Comprehensive and Detailed Explanation From Exact Extract:
The Qp/Qs ratio represents the ratio of pulmonary blood flow (Qp) to systemic blood flow (Qs). It is commonly calculated to quantify the magnitude of a left-to-right shunt in congenital heart disease.
To calculate Qp/Qs using echocardiography, stroke volumes across both the pulmonary and systemic outflow tracts are measured by combining the cross-sectional area of the outflow tract and the velocity time integral (VTI) of flow through it.
Pulmonary blood flow (Qp) is calculated using the right ventricular outflow tract (RVOT) diameter and RVOT VTI. Systemic blood flow (Qs) is calculated using the left ventricular outflow tract (LVOT) diameter and aortic valve VTI.
Thus, RVOT VTI is essential for Qp calculation, making option D correct.
This method is explained in detail in the "Textbook of Clinical Echocardiography, 6e", Chapter on Congenital Shunts and Quantification of Flow【20:360-365†Textbook of Clinical Echocardiography】.
