CVS Session 3 Flashcards
Where does septation occur?
Interarterial septum
Interventricular septum
Septation of ventricular outflow
What does septation achieve?
Creation of 4 chambers
Selective outflow
Where do endocardial cushions develop?
Point of constriction in the atrioventricular region - AV canal
In which direction do the endocardial cushions grow?
From dorsal and ventral walls towards middle
What is the function of the endocardial cushions?
Divide developing heart into right and left channels
Contribute tissues
What is the path of the septum primum?
Moves down to fused endocardial cushions
What is the ostium primum?
Hole present before septum primum fuses
What forms the ostium secundum?
Programmed cell death
When does the ostium secundum form?
Before ostium primum closes
Describe septum secundum formation.
Crescent-shaped septum grows with foramen ovale
How many holes and septa are involved in atrial septation?
3 holes
2 septa
Where does the muscular portion in ventricular septation grow upwards from?
Same platform as atrial septum
What is the primary interventricular foramen?
Small gap left by growth of muscular portion towards endocardial cushions in ventricular septation
What fills the primary interventricular foramen and forms the membranous portion of the interventricular septum?
Connective tissue from endocardial cushions
What are the stages of atrial septation?
Septum primum –> ostium secundum appearing –> ostium secundum complete –> septum secundum –> septum secundum complete w/foramen ovale –> R to L shunt
Where are the left and right auricles of the L and R atria derived?
Primitive atrium
What is the fossa ovalis?
Adult remnant of foramen ovale
What is the purpose of the foramen ovale?
In utero shunt to bypass lungs
How is the difference in atrial development identified in the developed heart?
R atrium has smooth but largely trabeculated walls
L atrium largely smooth walled
What is visible in the right and left atria?
R: fossa ovalis
L: pulmonary vein entrances
Describe the formation of the conotruncal septum.
Endocardial cushions appear staggered in the truncus arteriosus –> grow towards and twist around each other –> forms spiral septum
Are septation of the outflow tract and atrial septation simultaneous?
Yep
What is the result of successful outflow tract septation?
Left ventricle pumps to aorta
Right ventricle pumps to pulmonary trunk
Blood circulates in spiral flow
How does foetal blood return to the placenta?
Via umbilical arteries
What occurs to the foetal circulation during birth?
Respiration begins Left atrial pressure increases Foramen ovale closes Ductus arteriosus contracts Ductus venosus closes structurally
What prevents L to R bloodflow in the neonatal heart?
p(LA) > p(RA)
Septum primum pushed against septum secundum w/specific non-alignment
Under what circumstance does blood move through the foramen ovale?
p(LA)<p(RA)
What are the fates of each of the foetal shunts after birth?
Foramen ovale –> fossa ovalis
Ductus arteriosus –> ligamentum arteriosum
Ductus venosus –> ligamentum venosum
Umbilical vein –> ligamentum teres (hepatis)
What are the fates of each of the parts of the primordial heart tube?
Sinus venosus –> RA except L horn
Atrium –> auricles of atria
Ventricle –> left ventricle
Bulboventricular sulcus –> primary IV foramen
How does the bulbus cordis change during development?
Proximal third –> trabeculated RV
Conus cordis –> outflow tract of L and R ventricles
Truncus arteriosus –> roots of pulmonary trunk and proximal aorta
Why are congenital heart defects common?
Due to complexity of septation
Which type of congenital heart defect is most common?
Ventricular septal defects
What causes transposition of great vessels?
Conotruncal septum is not spiral
What causes tetralogy of Fallot?
Conus cordis not equally split into 2 therefore four separate defects arise
What are the three causes of congenital heart disease?
Genetics
Environmental
Maternal infections
Does glycaemia in maternal diabetes directly cause predisposition to congenital heart defects?
No
What is the normal physiology of the heart?
R ventricle pumps deoxygenated blood to lungs
Pulmonary circulation has low resistance
L ventricle pumps oxygenated blood at systemic BP to aorta
Each ventricle morphological lay adapted to task
What is the approximate oxygen saturation of blood in the right side of the heart?
67%
What happens to the blood flow in an acyanotic shunt?
L –> R
Blood from L heart returned to lungs instead of body
What must the heart do to maintain cardiac output in the event of an acyanotic shunt?
Pump harder
What is damaging to the lungs in the instance of a L–>R shunt?
Increased pulmonary artery and venous pressure
What can cause an acyanotic shunt?
Atrial/ventricular septal defects
Patent ductus arteriosus
Aortic/pulmonary/mitral stenosis
Coarctation of the aorta
What do both acyanotic and cyanotic shunts require?
A hole
What happens to the passage of blood in a cyanotic shunt?
R –> L
Deoxygenated blood bypasses the lungs
At what oxygen saturation is cyanosis seen?
What can cause a cyanotic shunt?
Pulmonary stenosis Tetralogy of Fallot Transposition of great arteries Total anomalous pulmonary venous drainage Univentricular heart
Why do atrial septal defects eventually lead to right heart failure?
Increased pulmonary blood flow –> right ventricle volume overload
What three locations are the common sites for an atrial septal defect?
Sinus venous defect
Secundum atrial defect
Primum atrium defect
Why is pulmonary resistance not usually damaged by an atrial septal defect?
Blood is at low pressure - pulmonary hypertension is rare
In which direction does blood flow in an atrial septal defect?
L –> R
Why does a ventricular septal defect lead to eventual pulmonary hypertension?
Left ventricle volume overload –> pulmonary venous congestion
Why is pulmonary resistance usually damaged in a ventricular septal defect?
Blood at high pressure
Why is a patent foramen ovale not a true ASD?
Usually clinically silent due to higher left atrial pressure closing flap
How does a patent foramen ovale allow the passage of a venous embolism into the systemic circulation?
Right heart pressure increases –> flap opens
Why is oxygenated and deoxygenated blood pumped to the lungs at high pressure in an atrio-ventricular septal defect?
Blood mixes in atria and ventricles as common AV valve leaks blood back into upper chambers
What causes an atrio-ventricular septal defect to form?
Faulty development of the embryonic endocardial cushions
Why do the ventricle muscle walls thicken in aortic stenosis?
To be able to contract with more force to push blood through narrowed aorta
What causes aortic stenosis?
Congenital defect
Calcium deposits in aortic valve
What predisposes aortic stenosis by calcium deposits in the aortic valve?
Abnormal aortic/bicuspid valves
Is aortic stenosis more common in men or women?
3x more common in men
Why must L–> R shunting be treated?
To avoid vascular remodelling of the pulmonary circulation
What happens if pulmonary vascular remodelling causes pulmonary resistance to increase beyond systemic circulation resistance?
Right heart pressure increases causing shunt to become R–> L
Eisenmenger syndrome
Why does coarctation of the aorta cause LV hypertrophy?
More muscle needed to push blood through narrowing in ductus arteriosus area
What vasculature in the body is affected by coarctation of the aorta?
All except head and upper limb
What signs related to the systemic circulation can be detected clinically in coarctation of the aorta?
Femoral pulse weak and delayed
Upper body hypertension
In what range can the extent of symptoms of coarctation of the aorta be found?
Ranging from neonate heart failure to detection only in adulthood
Which four congenital heart defects are present in Tetralogy of Fallot?
Overriding aorta
Ventricular septal defect
Pulmonary stenosis
Thickened R ventricle
What does the magnitude and severity of the shunt depend on in Tetralogy of Fallot?
Severity of pulmonary stenosis
What is an overriding aorta?
Aorta comes off both ventricles
In which direction is the blood shunted in Tetralogy of Fallot?
R–> L
What can overcome the excess bloodflow present in Tetralogy of Fallot?
Pulmonary stenosis
What is tricuspid atresia?
Absence of RV inlet causing R–> L atrial shunt of entire venous return
How is blood flow to the lungs achieved in tricuspid atresia?
Drugs followed by surgery to keep central septal defect or patent ductus arteriosus shunts open
What is a univentricular heart?
Only one giant ventricle present
Is univentricular heart seen with or without transposition of great arteries?
Either
What is hypoplastic left heart?
Left ventricle is underdeveloped and ascending aorta is very small
What supports the systemic circulation in hypoplastic left heart?
Right ventricle
How is hypoplastic left heart treated?
ASD or PDA must be kept open for short term survival to enable surgery to reconstruct R ventricle as pump
How are the great arteries arranged in transposition of the Great Arteries?
Aorta connected to R ventricle
Pulmonary artery connected to L ventricle
What must be present for transposition of the great arteries to be viable?
Atrial/ventricular/ductal shunt so two circuits can communicate
What is transposition of the great arteries an example of?
Bi-directional shunting
How is transposition of the great arteries treated?
With immediate surgery or use of drugs to keep shunts open until surgery can be performed
What is pulmonary atresia?
Absence of R ventricle outlet causing R–> L shunt of entire venous return
How is bloodflow to lungs achieved in pulmonary atresia?
PDA
How does an ASD usually present?
Asymptomatic late into adulthood
Late onset arrhythmia
R heart failure
How does a VSD usually present?
Unless v. small seen in infancy w/left heart failure
Very common
Causes heart murmurs
What does an untreated VSD lead to?
Inoperable pulmonary hypertension
What complicates coarctation of the aorta in adulthood?
Renal hypertension –> left ventricle hypertrophy
What is often associated with coarctation of the aorta in adulthood?
Aortic valve stenosis
How does Tetralogy of Fallot usually present?
In infancy/early childhood w/cyanotic spells
Mild cases compatible w/adulthood
Which congenital heart defects are neonatal emergencies due to reduced pulmonary bloodflow?
Transposition of the great arteries
Hypoplastic left heart
Preductal coarctation of the aorta
Pulmonary atresia
