A New Technic for the Detection of Left-to-right Cardiac Shunts by Use of an Esophageal Geiger-mueller Tube.

THE left-to-right shunts found in small atrial or ventricular septal defects or in patent ductus arteriosus are easily demonstrated during cardiac catheterization by both rightand left-sided approaches.' Efforts to evaluate shunting due to these defects without cardiac catheterization have depended on measurements of the cardiac output curves obtained by various external counting technics.Y Because the external monitoring sites are relatively distant from the circulating radioisotope, the descending slope of the curve is influenced by factors other than the shunt itself.8 In an attempt to de-emphasize these extraneous factors a new approach has been developed utilizing the esophagus as an avenue for positioning a miniature Geiger-Muller tube as a detector immediately adjacent to the left atrium and much closer to the radioisotope circulating through the heart. Radioisotope curves then monitor recirculation shunts in more concentrated form from the left atrium than from externally placed precordial, pulmonary, or peripheral counters.