Background
The aim of this study was to estimate geometric errors made by the two-dimensional (2D) transthoracic echocardiographic (TTE) pulsed-wave Doppler flow (PWDF) method in calculating regurgitant volume (RVol) and effective regurgitant orifice area (EROA) in degenerative mitral regurgitation (MR) by comparison with the three-dimensional (3D) transesophageal echocardiographic (TEE) PWDF method.
Methods
RVol and EROA were calculated in 22 patients with degenerative MR using the conventional 2D TTE PWDF method on the basis of monoplanar dimensions and a circular geometric assumption of the cross-sectional areas (CSAs) of the mitral annulus (MA) and the left ventricular outflow tract (LVOT) and the 3D TEE PWDF method, in which the CSAs of the MA and LVOT were measured directly in “en face” views. Diameters of the MA and LVOT were also measured in similar views as with TTE imaging in 3D TEE data sets.
Results
Both the MA and LVOT were oval. Mean MA diameters were 41 ± 4 mm (3D TEE major axis), 31 ± 4 mm (3D TEE minor axis), 39 ± 5 mm (2D TTE imaging), and 38 ± 5 mm (2D TEE imaging). Mean LVOT diameters were 29 ± 4 mm (3D TEE major axis), 21 ± 2 mm (3D TEE minor axis), 22 ± 2 mm (2D TTE imaging), and 23 ± 2 mm (2D TEE imaging). Compared with 3D TEE measurements, mitral annular CSA was overestimated by 13 ± 12% on 2D TTE imaging and by 7 ± 14% on 2D TEE imaging, while LVOT CSA was underestimated by 23 ± 10% and 17 ± 10%, respectively. Mean values of RVol were 95 ± 43 mL (3D TEE PWDF), 137 ± 56 mL (2D TTE PWDF), 120 ± 45 mL (2D TEE PWDF), and 111 ± 49 mL (flow convergence). Mean EROAs were 69 ± 34 mm 2 (3D TEE PWDF), 98 ± 45 mm 2 (2D TTE PWDF), 88 ± 42 mm 2 (2D TEE PWDF), and 79 ± 36 mm 2 (flow convergence). Observer variability for 3D TEE imaging was better than for 2D imaging.
Conclusions
The 2D TTE PWDF method overestimates mitral RVol and EROA significantly because monoplanar 2D measurements represent mitral annular major-axis diameter and LVOT minor-axis diameter, and assumed circular CSAs of the MA and LVOT are oval.
Quantification of mitral regurgitation (MR) is essential to determine the severity of MR and clinical outcomes. The two most used quantitative parameters are regurgitant volume (RVol) and effective regurgitant orifice area (EROA), which may be calculated by the flow convergence method and the pulsed-wave Doppler flow (PWDF) method as previously recommended. However, both of these methods suffer from geometric limitations of two-dimensional (2D) echocardiography. The flow convergence method potentially underestimates RVol and EROA in functional MR, because the shape of the flow convergence zone may be elliptic instead of hemispheric in this situation. In the PWDF method, important geometric errors are made in calculating the cross-sectional areas (CSAs) of the mitral annulus (MA) and left ventricular outflow tract (LVOT), because of the monoplanar measurements and geometric assumption. In this study, we sought to ascertain the geometric errors made by the traditional 2D transthoracic echocardiographic (TTE) PWDF method in calculating RVol and EROA in patients with degenerative MR, by comparison with the three-dimensional (3D) transesophageal echocardiographic (TEE) PWDF method. Using the latter method, the CSAs of the MA and LVOT were measured directly in state-of-the-art “en face” views on 3D TEE imaging.
Methods
Study Population
From November 2009 to September 2011, we prospectively enrolled 96 consecutive patients referred to our center for potential mitral valve (MV) repair who had undergone baseline TTE and TEE examinations. In the present study, we included patients with (1) degenerative MR according to preoperative TTE findings, (2) P2 scallop prolapse confirmed by both 3D TEE examination and surgery, and (3) good 3D image quality, with complete regions of interest and without stitching artifacts. The exclusion criteria were (1) MR due to other etiologies or mechanisms (e.g., endocarditis, functional MR; n = 39), (2) prolapse of other scallops ( n = 19), (3) a severely calcified MA ( n = 11), (4) more than trivial aortic valve regurgitation ( n = 3), and (5) poor general image quality ( n = 2). Eventually, 22 patients (12 men; mean age, 64 ± 10 years) were included in the study. The protocols were approved by the institutional review board, and informed consent was obtained from all patients.
PWDF Method
2D TTE Measurements
Two-dimensional TTE imaging was performed using the iE33 ultrasound system (Philips Medical Systems, Best, The Netherlands) with the S5-1 transducer. The pulsed-wave Doppler sample was carefully placed as parallel as possible (angle < 20°) to the blood flow in the apical four-chamber and three-chamber views to obtain the Doppler spectral profiles of the MA and LVOT. The mitral annular diameter was measured between the inner edges of the base of posterior and anterior leaflets in early to mid diastole at maximal MV opening in the apical four-chamber view; the LVOT diameter was measured just below the aortic valve in early to mid systole in the parasternal long-axis view. Both diameters were measured at the level at which the volume sample had been placed. The modal velocity profile on Doppler recordings was traced to obtain the velocity-time integral (VTI) ( Figure 1 ). The regurgitant VTI was averaged from measurements in the apical four-chamber and three-chamber views. All measurements were averaged over three cardiac cycles.
3D TEE Measurements
Three-dimensional TEE imaging was performed using the iE33 ultrasound system with the X7-2t matrix-array transducer. Electrocardiographically gated full-volume data sets (built from seven subvolumes) were acquired at the midesophageal level during breath-hold with the ultrasound focus on the MV in the four-chamber view and on the LVOT in the long-axis view. Care was taken to include the complete mitral annular and LVOT circumferences throughout the acquisition. Each full-volume data set was digitally stored and exported to QLAB 8.0 3DQ software (Philips Medical Systems) for offline analysis. The en face views of the MA and LVOT were revealed at time points during the cardiac cycle similar as for the 2D TTE measurements and adjusted to the level at which the pulsed-wave Doppler volume sample had been placed in the 2D TTE examinations. Subsequently, the inner border of the cross-sectional planes of the MA and LVOT as well as the major-axis and minor-axis diameters were measured ( Figure 2 ).
2D TEE Measurements
By adjusting the orthogonal multiplanar reconstruction views of the 3D TEE data sets, the diameter of the MA was measured in the four-chamber view in early to mid diastole at the maximal opening of the MV, and that of the LVOT was measured in early systole in the long-axis view ( Figure 2 ). Both diameters were measured at the level at which the volume sample had been placed.
Using the same VTI MR , VTI MA , and VTI LVOT values obtained during the 2D TTE examinations, the 2D TTE, 3D TEE, and 2D TEE measurements of the diameters or CSAs were used in the following formulas to calculate the RVol and EROA:
RVol = SV MA − SV LVOT = π r MA 2 × VTI MA − π r LVOT 2 × VTI LVOT ,
EROA = RVol / VTI MR ,
Flow Convergence Method
The flow convergence of MR was shown in a zoomed view of color flow Doppler aliasing at the Nyquist velocity limit (30–40 cm/sec) in the apical four-chamber and three-chamber views. The selected cine loop was reviewed stepwise, and a clearly defined mid to late systolic maximal flow convergence zone was measured from the zenith to the regurgitant orifice. The averaged values measured in both views were used to calculate the RVol and EROA using the following formulas:
EROA = 2 π r 2 × V a / Pk V Regurg ,
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