-Diagnostic shunt oximetry of atrial septal defect in adulthood-

There are several circumstances in which data obtained at catheterization should alert the cardiologist to look for a shunt that had not been suspected previously. Aim of the study was to explore the most sensitive parameter which is easily practicable and which gives strong evidence for an atrial septal defect (ASD). Moreover, a simplified method for quantifying left-to-right shunts was analyzed. In 84 patients (58 with an atrial septal defect and 26 patients without shunt) a complete oxygen saturation status was determined. The oxymetrically determined relation between pulmonary bloodflow QP and systemic bloodflow QS was 1.31 to 5.60 in patients with ASD and 0.75 to 1.19 in patients without shunt. The analysis of sensitivity and specificity was determined to define the marginal value which gives suspicion of an ASD. The best values for sensitivity and specificity was found for PA O2-SVC O2 = 7.4% (sens. = 98.3%, spec.= 96.2%), PA O2 -IVC O2 = 2.0% (sens./spec.= 100%), PA O2 - MV O2 = 5.0% (sens./spec.= 100%) and PA O2 = 78.4% (sens./spec. = 97.5%). The correlation between the modified ratio QP/QS and various differences in O2-saturation with the shunt size was examined. A high correlation was found for the modified QP/QS with SVC O2 instead of MV O2 (r = 0.98), PA O2-SVC O2 (r = 0.77) and PA O2 - MV O2 (r = 0.74) with QP/QS, respectively.

The results demonstrate that an O2-saturation >78% in the pulmonary artery is highly suspicious for the diagnosis of an ASD. With the modified ratio QP/QS = (ART O2-SVC O2)/(PV O2-PA O2) a high sensitive and specific modus of quantifying shunts can be reached. Determination of oxygen saturation from the V. cava interior is therefore not useful.