Clinical application of radionuclide quantitation of left to right cardiac shunts in children

The results of 341 radionuclide studies, using the method of Maltz and Treves to quantify left to right shunts, were reviewed to evaluate Its clinical usefulness in routine practice. In 245 children in whom a shunt was suspected, 140 were shown to have shunts at cardiac catheterlzatlon, the pulmonary to systemic blood flow ratio ($\text{Q}\text{?}\text{p}\text{Q}\text{?}\text{s}$) being greater than 1.15 in 121. In 92 of 105 normal children, the ratio was less than 1.05. Nineteen children with a shunt had a ratio in the borderline range of 1.05 to 1.15 as did 13 normal children. Only one normal child had a $\text{Q}\text{?}\text{p}\text{Q}\text{?}\text{s}$ ratio greater than 1.10 whereas seven children with a shunt had a ratio of less than 1.10, including one with a ratio of less than 1.05. A highly significant correlation (r = 0.71) existed between the shunt sizes estimated with the radionuclide method and with oximetry. However, in 10 of these patients a small shunt shown with the radionuclide method was not detected with oximetry but observed on indocyanine green dye curves. In 41 children, therefore, shunt size measured with the radionuclide method, oximetry and indocyanine green dye curves was compared. The correlation of shunt size was comparable with the three techniques. The radionuclide estimation is therefore considered to be more sensitive than oximetry in the detection of small shunts. The procedure was also valuable in 96 children studied after cardiac surgery; a $\text{Q}\text{?}\text{p}\text{Q}\text{?}\text{s}$ value greater than 1.15 was present in 17 children, 12 of whom have to date been shown to have a residual shunt.