Anatomical classification of defects
Depending on the exact location of the abnormal opening in the septum, several types of the defect are distinguished:
- Secundum ASD (secundum ASD) is the most classic variant, located in the area of the fossa ovalis.
- Primum ASD (primum ASD) is located in the lowermost part of the atrial septum and directly abuts the atrioventricular valves.
- Sinus venosus defect can be superior (superior) or inferior (inferior). The superior defect is characterized by an associated anomaly: partial anomalous pulmonary venous drainage. In this case, the right upper and middle pulmonary veins straddle (straddling) the defect, communicating with both atria simultaneously.
- Coronary sinus defect.
Capabilities of MRI in diagnosis and hemodynamic assessment
Magnetic resonance imaging plays a crucial role in preparation for intervention, especially when vascular anatomy is difficult to distinguish. Multislice 2D gradient echo techniques and 3D isotropic resolution scanning help to assess the morphology of the defect in detail.
In the b-SSFP mode, dilation of the right atrium and right ventricle is clearly visualized. Volume overload of the right ventricle leads to characteristic flattening of the interventricular septum.
A key tool for hemodynamic assessment is velocity-encoded phase-contrast MRI. When plotting the volumetric blood flow graph, the physician observes that the flow curve in the main pulmonary artery significantly exceeds the corresponding curve in the aorta. This confirms a significant left-to-right shunt. The method is as accurate as invasive catheterization, but carries no ionizing radiation.
Atrioventricular septal defects (AVSD)
AVSD occurs due to underdevelopment of the tissues separating the atrial and ventricular chambers (primum septum, inlet portion of the interventricular septum). The main feature of the pathology is a common atrioventricular junction with a common five-leaflet valve. In this condition, the normal offset of the tricuspid and mitral valves relative to each other is lost.
The classification of AVSD includes three forms:
- Complete form: a combination of ASD, ventricular septal defect (VSD), and a single valve orifice.
- Intermediate form: presence of a VSD with two formed valve orifices.
- Partial form: presence of an ASD only (ostium primum type) and two valve orifices (forming separate left and right AV valves).
AVSD is frequently associated with Down syndrome (trisomy 21), and postoperative mortality in this patient group is lower than in children without this syndrome.
Main goals of diagnostic imaging
The surgeon is faced with the task of choosing the optimal correction strategy (e.g., biventricular), for which the radiologist must evaluate:
| Imaging task | Key parameters evaluated |
|---|---|
| Defect anatomy | Location, diameter, size of rims for occluder fixation |
| Hemodynamics | Quantitative assessment of the left-to-right shunt |
| Ventricular status | Proportions (balance), function, and volume of the right-sided chambers |
| Complications | Search for signs of pulmonary vascular resistance (right ventricular hypertrophy, notching of the pulmonary artery flow curve) |
To differentiate AVSD forms by orifices: Complete = 1 common orifice (plus ASD and VSD). Intermediate and partial = 2 separate valve orifices.
Class and exam questions
Why is it important to measure defect rims on MRI?
The size of the rims (margins) determines the suitability of the defect for minimally invasive treatment. If the posterior rim is absent, transcatheter occluder fixation is impossible.
At what age is surgical correction of AVSD performed?
Surgery must be performed at 3–4 months of age, maximally up to 6 months. This is critically important to prevent the development of pulmonary vascular disease.
Which MRI findings indicate high pulmonary vascular resistance?
Such signs include right ventricular hypertrophy, systolic flattening of the interventricular septum, and a characteristic notching of the pulmonary blood flow curve.
What is the essence of the partial form of AVSD?
The partial form of AVSD is also referred to as a primum ASD (ostium primum type). It presents solely with an atrial septal defect, while the AV valve has two separate orifices.
What else to study on this topic
- Features of 3D cardiac scanning techniques with isotropic resolution for precise multiplanar reconstruction.
- Application of phase-contrast MRI to detect fenestrated and multiple defects.
- Associated anomalies in unbalanced AVSD: Tetralogy of Fallot, subaortic stenosis, and atrial appendage isomerism.
- Assessment of atrioventricular valve regurgitation in the long-term postoperative period.
- Analysis of the notching form of the pulmonary blood flow curve as a marker of pulmonary hypertension.
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