from the placenta enters the fetus through the umbilical vein
• The ductus venosus partially bypasses the liver to send the blood to the inferior vena cava
• The Foramen Ovale shunts some of the right atrial blood to the left atrium
• The ductus arteriosus allows oxygen-rich blood from the pulmonary artery into the aorta to circulate throughout the fetus

Normal Anatomy of the Fetal Chest

• Image the thorax in axial and coronal planes to demonstrate integrity
• Visualize fetal breathing, movement, and evaluate the size and shape of the structures within the thorax
• The fetal heart should occupy around 1/3 of the thoracic cavity
• Deflated lungs should appear as homogeneous, solid, and granular, like the liver
• Lung parenchyma is slightly more echogenic than the liver but similar in echotexture

Fetal Echocardiography

• The optimal time to perform a fetal echo is between 18-24 weeks
• Diagnoses can include:
• Structural heart abnormalities
• Fetal arrhythmias
• Coarctation (narrowing) of the aorta and other obstructive lesions
• Cardiomegaly
• Masses or pericardial effusion
• Assessment of ductus arteriosus patency in patients receiving indomethacin

Routine Views of the Fetal Heart – Four Chamber

• Normal features include:
• The left atrium is the chamber closest to the spine
• The apex of the heart points 45 degrees to the left anterior chest wall
• Ventricles should be about the same size (later in pregnancy, the right can be greater than the left)
• Flap of the foramen ovale will open to the left atrium
• Prominent moderator bands are present in the apex of the right ventricle
• Valves separate atria and ventricles

LVOT View

• Angle towards fetal right shoulder
• Identify the origin of the aorta arising from the Left Ventricle

RVOT View

• Identify the origin of the pulmonary trunk arising from the right ventricle
• Appropriate orientation of the pulmonary arteries involves draping anterior to the aorta when seen in a cross section
• The diameter of the pulmonary artery should be about 9% larger than the aorta

Aortic Arch

• Use an oblique, sagittal plane
• Look for "candy cane" appearance
• Head and neck vessels can be seen arising form the arch including the innominate, Lt CCA, and Lt subclavian

Ductal Arch (arch of the ductus arteriosus)

• Hockey stick appearance
• Arises more anterior in the heart
• There are no head or neck vessels arising from the arch

Fetal Circulation Distribution

• 60% of the right atrial blood passes through the Foramen Ovale into the left atrium and then into systemic circulation
• 40% of the right atrial blood enters the right ventricle
• Of that, 92% of the main pulmonary artery volume bypasses the lungs via the ductus arteriosus and passes into systemic circulation
• 8% of right ventricular blood reaches the lungs

Structural Cardiac Malformations: Ventricular Septal Defect (VSD)

• Most common defect found postnatally
• Incomplete closure of the interventricular foramen and failure of the membranous part of the IV septum cause VSDs
• VSDs are the most teratogen-associated fetal defect
• VSDs are associated with other cardiac anomalies 50% of the time.
• Sonographic findings:
• An opening between the ventricles on a 4-chamber view
• Bidirectional flow demonstrated with color Doppler
• Large defects are easier to diagnose

Atrial Septal Defect (ASD)

• ASD means any abnormal opening between the atria
• Most commonly, an ostium secundum defect
• Associated with a wide variety of cardiac and chromosomal abnormalities
• Diagnoses can be difficult in utero because of the patient foramen ovale and natural shunting of blood between the chambers

Hypoplastic Right Heart Syndrome

• Pulmonary atresia with an intact interventricular septum causes this syndrome
• Sonographic findings include an absent or very small RV on the 4 chamber view and an absent or small pulmonary artery
• Hypoplasia by definition is an incomplete development of a tissue or organ

Hypoplastic Left Heart Syndrome

• Small Left Ventricle due to decreased blood flow into or out of the left ventricle
• Primary abnormalities include aortic stenosis, mitral valve and or aortic valve atresia
• Sonographic findings include the absent or small left ventricle and hypoplastic or atretic (narrowed or closed) mitral valve and aorta

Transposition of the Great Arteries (TGA)

• Origins of the great vessels are transposed

• The aorta arises from the right ventricle

• The pulmonary trunk arises from the left ventricle

• Oxygen-poor blood returns to the right atrium from the body, passes through the right atrium and ventricle, and then goes into the misconnected aorta back to the body

• Oxygen-rich blood returns to the left atrium from the lungs, passes through the left atrium and ventricle, then goes into the pulmonary artery and back to the lungs

• Two separate circuits are formed - one that circulates oxygen-poor blood from the body back to the body, and another that recirculates oxygen-rich blood from the lungs back to the lungs

• Other heart defects are often associated with TGA which allows the infant to live

• Because of the low amount of oxygen provided to the body, TGA is considered a "blue-baby syndrome."

• Transposition of the great arteries is the second most common congenital heart defect that causes problems in early infancy

• TGA occurs in about 3% of all congenital heart defects

• Must maintain correct left and right orientation

• Images of outflow tracts demonstrate anomalous origin

• Difficult diagnosis sonographically and depends on orientation of outflow tracts

• Openings in the atrial or ventricular septum will allow blood from one side to mix with blood from another, creating blood with differing oxygen richness

• Patent ductus arteriosus will also allow such mixing through the connection between the aorta and pulmonary artery

• Mixing can be beneficial, providing oxygen to the body even if not in a normal amount

TGA Prognosis and Treatment

• Immediate management of an infant with transposition focuses on establishing safe oxygen levels and stable cardiac and pulmonary function.
• A continuous infusion of prostaglandin, a medication that will keep the ductus arteriosus open, is usually initiated when the diagnosis is suspected or confirmed.
• Prostaglandin will allow some mixing of oxygen-rich blood with oxygen-poor blood but may provide adequate mixing by itself.
• A procedure called a "balloon atrial septostomy" is often performed once the diagnosis is confirmed.
• The foramen ovale may be enlarged or stretched with a balloon, which will markedly improve mixing. A balloon atrial septostomy procedure is performed by passing a special balloon-tipped catheter into the heart from either a vessel in the umbilicus or a vessel in the groin.
• A large atrial septal defect is created, which typically allows mixing of oxygen-rich and oxygen-poor blood so that the body's oxygen saturation will remain within safe range.
• Following this procedure, the ductus arteriosus is no longer necessary, and prostaglandin infusion can be discontinued.
• Babies can be stabilized temporarily, but surgical correction of the defect is needed
• Corrective surgery is typically performed in the first week of life

Truncus Arteriosus

• A single large vessel arises from the base of the heart
• Outflow tracts are not separate
• VSD is usually present, and 48% of fetuses have other non-cardiac abnormalities
• Mix of blood results in good oxygen flow
• Can be treated with Raselli repair

Ectopia Cordis

• All or part of the heart is located OUTSIDE of the chest cavity
• Is associated with intracardiac anomalies and omphalocele
• Part of the Pentalogy of Cantrell
• Diagnosed by visualizing the soft tissue mass outside of the thorax

Double Outlet Right Ventricle

• The pulmonary artery and the aorta arise from the right ventricle
• This defect is associated with other cardiac defects, and maternal diabetes and ETOH consumption

Atrioventricular (A-V) Canal Defect/Endocardial Cushion Defect

• Atrial and ventricular septal defects from failure of the common AV orifice to separate into mitral and tricuspid valves
• Results in a defect in the center of the heart
• Associated with trisomy 21

Tetralogy of Fallot

• Consists of four anatomic abnormalities: VSD, overriding aorta, stenosis of right outflow tract and right Ventricular Hypertrophy
• An overriding aorta is a congenital heart defect where the aorta is positioned directly over a ventricular septal defect (VSD)
• Risk factors include a mother who uses alcohol, has diabetes, is over the age of 40, or gets rubella during pregnancy
• Also associated with Down syndrome- Trisomy 21
• Can be treated with Raselli repair

Ebstein's Anomaly

• Malformation of the tricuspid valve with low insertion
• Results in an enlarged right atrium
• The malformed Tricuspid Valve does not properly close to keep the blood flow moving in the right direction, thus blood can leak back from the lower to upper chambers
• The syndrome is also associated with an atrial septal defect

Ventricular Hypertrophy

• A condition in which the muscle wall of the ventricle becomes thickened
• Is associated with cardiac outlet obstruction
• Is also associated with maternal diabetes
• Attributed to a compensatory increase in fetal insulin secretion

Coarctation of the Aorta

• Coarctation of the aorta refers to narrowing of the aorta along the aortic arch, resulting in outflow obstruction
• The degree of obstruction is related to the degree of narrowing that occurs
• The type of coarctation is described as preductal, ductal, or postductal using the position of the lesion in comparison to the ductus arteriosus insertion, as a reference
• Coarctation can result in the narrowing of the aorta
• In severe cases, a complete interruption may be present
• Coarctation remains one of the most difficult cardiac anomalies to diagnose prenatally
• On the four-chamber view, LV enlargement without visualization of other abnormalities should engender a high degree of suspicion (especially in the second trimester)

Cardiosplenic Syndrome

• There are many cardiac defects associated with splenic defects
• Asplenia and polysplenia are defects of lateralization
• The fetus thus has either two left or two right sides
• Unpaired splanchnic organs such as liver, stomach, and spleen may be absent, midline, or duplicated
• Symmetric development of normally asymmetric organs occurs

Cardiac Tumors

• Rare
• Include: Rhabdomyomas, cardiac fibromas, myxomas, and teratomas
• 30-78% of those with Rhabdomyomas also have tuberous sclerosis
• Prognosis depends on the size, location, number of tumors, and other anomalies and arrhythmias
• Tuberous sclerosis complex (TSC) is a rare multisystem genetic disease that causes benign tumors to grow in the brain and in other vital organs such as the kidneys, heart, liver, eyes, lungs, and skin

Abnormalities of Fetal Heart Rhythm

• Cardiac rates vary with age during the first trimester
• Prior to 6 weeks, slow and typically between 100-115 BPM
• After six weeks, the rate increases rapidly, and from around 8 weeks is between 144-159 BPM
• After nine weeks, the rate should plateau, and normal fetal heart rate will be between 120-160 BPM

Irregular Fetal Heart Rhythm:

• Arrhythmias can be due to premature ventricular contractions (PVCs) or premature atrial contractions (PACS)
• Can be associated with maternal caffeine intake, cigarette smoking, and alcohol use
• Fetal arrhythmias are generally benign and will disappear in utero or the early neonatal period

Tachycardia

• Defined as having a heart rate greater than 180 BPM
• Most have a good prognosis
• Treated in utero with pharmacologic agents to slow the heart down
• Associated with maternal hyperthyroidism, maternal medications, maternal tachycardia (e.g., systemic infection), in utero infection and/or hypoxia, fetal anemia, and chromosomal anomalies

Bradycardia

• Bradycardia is a prolonged fetal heart rate of less than 100 BPM
• Associated with a complete heart block
• Congenital heart block is characterized by interference with the transfer of the electrical nerve impulses (conduction) that regulate the normal, rhythmic, pumping action of the heart muscle
• Is related to an increase in intrauterine pressure
• Rates below 80 BPM may be associated with fetal asphyxia
• If this is recurrent, it may warrant early delivery

Intrathoracic Abnormalities: Pleural Effusion

• Is the most commonly diagnosed fetal intrathoracic abnormality
• May be isolated or in association with other abnormalities like hydrops
• Sonographic Findings: Anechoic space seen in one or both sides of the thorax and conforms to the shape of the thoracic cavity

Congenital Diaphragmatic Hernia (CDH)

• Is the most common developmental abnormality of the diaphragm
• Results from defective fusion or formation of the diaphragm
• Allows the spleen, stomach, liver, or colon to herniate into the chest
• Bochdalek hernias on the left side occur most of the time 85%
• Hiatal hernias and Morgagni anterior hernias are less common
• If the hernia is large, they are associated with pulmonary hypoplasia
• Cardiomediastinal shift is the most recognizable sonographic feature (heart shifts to the right) and is associated with other anomalies of the heart and brain
• Sonographic findings: Identification of fluid filled bowel and stomach in the chest at the level of the 4-chamber heart, with the heart displaced from the left chest towards the right (there is also polyhydramnios)

Pulmonary Sequestration

• Uncommon malformation in which a mass of non-functioning pulmonary tissue is separate from the lung
• The "mass" gets its blood supply from the aorta and does not communicate with the bronchial tree
• Associated with a non-immune hydrops
• Sonographic findings include a homogeneous intrathoracic mass
• Color Doppler may demonstrate an arterial vessel arising from the aorta to the mass

Congenital Cystic Adenomatoid Malformation (CCAM) renamed Congenital Pulmonary Airway Malformation (CPAM)

• CCAM accounts for about 25% of lung malformations
• Unilateral condition characterized by the replacement of normal lung tissues by abnormal tissues and visible cysts
• Large lesions may shift the mediastinum away from the midline
• Three classes based on the size of the cysts, they include one or more large cysts, multiple small cysts, and multiple cysts too small to be resolved individually by ultrasound
• When not individually resolved, the lung will appear hyperechoic
• Sonographic Findings include demonstration of non-pulsatile echogenic/complex mass in the fetal lung showing lateral displacement of the fetal heart possible signs of hydrops (excessive fluid)
• Monitor a fetus with CRAM during pregnancy
• Removed via surgery after birth
• In situation with large cystic masses that may cause pose a danger during birth from a airway compression may require a surgical delivery called the EXIT procedure

Pulmonary Hypoplasia

• A decrease in number of lung cells, airways, and alveoli
• Results in decrease in organ volume, size, and weight
• Decreased ratio of lung weight to body weight is consistent method of diagnosing pulmonary hypoplasia
• Prognosis is grave, with 80% mortality following birth
• Severity depends on when hypoplasia occurred during pregnancy along with its severity and duration
• Severity can be influenced by pulmonary fluid dynamics, fetal breathing movements, and hormonal influences

Causes of Pulmonary Hypoplasia:

• Prolonged oligohydramnios or a small thoracic cavity
• Result of structural/chromosomal abnormality
• Oligohydramnios, with resultant decrease in overall thoracic size
• Severe IUGR and early rupture of membranes
• Masses within and cardiac defects
• Pulmonary hypoplasia occurs without either a cause or uterine problem

Bronchogenic Cysts

• Most common lung cyst
• Occur as result of abnormal budding of foregut
• Lack any communication with trachea/bronchial tree
• Typically occur within mediastinum/lung
• Are infrequently found inferior to diaphragm
• Amniotic fluid volume within normal range
• Without evidence of mediastinal shift or heart failure

How to Image the Fetal Thorax:

• Check if the heart occupies 1/3 of the chest
• If no, check the thoracic circumstance, amniotic fluid, check rib shape and size
• Check to see if the axis of the heart is oriented 45 degrees to the left
• If no, then consider a space occupying lesion CDH, CCAM, SEquestration and evaluate diaphragm and lungs
• Check if the diaphragm intact
• No means congenital diaphragmatic hernia and evaluate contents
• If the lungs appear homogeneous and are appropriate echogenicity
• Is the tissue homogenous with proper properties?
• The lungs should not be surrounded by anechoic fluid.
• Lungs are surrounded by anechoic fluid means pleural effusion and check for other signs of hydrops