Development Flashcards
What’s the incidence + mortality of congenital heart disease?
8/1000 births (25% of birth defects)
30-50%
What are the incidences of different defects of CHD?
-Ventricular septal defects (VSD): Membranous 9.9% Muscular 4.7% -Pulmonary stenosis (PS) 3.8% -Atrioventricular septal defects (AVSD) 3.3% -Atrial septal defects (ASD) 3.2% -Transposition of great arteries (TGA) 2.6% -Tetralogy of Fallot (ToF) 2.6%
When does the heart develop?
weeks 3-10 post-conception
What’s the cardiac crescent derived from?
mesodermal cells
How’s the heart 1st recognised by?
crescent-shaped tube of myocardium
Whats the lumen of the crescent-shaped tube lined by?
endocardium
Describe the process of expansion of the primary heart tube
- medial part of crescent expands (becoming L ventricle)
- endocardial tube attaches to developing aortic arches cranially (outflow) + systemic veins caudally (inflow)
Describe the process of elongation of the heart tube
- cells from 2nd heart field are added at outflow +inflow
- tube ends are fixed, so heart bends as it elongates
- direction of looping is genetically controlled (leftward)
What’s between the heart tube myocardium + endocardium?
cardiac jelly which is an acellular layer
What’s ‘looping’?
ends of tube are fixed to vessels in embryo so heart must bend as it elongates
Why do the ventricles come in front of the atria?
heart loops so much
Summary of early heart development:
- tube formation – muscle wrapped around endothelium
- tube attached to arteries + veins at diff ends
- tube elongates by adding cells at each end from 2nd heart field
- tube bends, loops, coils
- neural crest cells migrate into outflow region forming outflow cushions
- epicardium cells come from proepicardial organ forming epicardium (visceral serous pericardium)
- tube divided by partitioning into chambers
How are the primitive chambers formed?
expansion (ballooning) of tube
How are the ventricles characterised by?
trabeculae
Define septation
dividing the heart tube
What’s atrioventricular septation?
Atria from ventricles via AV cushions
What’s atrial septation?
L from R atrium via 1ᵒ interatrial septum
What’s ventricular septation?
L from R ventricle via interventricular septum
What’s outflow tract septation?
Pul artery from aorta via OFT cushions
How does the mitral valve develop?
Inferior + superior AV cushion fuse together leaving a hole/channel on each side. L is mitral orifice -> mitral valve
How does the tricuspid valve develop?
Inferior + superior AV cushion fuse together leaving a hole/channel on each side. R is tricuspid orifice -> tricuspid valve
What’s AVSD’s?
common AV junction common in down’s syndrome 40%
What orifice does the L atrium have?
pul vein
What orifice does the R atrium have?
systemic venous sinus
Why doesn’t the 1ᵒ interatrial septum fuse w AV septum in embryonic heart?
gaining O2 from mothers lungs via placenta so it diverts blood coming from RA into LA, then around the body. Pul circulation bypassed in early life
Describe the process of atrial septation
- 1ᵒ interatrial septum grows down fusing w AV cushions
- trailing edge of 1ᵒ septum breaks down allowing blood flow from R –> L atrium
- septum secundum grows down forming flap valve
- L atrial pressure increases after birth, closes valve, seals
What’s ostium secundum?
in 1ᵒ interatrial septum + forms as 1ᵒ interatrial septum closes
What’s foramen ovale?
in septum secundum
bypass circuit - blood from body of veins crosses foramen ovale via septum primum into left side of the heart + around body
What happens after ostium secundum formed?
septum secundum starts to grow
What’s persistent foramen ovale?
flap valve doesn’t seal completely
10% of population seen as probe patency
risk factor for stroke + in divers
Eg of atrial septal defects?
Persistent Foramen Ovale
Ostium primum defect
Ostium secundum defect
Define acyantoic defect + eg
L to R shunt so normal levels of oxyhaemoglobin in systemic circulation so no cyanosis atrial septal defects ventricular septal defects atrioventricular septal defect patent ductus arteriosus
Why don’t atrial septal defects cause cyanosis?
blood shunting from L -> R atria, but oxygenated blood entering RA then being passed around again
How does interventricular septum form?
grows from the wall, towards AV cushion, initially as thickened trabeculum
eg of Ventricular Septal Defects?
75% perimembranous 25% muscular Small - small L>R shunt Medium -moderate L>R shunt Large - large L>R shunt, surgically repaired in childhood
Describe the septation of the outflow tract
- single tube (bulbus + conus) separated into aorta+pul artery
- must be attached to the L + RV respectively
- 2 cushions spiral via truncus arteriousus
- complex remodelling at each end –> great vessels
What’s Ductus Arteriosus?
allows blood that does enter into the RV to be transferred into the aorta so allows fetal circulation to bypass lungs, closes after birth becoming ligamentum arteriosum
What’s patent ductus arteriosis?
when ductus arteriosis doesn’t close after birth so aorta blood crosses ductus arteriosis entering pul artery
Describe the process of the formation of the outflow tract
- spiralling cushions separate aorta + pul artery
- neural crest cells contribute to AP septum
- complex remodelling of aortic arches
- proximal cushions fuse w IVS + AVS
Describe diff types of OFT defects
- result in common truncus
- associated w neural crest defects (eg 22q11 Deletion Syndrome / DiGeorge Syndrome)
- unequal division of OFT leads to aortic or pulmonary stenosis
Features of transposition of the great arteries (TGA)?
- Aorta to right ventricle
- Pul trunk to left ventricle
- Arterial trunks side-by-side
- caused by abnormal outflow tract cushions
- lethal w/o VSD, ASD, PDA
- Cyanotic
How do you surgically correct transposition of the great arteries?
arterial switch
atrial switch
Features of tetralogy of fallot?
- venticular septal defect (large)
- pul stenosis
- right ventricular hypertrophy
- overriding aorta
- R to L shunt so cyanotic
- Abnormal looping leads to malalignment of segments
Define cyanotic defects + eg
R to L shunt transposition of the great arteries tetralogy of fallot truncus arteriosu TAPVC(Total anomalous pulmonary venous connection)
Why does squatting relieve cyanosis in tetralogy of fallot?
increases peripheral arterial resistance, decreasing R to L shunt so increases pul blood flow
Why’s there a R to L shunt in tetralogy of fallot?
pul stenosis
Why’s there right ventricular hypertrophy in tetralogy of fallot?
pul trunk more narrow
What’s the origin of conduction tissue?
come from neural crest cells BUT specialized myocardium
What are variations in conduction properties caused by?
diff in ion channel+connexin (gap junctions) expression
How does the conduction system differentiate?
by progressive, localised recruitment from heart tube myocardium
What are the diff electrical insulation layers?
- Fibro-fatty layer at AV junction (ex cushions)
- Ventricular bundle branches wrapped in fibrous sheath
