← Section IV · Congenital Heart Disease

IV.E

Doppler Estimation of Volumetric Flow

5 cards

Notes

Shunt flow - Qp:Qs

$Q_p:Q_s = \frac{CSA_{PV} \times VTI_{PV}}{CSA_{LVOT} \times VTI_{LVOT}}$

Qp:Qs > 1.5 = hemodynamically significant left-to-right shunt.
Qp:Qs > 2 in unrepaired ASD/VSD strongly favors closure (in absence of Eisenmenger physiology).
Qp:Qs < 1 suggests reversed (right-to-left) shunt.

Direct visualization of shunts

VSD: color Doppler across the septum (mosaic, high-velocity). Small restrictive VSDs have high velocity gradient (LV pressure ≫ RV pressure). Large unrestrictive VSDs equalize pressures → low-velocity flow.
ASD: color Doppler across the atrial septum, usually low-velocity. Best on subcostal view (perpendicular to septum). Agitated saline for bubble study (right-to-left shunt).
PDA: color Doppler in the descending aorta showing continuous flow into the PA at the level of the left pulmonary artery origin.

Pressure gradient across a shunt

ΔP = 4v² (modified Bernoulli).
Small restrictive VSD: peak systolic v ~4–5 m/s → ΔP ~80–100 mmHg → LV-RV pressure difference.
Large unrestrictive VSD (Eisenmenger): pressures equalize → low velocity.

RV pressure from a VSD jet

RV systolic pressure = SBP (LV systolic) − (4 × VSD peak velocity²).
Requires no LVOT obstruction.

Pulmonary vein flow in ASD

With significant L-to-R shunt: increased pulmonary venous return, dilated pulmonary veins.

Qp:Qs from oximetry (invasive, cath lab)

Qp:Qs = (SaO₂ − MVO₂) / (PVO₂ − PAO₂), where MV = mixed venous saturation, PV = pulmonary vein.

Cards

basicIV.E-001
State the echo formula for Qp:Qs.
→ Qp:Qs = (CSA_pulmonic × VTI_pulmonic) / (CSA_LVOT × VTI_LVOT).
basicIV.E-002
State the Qp:Qs threshold generally considered hemodynamically significant and the threshold favoring closure.
→ Hemodynamically significant > 1.5. Closure typically indicated at > 2.0 in unrepaired ASD/VSD (in absence of Eisenmenger physiology).
basicIV.E-003
How does peak flow velocity across a small restrictive VSD compare to a large unrestrictive VSD?
→ Small restrictive: HIGH velocity (~4–5 m/s), reflecting the large LV-RV systolic pressure difference. Large unrestrictive: pressures equalize → LOW velocity across the defect.
basicIV.E-004
Estimate RV systolic pressure from a VSD jet.
→ RVSP = systolic BP − (4 × VSD peak velocity²), assuming no LVOT obstruction. E.g., BP 120, VSD peak 4 m/s: RVSP = 120 − 64 = 56 mmHg.
basicIV.E-005
What color Doppler finding on the pulmonary artery suggests a PDA?
→ Continuous flow from the aorta into the pulmonary artery near the origin of the left PA. Best appreciated in the parasternal short-axis view of the great vessels and suprasternal notch view.