Cardiac Embryology and congenital HD

Question 1

Describe a brief timeline of the developmental stage of the heart

Answer 1

1. Tube formation day 15-20
2. Looping day 20-28
3. Atrial septation day 34-50
4. Outflow tract septation day 35-56
5. Ventricular septation day 38-45
6. Cardiac valves day 35-56

Question 2

Describe the formation of the heart tube

Answer 2

The primitive heart tube is initially a straight structure with distinct regions: the sinus venosus, atria, ventricles, and bulbus cordis. Two cardiogenic chords form and form 2 thin wall tubes called the endocardial & the Myo epicardial tubes.

These tubes fuse to form a single straight tube at day 22, pulse can be detected at day 22. The tube constricts and dilates to form regions that go on to form heart chambers & vessels.

Question 3

What structure is formed from the:
Sinus venosus
Primitive atria
Primitive ventricle
Bulbus cordis
Truncus arteriosus:

Answer 3

SV: Inflow region that later becomes a part of the atria
PA: Gives rise to LA & RA
PV: Inlet of ventricles forms the LV
BC: Region that forms the RV & outflow tract
TA: Area that gives rise to formation of PA and Aorta

Question 4

Describe the process of cardiac looping

Answer 4

Occurs between day 22-24, it establishes basic structure of the heart

The heart tube begins to bend and elongate. The restriction of the pericardial space forces the heart tube to ben/loop into a U shape, looping results in placement of atria’s above ventricles
It forms the primitive atria’s and ventricles

Question 5

Describe atrial septation

Answer 5

Occurs between day 28-42, The heart begins to form chambers

Atria’s begin to separate by formation of septum primum and septum secundum.
Septum primum begins rigid found on the roof of the superior aspect of the common atrium, the ridge develops and grows downwards into the atrial cavity. It creates a gap between the endocardial cushion and the lead edge of the septum
Ostium primum forms during growth (a hole)
The septum secundum also grows down & up into the atrial cavity, it forms a gap between called the ostium secundum.

The growth of the ostium primum and secundum create a small flap known as the foramen ovale, this enables blood to flow from the right to left side.

Question 6

Describe intraventricular septation

Answer 6

Occurs between day 38-45, IVS begins to form to separate ventricles

Primitive ventricles grow out creating a small ridge which develops into the IVS.
IVS forms by the dilation of the ventricles, their growth makes the IVS more prominent
Over time superior region will grow up to endocardial cushions to form a membranous regions of IVS

Muscular intraventricular septum allows blood to pass between the ventricles.

Question 7

Describe the formation of outflow tracts (aorta & PA)

Answer 7

Occurs between day 35-56:
Outflow tract separates, the bulbus cordis divides into the pulmonary trunk & aorta.
Bulbus ridges grows out from endocardial cushions, fuse & spiral by 180 to form the PA & aorta

Question 8

Describe the formation of valves during embryonic development

Answer 8

Occurs between day 35-56, AV valves (M & T) form from mesenchymal tissue.

Subendocardial tissue grows out inferiorly, it’s growth is regulated via apoptosis which sculpts the leaflets
Apoptosis carves out space for trabeculae and papillary muscles. Differentiation occurs between the mitral & tricuspid valves.

Semi lunar valve cusps also form via apoptosis.

Question 9

Describe foetal circulation

Answer 9

1. Oxygenated blood flows from placenta through umbilical veins towards the liver, it passes through the ductus venosum (shunt)
2. This allows oxygenated blood to bypass liver by flowing through DV and travels to the inferior VC
3. Oxygenated blood flows from RA to LA through foramen ovale.
4. O2 blood enters LV and travels through aorta
5. DA connects PA to aorta , the blood circulates the foetus and is returned to the placenta via umbilical arteries

Question 10

Describe the changes to a foetus’ circulation after birth

Answer 10

1. Foramen ovale closes as LA pressure is greater than RA due to breathing onset, flap seals off
2. DA constricts & forms ligamentum arteriosum
3. DV closes and blood starts to flow through the liver
4. Umbilical vessels close off and become ligaments, cord is cut

Question 11

Describe the environmental causes for congenital HD

Answer 11

Pregnant Mother partaking in:
Alcohol
Drugs
Warfarin
Rubella

Question 12

Define a Acyanotic defect

Answer 12

Refers to the mixing of oxygenated blood with deoxygenated blood, involves a Left-right shunt, blood that circulates body has a good O2 content.

E.g., ASD, VSD, PS, COAO, AV stenosis

Question 13

Define a Cyanotic defect

Answer 13

Refers to the mixing of deoxygenated blood with oxygenated blood, this involves a Right-left shunt, leading to a reduced O2 content in the blood, therefore less oxygen enters circulation. As a result it can cause cyanosis
e.g., Tetralogy of Fallot or transposition of great arteries

Question 14

Define Shunting and fenestrations

Answer 14

Shunting refers to a diversion of blood flow from one system to another. It can be right-left or left-right. Shunting determines the O2 content of the blood and volume of blood entering circulation

Fenestrations: refers to many holes

Question 15

Describe Atrial septal defects

Answer 15

A acyanotic defect in which there is a hole in the atrial septum which causes mixing of oxygenated and deoxygenated blood. An ASD can occur at any point of the septum

Question 16

What are the types of ASD

Answer 16

Named based in the location of ASD

1. Secundum ASD: most common, located in the middle of the atrial septum
2. Primum ASD: located in lower atrial septum, often associated with mitral valve problems
3. Sinus Venosus ASD: Located near upper region of Atrial septum, near entry point of Superior VC
4. Fossal ovalis: accounts for 80% of defects, a whole that fails to close after birth

Question 17

PFO VS Foramen ovale

Answer 17

A foramen ovale is NOT PFO as there is no hole as there is no tissue missing

A PFO is flap between the septum primum & secundum which fuses to close.

Question 18

Describe the symptoms, diagnosis & treatment of ASD

Answer 18

S: Murmur, SOB & fatigue

D: Echo is primary to use to assess heart structure and blood flow
ECG & chest X-ray can provide info e.g., size & shape of heart

T: Small ASDS may resolve as the child grows, larger ASDs may require surgery to close the hole or a patch

Question 19

Describe ventricular septal defects

Answer 19

VSD is a a cyanotic defect which refers to an abnormal opening in the ventricular septum, blood can flow from LV to RV instead of being pumped out into systemic circulation.
It accounts for 33% of defects and is associated with down syndrome

Question 20

What are the types of VSD

Answer 20

Defects can vary in size & location. There are 4 types of VSD:

1. Peri membranous VSD: Located near upper region of septum, most common
2. Muscular VSD: located in lower region in muscular region, can be single or multiple

3.Supracrustal VSD: Located near the AV, more complex

4. Inlet VSD: Located near the tricuspid & mitral valves, associated with other defects

Question 21

Describe the symptoms, diagnosis & treatment of VSD

Answer 21

S: mild cases are asymptomatic, Most VSD’s can close on their own, severe cases can cause SOB, fatigue, murmur and Rs infections

D: Doppler echo can be used to assess blood profile
ECG may look normal

T: Medications can be used to relieve symptoms e.g., diuretics to reduce fluid retention or inotropes
Surgery may be needed to close the hole if too large

Question 22

Describe patent ductus arteriosus

Answer 22

A acyanotic defect, PDA is a BV vessel that connects the PA to aorta in foetal circulation to bypass the lungs, however a defect occurs if this BV vessel fails to close after birth.

If PDA remains open it causes high pressure blood from aorta to flow into low pressure PA creating increased blood flow to lungs which could lead to pulmonary hypertension.

Question 23

Describe the symptoms, diagnosis & treatment of PDA

Answer 23

S: Large PDA shows symptoms of rapid breathing, respiratory infections, fatigue & heart murmur

D: Auscultation helps determine a machinery murmur as it is present throughout systole & diastole, a continuous murmur.
Echo can assess blood flow in chambers to identify PDA
Chest X-ray and electrocardiogram (EKG) may also be used to evaluate the heart’s size and function. Heart could be enlarged

T: Small PDA’s close in their own, larger PDA’s require anti-inflammatory drugs to help infants close the PDA, catheterisation to close PDA or surgical closure

Question 24

Describe Coarctation of the aorta

Answer 24

A acyanotic defect identified by the narrowing of a section of the aorta, Which restricts blood flow, increases BP in upper body regions & blood flow is reduced in lower body regions. This can lead to hypoperfusion of kidneys activating RAAS. This results in increased afterload LV leading to LV hypertrophy.

Significant when pressure grain is 20mmHg, most common in kids, accounts for 8-12% of defects, associated with PDA

Question 25

What are the types of COAO

Answer 25

COAO named after location 1. Pre-ductal Coarctation: narrowing occurs before the ductus arteriosus, most common/severe, blood flow to lower body is restricted, DA may remain open to compensate for reduction 2. Post-ductal Coarctation: Narrowing occurs after ductus arteriosus, less severe, DA remain open, compensatory vessels form to to bypass the narrowed area 3. Juxtaductal Coarctation: Narrowing occurs at/near DA attachment to aorta 4. Isolated Coarctation: occurs without no cardiovascular anomalies, aorta is narrowed, but no other defects present, less severe & more manageable

Question 26

Describe the symptoms, diagnosis & treatment of COAO

Answer 26

S: Depending on type of COAO, could cause poor growth/feeding/HF D: BP reading to identify abnormal BP readings, weak or absent pulse in lower limbs Echo can be used to confirm the diagnosis and location of the narrowing Chest X-ray, CT scan, or MRI may also be used to visualize the aorta and assess the extent of the coarctation. T: Requires treatment of surgery such as aortic bypass surgery or balloon angioplasty to widen narrowed section of aorta No treatment can lead to pulmonary hypertension, stroke or HF

Question 27

Describe congenital aortic stenosis

Answer 27

A acyanotic defect that involves the narrowing of the AV valve or aorta, this obstructs the blood flow leaving the LV creating an increased afterload in the LV eventually leading to LV hypertrophy. It could lead to HF Occurs in 5-8% of the population

Question 28

What are the types of CAS

Answer 28

CAS Defect types are named based on location of narrowing AV stenosis: AV valve is narrowed itself, leaflets become stiff & fuse together, obstructing blood flow Sub-valvular stenosis: Narrowing occurs below the AV valve due to abnormal band tissue growth Supravalvular stenosis: Narrowing occurs above the AV valve due to congenital malformations of aorta.

Question 29

Describe the symptoms, diagnosis & treatment of CAS

Answer 29

S: mild cases show no symptoms, however severe cases may show SOB, fatigue, chest pain, dizziness and soft murmur D: Echo used to assess blood flow to identify location and severity of narrowing Electrocardiogram (ECG) and Chest X-ray may also be used to assess heart size and electrical activity. T: Mild cases require no immediate treatment, some infants grow out of CAS,however severe cases require aortic valve replacement with a prosthetic valve or a Balloon valvuloplasty, balloon is used to widen narrowing If not treated over time increased LV afterload can result in HF & arrythmias, those with CAS may be more at risk of infective endocarditis.

Question 30

Describe congenital pulmonary stenosis

Answer 30

A acyanotic defect where the blood flow becomes obstructed due to a narrowing of the PA or PV, increases the afterload in the RV which could result in RV hypertrophy or tricuspid regurgitation. As atrial pressures rise resulting in blood shunting through foramen ovale, can be associated with VSD

Question 31

What are the types of CPS

Answer 31

CPS types are named based on location of narrowing Valvular PS narrowing of the pulmonary valve, most common, often involves deformities or thickening of PV valve leaflets which obstructs blood flow to the lungs Sub valvular PS: Narrowing occurs below the PV, where RV meets PA, an increases in muscular band or tissue causes an obstruction in blood flow leaving the RV Supravalvular PS: narrowing occurs above the PV in the PA, less common, caused by congenital malformation of PA creating narrowing

Question 32

Describe the symptoms, diagnosis & treatment of CPS

Answer 32

S: SOB due to reduced blood flow to lungs, fatigue, murmur, pulmonary hypertension D: Echo measures the sound waves of the heart to assess degree of narrowing, doppler can be used ECG & chest X-ray can be used to assess heart size and activity T: Mild cases may need no intervention, severe cases require surgery to repair or replace valve, a balloon valvuloplasty can be inserted to widen the narrowing

Question 33

Describe the tetralogy of fallot

Answer 33

TOF is a cyanotic congenital defect where there are 4 distinct abnormalities of VSD, RV hypertrophy, overriding aorta & pulmonary stenosis. Resulting in impaired blood flow to the lungs and low O2 in the systemic circulation. VSD causes blood mixing reducing the O2 content in the blood leaving the heart. PS causes increased afterload which results in RV hypertrophy. Overriding aorta covers VSD not LV & causes deoxygenated blood from RV to be pumped into aorta, so deoxygenated blood enters systemic circulation. TOF diagnosed in infancy or childhood, it occurs in premature babies or if mother was diabetic, smoker, alcoholic or had poor nutrition

Question 34

Describe the symptoms, diagnosis & treatment of tetralogy of Fallot

Answer 34

S: Fatigue due to poor infant feeding, cyanosis, SOB & fainting D: Echo is used to assess heart structure and monitor blood flow to confirm the 4 defects Chest X-ray can be used to identify TOF by looking for RV hypertrophy ECG can be used to assess degree of defects T: It involves multiple surgical procedures of closing the VSD, repairing the Pulmonary or artery valve and reconstruction of RV to enable smooth blood flow to the lungs These surgeries are performed in infancy or childhood if left untreated TOF can cause stroke, HF & death to hypoxia

Question 35

Describe transposition of the great arteries

Answer 35

A cyanotic defect where the aorta and PA are reversed in origin, aorta is connected to RV and PA connected to LV, this defect is present & identified at birth, it can be fatal if left untreated It results in mixing of blood which causes poor oxygen blood to enter systemic circulation and rich oxygen blood to be pumped back to the lungs. This leads to hypoperfusion of many organ systems

Question 36

Describe the symptoms, diagnosis & treatment of TGA

Answer 36

S: SOB due to low O2 levels, fatigue, lethargy & cyanosis D: echo to visualise heart and identify abnormal connections Chest X-ray can be used to assess heart size & shape ECG can be used to assess heart function and identify abnormalities T: Surgery involving switching of vessels, aorta & PA switched back to normal positions, occurs within first few weeks of life, coronary arteries are also reconnected Palliative procedures may occur e.g., balloon atrial septostomy (a procedure to create a hole between the heart’s atria) may be done to allow oxygenated blood to mix and flow to the body, temporarily improving oxygen levels.