Cardiology: ASD Flashcards
Describe fetal circulation, including the names of the fetal shunts [4]
Fetal blood travels to the placenta via the two umbilical arteries. The umbilical arteries originate from the internal iliac arteries.
Fetal blood travels back from the placenta to the fetus via the umbilical vein.
There are three fetal shunts:
* Ductus venosus
* Foramen ovale
* Ductus arteriosus
Describe the connections the following shunts provide:
* Ductus venosus
* Foramen ovale
* Ductus arteriosus
ductus venosus
- connects the umbilical vein to the inferior vena cava, allowing blood to bypass the liver.
foramen ovale
- connects the right atrium with the left atrium, allowing blood to bypass the right ventricle and lungs.
ductus arteriosus
- connects the pulmonary artery with the aorta, allowing blood to bypass the lungs.
Describe what happens to fetal circulation at birth
The first breaths after birth expand the alveoli, decreasing the pulmonary vascular resistance.
The decrease in pulmonary vascular resistance causes a fall in pressure in the right ventricle and atrium.
At this point, the left atrial pressure is greater than the right atrial pressure, which squashes the atrial septum, causing functional closure of the foramen ovale.
The foramen ovale is sealed shut within a few weeks, becoming the fossa ovalis.
Prostaglandins are required to keep the ductus arteriosus open.
Increased blood oxygenation causes a drop in circulating prostaglandins, causing the closure of the ductus arteriosus, which becomes the ligamentum arteriosum.
When blood stops circulating through the umbilical vein, the ductus venosus stops functioning.
The ductus venosus closes structurally a few days later and becomes the ligamentum venosum.
Describe the pathophysiology of ASDs
Caracterised by an abnormal opening in the atrial septum, allowing blood flow between the left and right atria. This occurs because:
The presence of an atrial septal defect creates a communication between the left and right atria. Due to higher pressure in the left atrium compared to the right atrium, there is typically a left-to-right shunt. This shunting of oxygenated blood from the left atrium into the right atrium results in increased pulmonary blood flow
The augmented volume load on the right side of the heart leads to dilation of both the right atrium and ventricle
Over time, this volume overload can cause right ventricular hypertrophy due to increased workload.
The increased pulmonary blood flow also leads to elevated pulmonary artery pressures, which may contribute to pulmonary hypertension if prolonged.
Increased pulmonary circulation results enhanced venous return to the left side of the heart, potentially causing enlargement of the left atrium and ventricle as well.
However, since a significant portion of oxygenated blood recirculates through the lungs rather than being delivered systemically, systemic cardiac output may be reduced despite overall increased cardiac work.
Chronically elevated pulmonary pressures can lead to vascular changes within the lungs, including medial hypertrophy and intimal proliferation within small pulmonary arteries
NB: essentially it causes the blood to take extra trips to the lungs. Therefore is acynanotic (because the blood is oxygenated)
What are the three types of ASD? [3]
Patent foramen ovale, where the foramen ovale fails to close (not strictly classified as an ASD)
Ostium secundum, where the septum secundum fails to fully close
Ostium primum, where the septum primum fails to fully close - doesn’t go all the way down (tends to lead to an atrioventricular septal defect)
Describe the process of atrial septum development [+]
Septum primum develops downwards, in the process makes the ostium primum (first opening)
- This then fuses with endocardial cushion and develops fully
Then second opening develops (ostrium secundum) at the bottom of the septum primum
Then the septum secundum grows downwards, but has a hole called the foramen ovale. This makes a makeshift valve that allows R-> L atrium
During development, oxygenated blood enters the R atrium, which then passes into L atrium to skip the non-needed pulmonary circuit (after development this is deoxygenated)
At birth, the septum primum and secundum fuse shut and form atrial septum
90% of ASD cases are due to the failure of which opening not close
The ostium secundum - the septum secundum doesn’t fuse with the septum primum
Down’s syndrome patients are most likely to suffer from which type of ASD? [1]
Ostium primum
Apart from DS patients, which other population group are likely to suffer from ASDs? [1]
Fetal alcohol syndrome
How would specific areas of the heart have different oxygen saturations in ASDs? [3]
Increased O2 sats in:
- R atrium
- R ventricle
- Pulmonary artery
Describe and explain the murmur heard in ASD [2]
Increased in blood volume in the pulmonary artery causes the pulmonary valve to have a delayed closure (relative to the aortic valve closure)
- splitting of S2 and systolic murmur
What is a paradoxical embolism seen in ASD? [1]
DVT may go into R Atrium and go into L atrium (instead of to the lungs), and enter systemic circulation and therefore lodge e.g. in the brain
TOM TIP: Normally when patients have a deep vein thrombosis (DVT) that breaks away and becomes an embolus, the clot travels through the right side of the heart to the lungs and becomes a pulmonary embolism. With an ASD, the clot is able to travel across the ASD, through the left side of the heart and into the systemic circulation. It can then travel up to the brain, causing a large stroke. An exam question may feature a patient with a DVT who develops a stroke and you have to identify that they have had a lifelong asymptomatic ASD.
Describe the is meant by Eisenmenger syndrome [1]
When the pulmonary pressure exceeds the systemic pressure, blood starts to flow from the right atrium to the left atrium, becoming a right-to-left shunt.
Blood bypasses the lungs, and the patient becomes cyanotic. The change to a right-to-left shunt with the development of cyanosis is called Eisenmenger syndrome.
What are 4 complications of ASD? [4]
Complications
* Stroke in the context of venous thromboembolism (see below)
* Atrial fibrillation or atrial flutter
* Pulmonary hypertension and right-sided heart failure
* Eisenmenger syndrome
Describe the presentation of a patient with an ASD [3]
Atrial septal defects cause a mid-systolic, crescendo-decrescendo murmur loudest at the upper left sternal border. There is a fixed split second heart sound.
- Splitting of the second heart sound is where you hear the closure of the aortic and pulmonary valves at slightly different times
- The pulmonary valve closes later than the aortic valve, causing a split second heart sound that does not vary with respiration.
Detected in antenatal scans or newborn exams
May be asymptomatic in childhood and present w dyspnoea, heart failure or stroke in adulthood
ASD:
TOMTIP: There appears to be a link between [condition] and [type of ASD].
There appears to be a link between migraine with aura and patent foramen ovale.
However, there are no recommendations in the guidelines for testing or treating patients with migraines for a PFO. It is unclear whether testing or treating improves symptoms or outcomes.
Management of atrial septal defect (ASD) requires a comprehensive approach that includes evaluation, decision-making and treatment. The following steps are generally followed:
[3+]
Evaluation
* Echocardiography: This is the primary diagnostic tool for ASD. It provides details about the size, location and number of defects, as well as right ventricular volume overload.
* Cardiac MRI or CT scan: These may be used for further assessment in cases where echocardiographic findings are inconclusive.
* Pulmonary function tests: These can help assess pulmonary hypertension.
Decision-Making
* The decision to close an ASD depends on several factors including the patient’s symptoms, size of the defect, presence of right ventricular enlargement, and evidence of significant left-to-right shunt or pulmonary hypertension.
* Percutaneous closure is preferred over surgical repair if anatomy permits due to its less invasive nature and comparable efficacy.
Treatment
* Percutaneous device closure: This is performed under fluoroscopic and echocardiographic guidance. Devices such as Amplatzer septal occluder or Gore Cardioform septal occluder are commonly used.
* Surgical repair: Indicated when percutaneous closure is not possible due to unfavourable anatomy or associated cardiac anomalies requiring surgery. Open heart surgery using cardiopulmonary bypass is typically performed with direct suture closure or patch placement.
* Medical management: In asymptomatic patients with small defects and no evidence of right ventricular volume overload or pulmonary hypertension, observation with periodic follow-up may be sufficient. Medical therapy may also be required for associated conditions such as arrhythmias or heart failure.
Describe the different categories of congential heart defects
Acyanotic (pink babies) x pulmonary blood flow
- ASD
- VSD
- PDA
Acyanotic x obstruction to flow of ventricles
- Co-arctation of the aorta
Cyanotic x pulmonary blood flow
- Tetralogy of Fallot
Cyanotic x obstruction to flow of ventricles
- Transposition of great arteries
