The estimation of aortic valve area (AVA) by Doppler echocardiography-derived left ventricular stroke volume (LVSV) remains controversial. We hypothesized that AVA estimated from directly measured LVSV by 3-dimensional echocardiography (3DE) on the continuity equation might be more accurate in classifying aortic stenosis (AS) severity. We retrospectively enrolled 265 patients with moderate-to-severe AS with preserved ejection fraction. Indexed AVA (iAVA) was calculated using LVSV derived by 2D Doppler (iAVA Dop ), Simpson’s method (iAVA Simp ), and 3DE (iAVA 3D ). During a median follow-up period of 397 days (interquartile range 197 to 706 days), 135 patients experienced the composite end point (cardiac death 9%, aortic valve replacement 24%, and cardiovascular event 27%). Estimated iAVA 3D and iAVA Simp were significantly smaller than iAVA Dop and moderately correlated with peak aortic jet velocity. Upper septal hypertrophy was a major cause of discrepancy between iAVA Dop and iAVA 3D methods. Based on the optimal cut-off point of iAVA for predicting peak aortic jet velocity >4.0 m/s, 141 patients (53%) were classified as severe AS and 124 patients (47%) as moderate AS by iAVA Dop . Indexed AVA 3D classified 118 patients (45%) as severe and 147 patients (55%) as moderate AS. Of the 124 patients with moderate AS by iAVA Dop , 22 patients (18%) were reclassified as severe AS by iAVA 3D and showed poor prognosis (hazard ratio 2.7, 95% CI 1.4 to 5.0; p = 0.001). In conclusion, 3DE might be superior in classifying patients with AS compared with Doppler method, particularly in patients with upper septal hypertrophy.
Aortic valve area (AVA) is one of the most reliable parameters to assess the severity of aortic stenosis (AS) and usually calculated using continuity equation. In continuity equation, left ventricular stroke volume (LVSV) is estimated by 2 parameters: left ventricular outflow tract (LVOT) diameter and the Doppler-derived velocity-time integral of LVOT flow (LVOT-VTI). Therefore, measurement errors directly affect LVSV calculation and AVA estimation, especially in patients with irregular LVOT geometry such as upper septal hypertrophy (USH) which affect the LVOT Doppler profile. To overcome this, 3-dimensional (3D) transesophageal echocardiography has been used as substitute for the 2D Doppler method in assessing the LVOT area or LVOT flow velocity. However, there are still concerns in terms of reliability of the measurements and their availability in clinical practice. Recently, the development of 3D echocardiography (3DE) has facilitated a more accurate and simple way of measuring left ventricle volume directly using commercially available echocardiographic systems. Thus, we hypothesized that the AVA estimated with 3DE-derived LVSV might be more accurate compared with the 2D Doppler method. The objectives of this study were to reveal differences in the classifications of AS severity using the 3DE, the 2D Doppler method, and the 2D biplane Simpson’s method of disk and agreement with peak aortic jet velocity (peak V). Further we sought to assess whether 3DE could improve the associations between classifications of AS severity and cardiovascular events compared with the 2D Doppler method.
Methods
From May 2008 to October 2013, we retrospectively studied 273 patients with moderate-to-severe AS and preserved LV ejection fraction (LVEF ≥50%) from 3 Japanese cardiovascular centers. AS severity was determined by indexed AVA (iAVA) measured by the 2D Doppler method. The AS severities were classified as moderate (iAVA >0.6 to ≤0.85 cm 2 /m 2 ) and severe (iAVA ≤0.6 cm 2 /m 2 ). Patients with moderate or severe mitral or aortic regurgitation, reduced LVEF, and an inadequate echocardiographic image quality were excluded. Among 273 study patients, 7 were excluded because of inadequate follow-up, and 1 patient was also excluded because of the poor image quality for 3DE analysis. The baseline clinical characteristics were collected at the time of echocardiographic examinations. The study protocol was approved by the ethics committee of each of the participating institution.
Comprehensive transthoracic echocardiographic examinations were performed by experienced sonographers using commercially available ultrasound systems (Vivid E9; GE Healthcare, Horton, Norway or Philips iE33; Philips Medical Systems, Andover, Massachusetts), and same measurement protocols were used to measure echocardiographic parameters in 3 participating centers. The LV end-diastolic (LVEDV) and end-systolic volumes (LVESV), LVSV, and LVEF were measured by the biplane Simpson’s method. All 2D and 3D AVA estimation were performed offline by independent investigators who were blinded to clinical data and outcomes. AVA by the 2D Doppler method (AVA Dop ) was estimated by the continuity equation as follows:
where CSA LVOT is cross-sectional area of LVOT, calculated from LVOT diameter (CSA LVOT = π[LVOT diameter /2] 2 ), LVOT-VTI is velocity-time integral of LVOT, and AV-VTI is the aortic valve velocity-time integral. In this study, LVOT diameter was measured at level of aortic valvular cusps. LVOT velocity is recorded with pulsed-wave Doppler from an apical approach, and sample volume is positioned just proximal to the aortic valve so that the location of the velocity recording matches the LVOT diameter measurement. As the second method of 2DE, the LVSV was calculated as the difference between the LVEDV and LVESV from Simpson’s method (LVSV Simp ), and AVA by Simpson’s method (AVA Simp )was calculated as follows:
3DE data sets were obtained from the LV apical 4-chamber view with 4 to 7 consecutive cardiac cycles. The 3DE data were measured by an off-line analysis using commercially available software (4DLVQ, EchoPAC PC, Ver. 104.3.0; GE Healthcare and 3DQ ADV, QLAB; Philips Medical Systems). The LVSV, as measured by 3DE (LVSV 3D ), was semiautomatically calculated by each software package after the manual identification of the specific landmarks. Manual adjustments were performed when necessary. Then, the AVA by 3DE (AVA 3D ) was calculated as follows:
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