Abstract
Objectives: Transthoracic echocardiography (TTE) is the standard technique for assessing aortic stenosis (AS), with effective orifice area (EOA) recommended for grading severity. EOA is operator-dependent, influenced by a number of pitfalls and requires multiple measurements introducing independent and random sources of error. We tested the diagnostic accuracy and precision of aliased orifice area planimetry (AOAcmr), a new, simple, non-invasive technique for grading of AS severity by low-VENC phase-contrast cardiovascular magnetic resonance (CMR) imaging.Methods: Twenty-two consecutive patients with mild, moderate, or severe AS and six age- and sex-matched healthy controls had TTE and CMR examinations on the same day. We performed analysis of agreement and correlation among (i) AOAcmr; (ii) geometric orifice area (GOAcmr) by direct CMR planimetry; (iii) EOAecho by TTE-continuity equation; and (iv) the “gold standard” multimodality EOA (EOAhybrid) obtained by substituting CMR LVOT area into Doppler continuity equation.Results: There was excellent pairwise positive linear correlation among AOAcmr, EOAhybrid, GOAcmr, and EOAecho (p < 0.001); AOAcmr had the highest correlation with EOAhybrid (R2 = 0.985, p < 0.001). There was good agreement between methods, with the lowest bias (0.019) for the comparison between AOAcmr and EOAhybrid. AOAcmr yielded excellent intra- and inter-rater reliability (intraclass correlation coefficient: 0.997 and 0.998, respectively).Conclusions: Aliased orifice area planimetry by 2D phase contrast imaging is a simple, reproducible, accurate “one-stop shop” CMR method for grading AS, potentially useful when echocardiographic severity assessment is inconclusive or discordant. Larger studies are warranted to confirm and validate these promising preliminary results.
Highlights
In daily clinical practice, transthoracic echocardiography (TTE) is the primary imaging modality for the initial assessment of suspected aortic stenosis (AS) and for the measurement of effective orifice area (EOA) and geometric orifice area (GOA) of the aortic valve [1,2,3]
EOA is the key metric in AS and it correlates with survival and need for valve replacement
Cardiovascular magnetic resonance (CMR) complements echocardiographic assessment of AS—e.g., by allowing planimetric measurement of the aortic valve area in systole (GOAcmr)—providing precise information in patients with reduced cardiac output or with conditions influencing the accuracy of flow velocities or pressure gradient measurement by TTE [7, 8]
Summary
Transthoracic echocardiography (TTE) is the primary imaging modality for the initial assessment of suspected aortic stenosis (AS) and for the measurement of effective orifice area (EOA) and geometric orifice area (GOA) of the aortic valve (class I, Level of Evidence B) [1,2,3]. EOA is the key metric in AS and it correlates with survival and need for valve replacement It is calculated using the continuity equation, with its multiple, independent measurements (aortic jet velocity, left ventricular outflow diameter, and left ventricular outflow velocity), assumptions (circular cross-section of the LVOT, location of the sample volume exactly in the same plane in which the LVOT diameter is measured), and propagating errors (LVOT diameter is divided by 2, squared, and multiplied by 3.14 and by the LVOT VTI, which magnifies any error considerably) [4,5,6]. CMR allows direct measurement of LV stroke volume (without using geometrical assumptions) and of LVOT area, and is more accurate and reproducible than echocardiography [9], but, when compared to Doppler echocardiography, it underestimates flow velocities [6] This has been attributed to intravoxel dephasing, loss of signal, pressure recovery, and its lower temporal resolution compared to Doppler echocardiography [10]
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