Correlation of transesophageal echocardiography acquired 3D-multiplane reconstruction-planimetry of aortic valve area (AVA) with AVA determined by standard and modified continuity equation

Abstract

Abstract Background Currently the most accepted method for measuring aortic valve area is the continuity equation. Planimetry is an alternative method that allows the direct measurement of the Aortic valve area (AVA). There are, however, pitfalls in this method, such as artifacts caused by valve calcification and difficulty with the correct alignment of the cusps. Furthermore, these measurements may not correlate linearly, as effective AVA may vary due to contraction of flow and specific 3-dimensional conformation of the aortic valve. The advent of new technology with three-dimensional multiplane reconstruction echocardiography (3D-MPR) could overcome some of those limitations. Methods Measurements were taken from 119 patients who underwent elective transesophageal echocardiography (TEE), encompassing the whole spectrum of aortic opening. AVA was first calculated with the standard continuity equation (CE) in which left ventricular outflow tract (LVOT) area was calculated from its 2D diameter (AVA-CEstd). Secondly, a modified CE (AVA-CEmod) was used, measuring the LVOT area with 3D-MPR. Thirdly, the AVA was directly measured by 3D-MPR planimetry using the maximal opening at mid-systole (AVA-3D). In a subset of 30 Patients in which right and retrograde left heart catheterization was clinically indicated and performed, cardiac output was estimated by the Fick formula and AVA was calculated by the Gorlin formula (AVAGorling). We determined the correlation and level of agreement of AVA-3D with AVA-CEstd, AVA-CEmod and AVAGorling. Lastly, inter-observer reproducibility was evaluated for AVA-3D. Results The mean AVA-3D, AVA-CEmod and CEstd were as wollows: 1.87cm2, 1.81cm2 and 1.69cm2 respectively. There was a strong correlation between AVA-3D and AVA-CEmod (r = 0.963, p < 0.001) with a mean difference of 0.056 cm2 ± 0.273. There was a strong correlation between AVA-3D and AVA-CEstd (r = 0.877, p < 0.001) with a mean difference of 0.179 cm2 ± 0.477. There was a moderate correlation between AVAGorling , AVA-3D (r = 0.40, p < 0.001), AVA-CEmod (r = 0.54, p < 0.001) and AVA-CEstd (r = 0.49, p < 0.001). Intra-observer (ICCs 0.991) and inter-observer (ICCs 0.983) agreement for AVA-3D measurements were excellent. Conclusion Comparison between AVA-3D, AVA-CEmod and CEstd showed a strong correlation and intra-observer and inter-observer variability for AVA-3D were excellent. The correlation of AVAGorling with the AVAs assessed by echocardiography was weaker. The mean differences and variability can be explained by the known hemodynamic and conceptual differences between the geometric AVA, effective AVA and AVA assessed by the Gorlin formula. We can therefore conclude that AVA-3D assessed by TEE is a useful tool in daily clinical practice as it overcomes some pitfalls of the planimetry method, although some of the limitations remain.