Highlights
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LVOT velocity is significantly underestimated by TEE compared with TEE
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Transgastric TEE probe aligns better than transapical TTE with aortic valve flow.
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TEE compared with TTE in aortic stenosis yields lower DVI despite larger LVOT area.
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Doppler probe insonation angle with TTE versus TEE accounts for these differences.
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TEE overestimates AS severity versus awake or simultaneous sedation state paired TTE.
Transthoracic echocardiography (TTE) is the gold standard for aortic stenosis (AS) assessment. Transesophageal echocardiography (TEE) provides better resolution, but its effect on AS assessment is unclear. To answer this question, we studied 56 patients with ≥moderate AS. Initial TTE (TTE1) was followed by conscious sedation with simultaneous TEE and TTE2. Based on conservative versus actionable implication, AS types were dichotomized into group A, comprising moderate and normal-flow low-gradient, and group B, comprising high gradient, low ejection fraction low-flow low-gradient, and paradoxical low-flow low-gradient AS. Paired analysis of echocardiographic variables and AS types measured by TEE versus TTE2 and by TEE versus TTE1 was performed. TEE versus simultaneous TTE2 comparison demonstrated higher mean gradients (31.7 ± 10.5 vs 27.4 ± 10.5 mm Hg) and velocities (359 ± 60.6 vs 332 ± 63.1 cm/s) with TEE, but lower left ventricular outflow velocity-time-integral (VTI 1 ) (18.6 ± 5.1 vs 20.2 ± 6.1 cm), all p <0.001. This resulted in a lower aortic valve area (0.8 ± 0.21 vs 0.87 ± 0.28 cm ), p <0.001, and a net relative risk of 1.86 of group A to B upgrade. TEE versus (awake state) TTE1 comparison revealed a larger decrease in VTI 1 because of a higher initial awake state VTI 1 (22 ± 5.6 cm), resulting in similar Doppler-velocity-index and aortic valve area decrease with TEE, despite a slight increase in mean gradients of 0.8 mm Hg (confidence interval −1.44 to 3.04) and velocities of 10 cm/s (confidence interval −1.5 to 23.4). This translated into a net relative risk of 1.92 of group A to B upgrade versus TTE1. In conclusion, TEE under conscious sedation overestimates AS severity compared with both awake state TTE and simultaneous sedation state TTE, accounted for by different Doppler insonation angles obtained in transapical versus transgastric position.
Hemodynamic thresholds for severe aortic stenosis (AS) are based on seminal studies that used transthoracic echocardiography (TTE). In critically ill patients and patients with poor acoustic windows, transesophageal echocardiography (TEE) improves aortic valve visualization, but its overall effect on AS severity assessment is unclear. Factors reducing AS severity with TEE assessment include a higher measured left ventricular outflow (LVOT) area compared with TTE, yielding a higher aortic valve area (AVA) by the continuity method, and sedation-induced reduction in left ventricular preload and flow across the aortic valve. , Indeed, precardiopulmonary bypass TEE under general anesthesia generates lower mean gradients (MGs) and higher calculated AVA compared with preoperative TTE. In contrast, a porcine, and ovine model study and a recent clinical study have directly shown that hypertension and reduced arterial compliance (which are attenuated by sedation) cause underestimation of AS severity by lowering MG and peak velocity (V max. ). Transgastric versus transthoracic probe position can also affect Doppler measurements. The purpose of our study was to perform a head-to-head comparison of TTE versus TEE assessment of all-comer patients with AS under identical sedation and hemodynamic conditions and secondarily to compare the same TEE studies with an immediately preceding awake state TTE study.
Methods
From 2016 to 2017, consecutive patients with a previous diagnosis of at least moderate AS referred to our medical institution for consideration of aortic valve replacement were enrolled in our study. Exclusion criteria were poor echocardiographic windows or technical inability to obtain reliable Doppler recordings, patients in whom the highest aortic valve gradients were obtained by a nonapical view TTE, age younger than 18 years of age, congenital heart disease (except bicuspid aortic valve), or previous valve replacement or repair. The study was approved by the hospital’s institutional review board, and all patients provided written consent.
A baseline TTE study (TTE1) was performed using a Philips EPIQ acquisition unit equipped with an S5-1 transducer (Philips Medical Systems, Andover, Massachusetts). Spectral Doppler tracings of the velocity-time integral (VTI) of LVOT and the aortic valve were performed as per guidelines , from all interrogation windows. The continuity equation was used for the calculation of AVA. An immediate consecutive TEE study followed under conscious sedation with intravenous 3 to 7 mg of Midazolam. Three-dimensional (3D) images were processed offline with LVOT cropped and planimetered. , , Transgastric interrogation was performed at deep (0° to 70°) and long-axis views (at 100° to 120°) to obtain the highest Doppler VTI of LVOT (VTI 1 ) and of the aortic valve (VTI 2 ). Three or more beats were averaged for all measurements. During the transgastric TEE study, a separate simultaneous TTE (TTE2) Doppler interrogation of LVOT and aortic valve in the 3-chamber apical view was acquired with the S5-1 transducer from the apical position. Two-dimensional (2D) LVOT diameter was used for calculation of stroke velocity index (SVI) and AVA for TTE1 and TTE2, whereas 3D planimetry of LVOT area was used for the respective calculations for TEE.
Because only left lateral decubitus apical views were feasible with TTE study during sedation, for the purpose of simultaneous TTE versus TEE comparison, we included only the patients in whom the apical view in the immediately previous TTE study during awake state generated the highest aortic valve gradients compared with all other TTE interrogation windows. Direct 3D planimetry of the LVOT area was used for the calculation of SVI and AVA values that served for the TEE classification of AS.
The cut-off values used for AS types classification correspond to the American College of Cardiology and the European Society of Cardiology definitions and were detailed in a previous study. Based on interventional implication, we dichotomized AS types into 2 groups: group A (Moderate AS and normal-flow low-gradient), which does not carry an invasive intervention indication in isolation, and group B (high gradient, low ejection fraction low-flow low-gradient, and paradoxical low-flow low-gradient) in which invasive treatment (percutaneous or surgical) may be warranted. ,
Continuous variables are expressed as means ± SDs, or as median (interquartile range 25% to 75%) where the distribution was non-Gaussian. Categorical variables are expressed as counts and percentages. Student’s t test, the Mann-Whitney U test, or the Wilcoxon rank sum test was used to compare continuous variables between group A and B patients. Differences in continuous variables between paired TTE and TEE studies were analyzed by paired Student’s t test or Wilcoxon matched-pair signed-rank test as indicated. Categories of AS were compared using the chi-square or Fisher’s exact test.
A 2-sided p <0.05 was considered to indicate statistical significance for all tests. Statistical analysis was performed using IBM SPSS Statistics for Windows, Version 21.0 (IBM Corp. Released 2012. Armonk, New York), and graphs were drawn with GraphPad Prism version 8.0.0 for Windows (GraphPad Software, San Diego, California).
Results
We recruited a total of 81 patients, of whom 61 had all pertinent data available on both TTE1 and consecutive TEE and simultaneous TTE2. A total of 20 patients were excluded for technical reasons: 2 for poor TTE apical windows, technical inability to obtain suitable transgastric views for VTI 1 -TEE Doppler measurements in 12 and for VTI 2 in 2, poor 3D image quality in 3, and premature TEE study abandonment because of hemodynamic instability in 2. A total of 5 patients with higher MGs in TTE1 right parasternal view than apical view were also excluded.
Baseline characteristics of the whole study population and stratified under sedation state by TTE2-derived A/B groups are displayed in Table 1 . Clinical variables were similar in the 2 groups. LVOT flow was smaller in group B versus A, as manifested by smaller VTI 1 and SVI. Doppler velocity index (DVI and AVA values were significantly lower. There was no significant difference in aortic valve gradients.
| Variable | All patients (N=56) | Group A (N=29) | Group B (N=27) | P value |
|---|---|---|---|---|
| Age [years] | 80 (75.1-84.1) | 80 (75.8-84.8) | 80 (75-83.1) | 0.9 |
| Men | 29 (52%) | 19 (66%) | 10 (37%) | 0.03 * |
| Body surface area [m 2 ] | 1.8 ± 0.19 | 1.84 ± 0.19 | 1.8 ± 0.18 | 0.31 |
| Weight [kg] | 76.3 ± 24.2 | 78 ± 30.1 | 74.4 ± 30.2 | 0.58 |
| Systolic blood pressure [mmHg] | 132 ± 33 | 131 ± 34 | 132 ± 32 | 0.18 |
| Diastolic blood pressure[mmHg] | 68 ± 16 | 70 ± 15 | 64 ± 18 | 0.3 |
| Heart rate | 69 ± 14 | 68 ± 14 | 72 ± 13 | 0.41 |
| Coronary artery disease | 36 (65%) | 18 (62%) | 18 (69%) | 0.39 |
| Diabetes mellitus | 31 (56%) | 17 (59%) | 14 (54%) | 0.47 |
| Hypertension | 52 (92.9%) | 27 (93%) | 25 (93%) | 0.7 |
| Chronic renal failure | 16 (30.2%) | 5 (18%) | 11 (42%) | 0.06 |
| Chronic pulmonary disease | 6 (11%) | 2 (7%) | 4 (15%) | 0.3 |
| Echocardiographic data | ||||
| Ejection fraction [%] | 60 (55-65) | 60 (57.5-65) | 60 (51.5-62.5) | 0.23 |
| SVI [cc/m 2 ] | 38.4 ± 12.2 | 44.8 ± 9.6 | 31.5 ± 11 | <0.001 * |
| AR moderate or greater | 2 (4%) | 2 (7%) | 0 | |
| MR moderate or greater | 1 (2%) | 1 (3%) | 0 | |
| TR moderate or greater | 3 (5%) | 2 (7%) | 1 (4%) | |
| PASP [mmHg] | 40 ± 11.3 | 38.7 ± 10 | 41.4 ± 12.7 | 0.45 |
| LVOTD [cm] | 2.06 (1.9-2.25) | 2.2 (2-2.3) | 1.97 (1.9-2.1) | 0.009 * |
| MG [mmHg] | 26 (21-41) | 25 (21-32) | 26 (20-38) | 0.5 |
| V max [cm/sec] | 332 ± 63.1 | 332.5 ± 47.3 | 331.5 ± 77.2 | 0.9 |
| VTI 1 [cm] | 20.2 ± 6 | 22.5 ± 5.6 | 17.7 ± 5.7 | 0.002 * |
| VTI 2 [cm] | 81 ± 20.9 | 77.9 ± 14.2 | 83.3 ± 26.4 | 0.34 |
| DVI (VTI ratio) | 0.26 ± 0.7 | 0.29 ± 0.07 | 0.22 ± 0.05 | <0.001 * |
| AVA [cm 2 ] | 0.8 ± 0.28 | 1.07 ± 0.22 | 0.67 ± 0.16 | <0.001 * |
⁎ P Value<0.05 SVI = Stroke velocity index; AR = aortic regurgitation; MR = mitral regurgitation; TR = tricuspid regurgitation; LVOTD = left ventricular outflow tract diameter; MG = mean pressure gradient; Vmax = peak aortic valve velocity; SVI = stroke volume index; VTI 1 = Velocity-Time-Integral of the left ventricular outflow tract; VTI 2 = Velocity-Time-Integral of the aortic valve area; DVI = Doppler velocity index; AVA = aortic valve area; Group A patients = moderate AS and normal-flow low-gradient AS; Group B patients = high-gradient, low ejection-fraction low-flow low-gradient, and paradoxical low-flow low-gradient AS.
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