Development of Heart & Great Vessels and Understanding Congenital Heart Disease Flashcards
What are the most common birth defects?
Congenital heart defects - 1% incidence
In an embryo, 2 areas of blood islands create a pair of endocardial tubes which fuse when folded, what type of tissue to they form from?
Splanchnic mesoderm.
Congenital birth defects (structural abnormality or complete absence of a structure) result from an interruption of normal development, what are the different types of causes?
Genetic
Exposure to drugs/infectious agents
Unexplained
What makes the development of the heart and vessels extra complicated and more prone therefore do congenital abnormalities?
Different circulatory needs of the foetus and the newborn (immediate change from in uterine to mature heart).
Heart defects can occur when there’s structural abnormality of chambers or vasculature or an obstruction or communication between pulmonary and systemic circuits.
What is the primitive heart tube and what changes must it go through?
A contraction tube with nothing to control the flow of blood. Zones starting from bottom are: Sinus Venosus, Atrium then Ventricle (primitive), Bulbis Cordis, Truncus Arteriosis and Aortic roots.
It might divide into 4 chambers and the inflow and outflow tubes must be remodelled.
What is cardiac looping and why does it occur?
When the ‘heart’ is enclosed in the pericardial cavity, it grows and becomes too big to occupy the space in a linear conformation, so it folds.
It places the inflow and outflow tubes in the correct orientation with respect to each other - atrium was caudal, now pushed posteriorly and cranially. There is differential growth of zones.
What does the mature right atrium develop from and what about the left? What effect does this have on the texture?
The right atrium develops from most of the primitive atrium (hence trubeculated walls, making it tough) and some of the Sinus Venosus.
The left atrium develops from a small portion of the primitive atrium and absorbs proximal parts of the pulmonary veins (and so is smooth walled).
What are the conflicting circulatory requirements of the foetus?
The lungs don’t work and so oxygenation and carbon dioxide removal occur at the placenta (reliant on maternal circulation for exchange), so shunts are required to maintain foetal life - they must be reversible at birth.
What is the pathway of blood in an embryo and which shunts are involved?
High pO2 blood travels through umbilicus vein to the liver and the DUCTUS VENOSUS shunts it around the liver then into the right atrium. From there it must bypass the right ventricle and lungs so enters the left atrium via the FORAMEN OVALE, but some blood manages to get through to the right ventricle and must be redirected from the pulmonary trunk to the aorta through the DUCTUS ARTERIOSUS.
What happens to the shunts at birth?
Respiration begins and left atrium pressure increases so the foramen ovale closes (before birth pressure in the RALA, so septum primum is pushed against septum secundum) and the ductus arteriosus contracts to shut. Placental support is removed, so the ductus venosus closes.
The early arterial system begins as a bilaterally symmetrical system of arched vessels, what are the 4th and 6th arches remodelled to become?
The 4th arch is remodelled on the right to become the proximal part of the right subclavian artery and on the left it becomes the arch of the aorta.
The 6th arch is remodelled on the right to form the right pulmonary artery and on the left side is forms the left pulmonary artery and the ductus arteriosus.
Explain why a hoarse voice might be a sign of heart pathology.
As the heart ‘descends’ (from its position at the embryonic neck), the left recurrent laryngeal nerve become hooked around the 6th aortic arch and turns back on itself and ends up around the closed shunt around the aorta and pulmonary artery (ductus arteriosus).
What is PDA in terms of heart pathology?
Patent Ductus Arteriosus - persistent communication between descending aorta and pulmonary artery - failure of physiological closure. Blood will flow from the aorta with higher pressure to the pulmonary artery.
How is the foramen ovale built?
Endocardial cushions make a shelf, the septum primum grows down from the roof of the primitive atrium, with the newly formed ostium primum allowing blood flow between the atria, then the osmium secundum appears before it closes (made by apoptosis). Then the septum secundum grows down in a characteristic arch shunt and the foramen ovale is complete, shunting blood from right to left.
When might an Atrial Septal Defect occur? What history might be present?
If the septum primum is resorbed or too short or if the septum secundum is too small.
Usually asymptomatic into late adulthood then late onset arrhythmia and right heart failure.
What is Hypoplastic Left Heart Syndrome and what is the course?
The left heart is underdeveloped. There is speculation as to the cause: defect in development of left valves, resulting in atresia (abnormal narrowing) and limited flow or ostium secundum is too small so there’s inadequate right to left flow in utero- not used = lost.
Ascending aorta very small so right ventricle must support systemic circulation. For survival, obligatory ASD and PDA.
