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Yr 4 - Paediatrics > Cardiology - Fetal Circulation & Murmurs > Flashcards

Cardiology - Fetal Circulation & Murmurs Flashcards

1
Q

Basic fetal circulation:

A

Blood goes via placenta to collect oxygen & nutrients and to dispose of waste products (CO2 & lactate).

As the fetal lungs are not fully developed or functional, it does not make sense for the fetal blood to pass through the pulmonary circulation.

Therefore there are three SHUNTS that allow blood to bypass the lungs.

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2
Q

What are the 3 fetal shunts?

A

1) Ductus venosus

2) Foramen ovale

3) Ductus arteriosus

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3
Q

What does the ductus venosus connect?

What does it allow blood to bypass?

A

This shunt connects the UMBILICAL VEIN to the INFERIOR VENA CAVA and allows blood to bypass the liver.

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4
Q

What does the foramen ovale connect?

What does it allow blood to bypass?

A

This shunt connects the LEFT and RIGHT atrium, and allows blood to bypass the right ventricle and pulmonary circulation.

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5
Q

What does the ductus arteriosus connect?

What does it allow blood to bypass?

A

This shunt connects the PULMONARY ARTERY with the AORTA, and allows blood to bypass the pulmonary circulation.

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6
Q

At birth what happens to the foramen ovale?

A

1) The baby breathes and this expands the alveoli, decreasing the pulmonary vascular resistance.

2) The decrease in pulmonary vascular resistance causes a fall in pressure in the right atrium.

3) At this point, the left atrial pressure is greater than the right atrial pressure –> which squashes the atrial septum to cause functional closure of the foramen ovale.

4) This then gets sealed shut structurally after a few weeks and becomes the fossa ovalis.

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7
Q

After birth, what does the foramen ovale become?

A

Fossa ovalis

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8
Q

After birth, what happens to the ductus arteriosus?

A

1) Prostaglandins are required to keep the ductus arteriosus open.

2) Increased blood oxygenation causes a drop in circulating prostaglandins.

3) This causes closure of the ductus arteriosus, which becomes the ligamentum arteriosum.

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9
Q

What does the ductus arteriosus become after birth?

A

Ligamentum arteriosum.

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10
Q

After birth, what happens to the ductus venosus?

A

1) Immediately after birth the ductus venosus stops functioning because the umbilical cord is clamped and there is no flow in the umbilical veins.

2) The ductus venosus structurally closes a few days later and becomes the ligamentum venosum.

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11
Q

What does the ductus venosus become after birth?

A

Ligamentum venosum

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12
Q

In the adult circulation system, how much blood is there?

A

Approx 5 litres within the circulation (8% of body weight).

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13
Q

What is the cardiac output in adults?

A

The cardiac output is approximately 5 litres/min, with 80% of circulating volume in the systemic veins, right side of the heart, and pulmonary circulation.

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14
Q

In adults, how does deoxygenated blood return to the heart?

A

Returns to the right atrium via the superior & inferior vena cava.

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15
Q

Brief description of adult circulation:

A

1) Deoxygenated blood returns to the right atrium via the vena cavae.

2) Passies through the right ventricle and then passes via the pulmonary arteries to the lungs to enable gas exchange.

3) Oxygenated blood then returns via the pulmonary veins to the left ventricle.

4) Then passes through the left ventricle and enters the systemic circulation via the aorta.

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16
Q

Describe foetal circulation at the liver

A

1) Oxygenated blood from the placenta travels via the umbilical vein, which branches into the left and right umbilical veins at the liver.

2) The right umbilical vein provides oxygenated blood to the liver via the portal vein, whilst the left umbilical vein branches into the ductus venosus, which bypasses the liver to carry oxygenated blood directly into the inferior vena cava (IVC).

3) A mix of oxygenated (from ductus venosus) and deoxygenated (from liver and the rest of the body) blood then enters the right atrium via the IVC, also mixing with the SVC (50:50 split of blood entering the heart from SVC and IVC).

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17
Q

Which vessel provides oxygenated blood to the liver in foetal circulation?

A

Right umbilical vein.

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18
Q

Which vessel branches into the ductus venosus in fetal circulation?

A

The left umbilical vein.

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19
Q

Describe the foetal circulation at the lungs and the heart

A

1) As the lungs have no role in gas exchange, the pulmonary arterioles are in a hypoxic state.

2) Hypoxia causes a pulmonary vasoconstriction, which in turn increases pulmonary vascular resistance and pressure within the pulmonary circulation.

3) This means that in foetal circulation, unlike in the adult, the pressure is higher in the right side of the heart.

4) As a result, the right ventricular afterload increases, causing blood to preferentially shunt away from the right ventricular outflow tract, via the ductus arteriosus (between pulmonary artery and aorta) and foramen ovale (between right atrium and left atrium).

5) Consequently, most of the blood bypasses the right ventricle and lungs altogether, entering the left atrium or directly into the aorta, to then be pumped around the systemic circulation.

6) This allows relatively oxygen-rich blood to be pumped to the body.

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20
Q

What do the umbilical arteries arise from?

A

1) The aorta bifurcates into the right and left common iliac arteries.

2) These split further into the internal and external iliac arteries.

3) Each of the internal iliac arteries give rise to an umbilical artery, which travel alongside the umbilical vein to bring deoxygenated blood back to the placenta.

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21
Q

What do the umbilical vessels become after birth?

A

After birth, the umbilical vessels constrict, forming the round ligament of the liver (umbilical vein), ligamentum venosum of the liver (ductus venosus), and superior vesical arteries (umbilical arteries).

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22
Q

What does the umbilical vein become after birth?

A

Round ligament of the liver

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23
Q

What do the umbilical arteries become after birth?

A

Superior vesical arteries.

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24
Q

Affinity for O2 of foetal Hb vs adult Hb?

A

Foetal Hb has a higher affinity for oxygen compared to maternal Hb.

This means foetal Hb binds to oxygen more strongly and enables the transfer of oxygen from mother to foetus prenatally.

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25
Q

Describe oxygen dissociation curve of foetal Hb vs adult Hb

A

Foetal Hb has an oxygen dissociation curve that is displaced to the LEFT compared to adult Hb. As a result, for a given partial pressure of oxygen (pO2), the Hb is more saturated than adult Hb.

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26
Q

What are innocent murmurs also known as?

A

Flow murmurs.

They are very common in children.

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27
Q

What are innocent murmurs caused by?

A

Fast blood flow through various areas of the heart during systole.

28
Q

Features of innocent murmurs?

A
  • soft
  • short
  • systolic
  • symptomless
  • situation dependent, particularly if the murmur gets quieter with standing or only appears when the child is unwell or feverish
29
Q

Clear innocent murmurs with no concerning features may not require any investigations.

What features of a murmur would prompt further investigations and referral to a paediatric cardiologist?

A
  • Murmur louder than 2/6
  • Diastolic murmurs
  • Louder on standing
  • Other symptoms such as failure to thrive, feeding difficulty, cyanosis or shortness of breath
30
Q

What are the key investigations to establish the cause of a murmur and rule out abnormalities in a child?

A

1) ECG

2) CXR

3) Echocardiography

31
Q

Does a murmur becoming louder on standing indicate an innocent murmur or not?

A

No - requires more investigations.

32
Q

What are the 3 differentials of a pansystolic murmur?

A

1) Mitral regurgitation

2) Tricuspid regurgitation

3) Ventricular septal defect

33
Q

What does pansystolic mean?

A

persisting throughout systole.

34
Q

Where would a pansystolic murmur caused by mitral regurgitation be heard loudest?

A

At the mitral area (fifth intercostal space, mid-clavicular line).

35
Q

Where would a pansystolic murmur caused by tricuspid regurgitation be heard loudest?

A

At the tricuspid area (fifth intercostal space, left sternal border).

36
Q

Where would a pansystolic murmur caused by a ventricular septal defect be heard loudest?

A

At the left lower sternal border

37
Q

What are the 3 differentials for an ejection systolic murmur?

A

1) Aortic stenosis

2) Pulmonary stenosis

3) Hypertrophic obstructive cardiomyopathy heart

38
Q

Where would an ejection systolic murmur caused by aortic stenosis be heard loudest?

A

at the aortic area (second intercostal space, right sternal border)

39
Q

Where would an ejection systolic murmur caused by pulmonary stenosis be heard loudest?

A

At the pulmonary area (second intercostal space, left sternal border).

40
Q

Where would an ejection systolic murmur caused by hypertrophic obstructive cardiomyopathy be heard loudest?

A

at the fourth intercostal space on the left sternal border

41
Q

What causes splitting of the second heart sound?

A

When the pulmonary valve closes slightly later than the aortic valve, this causes the second heart sound to be “split”.

Physiology:

1) During inspiration the chest wall and diaphragm pull the lungs open. This also pulls the heart open. This is called negative intra-thoracic pressure.

2) This causes the right side of the heart to fill faster as it pulls in blood from the venous system.

3) The increased volume in the right ventricle causes it to take longer for the right ventricle to empty during systole, causing a delay in the pulmonary valve closing.

4) When the pulmonary valve closes slightly later than the aortic valve, this causes the second heart sound to be “split”.

42
Q

What murmur does an atrial septal defect cause?

A

Atrial septal defects cause a mid-systolic, crescendo-decrescendo murmur.

This is heard loudest at the upper left sternal border, with a fixed split second heart sound.

43
Q

Where is an atrial septal defect (ASD) heard loudest?

A

At the upper left sternal border.

44
Q

What does a ‘fixed split’ second heart sound mean?

A

Splitting of the second heart sound can be normal with inspiration, however a “fixed split” second heart sound means the split does NOT change with inspiration and expiration.

45
Q

What causes a fixed split second heart sound in ASD?

A

Blood is flowing from the left atrium into the right atrium across the atrial septal defect, increasing the volume of blood that the right ventricle has to empty before the pulmonary valve can close. This doesn’t vary with respiration.

46
Q

What type of murmur can a patent ductus arteriosus cause?

A

A small patent ductus arteriosus may not cause any abnormal heart sounds.

More significant PDAs cause a normal first heart sound with a continuous crescendo-decrescendo “machinery” murmur that may continue during the second heart sound, making the second heart sound difficult to hear.

47
Q

Why may the murmur in a PDA be difficult to hear?

A

As the murmur may continue during the second heart sound, making the second heart sound difficult to hear.

48
Q

What does the murmur in Tetralogy of Fallot arises from?

A

pulmonary stenosis

49
Q

What murmur is heart in Tetralogy of Fallot?

Where is it heard loudest?

A

Ejection systolic murmur, loudest at the pulmonary area (second intercostal space, left sternal border).

50
Q

What is cyanosis?

A

Cyanosis occurs when deoxygenated blood enters the systemic circulation.

51
Q

What happens in cyanotic heart disease?

A

Blood is able to bypass the pulmonary circulation and the lungs –> occurs across a right-to-left shunt.

52
Q

What is a right to left shunt?

A

A right-to-left shunt describes any defect that allows blood to flow from the right side of the heart (the deoxygenated blood returning from the body) to the left side of the heart (the blood exiting the heart into the systemic circulation) without travelling through the lungs to get oxygenated.

53
Q

What are 4 heart defects that can cause a right-to-left shunt, and therefore cyanotic heart disease?

A

1) Ventricular septal defect (VSD)

2) Atrial septal defect (ASD)

3) Patent ductus arteriosus (PDA)

4) Transposition of the great arteries

54
Q

Why are patients with a VSD, ASD or PDA usually not cyanotic?

A

This is because the pressure in the left side of the heart is much greater than the right side, and blood will flow from the area of high pressure to the area of low pressure.

This prevents a right-to-left shunt.

55
Q

When will patients with VSD, ASD or PDA be cyanotic?

A

If the pulmonary pressure increases beyond the systemic pressure blood will start to flow from right-to-left across the defect, causing cyanosis.

This is called Eisenmenger syndrome.

56
Q

What is Eisenmenger syndrome?

A

Describes the reversal of a left-to-right shunt in a congenital heart defect due to pulmonary hypertension.

This occurs when an uncorrected left-to-right leads to remodeling of the pulmonary microvasculature, eventually causing obstruction to pulmonary blood and pulmonary hypertension.

57
Q

What 3 defects is Eisenmenger’s syndrome associated with?

A

1) VSD

2) ASD

3) Patent ductus arteriosus

58
Q

Features of Eisenmenger’s syndrome?

A

1) original murmur may disappear
2) cyanosis
3) clubbing
4) right ventricular failure
5) haemoptysis, embolism

59
Q

Management of Eisenmenger’s syndrome?

A

Heart-lung transplantation is required

60
Q

Why will patients with transposition of the great arteries always have cyanosis?

A

Because the right side of the heart (deoxygenated) pumps blood directly into the aorta and systemic circulation.

61
Q

What are the 2 types of innocent ejection murmurs heard in children?

A

1) Venous hums

2) Still’s murmur

62
Q

What is venous hums murmur caused by?

A

Due to the turbulent blood flow in the great veins returning to the heart.

63
Q

How is a venous hums murmur heard?

A

Heard as a continuous blowing noise heard just below the clavicles.

64
Q

How is a Stills murmur heard?

A

Low-pitched sound heard at the lower left sternal edge

65
Q
A

Yr 4 - Paediatrics (78 decks)

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