Development of the heart 2

Question 1

What is dextrocardia?

Answer 1

Dextrocardia is a rare heart condition in which your heart points toward the right side of your chest instead of the left side.

Question 2

What is dextrocardia a result of?

Answer 2

• Dextrocardia may be a result of abnormal cardiac looping or may be induced during gastrulation (week 3) when laterality (left and right sides) is determined

Question 3

What is isolated dextrocardia?

Answer 3

• Isolated dextrocardia is associated with other structural defects including abnormal connections with veins and arteries or abnormal septation of the heart

Question 4

What normally happens to the ductus arteriosus shortly after birth?

Answer 4

The ductus arteriosus closes soon after birth due to increasing oxygen tension and a decrease in circulating prostaglandins.

Question 5

What does a patent ductus arteriosus allow?

Answer 5

A patent ductus arteriosus after birth allows shunting of blood from the aorta to the pulmonary artery.

Oxygenated blood travels back to the lungs then returns to the heart to be pumped out again – increases workload of the heart

Question 6

What does patent ductus arteriosus lead to in terms of conditions?

Answer 6

Can lead to pulmonary hypertension, ventricular hypertrophy and heart failure.

Question 7

How is patent ductus arteriosus treated?

Answer 7

Normally- Ductus arteriosum has contractile cells begin to contract so opening gets smaller. In response to decreasing prostaglandins causes contractile cells to contact.

Patent ductus arteriosus doesn’t have a decrease in prostaglandins.

• Treated with prostaglandin inhibitors- help decrease prostaglandins so closes ductus arteriosus
• Patent ductus arteriosus may be an isolated defect or occur with other cardiac defects
• Note – in some cardiac defects a patent ductus arteriosus is essential to life

Question 8

How do atrial septal defects occur?

Answer 8

secundum to fuse after birth – probe patent foramen ovale
Can be due to malformations in the septum primum or secundum such that they do not overlap and therefore leave a gap (most commonly due defects in septum secundum)

Question 9

What is probe patent foramen ovale?

Answer 9

A “probe patent” foramen ovale is defined as a defect in the fossa ovalis that would be revealed with instrument probing.

Question 10

How does the body react to have a probe patent foramen ovale?

Answer 10

• Usually asymptomatic, higher pressure in LA pushes septum primum against septum secundum and mechanically shuts valve
• However, if there is higher pressure in RA e.g. pulmonary hypertension this can push flimsy septum primum open and allow blood to shunt from right to left

Question 11

What is a ostium secundum defect caused by?

Answer 11

• Can be caused by excessive apoptosis in septum primum or by inadequate development of the septum secundum such as the foramen ovale and foramen (ostium) secundum overlap
• Blood is shunted left to right – can cause enlargement of right atrium and ventricle
• Small defects (<5mm) may be asymptomatic, however, larger defects may require surgical repair

Question 12

What is a common atrium defect? (cor triloculare biventriculare)

Answer 12

Cor= heart
Triloculure= three chambers
Biventricular= 2 ventricles

• Rare cardiac defect with complete absence of atrial septum
• Failure of development of the septum primum and septum secundum
• Reports of people undiagnosed until 20-30 years of life

Question 13

What does premature closure of the foramen ovale result in?

Answer 13

• Closure of foramen ovale during prenatal life
• Results in hypertrophy of the right side of the heart and underdevelopment of the left side
• Death usually occurs shortly after birth

Question 14

What are ventricular septal defects?

Answer 14

• Defects can affect the muscular or membranous part of the interventricular septum
• Defects affecting the muscular part of the interventricular septum often resolve themselves as the child grows- during development heart muscle grows and is repaired naturally. Heart muscle develops and covers ventricular septal defect
• Ventricular septal defects allow left to right shunting of blood – LHS greater pressure so shunts blood to RHS
• Can result in pulmonary hypertension and hypertrophy of right ventricle- when muscle of heart gets bigger

Question 15

What is a trunks arteriosus?

Answer 15

Truncus arteriosus is a rare type of heart disease in which a single blood vessel (truncus arteriosus) comes out of the right and left ventricles, instead of the normal 2 vessels (pulmonary artery and aorta).

Question 16

What is the Septation Defects of the Truncus Arteriosus?

Answer 16

• The conotruncal swellings that form the conotruncal septum rely in the migration of neural crest cells from the neural tube
• Abnormal neural crest cell development or migration can lead to a number of defects in septation of the truncus arteriosus into pulmonary trunk and aorta
• These include persistent truncus arteriosus (one common outflow tract), transposition of the great vessels (abnormal connections of chambers of heart) and Tetralogy of Fallot

Question 17

What is persistent truncus arteriosus?

Answer 17

Conotruncal septum completely absent therefore cannot fuse with interventricular septum – ventricular septal defect

Undivided truncus is in communication with both ventricles – receives oxygenated and deoxygenated blood

Question 18

What are symptoms of persistent truncus arteriosus?

Answer 18

• Symptoms include cyanosis (blue colour) at birth, lethargy, breathlessness, delayed growth
• Must be corrected surgically or will result in heart failure and death within 2 years

Question 19

What is the transposition of the Great Vessels?

Answer 19

• Conotruncal septum does not form in a spiral but instead runs straight down
• Aorta arises from right ventricle and pulmonary artery from left ventricle

Question 20

Are you able to live with transposition of the Great Vessels?

Answer 20

• Incompatible with life unless an accompanying shunt such as a VSD, patent foramen ovale or patent ductus arteriosus exists

Question 21

What are the symptoms of transposition of the Great Vessels?

Answer 21

• Similar symptoms to persistent truncus arteriosus including cynaosis but can corrected surgically

Question 22

How can we stay alive even if we have transposition of the Great Vessels?

Answer 22

Ductus arteriosus

Question 23

What is the primary defect that causes Tetralogy of Fallot?

Answer 23

Unequal division of the truncus arteriosus caused by anterior displacement of the aorticopulmonary septum. Displacement of the septum produces four classic cardiac defects.

Question 24

What are the four abnormalities of the Tetralogy of Fallot?

Answer 24

1. pulmonary stenosis (narrowing)
2. ventricular septal defect
3. overriding aorta (rightward displacement of the aorta)
4. right ventricular hypertrophy caused by higher pressure on the right side

Question 25

What is coarctation of the aorta? What is the cause of this? How can it be classified?

Answer 25

• Narrowing of the aorta that occurs near the ductus arteriosus
• Cause is unknown but may be due to abnormal migration of cells from the ductus arteriosus
• Can be classifies as preductal or postductal in relation to ductus arteriosus

Question 26

How can someone survive if they have preductal coarctation of the aorta?

Answer 26

• During development, the ductus arteriosus compensates for the narrowing
• After birth, the ductus arteriosus usually remains patent

Question 27

What happens when someone that has preductal coarctation of the aorta but the ductus arteriosus is obliterated after birth? How can it be treated? What are the symptoms of this?

Answer 27

• Obliteration of the ductus arteriosus causes rapid decline of infant with hypoperfusion of the lower body
• Can be treated by administering prostaglandins to keep ductus arteriosus open
• Differential cyanosis – upper body and head well perfused, lower body cyanotic

Question 28

How does post ductal coarctation of the aorta work?

Answer 28

• During development, a collateral circulation is established to bypass the narrowing
• Blood passes through the subclavian arteries to the internal thoracic arteries to intercostal arteries to the descending aorta
• Internal thoracic and intercostal arteries enlarge to carry greater blood flow