Discrepancies between cardiovascular magnetic resonance and Doppler echocardiography in the measurement of transvalvular gradient in aortic stenosis: the effect of flow vorticity

BACKGROUND Valve effective orifice area EOA and transvalvular mean pressure gradient (MPG) are the most frequently used parameters to assess aortic stenosis (AS) severity. However, MPG measured by cardiovascular magnetic resonance (CMR) may differ from the one measured by transthoracic Doppler-echocardiography (TTE). The objectives of this study were: 1) to identify the factors responsible for the MPG measurement discrepancies by CMR versus TTE in AS patients; 2) to investigate the effect of flow vorticity on AS severity assessment by CMR; and 3) to evaluate two models reconciling MPG discrepancies between CMR/TTE measurements. METHODS Eight healthy subjects and 60 patients with AS underwent TTE and CMR. Strouhal number (St), energy loss (EL), and vorticity were computed from CMR. Two correction models were evaluated: 1) based on the Gorlin equation (MPG(CMR-Gorlin)); 2) based on a multivariate regression model (MPG(CMR-Predicted)). RESULTS MPGCMR underestimated MPGTTE (bias = -6.5 mmHg, limits of agreement from -18.3 to 5.2 mmHg). On multivariate regression analysis, St (p = 0.002), EL (p = 0.001), and mean systolic vorticity (p < 0.001) were independently associated with larger MPG discrepancies between CMR and TTE. MPG(CMR-Gorlin) and MPGTTE correlation and agreement were r = 0.7; bias = -2.8 mmHg, limits of agreement from -18.4 to 12.9 mmHg. MPG(CMR-Predicted) model showed better correlation and agreement with MPGTTE (r = 0.82; bias = 0.5 mmHg, limits of agreement from -9.1 to 10.2 mmHg) than measured MPGCMR and MPG(CMR-Gorlin). CONCLUSION Flow vorticity is one of the main factors responsible for MPG discrepancies between CMR and TTE.