Background
In this study, advanced postprocessing of three-dimensional echocardiographic (3DE) data sets was used to identify tricuspid valve (TV) leaflets in two-dimensional echocardiographic (2DE) views, and the feasibility of the subcostal view to obtain 2DE en face views of the TV, as an alternative imaging option to image reconstruction from 3DE imaging, was also tested.
Methods
In 155 consecutive patients, attempts were made to obtain the en face view of the TV by 2DE imaging (from the subcostal window) and by reconstruction from 3DE imaging. Using both in-house-developed and commercially available software for postprocessing of 3DE data, image planes from the standard 2DE views were reconstructed and TV leaflets identified in each view.
Results
With 2DE imaging, all TV leaflets could be visualized in 58% of patients, compared with 56% using 3DE imaging. In 30 patients (19%), en face views of the TV could be obtained only by 3DE imaging. The anterior leaflet was the largest one in 90% of patients, and the smallest leaflet was either the posterior (49%) or septal (41%) leaflet. In 12% of patients, the TV was either bicuspid or quadricuspid. In patients with pacemakers, the position of the right ventricular lead relative to the TV leaflets was readily determined using both imaging techniques. Visible TV leaflets varied in all standard 2DE views because of variability in image planes and leaflet morphology.
Conclusions
High variability in TV leaflet anatomy and the dependence on transducer position do not allow schematic leaflet identification. All existing TV leaflet identification schemes are therefore only partially correct, and if correct leaflet identification is needed, the use of an en face view is recommended.
Increased mortality among patients with moderate and severe tricuspid regurgitation (TR), regardless of pulmonary pressure and left ventricular ejection fraction, has revived interest in better visualization of the tricuspid valve (TV). Two-dimensional (2D) echocardiographic (2DE) assessment of the TV is a challenging task because of complex anatomy and the unfavorable retrosternal position of the valve. Only two TV leaflets are routinely visualized in standard 2DE views, and cumbersome mental three-dimensional (3D) reconstruction of the TV is needed for individual leaflet identification. Unfortunately, currently available schemes for the identification of TV leaflets in existing guidelines, the most influential textbooks, and previous studies are conflicting.
Simultaneous visualization of all TV leaflets in one 2DE cross-sectional view would allow immediate leaflet identification, but achieving an en face view of the TV on 2DE imaging is widely believed to be impossible. A subcostal approach to obtain an en face view of the TV has been suggested, but the feasibility and usefulness of this approach are unknown. Three-dimensional echocardiographic (3DE) imaging permits the en face visualization and comprehensive evaluation of the TV leaflets, annulus, subvalvular apparatus, and surrounding structures, but the need for expensive equipment still delays the integration of this technique in routine clinical practice.
The primary objectives of this study, therefore, were to clarify TV leaflet identification in standard 2DE views by advanced postprocessing of 3DE data sets and to test the feasibility of obtaining an en face view of the TV from a modified subcostal short-axis view.
Methods
Two-dimensional and 3D transthoracic echocardiography was performed in 155 consecutive patients (mean age, 59 ± 15 years; range, 19–94 years; 76% men) referred for standard 2DE studies. All patients were examined using the commercially available Vivid E9 scanner (GE Vingmed Ultrasound AS, Horten, Norway) equipped with a 3V or 4V matrix-array transducer. The same echocardiographer (I.S., A.M.D., or R.J.) acquired both 2D and 3D data sets. A four-point scale (0 = not visualized, 1 = poor, 2 = sufficient, 3 = good) was used to assess the image quality of 2DE and 3DE en face views of the TV. Only data sets with sufficiently good image quality were further analyzed. The relative sizes of the leaflets were assessed semiquantitatively, ranking the leaflets from largest to smallest.
2DE
All patients underwent the standard 2DE imaging of the TV, comprising the parasternal right ventricular (RV) inflow (RVI) view, the parasternal short-axis (PSAX) view at the aortic valve level, and the apical four-chamber (A4C) view. The acquisition of the en face view of the TV was attempted from the subcostal window in all patients. Given the nearly vertical position of the TV (approximately 45° to the sagittal plane), the en face view of the TV can be obtained by directing the transducer to a slightly modified subcostal short-axis imaging plane. Patients were placed in the supine position and scanned during a breath hold after deep inspiration. Relative to the subcostal four-chamber view, the transducer was rotated counterclockwise and tilted inferiorly and slightly to the patient’s right ( Figure 1 , Video 1 ; available at www.onlinejase.com ). Depending on the patient’s constitution, inspiration depth and the degree of probe rotation and angulation were adjusted to optimize viewing of the TV. Image loops of three consecutive heart cycles were digitally stored for further offline analysis (EchoPAC version BT12; GE Healthcare, Milwaukee, WI). Assessment of the subcostal en face view of the TV comprised (1) identification of individual leaflets, (2) anatomy (the number, relative sizes, and mobility of the leaflets), (3) the anatomic relationship between the RV leads and leaflets (in patients with pacemakers), and (4) the origin and size of the regurgitant orifice by color Doppler (in patients with TR).
3DE
During a breath hold, full-volume 3D data sets were acquired from the apical and parasternal windows by stitching partial volumes from six cardiac cycles. From the apex, full-volume 3D data sets were acquired using a modified A4C view as a scout image (for this, the imaging plane was slightly inclined to cover the entire the right heart chamber and to obtain a good view of the TV). For acquisitions from the parasternal window, the transducer was placed in a modified RVI or PSAX position and adjusted to center the TV in the 3D volume. Because we aimed to determine the spatial relationships of individual TV leaflets and surrounding cardiac structures in all standard 2DE views, a gated full 3D volume was acquired that included the whole heart, with the largest acquisition sector possible, at the expense of a loss of spatiotemporal resolution (frame rates typically of 20–25 Hz). Data sets were digitally stored for further offline analysis.
Postprocessing of 3DE Data Sets
Postprocessing of 3DE data sets was performed using both a commercially available EchoPAC workstation (version BT12; GE Healthcare) and customized research software (Software Package for Echocardiographic Quantification Leuven 3D [Speqle_3D]; P. Claus, Leuven, Belgium), based on different approaches for leaflet identification in the reconstructed 2DE views.
EchoPAC
Flexislice and Laser Lines are part of the commercially available 3D toolbox in EchoPAC. The Flexislice tool allows the user to slice in any direction, and full-volume 3DE data sets were sliced along the 2D tomographic planes for standard apical (A4C) and parasternal (PSAX and RVI) views. These 2D tomographic planes remained visible on the 3D volume rendered image as “laser lines”: transparent colored lines showing the origin of reconstructed 2D slices. Simultaneous display of reconstructed standard 2DE and volume-rendered en face view of the TV using the Laser Lines tools allowed immediate identification of the TV leaflets in each view ( Figure 2 , Videos 2 and 3 ; available at www.onlinejase.com ).
Speqle_3D
Volumetric echocardiographic data sets were postprocessed using dedicated, in-house-developed research software (Speqle_3D). This software allows colorization of a partial volume of the 3DE data set semitransparently in such a way that the coloring remains visible when the 3D data set is resliced. At first, all three TV leaflets were visualized in a ventricular en face view and then manually delineated and colored, using different color for each leaflet. Second, image planes from the standard A4C, PSAX, and RVI views were reconstructed from the colorized 3DE data set ( Figure 3 ). Colors allowed the reliable identification of TV leaflets in any 2DE view, and the frequency of occurrence of individual leaflets was counted. The agreement of results obtained by EchoPAC and Speqle_3D was assessed for all reconstructed 2DE views, in all patients.
Statistical Analysis
Continuous data are expressed as mean ± SD. Interobserver and intraobserver agreement on categorical variables (2DE and 3DE image quality and the relative sizes of the TV leaflets) was estimated using the κ statistic in a randomly selected group of 30 patients. The feasibility of obtaining the en face view by 2DE and 3DE imaging (yes or no) was compared using the χ 2 test.
Results
Baseline patient characteristics and indications for standard 2DE imaging are shown in Table 1 . En face views of the TV, demonstrating all three leaflets, could be obtained in 119 of the 155 patients (77%) by means of echocardiographic imaging. Using 2DE imaging from a subcostal view, a technically adequate en face view of the TV leaflets could be obtained in 90 patients (58%), compared with 87 (56%) using 3DE imaging. En face views of the TV were feasible using both methods in 57 patients (37%), while in 30 patients (19%), en face views of the TV were possible only using 3DE imaging. In 36 patients (23%), technically adequate en face views of the TV could not be obtained using either technique because of poor acoustic windows related to body size, chronic obstructive pulmonary disease, previous thoracotomy, or chest radiotherapy.
| Characteristic | Value |
|---|---|
| Age (y) | 59 ± 15 |
| Men/women | 118 (76%)/37 (24%) |
| Body mass index (kg/m 2 ) | 26 ± 4 |
| Body surface area (m 2 ) ∗ | 1.9 ± 0.2 |
| RV dilation (yes/no) † | 24 (15%)/131 (85%) |
| Indication for 2D TTE | |
| Heart failure | 24 (16%) |
| Coronary artery disease ‡ | 89 (57%) |
| Chemotherapy follow-up | 9 (6%) |
| Evaluation of suspected heart disease | 33 (21%) |
∗ Calculated using the Mosteller formula.
† Defined as RV basal diameter in the A4C view > 42 mm.
‡ Previous coronary artery bypass grafting, percutaneous intervention, or myocardial infarction.
Usefulness of the En Face View of the TV
The en face view of the TV, obtained by either 2DE or 3DE imaging, allowed the assessment of leaflet anatomy (number, relative size, and mobility) and the simultaneous visualization of all leaflets. The anterior leaflet was the largest leaflet in 90% of patients, while in the remaining 10%, all three leaflets were of similar size. The smallest leaflet was either posterior (49%) or septal (41%). In 8% of patients, it was not possible to clearly distinguish between the anterior and posterior leaflets, while in 4% of patients, deep indentations between the scallops gave the valve an appearance of being quadricuspid. Of note, the appearance of the TV in standard 2DE views was never indicative of unusual valve anatomy. The variability in TV leaflet number and morphology, as seen by 2DE (subcostal approach) and 3DE imaging, is shown in Figure 4 .
Clinical Context
Similar to the parasternal en face view of the mitral valve, it would have been theoretically possible to estimate the TV orifice area from the subcostal en face view of the TV. In addition, color Doppler could identify size and position of the regurgitant orifice in patients with TR. In one patient with annular dilation and TR that appeared to be functional at the initial standard 2DE evaluation, the en face view of the TV obtained by both 3DE and subcostal 2DE imaging revealed the organic origin of TR, due to a prolapsed anterior leaflet ( Figure 5 , Videos 4–7 ; available at www.onlinejase.com ).
In all patients with pacemaker leads ( n = 9), the position of the RV lead relative to the TV leaflets was readily determined by the en face view obtained by both 2DE and 3DE imaging; in seven patients, the RV lead was positioned between the posterior and septal leaflets, whereas in two patients, the leads traversed and obstructed the septal leaflet ( Figure 6 , Videos 8 and 9 ; available at www.onlinejase.com ). The relationship between the RV leads and the TV leaflets could be appreciated by standard 2DE evaluation only in one patient, in whom the lead obstructing the septal leaflet could be seen in the A4C view.
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