Qp/Qs
The pulmonary to systemic flow ratio from outflow tract diameters and VTIs, for ASD, VSD and PDA.
Doppler volumetric method
How it's calculated
Formula
Flow = π × (diameter ÷ 2)² × VTI, diameter in cm (mm ÷ 10) ASD or VSD: Qp/Qs = RVOT flow ÷ LVOT flow PDA: Qp/Qs = LVOT flow ÷ RVOT flowReading the ratio
- 0.9 to 1.2: no significant shunt.
- 1.2 to 1.5: small shunt.
- 1.5 to 2.0: significant shunt; with RV volume overload, closure is usually considered.
- 2.0 or more: large shunt.
- Below 0.9: net right-to-left shunting, or a measurement error.
The diameter is squared, so a 1 mm error changes the ratio by about 10%. Average several beats, and repeat the RVOT diameter in more than one view.
For education and as a reporting aid. A result supports the reading of the full study and does not replace it.