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A novel approach to determine aortic valve area with phase-contrast cardiovascular magnetic resonance
Felix Troger1, Ivan Lechner2, Martin Reindl2
1University Clinic of Radiology, Medical University of Innsbruck, Anichstrasse 35, 6020, Innsbruck, Austria.
Insights
Phase-contrast cardiovascular magnetic resonance imaging (PC-CMR) offers a precise, non-invasive method for assessing aortic stenosis (AS) by accurately measuring aortic valve area (AVA). This validated PC-CMR approach provides reliable results comparable to invasive methods, aiding in AS diagnosis.
Area of Science:
- Cardiovascular Imaging
- Medical Physics
- Diagnostic Accuracy
Background:
- Transthoracic echocardiography (TTE) is standard for aortic stenosis (AS) assessment.
- TTE has limitations in accurately determining stroke volume (SV) and aortic valve area (AVA).
- Phase-contrast cardiovascular magnetic resonance imaging (PC-CMR) presents a promising alternative for precise measurements.
Purpose of the Study:
- To validate a novel PC-CMR approach for measuring AVA in AS patients.
- To compare PC-CMR derived AVA and SV with invasive methods and TTE.
- To assess the accuracy and reliability of PC-CMR in AS assessment.
Main Methods:
- Fifty patients with moderate to severe AS underwent TTE, cardiac catheterization, and CMR.
- AVA and SV were measured using PC-CMR, cine-CMR, and invasive methods (Fick principle, Gorlin formula).
- TTE measurements used the continuity equation; gradients were calculated via the modified Bernoulli equation.
Main Results:
- PC-CMR derived SV showed strong correlation (r=0.73) with cine-CMR without significant bias.
- Mean pressure gradient by PC-CMR correlated significantly with invasive measurements (r=0.36, p=0.011).
- Mean AVA by PC-CMR (0.78 cm² ± 0.25) moderately correlated with invasive AVA (0.70 cm² ± 0.23, r=0.54, p<0.001) with minimal bias.
- TTE-derived AVA showed similar correlation (r=0.58) and bias to invasive AVA as PC-CMR.
- Excellent intra- and interobserver reproducibility was observed for PC-CMR AVA measurements.
Conclusions:
- The novel PC-CMR approach allows for simple AVA measurement with no bias to invasive assessment.
- PC-CMR offers a reliable non-invasive method for grading AS, particularly when TTE results are inconclusive.
- This technique enhances the non-invasive assessment capabilities of cardiovascular magnetic resonance imaging in AS.
Background:
Transthoracic echocardiography (TTE) is the diagnostic routine standard for assessing aortic stenosis (AS). However, its inaccuracies in determining stroke volume (SV) and aortic valve area (AVA) call for a more precise and dependable method. Phase-contrast cardiovascular magnetic resonance imaging (PC-CMR) is a promising tool to push these boundaries. Thus, the aim of this study was to validate a novel approach based on PC-CMR against the gold-standard of invasive determination of AVA in AS compared to TTE.
Methods:
A total of 50 patients with moderate or severe AS underwent TTE, cardiac catheterization and CMR. AVA via PC-CMR was determined by plotting momentary flow across the valve against flow-velocity. SV by CMR was measured directly via PC-CMR and volumetrically using cine-images. Invasive SV and AVA were determined via Fick-principle and Gorlin-formula, respectively. TTE yielded SV and AVA using continuity equation. Gradients were calculated via the modified Bernoulli-equation.
Results:
SV by PC-CMR (85 ± 31 ml) correlated strongly (r: 0.73, p < 0.001) with cine-CMR (85 ± 19 ml) without significant bias (lower and upper limits of agreement (LLoA and ULoA): - 41 ml and 44 ml, p = 0.83). In PC-CMR, mean pressure gradient correlated significantly with invasive determination (r: 0.36, p = 0.011). Mean AVA, as determined by PC-CMR during systole (0.78 ± 0.25 cm2), correlated moderately (r: 0.54, p < 0.001) with invasive AVA (0.70 ± 0.23 cm2), resulting in a small bias of 0.08 cm2 (LLoA and ULoA: - 0.36 cm2 and 0.55 cm2, p = 0.017). Inter-methodically, AVA by TTE (0.81 ± 0.23 cm2) compared to invasive determination showed similar correlations (r: 0.58, p < 0.001 with a bias of 0.11 cm2, LLoA and ULoA: - 0.30 and 0.52, p < 0.001) to PC-CMR. Intra- and interobserver reproducibility were excellent for AVA (intraclass-correlation-coefficients of 0.939 and 0.827, respectively).
Conclusions:
Our novel approach using continuous determination of flow-volumes and velocities with PC-CMR enables simple AVA measurement with no bias to invasive assessment. This approach highlights non-invasive AS grading through CMR, especially when TTE findings are inconclusive.
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