Detection of intracardiac shunts with radionuclide imaging

Abstract

Cardiac catheterization for the performance of contrast angiography is accepted presently as method for the demonstration of intracardiac shunts in children and adults. The procedure is an essential part of the presurgical workup. Cardiac angiography requires a skilled team of pediatric cardiologists, radiologists, technical personnel, and excellent equipment; consequently, it is a time consuming and expensive procedure. In addition, cardiac catheterization is not without risk, and is particularly hazardous in the cyanotic newborn. The use of the angiographic contrast medium provides additional hazards. Prior to the development of the Anger camera, the precordial radiocardiogram was the major nuclear medicine technique used for the diagnosis of intracardiac shunts. Scintillation probes, well counters, strip-chart recorders, and, occasionally, cardiac catheterization were required to perform the radiocardiogram. It was a time consuming procedure. Pulmonary dilution curves were also used for the diagnosis of intracardiac shunts. Although various types of intracardiac shunts could be detected with these two types of dilution curves, no satisfactory method of accurate shunt quantitation was developed. After adequate experience was obtained with the Anger camera, radionuclide angiocardiography became a major investigative technique in nuclear medicine for the diagnosis of intracardiac shunts. The technique has several potential technical and clinical advantages over heart catheterization and contrast angiography. These advantages are (1) there is no need for withdrawal of arterial or venous blood, (2) it can be performed simply and quickly, (3) it requires only an intravenous bolus injection, (4) it is reliable in all age groups, (5) it may be performed in patients who are sensitive to cardiographic agents or in those too ill to undergo heart catheterization and contrast angiography, and (6) its risks to the patient are negligible. Characteristic nuclide flow patterns and images have been demonstrated in patients with left-to-right and right-to-left intracardiac shunts. Techniques for the quantitation of shunts employing nuclide angiocardiography are being developed.