Author + information
- Published online January 7, 2019.
- Dimitri Arangalage, MD,
- Mikael Laredo, MD,
- Phalla Ou, MD, PhD,
- Eric Brochet, MD,
- Claire Cimadevilla, MD,
- Maurice Enriquez-Sarano, MD,
- Alec Vahanian, MD and
- David Messika-Zeitoun, MD, PhD∗ ()
- ↵∗University of Ottawa Heart Institute, 40 Ruskin Street, Ottawa, Ontario K1Y 4W7, Canada
Up to 30% of patients with aortic stenosis (AS) present with discordant grading (aortic valve area [AVA] <1 cm2, but the mean pressure gradient [MPG] ≥40 mm Hg), raising uncertainty regarding the degree of AS severity (1). The aortic root is elliptical and transthoracic echocardiography (TTE)-derived left ventricular outflow tract (LVOT) area may be underestimated as based on a single diameter (TTELVOTd) (2). Combining computed tomography(CT) measurement of the LVOT area with TTE hemodynamic parameters has been proposed to solve the issue of discordant grading (3).
We enrolled 70 consecutive patients with moderate/severe bicuspid AS and 140 sex-, body surface area-, and MPG-matched patients with moderate/severe tricuspid AS. The AVAECHO was calculated using the continuity equation as: Π/4 × (TTELVOTd)2 × VTILVOT/VTIAV (where VTI is the velocity–time integral and AV is aortic valve). Using CT scans, from the true double oblique transverse view, maximum (Dmax) and minimal (Dmin) diameters, and annulus area (CTLVOTarea) were measured and eccentricity index (1 − [Dmin/Dmax]) was calculated. Fused AVA (AVACT) was calculated as: CTLVOTarea × VTILVOT/VTIAV.
The MPG was 53 ± 15 mm Hg, AVAECHO was 0.77 ± 0.20 cm2, and 180 patients (86%) presented with an AVA <1 cm2. By design, there was no difference in terms of sex, body surface area, and MPG (all p > 0.80); however, patients with bicuspid valves were younger (age 70 ± 14 years vs. 82 ± 8 years; p < 0.0001). Although the MPG was not different, the TTELVOTd (24 ± 3 mm vs. 23 ± 2 mm; p = 0.0002), CTLVOTarea (586 ± 155 mm2 vs. 484 ± 103 mm2; p = 0.0001), and consequently, AVAECHO were larger (0.85 ± 0.23 cm2 vs. 0.74 ± 0.17 cm2; p = 0.0005) in patients with bicuspid AS. The Dmax but not Dmin was different resulting in a higher eccentricity index (0.22 ± 0.07 vs. 0.14 ± 0.07; p < 0.0001) in patients with bicuspid AS.
Compared with the AVAECHO, the AVACT was larger overall (0.97 ± 0.31 cm2 vs. 0.77 ± 0.20 cm2; p < 0.0001) and in patient’s tricuspid (0.88 ± 0.23 cm2 vs. 0.74 ± 0.17 cm2; p < 0.0001) and bicuspid aortic valve (1.13 ± 0.39 cm2 vs. 0.85 ± 0.23 cm2; p < 0.0001) but more markedly in the latter group (+0.25 ± 0.31 cm2 vs. +0.15 ± 0.20 cm2; p = 0.004) (Figure 1). The rate of discordant grading increased from 24% to 34% (+10%; p < 0.0001) and the profile changed with more patients presenting with a high gradient (MPG ≥40 mm Hg/AVA ≥1 cm2, 28% vs. 12%; p < 0.0001) and fewer patients with a low gradient (AVA <1 cm2/MPG <40 mm Hg, 6% vs. 12%; p < 0.0001). Changes were again more marked in patients with bicuspid AS (+16% vs. +7%; p = 0.03).
Interobserver and intraobserver agreement rates of the TTELVOTd and CTLVOTarea measurements were 0.917 (95% confidence interval [CI]: 0.816 to 0.963) and 0.950 (95% CI: 0.888 to 0.978) for TTE and 0.983 (95% CI: 0.958 to 0.993) and 0.993 (95% CI: 0.982 to 0.997) for CT scans, showing excellent and similar reproducibility of both methods.
TTE wrongly assumes a circular LVOT shape, resulting in an underestimation of the “true” anatomic LVOT area and AVA. This incorrect assumption has been regarded as the main cause for discordant AS grading. In a recent study, fusion imaging led to a significant decrease in the rate of inconsistently graded severe AS with low gradient, with most patients being “reclassified” as moderate AS (3). However, no reference method was used to demonstrate that fusion imaging truly reclassified patients. Using the same methodology, we observed that fusion imaging decreased the rate of discordant AS with low gradient, but increased the rate of discordant AS with high gradient, leading to a total higher rate of discordant grading that was even more marked in bicuspid AV due to the more eccentric shape of the LVOT. Thus, fusion imaging mainly acts as a mathematical 1.5- to 2.0-mm shift of the LVOT diameter measured by TTE. The fact that 1.2 cm2 using the AVACT has the same prognostic value as AVAECHO of 1 cm2 strengthens this explanation (4). Although fusion imaging may provide a more accurate assessment of the “true” AVA, TTE should remain the reference method for the assessment of AS severity. Other methods such as calcium scoring are in our opinion better suited to further refine the assessment of AS severity in patients with discordant grading (5).
This study has several limitations. This was a single-center observational study, we could not evaluate the prognostic value of AVACT and AVATTE, and calcium measurements were not reported.
Fusion imaging did not resolve the issue of discordant AS grading and even worsened it, more markedly in patients with bicuspid AS. Our results do not support its use to assess AS severity.
Please note: †Drs. Arangalage and Laredo contributed equally to this work and are joint first authors. Dr. Enriquez-Sarano has received a research grant from Edwards LifeSciences, LLC. Dr. Vahanian has served as a consultant for Edwards LifeSciences, Abbott Vascular, and Mitral Tech. Dr. Messika-Zeitoun has received research grants from Edwards LifeSciences and Abbott Vascular; and has served as a consultant for Edwards LifeSciences, Valtech, Cardiawave, and Mardil. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.
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