ASD: Echo-Diagnosis of Types and Shunt Volume Assessment Qp/Qs

Definition and Pathophysiology

Atrial septal defect (ASD) is a defect leading to the presence of flow (shunt) between the atria (Blagodir B.V., 2024). The presence of an intracardiac shunt is one of the causes of volume overload, which increases preload. A similar mechanism is characteristic of valve regurgitation, ventricular septal defect (VSD), and patent ductus arteriosus (PDA).

Increased preload due to volume overload leads to chamber dilation, which is an important indirect echographic sign of a hemodynamically significant shunt.

Echo Visualization of the Shunt

The septal defect is defined as an opening in the atrial/ventricular septum, leading to the presence of a shunt. Color Doppler mapping (CFD) is used to display flow.

The manifestation of flow in CFD directly depends on several factors (Blagodir B.V., 2024):

• quality of 2D imaging: the higher the quality in 2D, the better the flow display in CFD;
• the specialist's choice of color map — velocity map or variance map.

Types of Defects and Anatomy Clarification

The classification of anatomical types of ASD itself is not provided in the source fragments [clarify]. The fragments present types of Gerbode defect (LV–RA communication): type 2 (supravalvular/direct) — direct communication between the LV and RA through the upper part of the membranous septum above the tricuspid valve, the most common variant; type 3 (intermediate) — a combination of supra- and infravalvular defects, the least common (Manual of Echocardiography for Congenital Heart Diseases, 2024).

When assessing the membranous septum, aneurysmal accessory tissue associated with the tricuspid valve and/or aneurysm of the membranous septum may be identified, leading to variable TR and/or shunting from the LV to the right atrium. Aneurysms of the membranous septum may contain multiple defects, which are difficult to delineate individually due to the hypermobility of the thin tissue (Hahn R.T., Saric M. et al., 2022).

The Role of Transesophageal and 3D Echocardiography

The atrial septum is easily visualized in biplane 3DE modes. 2D and 3D TEE are also used to monitor the passage of a balloon catheter through the atrial septum during transseptal interventions (Pandian N.G. et al., 2023).

Calculation of Qp/Qs

The specific method for calculating the pulmonary to systemic flow ratio (Qp/Qs), formulas, and threshold values for the hemodynamic significance of the shunt are not provided in the source fragments [clarify]. General limitations of Doppler quantitative assessment should also be considered, including an unfavorable angle θ >20° between the ultrasound beam and the direction of blood flow and limitations of the simplified Bernoulli equation (Mukherjee M., Rudski L.G. et al., 2025).