OXYMETRIC SHUNT DETECTION OF THE ATRIAL S EPTAL-DEFECT

There are several circumstances in which data obtained at catheterizat ion should alert the cardiologist to look for a shunt that had not bee n suspected previously. Aim of the study was to explore the most sensi tive parameter which is easily practicable and which gives strong evid ence 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 Q(p) and systemic bloodflow Q(s) was 1.31 to 5.60 in patients with ASD and 0.75 to 1.19 in patients wi thout shunt. The analysis of sensitivity and specifity was determined to define the marginal value which gives suspiction of an ASD. The bes t values for sensitivity and specificity was found for PA O-2 - SVC O- 2 = 7.4% (sens. = 98.3%, spec. = 96.2%), PA O-2 - IVC O-2 = 2.0% (sens ./spec. = 100%), PA O-2 - MV O-2 = 5.0% (sens./spec. 100%) and PA O-2 = 78.4% (sens./spec. = 97.5%). The correlation between the modified ra tio Q(p)/Q(s) and various differences in O-2-saturation with the shunt size was examined. A high correlation was found for the modified Q(p) /Q(s) with SVC O-2 instead of MV O-2 (r = 0.98), PA O-2 - SVC O-2 (r = 0.77) and PA O-2 - MV O-2 (r = 0.74) with Q(p)/Q(s), respectively. Co nclusion: The results demonstrate that an O-2-saturation > 78% in the pulmonary artery is highly suspicious for the diagnosis of an ASD. Wit h the modified ratio Q(p)/Q(s) = (ART O-2 - SVC O-2)/(PV O-2 - PA O-2) a high sensitive and specific modus of quantifying shunts can be reac hed. Determination of oxygen saturation from the V. cava interior is t herefore not useful.