From the Guidelines
Cardiac pressures calculated using MR velocities primarily include pressure gradients across heart valves and estimated pulmonary pressures, which can be accurately determined using phase-contrast MRI and 4-D flow techniques, as demonstrated in the 2022 study by 1.
Key Findings
The study found that MRI can noninvasively assess the main pulmonary artery and right ventricle for pulmonary hypertension with good sensitivity and specificity, and is useful for right ventricular morphology and function assessment.
- RV functional abnormalities secondary to PH-related cardiac remodeling include RV hypokinesis, leftward bowing and/or paradoxical movement of the interventricular septum, RV dysfunction, and pulmonary and tricuspid insufficiency.
- Cardiac MRI shows many of the morphologic changes of PH that are also depicted by chest CT and CTPA, including PA enlargement, MPA to adjacent ascending aorta ratio > 1, RV enlargement and hypertrophy, straightening of the interventricular septum, and pericardial thickening and effusion.
- Measured parameters of RV ejection fraction, RV end diastolic volume, and RV-PA coupling metrics measured on cardiac MR have been shown to be important prognostic indicators of PH.
Pressure Calculations
MR velocity mapping, particularly phase-contrast MRI, allows for the calculation of pressure gradients using the modified Bernoulli equation (ΔP = 4v²), where v is the peak velocity across a stenotic valve.
- This technique enables estimation of transvalvular pressure gradients across aortic, mitral, pulmonic, and tricuspid valves, which are crucial for evaluating valvular stenosis severity.
- Additionally, tricuspid regurgitation velocity can be used to estimate right ventricular systolic pressure and pulmonary artery systolic pressure by adding estimated right atrial pressure.
- MR can also assess diastolic filling pressures through evaluation of mitral inflow patterns and pulmonary vein flow.
Clinical Implications
These pressure calculations are valuable because they are non-invasive alternatives to cardiac catheterization and can be obtained simultaneously with anatomical and functional cardiac assessment.
- The accuracy of these pressure estimations depends on proper alignment of the imaging plane perpendicular to blood flow and adequate temporal resolution to capture peak velocities, as noted in the study by 1.
- The use of MRI and MR velocities in calculating cardiac pressures has been supported by recent studies, including the 2022 update by 1, which highlights the importance of non-invasive imaging modalities in the diagnosis and management of pulmonary hypertension.
From the Research
Cardiac Pressures Calculated Using MR Velocities
- Mean pulmonary artery pressure (mPAP) can be calculated using cardiac magnetic resonance (CMR) indices, including ventricular mass index (VMI), interventricular septum curvature ratio (CR), and positive pulmonary arterial flow (QP) 2
- The equation for predicting mPAP using CMR indices is: mPAPCMR=28.837VMI-26.479CR-0.201QP+57.021 2
- Pulmonary vascular resistance (PVR) can also be calculated from CMR (PVRCMR) and is correlated with the gold standard PVR measured from right heart catheterization (PVRRHC) 2
- Left ventricular end-diastolic pressure (LVEDP) and pulmonary arterial wedge pressure (PAWP) are also important cardiac pressures, but PAWP is a better predictor of outcome in heart failure with preserved ejection fraction (HFpEF) than LVEDP 3
- PAWP is associated with outcome in HFpEF, whereas LVEDP is not 3