Tricuspid flow and regurgitation in congenital heart disease and pulmonary hypertension: comparison of 4D flow cardiovascular magnetic resonance and echocardiography.

Background: Tricuspid valve (TV) regurgitation (TR) is a common complication of pulmonary hypertension and right-sided congenital heart disease, associated with increased morbidity and mortality. Estimation of TR severity by echocardiography and conventional cardiovasvular magnetic resonance (CMR) is not well validated and has high variability. 4D velocity-encoded (4D-flow) CMR was used to measure tricuspid flow in patients with complex right ventricular (RV) geometry and varying degrees of TR. The aims of the present study were: 1) to assess accuracy of 4D-flow CMR across the TV by comparing 4D-flow CMR derived TV effective flow to 2D-flow derived effective flow across the pulmonary valve (PV); 2) to assess TV 4D-flow CMR reproducibility, and 3) to compare TR grade by 4D-flow CMR to TR grade by echocardiography.
Methods: TR was assessed by both 4D-flow CMR and echocardiography in 21 healthy subjects (41.2 ± 10.5 yrs., female 7 (33%)) and 67 RV pressure-load patients (42.7 ± 17.0 yrs., female 32 (48%)). The CMR protocol included 4D-flow CMR measurement across the TV, 2D-flow measurement across the PV and conventional planimetric measurements. TR grading on echocardiographic images was performed based on the international recommendations. Bland-Altman analysis and intra-class correlation coefficients (ICC) were used to asses correlations and agreement.
Results: TV effective flow measured by 4D-flow CMR showed good correlation and agreement with PV effective flow measured by 2D-flow CMR with ICC = 0.899 (p < 0.001) and mean difference of -1.79 ml [limits of agreement -20.39 to 16.81] (p = 0.084). Intra-observer agreement for effective flow (ICC = 0.981; mean difference - 1.51 ml [-12.88 to 9.86]) and regurgitant fraction (ICC = 0.910; mean difference 1.08% [-7.90; 10.06]) was good. Inter-observer agreement for effective flow (ICC = 0.935; mean difference 2.12 ml [-15.24 to 19.48]) and regurgitant fraction (ICC = 0.968; mean difference 1.10% [-7.96 to 5.76]) were comparable. In 25/65 (38.5%) TR grade differed by at least 1 grade using 4D-flow CMR compared to echocardiography.
Conclusion: TV effective flow derived from 4D-flow CMR showed excellent correlation to PV effective flow derived from 2D-flow CMR, and was reproducible to measure TV flow and regurgitation. Twenty-five out of 65 patients (38.5%) were classified differently by at least one TR grade using 4D-flow CMR compared to echocardiography.