Development of Heart & Great Vessels and Understanding Congenital Heart Disease

Question 1

What are the most common birth defects?

Answer 1

Congenital heart defects - 1% incidence

Question 2

In an embryo, 2 areas of blood islands create a pair of endocardial tubes which fuse when folded, what type of tissue to they form from?

Answer 2

Splanchnic mesoderm.

Question 3

Congenital birth defects (structural abnormality or complete absence of a structure) result from an interruption of normal development, what are the different types of causes?

Answer 3

Genetic
Exposure to drugs/infectious agents
Unexplained

Question 4

What makes the development of the heart and vessels extra complicated and more prone therefore do congenital abnormalities?

Answer 4

Different circulatory needs of the foetus and the newborn (immediate change from in uterine to mature heart).

Heart defects can occur when there’s structural abnormality of chambers or vasculature or an obstruction or communication between pulmonary and systemic circuits.

Question 5

What is the primitive heart tube and what changes must it go through?

Answer 5

A contraction tube with nothing to control the flow of blood. Zones starting from bottom are: Sinus Venosus, Atrium then Ventricle (primitive), Bulbis Cordis, Truncus Arteriosis and Aortic roots.
It might divide into 4 chambers and the inflow and outflow tubes must be remodelled.

Question 6

What is cardiac looping and why does it occur?

Answer 6

When the ‘heart’ is enclosed in the pericardial cavity, it grows and becomes too big to occupy the space in a linear conformation, so it folds.
It places the inflow and outflow tubes in the correct orientation with respect to each other - atrium was caudal, now pushed posteriorly and cranially. There is differential growth of zones.

Question 7

What does the mature right atrium develop from and what about the left? What effect does this have on the texture?

Answer 7

The right atrium develops from most of the primitive atrium (hence trubeculated walls, making it tough) and some of the Sinus Venosus.

The left atrium develops from a small portion of the primitive atrium and absorbs proximal parts of the pulmonary veins (and so is smooth walled).

Question 8

What are the conflicting circulatory requirements of the foetus?

Answer 8

The lungs don’t work and so oxygenation and carbon dioxide removal occur at the placenta (reliant on maternal circulation for exchange), so shunts are required to maintain foetal life - they must be reversible at birth.

Question 9

What is the pathway of blood in an embryo and which shunts are involved?

Answer 9

High pO2 blood travels through umbilicus vein to the liver and the DUCTUS VENOSUS shunts it around the liver then into the right atrium. From there it must bypass the right ventricle and lungs so enters the left atrium via the FORAMEN OVALE, but some blood manages to get through to the right ventricle and must be redirected from the pulmonary trunk to the aorta through the DUCTUS ARTERIOSUS.

Question 10

What happens to the shunts at birth?

Answer 10

Respiration begins and left atrium pressure increases so the foramen ovale closes (before birth pressure in the RALA, so septum primum is pushed against septum secundum) and the ductus arteriosus contracts to shut. Placental support is removed, so the ductus venosus closes.

Question 11

The early arterial system begins as a bilaterally symmetrical system of arched vessels, what are the 4th and 6th arches remodelled to become?

Answer 11

The 4th arch is remodelled on the right to become the proximal part of the right subclavian artery and on the left it becomes the arch of the aorta.
The 6th arch is remodelled on the right to form the right pulmonary artery and on the left side is forms the left pulmonary artery and the ductus arteriosus.

Question 12

Explain why a hoarse voice might be a sign of heart pathology.

Answer 12

As the heart ‘descends’ (from its position at the embryonic neck), the left recurrent laryngeal nerve become hooked around the 6th aortic arch and turns back on itself and ends up around the closed shunt around the aorta and pulmonary artery (ductus arteriosus).

Question 13

What is PDA in terms of heart pathology?

Answer 13

Patent Ductus Arteriosus - persistent communication between descending aorta and pulmonary artery - failure of physiological closure. Blood will flow from the aorta with higher pressure to the pulmonary artery.

Question 14

How is the foramen ovale built?

Answer 14

Endocardial cushions make a shelf, the septum primum grows down from the roof of the primitive atrium, with the newly formed ostium primum allowing blood flow between the atria, then the osmium secundum appears before it closes (made by apoptosis). Then the septum secundum grows down in a characteristic arch shunt and the foramen ovale is complete, shunting blood from right to left.

Question 15

When might an Atrial Septal Defect occur? What history might be present?

Answer 15

If the septum primum is resorbed or too short or if the septum secundum is too small.

Usually asymptomatic into late adulthood then late onset arrhythmia and right heart failure.

Question 16

What is Hypoplastic Left Heart Syndrome and what is the course?

Answer 16

The left heart is underdeveloped. There is speculation as to the cause: defect in development of left valves, resulting in atresia (abnormal narrowing) and limited flow or ostium secundum is too small so there’s inadequate right to left flow in utero- not used = lost.

Ascending aorta very small so right ventricle must support systemic circulation. For survival, obligatory ASD and PDA.

Question 17

Describe the 2 components of the ventricular septum.

Answer 17

Muscular - forms most of the septum and grows upwards to the fused endocardial cushions. After it grows there’s a small gap left called the primary interventricular foramen.
This spaced is filled by the membranous portion, formed by connective tissue from the endocardial cushions.

Question 18

Which portion of the interventricular septum is most commonly involved in a Ventricular Septal Defect? What history might be presented?

Answer 18

The membranous portion.

Unless very tiny, a VSD would present in infancy with left heart failure. If left untreated it could lead to inoperable pulmonary hypertension.

Question 19

Apart from in the middle of the heart, where do endocardial cushions form and why?

Answer 19

In the truncus arteriosus - grow towards and twist around each other to form spiral septum. Dividing outflow involves routing oxygenated and deoxygenated blood appropriately.

Question 20

What is the anatomy of someone with Transposition of the Great Arteries?

Answer 20

The aorta arises from the right ventricle. The pulmonary trunk arises from the left ventricle. This may result in cyanosis depending on what, if any other defects are present.

Not viable unless atrial, ventricular or ductal shunts allow communication between 2 isolated circuits.

Question 21

What are the 4 parts of the Tetralogy of Fallot?

Answer 21

Large ventricular septal defect (as a result of …)
Overriding aorta
Right ventricle outflow tract obstruction (so …)
Right ventricle hypertrophy

Conotruncal formation defective showing the importance of neural crest cells.

Question 22

Why will Tetralogy of Fallow cause cyanosis?

Answer 22

Right to left low of blood (doesn’t go through pulmonary loop and become oxygenated).

Question 23

What is the aetiology of Congenital Heart Disease?

Answer 23

Genetic - Down’s, Turner’s, Marfan’s syndrome
Environmental - tetragenicity from drugs/alcohol etc)
Maternal infections - Rubella, Toroplasmosis etc.

Question 24

Fill in the blanks- pathophysiology in normal heart:
______ ventricles pumps deoxygenated blood to lungs. The pulmonary circulation has _____ resistance, which is _____ when you’re young. _____ ventricle pumps _____ blood at system blood pressure to the aorta.

Answer 24

Right
Low
Higher
Left

Question 25

Each ventricle is morphologically adapted for its task. What are their shapes.

Answer 25

The left ventricle is cylindrical and the right ventricles almost wraps around it.

Question 26

What percentage oxygen saturation does the haemoglobin have in the arteries and left heart, compared to the value for the veins and right side of the heart?

Answer 26

The arteries and left side of the heart have a near 100% saturation, whereas the veins and right side of the heart have 60-70%.

Question 27

What are the consequences of blood being shunted from left to right? It needs a hole.

Answer 27

Blood from the left heart returns to the lungs instead of being pumped round the body. Increased blood flow to the lungs is not damaging, but increased pulmonary artery/venous pressure is.

Question 28

What is the result of a right to left shunt? It needs a hole and distal obstruction.

Answer 28

Deoxygenated blood bypasses the lungs. Cyanosis.

Question 29

What is cyanosis and what could cause it?

Answer 29

Blueness, with deoxygenated blood in arterial circulation. It may be a cardiac issue (hole and obstructing resulting in R->L) or pulmonary (inadequate oxygenation), which is worse.

Question 30

Congenital Heart Disease is sometimes classed as acyanotic, give some examples when.

Answer 30

Left to right shunts: atrial septal defects, ventricular septal defects, patent ductus arteriosus, as well as obstructive legions: aortic stenosis, pulmonary stenosis, coarctation of the aorta, mitral stenosis.

Question 31

Congenital Heart Disease may be classed as cyanotic in which circumstances?

Answer 31

Complex right to left shunts: Tetralogy of Fallow (VSD & pulmonary stenosis), transposition of the great arteries, total anomalous venous drainage, univentricular heart.

Question 32

What are the differing haemodynamic effects of ASD and VSD?

Answer 32

Both left to right shunt.
Atrial Septal Defects - increased pulmonary blood flow, right ventricle overload, pulmonary hypertension is rare, eventual right heart failure.
Ventricular Septal Defect - left ventricular volume overload (as a greater amount is returning from the lungs), so pulmonary venous congestion and eventual pulmonary hypertension.

Question 33

Which congenital condition are atrioventricular septal defects commonly associated with?

Answer 33

Down’s syndrome.

Question 34

In aortic stenosis, why would the muscle develop?

Answer 34

To maintain cardiac output.

Question 35

What is coarctation and what history may be presented with an aortic coarctation?

Answer 35

Obstruction (which collateral arteries serve to bypass).
Neonatal variety is associated with patent ductus arteriosus, with right to left shunting. The adult variety is complicated by renal hypertension

Question 36

What’s the pathophysiology of tricuspid atresia?

Answer 36

Valve is closed/absent - no right ventricle inlet, so right to left atrial shunt of entire venous return and blood flow to lungs is via a ventricular septal defect or a patent ductus arteriosus.

Question 37

What’s the pathophysiology of pulmonary atresia?

Answer 37

No right ventricle outlet, so right to left atrial shunt of entire venous return - blood flow to lungs via PDA.

Question 38

Left ventricle hypertrophy is often associated with which valvular problem?

Answer 38

Aortic valve stenosis.

Question 39

How may Tetralogy of Fallow present?

Answer 39

It may present in infancy with cyanotic spells - mild cases are compatible with adulthood.

Question 40

Which types of CHD present as neonatal emergencies, often due to reduced pulmonary blood flow?

Answer 40

Transposition of the great arteries, hypoplastic left heart failure, predictable coarctation, pulmonary atresia.