A 12 mm ASD, a Dilated Right Ventricle and a Qp/Qs of 1.4

Calculation: Qp = pi x (0.6)^2 x 13 = 1.131 x 13 = 14.7 mL/beat. Qs = pi x (0.5)^2 x 13 = 0.785 x 13 = 10.2 mL/beat. Qp/Qs = 14.7/10.2 = 1.44, i.e. 1.4.

The discrepancy is expected and is the crux of the case. A Qp/Qs of 1.4 is only modestly above normal, yet the RV is dilated and the pulmonary artery is bigger than the aorta - findings that imply a larger shunt. The reasons:

• Diameter error dominates. Area varies with the square of the radius. At an RVOT of 1.2 cm, a 1 mm error alters the pulmonary area by roughly -16% or +17% and moves Qp/Qs by about 0.25 in each direction. Two such errors in opposite directions easily turn 1.9 into 1.4.
• The RVOT is a poor measurement site. It is distensible, changes diameter through systole, and in the presence of an ASD its flow profile is distorted by the shunt stream.
• Shunt flow itself is not measured. Any error in the assumed flows is not corrected by the shunt jet velocity - the 1.0 m/s across the defect simply reflects a 4 mmHg interatrial gradient.
• Doppler Qp/Qs is least reliable at small shunt fractions, which is exactly the borderline range where the decision matters.

So the number and the morphology are telling different stories, and I would not let the number overrule the anatomy.

Supporting significance:

• RV basal dimension of 3.4 cm against an LV of 3.6 cm - an RV/LV ratio near 0.95, well above the normal paediatric value of roughly 0.7-0.8, and RV dimensions should be indexed to body surface area and expressed as z-scores.
• Right atrial dilation and a main pulmonary artery larger than the aorta.
• Diastolic septal flattening or a 'D-shaped' LV in diastole, indicating RV volume loading rather than pressure loading.
• A colour jet width that is a large fraction of the defect diameter, and a defect large enough that it is unrestrictive by inspection.
• Normal or only mildly elevated RVSP (26 mmHg) fits a high-flow, low-resistance shunt rather than pulmonary vascular disease.

Arguing against:

• A small, restrictive defect with a narrow colour jet and a high trans-defect velocity gradient.
• Normal RV and RA dimensions when indexed to BSA, and normal septal motion.
• An alternative explanation for RV dilation - pulmonary regurgitation, a sinus venosus defect with anomalous pulmonary venous drainage, or pulmonary hypertension.

In a child whose RV is dilated but whose Doppler shunt fraction is borderline, the morphology of volume loading is the more reliable signal.

Not on these data alone - this is borderline and needs one more measurement, not a decision.

Reasoning: the accepted threshold for closing an asymptomatic secundum ASD is Qp/Qs of about 1.5 or greater together with right heart enlargement, or documented right heart enlargement with a shunt fraction that is not clearly trivial. Here we have the enlargement but a shunt fraction of 1.4 that sits inside the measurement error of the technique. A 12 mm defect in a 7-year-old is unlikely to close spontaneously, so the question is timing rather than whether, but an unnecessary or premature closure in a truly small shunt has its own consequences.

Next steps:

• Repeat the Doppler measurement with the RVOT diameter taken in mid-systole at the annulus with inner-edge-to-inner-edge technique, averaging 3-5 beats, and quote a range rather than a single figure.
• Confirm the defect subtype - exclude a sinus venosus defect with partial anomalous pulmonary venous return, which a transthoracic study can miss and which changes the operation.
• If the decision remains unclear, obtain cardiac MRI (or a shunt study at catheterisation) for direct measurement of RV end-diastolic volume index and shunt fraction.
• Proceed to closure if RV end-diastolic volume index is more than 2 SD above normal or MRI confirms Qp/Qs of 1.5 or greater; otherwise follow with serial imaging, since the child is asymptomatic and growing.