Introduction: Transthoracic echocardiography (TTE) is the gold standard in the assessment of diastolic dysfunction, however, measurement of diastolic markers such as the pulmonary vein (PV) inflow velocities is often challenging. 4D flow cardiac magnetic resonance imaging (CMR) enables quantification of velocities in any target volume without the constraints faced by TTE. We explored the use of 4D flow CMR in generating Doppler-like velocity spectrograms of mitral and PV inflow and comparing them to actual echo-based pulsed-wave (PW) Doppler velocity curves.
Patients and Methods: A total of 6 HCM patients were included (P1-6). TTE was performed with a GE E95 system. Mitral and PV inflow PW Doppler was performed in the apical 4-chamber view by placing the sample volume at the level of the leaflet tips and at the inflow of the PV. The CMR data was acquired through a GE SIGNA Architect 3.0T scanner. The left atrium (LA), ventricle and outflow tract (LVOT) were segmented from a 4D flow phase contrast angiogram. The sample volume of PW Doppler was imitated using spheres of 4 mm radius placed in the same positions as in TTE. Velocities were projected in the direction typically captured by the echo transducer generating Doppler-like images. The duration of the pulmonary Ar and the mitral A wave was measured using both methods.
Results: Figure 1 shows volumetric renderings of velocity at mid-systole. Compared to P1 and P2, P3-6 present an accelerated LVOT flow due to obstruction caused by systolic anterior motion, causing posterolateral mitral regurgitation disrupting LA hemodynamics.Figure 2 demonstrates the mitral and pulmonary inflow patterns obtained with TTE and CMR. Peak velocities and the duration of the A/Ar waves were comparable when quantified using both modalities (Table 1). Ar wave duration could be quantified in all CMR studies, showing heterogeneity between the four PVs, whereas AR could be measured in only 3/6 of the echo studies.
Conclusion: 4D CMR shows potential for blood flow assessment previously feasible only via TTE. CMR could provide a more reproducible assessment of PV inflow velocities, relevant in assessing diastolic function, and potentially reveal new insights about LA hemodynamics.