S3) Congenital Heart Defects

Question 1

What is hypoplastic left heart syndrome?

Answer 1

Hypoplastic left heart syndrome (HLHS) is a rare congenital heart defect in which the left heart is severely underdeveloped resulting in inadequate right to left flow in utero

Question 2

The exact cause of Hypoplastic left heart syndrome is unknown.

However, identify 2 possible causes

Answer 2

• Defect in development of mitral and aortic valves, resulting in atresia and limited flow
• Ostium secundum too small

Question 3

Identify 5 different kinds of atrial septal defects which might occur

Answer 3

Question 4

Describe ventricular septation in terms of the 2 components of the ventricular septum

Answer 4

• Muscular portion forms most of the septum and grows upwards towards the fused endocardial cushions
• Small gap - primary interventricular foramen
• Membranous portion of the IV septum derived from endocardial cushions to “fill the gap”

Question 5

What is Tetralogy of Fallot?

Answer 5

Tetralogy of Fallot is a group of 4 abnormalities occurring together as the result of a single developmental defect which places the outflow portion of the interventricular septum too far in the anterior and cephalad directions:

Mnemonic: Pulmonary stenosis, Overriding aorta, ventricular Septal defect, right ventricular Hypertrophy

Question 6

Explain why Tetralogy of the Fallot presents with cyanosis

Answer 6

• Increased pressure on the right side of the heart, VSD and overriding aorta allows right to left shunting
• Deoxygenated blood mixes with oxygenated blood, resulting in cyanosis

Question 7

What is an ASD?

Answer 7

An atrial septal defect (ASD) is an opening in the septum/wall between the two atria which persists following birth

Question 8

Why are ASD’s not life-threatening?

Answer 8

• Left atrial pressure > right atrial pressure
• Flow is from left ⇒ right
• Deoxygenated blood does not mix with the oxygenated blood

Question 9

Describe the ostium secundum atrial septal defect

Answer 9

Ostium secundum atrial septal defect occurs when the ostium secundum fails to close completely while the heart is developing, causing an opening to develop in the centre of the wall separating the two atria

Question 10

What is a patent foramen ovale?

Answer 10

A patent foramen ovale is a condition when the foramen ovale doesn’t close and persists after birth

Question 11

PFOs may be present in around 20% of the population.

Provide 2 reasons as to why this often clinically silent?

Answer 11

• Higher left atrial pressure causes functional closure of the flap valve
• No symptoms/complications, hence, not a concern unless you have other heart conditions

Question 12

What is a VSD?

Answer 12

A ventricular septal defect (VSD) is an abnormal opening in the interventricular septum, commonly occurring in the membranous portion of the septum

Question 13

Describe blood flow in the case of a VSD

Answer 13

• Left ventricular pressure > right ventricular pressure so blood will flow from left to right
• The amount of flow depending on the size of the lesion

Question 14

Explain the effects of a left to right shunt

Answer 14

Although left to right shunting of blood does not cause cyanosis it can be problematic later on if untreated, with the extent of the problems depending on the degree of shunting

Question 15

Describe what occurs in transposition of the great vessels

Answer 15

• Transposition of the great arteries results in two unconnected parallel circulations instead of two circulations in series
• In this defect the right ventricle is connected to the aorta and the left ventricle to the pulmonary trunk

Question 16

Briefly, state the effect and treatment of transposition of the great vessels

Answer 16

A baby with transposed arteries is cyanotic and requires immediate surgical intervention

Question 17

Describe the functional importance of tricuspid atresia

Answer 17

- Tricuspid atresia (lack of development of the tricuspid valve) leaves no inlet to the right ventricle

• Hence, there must be a complete right to left shunt of all the blood returning to the right atrium (ASD/PFO) and a VSD/PDA to allow blood flow to the lungs

Question 18

What is the ductus arteriosus?

Answer 18

The ductus arteriosus is a vessel that exists in the foetus to shunt blood from the pulmonary artery to the aorta before the lungs are functioning

Question 19

What is a patent ductus arteriosus and how does it occur?

Answer 19

• The ductus arteriosus should close shortly after birth as the pressure in the pulmonary artery drops following perfusion of the lungs
• Failure to close leads to a patent ductus arteriosus and blood flows from aorta to pulmonary arteries

Question 20

What is coarctation of the aorta?

Answer 20

Coarctation of the aorta: a narrowing of the aortic lumen in the region of the ligamentum arteriosum (former ductus arteriosus)

Question 21

Explain the pathophysiology of coarctation of the aorta

Answer 21

• The narrowing of the aorta increases the afterload and can lead to LV hypertrophy
• Vessels to the head and upper limbs emerge proximal to the coarctation, so blood supply is not compromised but is reduced in rest of body

Question 22

Where is a common location for coarctation of the aorta?

Answer 22

The coarctation typically occurs after the left subclavian artery (ligamentum arteriosum)

Question 23

Identify 2 symptoms of coarctation of the aorta

Answer 23

• Hypertension in the upper extremities
• Hypotension in the lower extremities