European Heart Journal Advance Access published online on February 9, 2008
European Heart Journal, doi:10.1093/eurheartj/ehn022
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Assessing aortic valve area in aortic stenosis by continuity equation: a novel approach using real-time three-dimensional echocardiography
1 Cardiac Ultrasound Laboratory, Division of Cardiology, Blake 256, Massachusetts General Hospital, Harvard Medical School, 55 Fruit Street, Boston, MA 02114, USA
2 Cardiac Department, National University Hospital, Singapore
3 Biostatistics Unit, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
Received 5 July 2007; revised 17 December 2007; accepted 10 January 2008.
* Corresponding author. Tel: +1 617 726 0995, Fax: +1 617 726 8383, Email: jhung{at}partners.org
Aims: Two-dimensional echocardiographic (2DE) continuity-equation derived aortic valve area (AVA) in aortic stenosis (AS) relies on non-simultaneous measurement of left ventricular outflow tract (LVOT) velocity and geometric assumptions of LVOT area, which can amplify error, especially in upper septal hypertrophy (USH). We hypothesized that real-time three-dimensional echocardiography (RT3DE) can improve accuracy of AVA by directly measuring LVOT stroke volume (SV) in one window.
Methods and results: RT3DE colour Doppler and 2DE were acquired in 68 AS patients (74 ± 12 yrs) prospectively. SV was derived from flow obtained from a sampling curve placed orthogonal to LVOT (Tomtec Imaging). Agreement between continuity-equation derived AVA by RT3DE (AVA3D-SV) and 2DE (AVA2D) and predictors of discrepancies were analysed. Validation of LVOT SV was performed by aortic flow probe in a sheep model with balloon inflation of septum to mimic USH. There was only modest correlation between AVA2D and AVA3D-SV (r = 0.71, difference 0.11 ± 0.23 cm2). The degree of USH was significantly associated with difference in AVA calculation (r = 0.4, P = 0.005). In experimentally distorted LVOT geometry in sheep, RT3DE correlated better with flow probe assessment (r = 0.96, P < 0.001) than 2DE (r = 0.71, P = 0.006).
Conclusion: RT3DE colour Doppler-derived LVOT SV in the calculation of AVA by continuity equation is more accurate than 2D, including in situations such as USH, common in the elderly, which modify LVOT geometry.
Key Words: Aortic stenosis • Real-time three-dimensional echocardiography • Colour Doppler • Valvular heart disease • Continuity equation
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