First-pass radionuclide angiocardiography in the determination of left-to-right cardiac shunt site in children.

To ascertain if the level of a left-to-right cardiac shunt can be reliably established by first-pass radionuclide angiocardiography with 99mTc-pertechnetate, 102 children have been studied; 19 without a shunt, 26 with an atrial septal defect (ASD), 45 with a ventricular septal defect (VSD), and 12 with a patent ductus arteriosus (PDA). Time-activity curves were generated over the right atrium and ventricle, and several quantitative parameters were derived from the curves. It was concluded that in the absence of right-sided valvular incompetence, the time-activity curves show the greatest abnormality in the cardiac chambers distal to the left-to-right shunt. The right ventricular curve is typically altered in ASD but cannot be relied upon to differentiate VSD or PDA. The identification of ASD is assisted by the use of two of the parameters, the count ratio C4:C1 and time ratio T2:T1.