Assessment of Shunts, Valves, Ventricles, and Great Vessels
Shunt assessment
Two-dimensional imaging and color Doppler localize a shunt, but quantification requires flow data. The pulmonary-to-systemic flow ratio (Qp/Qs) can be calculated from the right and left ventricular outflow tract areas and velocity-time integrals. Area is πr², so diameter measurement errors are squared and magnified. Qp/Qs assumes circular orifices, stable flow, and no additional shunts. A ratio near 1 indicates no significant shunt; a ratio above about 1.5 suggests a hemodynamically important left-to-right shunt.
Valves, ventricles, and great vessels
Valve assessment includes peak and mean gradients, continuity-equation valve area, pressure half-time, and regurgitant jet characteristics. Ventricular assessment includes dimensions indexed to body surface area, fractional shortening, ejection fraction, tricuspid annular plane systolic excursion, and strain. Great-vessel assessment includes aortic arch sidedness, branch pulmonary arteries, isthmus dimensions, and ductal anatomy. Measurements in children are best interpreted as z-scores for body surface area.
Traps
Do not calculate Qp/Qs from a single diameter or from a non-perpendicular image. Do not compare a child's raw ventricular dimension to an adult normal range. Do not equate a high gradient with severity when flow is low. Do not confuse a shunt murmur with valve regurgitation.
Rule of thumb
Qp/Qs = (RVOT area × RVOT VTI) ÷ (LVOT area × LVOT VTI) when no other shunt is present.
Worked example
RVOT diameter 2.0 cm gives an area of 3.14 cm² and VTI 15 cm, so Qp is 47.1. LVOT diameter 1.8 cm gives an area of 2.54 cm² and VTI 18 cm, so Qs is 45.7. Qp/Qs is about 1.03, indicating no significant shunt.