This is clearly a case of ASD, as the entire right heart is dilated. Calculating the shunt ratio will give the sonographer an idea as the severity of the lesion, which in turn decides treatment.
So, here we have the outflow tract diameters and the flow across each valve. This should help calculate the cross-sectional area as follows
Cross-sectional area (CSA) = 𝚷 x (D/2)2
where 𝚷 = 3.14, and D is the outflow tract diameter.
Hence
CSA RVOT = 3.14 x (2.4/2)2 = 3.14 x 1.44 = 4.5 cm2
CSA LVOT = 3.14 x (2.3/2)2 = 3.14 x 1.32 = 4.2 cm2
So now, calculate the flow across the valve.
Pulmonic flow (QP) = CSA RVOT x RVOT vti = 4.5 x 33 = 148.5 cm3
Systemic flow (QS) = CSA LVOT x LVOT vti = 4.2 x 19 = 79.8 cm3
Finally, the ratio QP:QS = 148.5/79.8 = 1.9
Given the right heart dilatation, symptoms and shunt ratio > 1.5, closure either with a device or surgically is indicated.
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