Atrial Septal Defects Flashcards
ASDs: General Info
- Communication between LA and RA
- Accounts for 10% of all CHDs
- Shunt usually L-R (LAP > RAP)
- Dilatation of high heart (increased volume of blood to right side of heart)
Emybyological contribution of which structures form the IAS?
- Primum atrial septum
- Secundum atrial septum
- Endocardial cushions
Contribution of premium atrial septum in forming IAS?
- First atrial septum to form
- Arises from roof of the atrium and grows inferiorly towards the endocardial cushions
Contribution of secundum atrial septum in forming IAS?
- Grows from roof of atria and overlaps with primum septum
- Doesn’t grow far enough to lose opening = forming foramen ovale
Contribution of endocardial cushions in forming IAS?
- Before primum fuses with cushions, septum is performed in upper part forming foramen secundum
What is the importance of the foramen ovale in foetal circulation?
- Remains open until birth to allow oxygenated blood to be shunted to rest of the body
- Allows blood supply to the LA
Overview of foetal circulation?
- Oxygenated blood from maternal placenta travels to foetal heart via the IVC
- Within RA, majority of oxygenated blood shunted across foramen ovale with help of Eustachian valve
- Oxygenated blood in RA travels to LV and aorta, and to foetal brain
Modifications of Sinus Horns throughout development?
- Progressive enlargement of right sinus horn develops into SVC and IVC
- Regression of left sinus horn contributes to formation of coronary sinus
What are the types of ASDs from most to least common?
- Osmium secundum ASD (80% of all ASDs)
- Ostrium primum ASD (15% of all ASDs)
- Sinus Venosus (SV) ASD
a. Superior SV ASD 5-10%
b. Inferior SV ASD 2% - Coronary Sinus (CS) ASD (<1%)
Secundum ASD location?
- Fossa ovalis
- Seen towards top of atria
- Difficult to identify when IAS orientated parallel to u/s beam due to drop out of septum
Cause of secundum ASD?
- Excessive cell death or inadequate development
- Reabsorption of septum premium
- Or inadequate development of septum secundum
Location of primum ASD?
- Inferior portion of atrial septum near primitive foramen primum
- Inferior atrial septum near the cardiac crux
Cause of primum ASD?
- Failure of primum septum to fuse with the endocardial cushion
- Or deficiency of endocardial cushion tissue
What are the two types of sinus venosus ASD?
- Superior SV ASD
- Inferior SV ASD
How to sinus venosus ASDs occur?
Defects result from maldevelopment of the sinus venosus and sinus horns
Where is the superior SV ASD located?
- Located near SVC
- Accounts for 5-10% of all ASDs
Associated lesion with superior SV ASD?
Anomalous PVD (pulmonary venous drainage); RUPV to RA
Where is the inferior SV ASD located?
- Located near IVC
- Rare, accounts for around 2% of all ASDs
Associated lesion with inferior SV ASD?
Anomalous PVD; RLPV to RA
Cause of coronary sinus ASD?
- Occurs when improper development of wall of CS, so CS communicates directly with the LA
- Defect in CS wall may be fenestrated or totally absent/unroofed
- Communication from LA to CS to RA
Best views for identifying secundum ASD on echo?
- Best views where IAS perpendicular to ultrasound beam
- Subcostal 4 chamber
- Subcostal SAX
- When defect is large, also seen from PSAX
Best views for identifying primum ASD on echo?
- Apical 4 chamber best view as this nicely shows the cardiac crux
- Subcostal 4 chamber
- PSAX - inferior portion of IAS
Best views for identifying sinus venosus ASD on echo?
- Located superiorly so marked anterior tilting required
- Seen in apical 5 chamber
- Difficult to see from 2D echo alone, CFI useful (flow from RUPV/RLPV into RA)
Best views for identifying coronary sinus ASD on echo?
- Difficult to detect with TTE in adult patients
- Apical and subcostal 4 chamber with posterior tilt
Clues to coronary sinus ASD?
- Dilated CS in apical view but not in PLAX: occurs as CS is unroofed therefore typical circular appearance in PLAX not present
- “Prominent” flow within dilated CS: flow from CS into RA is seen
How to measure size of ASD?
- Measure size with 2D echo
- CFI useful to delineate boarders
- Should be measured in at least 2 orthogonal planes as they are often oblong or elliptical in shape
Normal ASD shunt direction?
- Shunting usually from LA to RA as LAP > RAP
- Marked increase in right heart pressures means shunting may be bidirectional, reversed or abolished
What is Eisenmenger’s Syndrome?
Long-standing, significant L-R shunting at any level causing PHTN and secondary pulmonary vascular disease = reversal of shunt resulting in cyanosis
Indication of ASD with a haemodynamically significant shunt?
- Dilatation of right heart chambers due to increased volume of blood being shunted into the RA and RV
- RV volume overload; abnormal septal motion, D-shaped septum
Significance of Relative Atrial Index (RAI) in predicting if patient has ASD?
- RAA:LAA
- RAI > 0,92 predicts patients with ASDs
What is the QP:QS ratio?
Calculates ratio of pulmonary venous flow (QP) to systemic venous flow (QS)
What is QP?
- Pulmonary venous volume to or from lungs
- SV RVOT (can also be calculated from TV or MPA)
- QP = 0.785 x d^2 x RVOT VTI
What is QS?
- Systemic volume to or from the body
- SV LVOT (can also be calculated using MV or ascending aorta)
- QS = 0.785 x d^2 x LVOT VTI
What QP:QS shunt ratio is haemodynamically significant?
QP:QS > 1.5:1
Calculating RVSP in ASDs?
Performed in usual way, RVSP = 4 x VTR^2 + RAP
Associated lesions with osmium primum ASD?
- “Cleft” anterior mitral valve leaflet (amvl looks like two hands clapping)
- Atrioventricular canal defect (AVCD)
Associated lesions with osmium secundum ASD?
Usually isolated; however MVP and/or PS may be present
Associated lesions of coronary sinus ASD?
- Persistent left SVC
- To confirm, image left SVC from supraclavicular fossa; normally should not be able to see vertical vein draining down
