Quantitative radionuclide angiocardiography for left-to-right cardiac shunts in children.

Pulmonary to systemic flow ratios (Qp/Qs) were estimated by quantitative radionuclide angiocardiography (QRAC) in 135 children. The Qp/Qs ratios were derived from pulmonary time/activity curves using a gamma variate model. Eighty-five of these children also had Qp/Qs ratios estimated by oximetry at cardiac catheterization. Left-to-right shunts with a Qp/Qs range of 1.2 to 3.0 were detected and quantitated by radionuclide angiography with an accuracy similar to that for oximetry. The correlation between Qp/Qs, determined by QRAC and by oximetry was good (r = .93; SEE .31). This relatively noninvasive technique has now been used to estimate the Qp/Qs ratio in 34 children with a clinically suspected left-to-right shunt, and postoperatively in 16 cases with residual murmurs; it has obviated the need for catheterization in many of these patients. The technique may also be used serially to determine changes in the Qp/Qs ratio in patients with known left-to-right shunts.