Abstract 11006: Fick’s versus Cardiac MRI Measured Pulmonary Blood Flow in Pre-Fontan Assessment

Abstract

Background: Fick’s principle (FP) is unreliable if there are two sources of pulmonary blood flow (Q p ) with different saturations. We compared Q p and pulmonary vascular resistance (PVRI) measured by cardiac MRI (CMR) and FP in pre-Fontan patients. Material and Methods: Retrospective analysis of CMR and catheterization data obtained under the same general anesthetic from Jan 2009 to March 2021. FP derived Q p and PVRI used assumed O 2 consumption from Sackler’s equation. Paired T test was used for comparison between FP and CMR parameters. Results: 98 patients, with (mean ± sd): age 3.01±1.38 years and weight 13.31±2.4 kg. The FP derived Q p was 2.5(± 0.58) L/min/m 2 and PVRI1.91±0.61 Woods units*m 2 (WU*m 2 ). CMR measured pulmonary arterial flow (Q pa ) and pulmonary venous flow (Q pv ) were 1.97±0.55 L/min/m 2 and 3.49±0.76 L/min/m 2 , respectively. The PVRI using CMR Q pv was 1.38±0.47 WU*m 2 . The paired mean differences between Q p by FP and CMR Q pa or CMR Q pv were 0.53 (95%CI 0.41, 0.66; p<0.001) and -0.98(95%CI -1.13, -0.83; p<0.001), respectively. The paired mean difference between PVRI by FP and PVRI by CMR Qpv was 0.53(95%CI 0.44, 0.61; p<0.001). The difference between CMR Q pv and FP derived Q p were correlated with aortopulmonary collateral flow (Pearson r=0.615, p<0.001). PVRI derived from FP (1.91±0.61 WU*m 2 ) was higher than that from CMR (1.38±0.47, p<0.001). However, this only resulted in one FP based PVRI estimate being >4.0WU*m 2 when the CMR PVRI was <4.0WU*m 2 . Conclusion: s: FP derived Q p is lower than CMR Q pv resulting in higher PVRI estimates by FP. In most patients this will not affect clinical risk stratification based on PVRI. In high-risk candidates for the Fontan, CMR based flow measurements are preferrable.