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

doi:10.1016/j.jcct.2013.12.006

Journal of Cardiovascular Computed Tomography

Volume 8, Issue 1, January–February 2014, Pages 52-57

https://doi.org/10.1016/j.jcct.2013.12.006 Get 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 (AVA^TTE) 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 (AVA^MDCT).⁴ Several studies showed good correlation between AVA^MDCT and AVA^TTE.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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Prosthesis-patient mismatch defined by cardiac computed tomography versus echocardiography after transcatheter aortic valve replacement
2021, Journal of Cardiovascular Computed Tomography
Evaluation of prosthesis-patient mismatch (P-PM) after transcatheter aortic valve replacement (TAVR) by transthoracic echocardiography (TTE) has provided conflicting results regarding its impact on outcomes. Whether post-TAVR computed tomography angiography (CTA) evaluation of P-PM can improve our understanding is unknown. We aimed to evaluate the inter-modality (TTE vs. CTA) agreement, inter-valve platform (balloon-expanding valve [BEV] vs. self-expandable valve [SEV]) differences in P-PM severity, and outcomes related to P-PM after TAVR.
We analyzed patients with both CTA and TTE before and after TAVR. Indexed effective orifice area was calculated using two methods: TTE-derived left ventricular outflow tract (LVOT) area from measured diameter and post-TAVR CTA-measured area. Body size specific cut-offs for P-PM severity were used: for body mass index (BMI) < 30 kg/m², moderate = 0.66–0.85 cm²/m² and severe≤0.65 cm²/m²; for BMI ≥30 kg/m², moderate = 0.56–0.70 cm²/m² and severe≤0.55 cm²/m².
A total of 447 patients were included (median age, 83 years; 54% male). The prevalence of P-PM (moderate or severe) was lower with CTA vs. TTE (3.5% vs. 19.5%, p < 0.001). The prevalence of P-PM measured by TTE was more common in BEV compared to SEV (p = 0.002), while CTA assessment showed no difference in P-PM incidence and severity between TAVR platforms (p = 0.40). In multivariable analysis, CTA-defined but not TTE-defined P-PM was associated with mortality after TAVR (HR:3.97; 95%CI,1.55–10.2; p = 0.004). Both CTA-defined and TTE-defined P-PM were associated with the composite of death and heart failure rehospitalization.
Although post-TAVR CTA substantially downgraded the prevalence of P-PM compared to TTE, it identified a subset of patients with clinically relevant P-PM which associated with outcomes.
Direct Planimetry of Left Ventricular Outflow Tract Area by Simultaneous Biplane Imaging: Challenging the Need for a Circular Assumption of the Left Ventricular Outflow Tract in the Assessment of Aortic Stenosis
2020, Journal of the American Society of Echocardiography
Citation Excerpt :
Continuing to use a circular LVOT assumption in routine TTE is problematic in the assessment of AS. Prior studies using 3D imaging have demonstrated that the LVOT geometry is elliptical in 70% to 100% of patients with AS.5-9,15,16 Our study is consistent with these findings, demonstrating that 81% of patients with AS had elliptical LVOTs on biplane TTE.
Evaluation of aortic stenosis (AS) requires calculation of aortic valve area (AVA), which relies on the assumption of a circular-shaped left ventricular outflow tract (LVOT). However, the LVOT is often elliptical, and the circular assumption underestimates the true LVOT area (LVOTA). Biplane imaging using transthoracic echocardiography allows direct planimetry of LVOTA. The aim of this study was to assess the feasibility of obtaining LVOTA using this technique and its impact on the discordance between AVA and gradient criteria in AS grading.
We prospectively studied 134 patients (median age, 80 years; interquartile range, 73–87 years; 39% women) with AS, including 82 (61%) with severe AS and 52 (39%) with mild or moderate AS. LVOTA was traced using direct planimetry (LVOTA_biplane) and compared with LVOTA calculated using the circular assumption (LVOTA_circ). In a subset of patients who underwent cardiac computed tomography, direct planimetry of LVOTA was used as a reference standard.
LVOTA_biplane was significantly larger than LVOTA_circ (4.20 cm² [interquartile range, 3.66–4.90 cm²] vs 3.73 cm² [interquartile range, 3.14–4.15 cm²], P < .001). Among 30 patients who underwent cardiac computed tomography, LVOTA_biplane had better agreement with LVOTA by direct planimetry than LVOTA_circ (mean bias, −0.45 ± 0.63 vs −1.02 ± 0.63 cm²; P < .0001). Of 82 patients with severe AS (AVA ≤ 1 cm² using LVOTA_circ), 40 (49%) had discordant mean gradient (<40 mm Hg). By using LVOTA_biplane, patients with discordant AVA and mean gradient decreased from 49% to 27% (P = .004), and 29% of patients with severe AS were reclassified with moderate AS, with the highest percentage of reclassification in the group with low-gradient AS with preserved left ventricular ejection fraction.
Direct planimetry using biplane imaging avoids the inherent underestimation of LVOTA using the circular assumption. LVOTA obtained by biplane planimetry can lead to better concordance between AVA and mean gradient and classification of AS severity.
Aortic Valve Prosthesis-Patient Mismatch in a Patient Undergoing Redo Mitral Valve Replacement for Infective Endocarditis
2018, Journal of Cardiothoracic and Vascular Anesthesia
Citation Excerpt :
Three-dimensional TEE analysis has revealed that the LVOT is a funnel-shaped structure with larger cross-sectional areas at its base than at the AV hinge-points.56,57 Therefore, depending on the level along the longitudinal axis at which the LVOT area is obtained, the same AV prosthesis may have erroneously larger or smaller EOAs calculated by the continuity equation.46,47,56–58 Furthermore, the LVOT medial-lateral diameter was found to increase gradually deeper into the LV, while the anterior-posterior diameter did not differ significantly.58,59
Multidetector computed tomography sizing of aortic annulus prior to transcatheter aortic valve replacement (TAVR): Variability and impact of observer experience
2018, Diagnostic and Interventional Imaging
To evaluate intra- and inter-observer variability of multidetector computed tomography (MDCT) sizing of the aortic annulus before transcatheter aortic valve replacement (TAVR) and the effect of observer experience, aortic valve calcification and image quality.
MDCT examinations of 52 consecutive patients with tricuspid aortic valve (30 women, 22 men) with a mean age of 83 ± 7 (SD) years (range: 64–93 years) were evaluated retrospectively. The maximum and minimum diameters, area and circumference of the aortic annulus were measured twice at diastole and systole with a standardized approach by three independent observers with different levels of experience (expert [observer 1]; resident with intensive 6 months practice [observer 2]; trained resident with starting experience [observer 3]). Observers were requested to recommend the valve prosthesis size. Calcification volume of the aortic valve and signal to noise ratio were evaluated.
Intra- and inter-observer reproducibility was excellent for all aortic annulus dimensions, with an intraclass correlation coefficient ranging respectively from 0.84 to 0.98 and from 0.82 to 0.97. Agreement for selection of prosthesis size was almost perfect between the two most experienced observers (k = 0.82) and substantial with the inexperienced observer (k = 0.67). Aortic valve calcification did not influence intra-observer reproducibility. Image quality influenced reproducibility of the inexperienced observer.
Intra- and inter-observer variability of aortic annulus sizing by MDCT is low. Nevertheless, the less experienced observer showed lower reliability suggesting a learning curve.
Echocardiographic Imaging for Transcatheter Aortic Valve Replacement
2018, Journal of the American Society of Echocardiography
Citation Excerpt :
Although echocardiographic guidelines recommend a single diameter measurement of the LVOT to calculate AVA, planimetry of the aortic valve and LVOT area by real-time three-dimensional (3D) methods has been shown to be accurate and reproducible48,49 and to compare favorably with MSCT.50,51 Some studies suggest that using a direct area measurement of the LVOT in the continuity equation may yield a more accurate measurement of AVA.52,53 However, Clavel et al.54 compared the two methods for calculating AVA: the hybrid multislice computed tomographic planimetered LVOT in the continuity equation and the standard echocardiographic continuity equation.
Transcatheter aortic valve replacement has become an accepted alternative to surgery for patients with severe, symptomatic aortic stenosis who are inoperable or are at high surgical risk. Recent trials support the use of transcatheter aortic valve replacement also in patients at intermediate risk, and ongoing trials are assessing appropriateness in other patient groups. The authors review the key anatomic features integral to the transcatheter aortic valve replacement procedure and the echocardiographic imaging required for preprocedural, intraprocedural, and postprocedural assessment.
Resolving Apparent Inconsistencies Between Area, Flow, and Gradient Measurements in Patients With Aortic Valve Stenosis and Preserved Left Ventricular Ejection Fraction
2018, American Journal of Cardiology
Citation Excerpt :
The most important measurement error in the calculation of AVA by echocardiography is the LVOT diameter measurement and because this value is squared for the calculation of LVOT area, even mild errors lead to important errors in area calculation. The LVOT evaluated by 3-dimensional echocardiography, multidetector computed tomography, and cardiac magnetic resonance imaging is proved to be an elliptical shape rather than circular shape.20–23 Unger et al demonstrated that SVi determined by right heart catheterization can be used together with echocardiography to give a reliable hybrid AVA measurement in low-gradient SAS.24
Inconsistencies between area (aortic valve area [AVA])-flow-gradient are common during the echocardiographic assessment of aortic stenosis (AS). This study was conducted to investigate the importance of these inconsistencies and the impact of 3 methods to resolve these inconsistencies. The study population consisted of 327 patients (age: 76.3 ± 8.6 years, 49.5% males) with severe AS (SAS) (AVA ≤ 1 cm²) and preserved left ventricular ejection fraction (≥50%). Inconsistent findings between AVA, flow, and mean gradient (MG) were observed in 78 (23.9%) patients with low flow and a high MG, 52 (15.9%) patients with normal flow and a low MG, and 37 (11.3%) patients with a low flow and a low MG. Using stroke volume index by catheterization for AVA recalculation showed the greatest effect to resolve inconsistencies in the low flow and a high MG group (85%). Decreasing the AVA cut-off values for SAS to ≤0.8 cm² resulted in a shift from SAS to moderate AS in 36 patients (69%) in the normal flow and a low MG. Indexing AVA to body surface area had only a minor impact on reclassification. In conclusion, in patients with SAS and preserved left ventricular ejection fraction, the majority of area-flow-gradient inconsistencies at echocardiography can be resolved by correcting errors in stroke volume index measurements by alternative techniques and by redefining the cut-off value for SAS to ≤0.8 cm².

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

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

Abstract

Background

Objective

Methods

Results

Conclusion

Introduction

Section snippets

Patients

Patients

Discussion

Conclusion

J Am Coll Cardiol

J Am Coll Cardiol

JACC Cardiovasc Imaging

Am J Cardiol

J Am Coll Cardiol

JACC Cardiovasc Imaging

J Am Coll Cardiol

Int J Cardiol

Joint Task Force on the Management of Valvular Heart Disease of the European Society of Cardiology (ESC); European Association for Cardio-Thoracic Surgery (EACTS)

Eur Heart J

Echocardiographic assessment of valve stenosis: EAE/ASE recommendations for clinical practice

Eur J Echocardiogr

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