Quantification of left-to-right shunting in adult congenital heart disease: phase-contrast cine MRI compared with invasive oximetry

Abstract

Atrial septum defects (ASDs), ventricular septum defects (VSDs) and patent ductus arteriosus (PDA) are the most common adult congenital heart defects. The degree of left-to-right shunting as assessed by the ratio of flow in the pulmonary (Qp) and systemic circulation (Qs) is crucial in the management of these conditions. This study compared phase-contrast cine magnetic resonance imaging (PC-MRI), a non-invasive imaging technique, with invasive oximetry for the measurement of shunt volumes during cardiac catheterisation in adults with left-to-right shunting. Both invasive oximetry and shunt quantification by PC-MRI (1.5 T scanner; Sonata, Siemens Medical Solutions) were performed on 21 patients with left-to-right shunting (14 ASD, 5 VSD, 2 PDA) and data on Qp/Qs ratios and left-to-right shunt fraction compared. Mean Qp/Qs ratios assessed by PC-MRI and oximetry were 2.10+/-0.76 and 1.96+/-0.77, respectively (p = 0.37). Mean shunt fraction was 46.3+/-19.6% when calculated by PC-MRI and 42.3+/-20.1% when obtained by oximetry (p = 0.12). There was a strong correlation of Qp/Qs ratios and shunt fraction between both methods (r = 0.61, p < 0.01 and r = 0.84, p < 0.0001, respectively). The two methods had a good agreement according to Bland and Altman plots with a small but non-significant overestimation of Qp/Qs-ratios and shunt fraction by PC-MRI. On receiver operating characteristic analysis, the sensitivity and specificity of PC-MRI to detect an oximetry-derived Qp/Qs ratio of > or =1.5:1 were 93% and 100% at a PC-MRI threshold of a Qp/Qs ratio > or =1.75:1 (area under curve (AUC) = 0.99). Quantification of left-to-right shunting can be performed reliably and accurately by PC-MRI and the data obtained by this method correlate closely to those from invasive oximetry.