CARDIO MODULE

Atrial Septal Defects (ASD) are one of the most common congenital heart diseases diagnosed in paediatrics and adults, accounting for around 5-12% of all congenital heart diseases and 25-30% of all adult diagnoses. 

There are four main types of ASD, and only the first two types are true ASD’s. 

1. Secundum (80%) 
2. Primum (15%) 
3. Coronary Sinus (1%)
4. Sinus venosus (5-6%) 

Secundum ASD defects account for over 80% and are located within the fossa ovalis, as can be seen in the image below. 

A cardiac shunt defines an abnormal connection that allows blood to flow directly from the left to the right side of the heart and vice versa, depending on the conditions, and the severity depends on the volume of shunted blood and the size of the defect. 

Echocardiography remains the modality of imaging for diagnosis. Within Nova Heart, we reconstruct the ASD from a 2D transthoracic echocardiogram and provide a sophisticated intracardiac hemodynamic model to understand in detail the interplay of echocardiogram parameters and pathophysiological consequences.
AtrialSpetalDefect-img1
An example of a patient with an Atrial Septum Defect(ASD)

3D visualization

Within Nova Heart, we provide a key input parameter for the intra-cardiac hemodynamics model called ASD Factor. This novel parameter is calculated from the relationship between the ASD area and the whole intra-atrium septum area. The ASD area itself is calculated using data from echocardiogram measurements, including ASD rims.
Parameter Name
Parameter Description
IAS_BIC
Total intra-atrial septum in bicaval view
ASD_IVC
Distance of the rim from ASD to inferior vena cava
ASD_BIC_DEF
Diameter of Atrial Septal Defect in bicaval view
ASD_SVC
Distance of the rim from ASD to superior vena cava
IAS_4CH
Total intra-atrial septum in 4 CH
ASD_CC
Distance of from the rim ASD to Crux cordis
ASD_4CH_DEF
Diameter of Atrial Septal Defect in 4 chamber view
ASD_RO_4CH
Distance of the rim ASD to atrial roof in 4 chamber view
IAS_PS
Total intra-atrial septum in PSAX
ASD_AO
Distance rim ASD - Aortic root
ASD_PSAX_DEF
Diameter of the Atrial Septal Defect in PLAX view
ASD_RO_PS
Distance of rim from ASD to Atrial roof in PSAX
AtrialSpetalDefect-img2

Below are examples of different types of ASD depending on the key parameters

AtrialSpetalDefect-img3-1
AtrialSpetalDefect-img3-2
AtrialSpetalDefect-img3-3
The guidelines recommend diagnosing an ASD by demonstrating the shunt across the interatrial septum, with evaluation of the right heart and for associated abnormalities using 2D transthoracic echocardiography (2D TTE). 

The components of a comprehensive echocardiographic evaluation are shown in the table.


Elements of a comprehensive echocardiographic evaluation for ASD.2

Visualization of ASD and characterization of its size

Determination of the direction of flow

Evaluation for associated abnormalities*

Examination of right heart

Quantification of pulmonary artery pressure

Estimation of the pulmonary/systemic flow ratio

The echocardiogram images below show this interatrial septum communication and demonstrate this shunt.
The color Doppler image shows the flow from the left atrium(LA) to the right atrium(RA) in red.2

Two-dimensional echocardiogram (four-chamber view) of a large secundum atrial septum defect(ASD)(arrow). The right atrium(RA) and right ventricle(RV) are larger than the left atrium(LA) and left ventricle(LV).2

Hemodynamics

Initially, an atrial septal defect(ASD) allows a left to right shunt (oxygenated blood from pulmonary veins and left atrium enters right atrium) which in turn causing right atrium, right ventricle and pulmonary artery dilatation. Eventually these changes lead to pulmonary hypertension and pulmonary vascular obstruction (Eisenmenger reaction), and an increase right atrial pressure that results in the shunt changing from Right to Left. This results in systemic desaturation and cyanosis.
Below within NovaHeart are two ASD pathology’s of different severity. We can compare the changes in hemodynamics based upon the patient specifics defects
The graphs and the heart model show that changes depend on the degree of our ASD factor and how these change the volume and pressure relationships.

In normal cardiac anatomy, oxygenated and deoxygenated blood is separated by the septum of the heart, with pulmonary and systemic circulations running in parallel.

In healthy patients, a 1 to 1 volume relationship is maintained between the left and right-sided chambers of the heart. The deoxygenated blood is pumped to the lungs from systemic venous return, and we call this pulmonary blood flow (Qp). The oxygenated blood from the lungs is pumped through to the systemic circulation, and we call this the systemic blood flow (Qs). We can measure the ratio of Qp/Qs, and in normality, it equals one.

Additionally, the cardiac output, defined as the amount of blood flow per minute, has a 1:1 relationship in normality.
In patients with ASD, the Qp/Qs ratio increases as more blood volume flows through the pulmonary circulation than systemic circulation. In patients with severe forms of ASD, this Qp/Qs can be higher than 1.5, as can be seen in the right-side images.

By changing the ASD factor and the anatomy of the defect, we can see how this influences the Qp/Qs ratio within Nova Heart using our haemodynamic model. This is a multifactorial relationship, including age, size of defect and shunt volume size, can influence the Qp/Qs ratio.
This graph shows the multifactorial relationship between predicted Qp/Qs ratio and ASD Size.7
In the graphs above, we can see the volume and pressure changes in four chambers on the graphs.

In the milder forms of ASD (left to right), there is a decrease in volume and pressure in the left atrium and left ventricle and a corresponding increase in volume and pressure in the right atrium and ventricle.

As the severity of the ASD increases, reverse shunting occurs where the right-sided pressures are increased; we can see on the right-hand side images the volume and pressure changes are increased because of the larger defect.

Within our model, we also provide the ASD total shunt volume over the cardiac cycle and the shunt volume in systole, as can be seen in the diagram above, to quantify more accurately the severity of the defect.

References:

  1. Park IS, Goo HW. In: Park IS, editor. An Illustrated Guide to Congenital Heart Disease: From Diagnosis to Treatment – From Fetus to Adult. Singapore: Springer; 2019;2: 17–32.
  2. Martin SS, Shapiro EP, Mukherjee M. Atrial Septal Defects – Clinical Manifestations, Echo Assessment, and Intervention. Clin Med Insights Cardiol. 2014;8(Suppl 1): 93–98.
  3. Van Praagh Richard. Congenital heart disease: a clinical, pathological, embryological, and segmental analysis. 1st ed. Philadelphia: Elsevier; 2023.
  4. Camm J, Luscher, TF, Serruys PW. The ESC Textbook of cardiovascular medicine. 2nd ed. Oxford: Oxford University Press; 2009.
  5. Themes UFO. Shunt Detection and Quantification [online]. Thoracic Key; 2016 [Accessed 20 October 2023].
    Available from: https://thoracickey.com/shunt-detection-and-quantification/
  6. Denise Nedea. Qp/Qs Ratio Calculator [online]. MDApp; 2020 [Accessed 2023 Oct 20]. Available from: https://www.mdapp.co/qp-qs-ratio-calculator-508/
  7. Kurishima C, Inuzuka R, Kuwata S, Iwamoto Y, Sugimoto M, Saiki H, et al. Influence of Left Ventricular Stiffness on Hemodynamics in Patients With Untreated Atrial Septal Defects. Circulation. 2015;79(8):1823–7.
  8. Brida M, Chessa M, Celermajer D, Li W, Geva T, Khairy P, et al. Atrial septal defect in adulthood: a new paradigm for congenital heart disease. European Heart Journal. 2022 Jul 21;43(28):2660–71.
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