A total of 121 consecutive patients were included in this study. All patients were diagnosed with symptomatic severe aortic stenosis who underwent TAVR with Venusmedtech-VenusA valve (Figure 1) (Venusmedtech, Hangzhou, China) at Fuwai Hospital. All patients were in outpatient follow-up at our center. TTE data were collected before the procedure and 12 months after the procedure. Exclusion criteria included valve-in-valve TAVR (N=3), patients who could not complete 12 months follow-up for various reasons(N=5): 2 patients died for all causes and 3 patients could not complete follow-up at our center. Finally, in total, 113 patients were included in this study. The local institutional review board approved the study, and written informed consent was obtained from all participants.
The THV was implanted based on CT measurements of the aortic valve annulus. Venusmedtech-VenusA valves with a diameter of 23 mm, 26 mm, 29 mm and 32 mm were used for annulus sizes ranging from 17 to 20 mm, 20 to 23 mm, 23 to 26 mm and 26 to 29 mm, respectively. All clinical, echocardiographic, pre-procedural, and post-procedural data were prospectively collected.
Two-dimensional and Doppler Echocardiography
TTE was performed using a commercially available system (E9 ultrasound system, GE Healthcare, Horten, Norway). Standard two-dimensional and Doppler echocardiographic images were acquired using a phased-array transducer in the parasternal and apical views and stored digitally for offline analysis using EchoPAC software version BT 113 (GE Healthcare, Horten, Norway). Each echocardiographic measurement was averaged from three consecutive cardiac cycles for patients in sinus rhythm and from five consecutive cycles in patients with atrial fibrillation. All measurements were performed according to the recommendations of the American Society of Echocardiography [7].
Continuity Equation for aortic valve effective orifice
The EOA for THV was calculated according to the continuity equation as (LVOTd)2×0.785 × (VTILVOT/ VTITHV) [7]. The indexed EOA (EOAI) was calculated as EOA/body surface area (BSA).
LVOTd was measured from a zoomed parasternal long-axis acquisition. Two methods were constructed (Figure 2). In Method #1, LVOTd1 was measured at the entry of the prosthesis stent and from the trailing to the leading edge of the stent, whereas in Method #2, LVOTd2 was measured proximal to the prosthetic valve leaflets (0.5 to 1.0 cm below the aortic valve annulus) and from the trailing to leading edge.
VTITHV was mainly measured by CW from apical windows or occasionally from other acoustic windows (e.g., the right parasternal or suprasternal) to obtain the highest VTITHV. VTILVOT was recorded by PW from apical windows. The region of the PW sampling should match that of the LVOTd measurement with precise localization.
Due to the LVOT’s elliptical geometry, the LVOTd was measured in the 5-chamber view again (the parasternal long axis view and 5-chamber view are two planes lying perpendicular to each other). The minimal diameter and maximal diameter were defined as the shorter LVOTd and the longer LVOTd, respectively. The circularity of the basal plane was expressed as the eccentricity index (EI =1- (minimal diameter / maximal diameter)) [8].
Intra-observer and interobserver measurement variability
Twenty-six patients were randomly selected, and EOA measurements were repeated in these patients by 2 independent observers. Intra-observer and interobserver variability in the measurements were calculated.
Relationships between EOAIs and mean gradient (MG)
The relationships between the EOAIs and the MG were evaluated to validate the measurements of EOA obtained by Method #1 and Method #2.
In low flow-state conditions, the MG may be pseudo-normalized, and the EOA may be pseudo-severized, which may alter the relationship between the EOAI and the MG [9]. Taking into account of the stroke volume (SV) could be quantitated with either pulsed-wave Doppler at the LVOT site or with a volumetric approach. In our study, for Method #1 and Method #2, the different LVOTd measurement got different SV. So, SV was measured with the volumetric approach: LV end-diastolic volume minus end-systolic volume (evaluated via the biplane Simpson method). It was indexed for BSA (SVi). Therefore, we grouped patients by SVi as follows: group 1 (N=57): SVi >35 ml/m2 and group 2 (N=56): SVi<35 ml/m2, and we performed a sub-analysis of the Doppler echocardiographic data.
Depth of THV placement in LVOT was also studied. The depth of delivery was defined as the distance from the native aortic annular margin on the side of the noncoronary cusp (leftward on the described projection) to—on the corresponding side—the most proximal edge (deepest in the left ventricle) of the deployed stent-frame. This was measured using 2D TTE.
Statistical analysis
Data are expressed as the mean with standard deviation or the number of patients (percentages), as appropriate. The χ2 test was used with 2-tailed p values to compare categorical variables. The paired samples t test was used to compare variables between different methods of EOA measurement. Correlations between variables were determined using Pearson correlation methods. Relationships between EOAIs and MG were assessed with multiple nonlinear regression models, and the equation providing the best fit was retained. The results for intra-observer and interobserver variability between methods of measurement were assessed using the intraclass correlation coefficient (ICC) [10] and Bland-Altman [11] methods, respectively. All statistical analysis was performed with IBM SPSS Statistics, version 20.0. software (SPSS Inc., Chicago, IL). p < 0.05 was considered statistically significant.