Clinical Embryology Of The Heart

Question 1

Discuss fetal circulation

Answer 1

Placental circulation is the source of oxygenated blood

Little pulmonary blood flow

Non-functional lungs

Observe how blood is shunted before birth:
-Umbilical vein from placenta

• Ductus venosus bypasses liver sinusoids
• Foramen ovale bypasses lungs
• Ductus arteriosus

Question 2

Discuss events of neonatal circulation

Answer 2

Closure of Foramen ovale
-fossa ovalis and limbus of fossa ovalis

Closure of Ductus arteriosus
-Ligamentum arteriosum

Closure of Ductus venosus
-Ligamentum venosum

Contraction and fibrosis of the umbilical vein
-Ligamentum teres hepatis

Question 3

What is ectopia cordis?

Answer 3

Heart is in an abnormal location

Thoracic ectopia cordis —>
-heart is partly or completely exposed on the thoracic wall

• Results from faulty development of the sternum and pericardium because of failure of complete fusion of the lateral folds in the formation of the thoracic wall during the fourth week
• Widely separated halves of the sternum (nonfusion) and an open pericardial sac

Abdominal ectopia cordis—> the heart protrudes through the diaphragm into the abdomen

Death occurs in most cases during the first few days after birth, usually from infection, cardiac failure, or hypoxemia

Question 4

What is frequency/etiology of congenital heart defects(CHD)?

Answer 4

Common- about 6 to 8 per 1000 births

Most (about 80% ) etiology is unknown

Question 5

What often results from congenital heart diseases?

Answer 5

Infections e.g. rubellain early pregnancy is associated with increased risk for patent ductus arteriosus (PDA)

Question 6

What are the genetic factors of congenital heart defects?

Answer 6

Chromosomal abnormalities
-Turner syndrome associated with contraction of aorta

• Down syndrome associated with Endocardial cushion defects resulting in ASD/VSD, as well as patent ductus arteriosus
• Variable deletions from a small region of chromosome 22 results in cardiac and extra-cardiac abnormalities= DiGeorge’s syndrome or conotruncal anomaly face syndrome or “CATCH 22” syndrome

Question 7

What are the environmental factors of congenital heart diseases?

Answer 7

Environmental factors (maternal alcohol abuse, and maternal diabetes interfere, among other things, with normal neural crest migration)

Question 8

How are congenital heart defects found?

Answer 8

Well-tolerated in fetal life, but become more appearent once the baby loses the connection o the maternal circulation

-Can be asymptomatic and discovered during routine imaging studies, cardiac catheterization or cadaveric dissection or can cause severe morbidity or be incompatible with life

Question 9

What are the common findings of congenital heart defects?

Answer 9

• murmurs and/or abnormal heart sounds
• failure to thrive
• Dyspnea on exertion
• recurrent pulmonary infections
• cardiac failure
• pulmonary hypertension
• infective endocarditis

Often leads to cardiac shunts

Question 10

What is a cardiac shunt?

Answer 10

A cardiac shunt is an abnormal communication between the right and left sides of the heart or between the systemic and pulmonary vessels, allowing blood to flow directly from one circulatory system to the other.

Can be right to left shunting of blood

Question 11

When is atrioventricular septal defect(AVSD) most common?

Answer 11

Most frequent defect in trisomy 21(Down syndrome)

Question 12

What is atrioventricular septal defect?

Answer 12

• Severe Endocardial cushion defect where there is a large defect in the atrioventricular wall
• Primum type ASD & membranous type VSD
• Always affects AV valve with a common AV valve in the most severe form.
• In the incomplete form there may be an ASD or VSD associated with a defective AV valve (usually the anterior cusp of the mitral valve)

Additionally you may see:

• isolated ASD or VSD
• tetralogy or fallout
• patent ductus arteriosus

Question 13

What are right to left shunts?

Answer 13

Right to left shunts allows deoxygenated systemic veinous blood to bypass the lungs and return to the body. Venous blood from the right heart (pulmonary circuit)mixes with arterial blood in the left side of the heart.

-This decrease in oxygenated blood in the systemic circulation results in cyanosis. This usually occurs at birth and in infancy (blue babies)

Question 14

What is cyanosis?

Answer 14

-Bluish discoloration in skin and mucous membranes, due to excessive concentration of deoxyhemoglobin in the blood caused by deoxygenation.

Two main types: central (around the core, lips, and tongue) and peripheral (only the extremities or fingers)

Usually require surgical treatment or maintenance of the ductus arteriosus (PDA)

Question 15

What are the diseases that involve a right to left shunt?

Answer 15

• Truncus arteriosus
• Transposition of the great vessels
• Tricuspid atresia
• Total anomalous pulmonary venous return

Question 16

What are the components of tetralogy of fallot?

Answer 16

Right to left shunts
1. Pulmonary stenosis

2. Right ventricular hypertrophy
3. VSD (membranous)
4. Overriding aorta

Question 17

What is a pulmonary stenosis?

Answer 17

-anterior superior displacement of the bulbar (infundibular) septum—> results in unequal division of the truncus arteriosus into a small (stenotic) pulmonary trunk and a large aorta riding over the interventricular septum

Question 18

What is Right ventricular hypertrophy?

Answer 18

Right ventricular hypertrophy- due to increased workload resulting from pulmonary stenosis

Question 19

What is VSD (membranous)?

Answer 19

Malignment of the truncal ridges, bulbar ridges and Endocardial cushions results in failed fusion of these membranous septum components

Question 20

What is overriding aorta?

Answer 20

aorta “rides over” the interventricular septum (there is a membranous VSD as described above), receiving blood pumped from both ventricles

Question 21

Give an overview of tetralogy of fallot?

Answer 21

“TET SPELLS” —> “cyanosis “ occurs with vigorous crying, feeding or agitation

This is an example of R—> L shunt (venous blood from the right ventricle and poorly arterialized blood from the left ventricle are both being pumped into the aorta)

-Common CHD in DiGeorge syndrome, Down’s syndrome and fetal alcohol

Question 22

What is persistent truncus arteriosus?

Answer 22

Right to left shunts

• Failure of neural crest cells migration leads to failure in formation of aorticopulmonary septum
• A VSD is always present and the truncus arteriosus straddles the VSD
• Common defect in baby with Microdeletion chromosome 22 (22q11) or DiGeorge syndrome

Initially MILD CYANOSIS

Question 23

Explain transposition of the great vessels

Answer 23

• switching of aorta and pulmonary trunk
• Faulty migration of neural crest cells leads to the absence of the spiral-twist in the aorticopulmonary septum
• this results in SEVERE CYANOSIS immediately at birth
• Immediately lethal unless combined with another defect-ASD, VSD or PDA
• Frequently associated with maternal diabetes

Question 24

What is a total anomalous pulmonary venous return?

Answer 24

-Abnormal drainage of the pulmonary veins into the systemic venous circulation. This results in SEVERE CYANOSIS immediately at birth.

An ASD, VSD, or PDA must exist to be compatible with life.

Question 25

What are the common sites of total anomalous pulmonary venous return?

Answer 25

- superior vena cava - brachiocephalic vein - coronary sinus - inferior vena cava - portal vein/hepatic vein

Question 26

What are the significance of left to right shunts in congenital heart defects?

Answer 26

- left to right shunts are characterized by a “back-leak” of blood from the systemic to the pulmonary circulation. This is due to a defect in the heart wall and causes the pulmonary flow to be larger than the systemic flow - Ventrivular septal defects (VSD), Atrial septal defects (ASD), Patent ductus arteriosus (PDA), Atrioventricular septal defects (AVSD) - ACYANOTIC (without Cyanosis)—> there is no flow of deoxygenated blood through the systemic circulation Excess volume through the right heart and pulmonary circuit causes progressive damage to the pulmonary vasculature and the development of pulmonary hypertension If untreated the workload of the right ventricle is increased—> right ventricular hypertrophy

Question 27

What is the significance of the ductus arteriosus?

Answer 27

The ductus arteriosus is one of the essential shunts of intrauterine life: - Functional closure within first few days of birth - Anatomical closure by 12th week - If it does not close at birth, it results in a L-R shunt (when pressure drops in the pulmonary arteries after the lungs expand)

Question 28

Who most frequently has patent ductus arteriosus (PDA)?

Answer 28

Most frequent on females than in males (2:1) Most common birth defect associated with maternal rubella infection in early pregnancy Frequently associated with Down Syndrome -Failure of the ductus arteriosus to involute due to failure of contraction of the muscular wall of the ductus A common funding in: - premature infants, infants at high altitudes, hypoxia and low birth weight (less than 1750 g)

Question 29

How is patent ductus arteriosus treated?

Answer 29

Administration of anti-prostaglandin (NSAID- indomethacin) Surgery

Question 30

What are the effects of prostaglandins in PDA?

Answer 30

Allow continued patency while awaiting surgery

Question 31

What is Eisenmenger’s Syndrome?

Answer 31

Large VSD, PDA & AVSD quickly lead to excess volume through the right heart and pulmonary circuit causing progressive damage to the pulmonary vasculature and the development of pulmonary hypertension The pressure in the pulmonary circuit may ultimately exceed the systemic pressure causing reversal of blood flow from the right side of the circulation to the left (right to left shunt) Results in late cyanosis (blue kids) due to deoxygenated blood from the right now flowing through the systemic circulation This may take as short as 1-2 years in a large VSD, AVSD or PDA or as Long as a few decades as in ASD

Question 32

Describe the occurrence of coarctation of the aorta (CoA)

Answer 32

Congenital narrowing of a segment of aorta most frequent at the arch of the aorta Incidence: male > female (2:1) and present in 15- 20% of Turner syndrome

Question 33

What are the embryological theories surrounding coarctation of the aorta (CoA)?

Answer 33

- abnormal involution of a small distal segment of the left dorsal aorta - muscle tissue of the ductus incorporates into the wall of aorta, which constricts when ductus closes at birth

Question 34

What are the different sites can the coarctation of the aorta be located?

Answer 34

-Directly opposite the ductus arteriosus - Preductal- proximal to ductus arteriosus - Before birth, blood flows through the ductus to the descending aorta for distribution to the lower body - Postductal- Distal to ductus arteriosus - development of collateral circulation during fetal life which assist with passage of blood to the lower body

Question 35

What is the collateral pathway of the collateral pathway for the coarctation of the aorta?

Answer 35

Anterior intercostal arteries (branches of internal thoracic artery) will shunt blood through the Subclavian system of arteries as follows: -Subclavian —> internal thoracic —> anterior intercostals—> posterior intercostals—> descending aorta

Question 36

What is CoA characterized by?

Answer 36

Characterized by development of collateral circulation from the branches of the arch of the aorta. The aorta distal to the coarctation can be observed narrowed while an enlarged arch branches are evident. Note the increased size of the internal thoracic and posterior intercostals

Question 37

What are common features of aortic coarctation?

Answer 37

- Inferior rib notching is common in 75% of adults with coarctation - Increased size of the vessels due to increased pressure in intercostal collaterals - Most readily observed at the inferior margin of 3rd to 8th ribs

Question 38

How is coarctation of the aorta managed?

Answer 38

Prostaglandins in neonates to keep the ductus arteriosus open. Surgical intervention to correct defect

Question 39

Where are imaging studies done on coarctation of the aorta ?

Answer 39

Rib notching, enlarged collaterals, cardiomegaly

Question 40

What are the main features of coarctation of the aorta?

Answer 40

- patient may complain of headache, fatigue - underdevelooped lower extremities which may be cyanotic - Disparity between pulses and blood pressure in upper & lower limbs - Extremely strong pulse and hypertension in the upper limb -Delay between femoral and brachial/radial pulse, further femoral pulse is significantly weaker than brachial/radial