Original Research Article
Effect of the ellipsoid shape of the left ventricular outflow tract on the echocardiographic assessment of aortic valve area in aortic stenosis

https://doi.org/10.1016/j.jcct.2013.12.006Get rights and content

Abstract

Background

Previous studies showed discrepancies between echocardiographic and multidector row CT (MDCT) measurements of aortic valve area (AVA).

Objective

Our aim was to evaluate the effect of the ellipsoid shape of the left ventricular outflow tract (LVOT), as shown and measured by MDCT, on the assessment of AVA by transthoracic echocardiography (TTE) in patients with severe aortic stenosis.

Methods

This retrospective single-center study involved 49 patients with severe aortic stenosis referred before transcatheter aortic valve implantation. The AVA was deduced from the continuity equation on TTE and from planimetry on cardiac MDCT. Area of the LVOT was calculated as follows: on TTE, from the measurement of LVOT diameter on parasternal long-axis view; on MDCT, from manual planimetry by using multiplanar reconstruction perpendicular to LVOT.

Results

At baseline, correlation of TTE vs MDCT AVA measurements was moderate (R = 0.622; P < .001). TTE underestimated AVA compared with MDCT (0.66 ± 0.15 cm2 vs 0.87 ± 0.15 cm2; P < .001). After correcting the continuity equation with the LVOT area as measured by MDCT, mean AVA drawn from TTE did not differ from MDCT (0.86 ± 0.2 cm2) and correlation between TTE and MDCT measurements increased (R = 0.704; P < .001).

Conclusion

Assuming that LVOT area is circular with TTE results in constant underestimation of the AVA with the continuity equation compared with MDCT planimetry. The elliptical not circular shape of LVOT largely explains these discrepancies.

Introduction

Aortic stenosis (AS) is the most common valvular disease in western countries, mainly represented by calcific degenerative disease that affects 2% to 7% of the population older than 65 years.1 Surgical aortic valve replacement is the reference treatment in patients with reasonable operative risk. The decision to perform surgery is based on clinical symptoms and the severity of stenosis.2 Currently, transthoracic echocardiography (TTE) is the noninvasive reference method for evaluating AS severity. Severe AS is defined by TTE criteria as follows: aortic valve area (AVA) < 1 cm2 or AVA <0.6 cm2/m2 body surface area or mean transvalvular gradient >40 mm Hg, or peak transvalvular velocity > 4 m/s or any combination.1, 2

The AVA can be assessed by TTE (AVATTE) with the use of the continuity equation (Fig. 1),3 in which the left ventricular outflow tract (LVOT) is considered circular. Recently, cardiac multidetector row CT (MDCT) gained acceptance in the assessment of the AVA. It was found that MDCT could accurately evaluate aortic valve planimetry (AVAMDCT).4 Several studies showed good correlation between AVAMDCT and AVATTE.5, 6, 7, 8 However, AVA as evaluated by echocardiography and the continuity equation was shown to be underestimated compared with CT planimetry. Finally, CT studies have shown that LVOT was ellipsoidal in its short axis.9, 10

The aim of this study was to evaluate the effect of the noncircular shape of the LVOT in assessing AVA in patients with severe AS.

Section snippets

Patients

This retrospective study involved 49 patients from July 2010 to July 2011. All patients had severe AS documented by TTE, catheterization, or both. None of those patients was eligible for conventional surgery, then transcatheter aortic valve implantation (TAVI) was decided.11

Medical records were studied, and patients could be included if MDCT and TTE were available and considered interpretable. Patients were excluded in cases of balloon aortic valvuloplasty, and when delay between TTE and MDCT

Patients

From July 2010 to July 2011, 110 patients were referred to our department for CT evaluation before TAVI. Sixty-one patients were excluded from the study for the following reasons: 29 had TTE performed in another center, 14 had a history of balloon aortic valvuloplasty, 8 had incomplete TTE, 5 had a delay between TTE and CT >90 days, 3 had noncontributive cardiac CT, and 2 did not have cardiac CT. Finally, 49 patients were included, aged 83.9 ± 6.8 years, and 32 (65%) were women. Most patients

Discussion

Accurate assessment of the AVA is essential in the management of patients with AS. Besides clinical symptoms, AVA is important for choosing treatment.1, 2 Previous studies have shown that MDCT and TTE correlated in the assessment of AVA, and constant discrepancy between the 2 methods was also found, raising the question of an overestimation with MDCT vs underestimation with TTE.5, 6, 7, 8

In this study, volume analysis provided by CT confirmed the noncircular ellipsoidal shape of the LVOT.

Conclusion

Assuming that LVOT is circular with TTE results in constant underestimation of the AVA compared with MDCT planimetry. This is largely explained by the ellipsoid noncircular shape of the LVOT.

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Conflict of interest: The authors report no conflict of interest.

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