Author + information
- Received June 11, 2018
- Revision received September 13, 2018
- Accepted October 19, 2018
- Published online March 4, 2019.
- Denisa Muraru, MD, PhDa,b,
- Rebecca T. Hahn, MDc,
- Osama I. Soliman, MDd,
- Francesco F. Faletra, MDe,
- Cristina Basso, MDa and
- Luigi P. Badano, MD, PhDa,b,∗ ()
- aDepartment of Cardiac, Thoracic, Vascular Sciences and Public Health, University of Padua, Padua, Italy
- bIRCCS, Instituto Auxologico Italiano, S. Luca Hospital, University of Milano-Bicocca, Milan, Italy
- cColumbia University Medical Center, New York-Presbyterian Hospital, New York, New York
- dDepartment of Cardiology, Thoraxcenter, Erasmus Medical Center, Rotterdam, the Netherlands
- eDepartment of Cardiology, Fondazione Cardiocentro Ticino, Lugano, Switzerland
- ↵∗Address for correspondence:
Dr. Luigi P. Badano, IRCCS, Istituto Auxologico Italiano, S. Luca Hospital, University of Milano-Bicocca, Milan, Italy.
Tricuspid regurgitation (TR) is an independent predictor of death. Lately, emerging technologies for the treatment of TR have increased the interest of physicians. Due to the complex 3-dimensional (3D) geometry of the tricuspid valve (TV) and its anterior position in the mediastinum, conventional 2D echocardiography is unsuitable to study the anatomy and pathophysiologic mechanisms of the regurgitant TV. 3D echocardiography has emerged as a very cost-effective imaging modality with which to: 1) visualize the TV anatomy; 2) define the mechanism of TR; 3) measure the size and geometry of the tricuspid annulus; 4) analyze the anatomic relationships between TV apparatus and surrounding cardiac structures; 5) assess volumes and function of the right atrium and ventricle; and 6) plan surgical repair or guide and monitor transcatheter interventional procedures.
Echocardiographic Examination of the Tricuspid Valve
Two-dimensional transthoracic echocardiography (2DE) of the tricuspid valve (TV) is challenging because of the complex, nonplanar geometry of the annulus and the highly variable anatomy of the valve (1–3). Moreover, with 2DE, it is difficult to visualize all 3 leaflets simultaneously in a single tomographic view (Figure 1). Therefore, 3D echocardiography (3DE) is needed to perform a comprehensive evaluation of the TV (4). Transthoracic 3DE (3DTTE) can often be used in experienced centers to provide a comprehensive interrogation of the TV leaflets, annulus, and subvalvular apparatus as well as to quantitate the geometry and the function of the right heart chambers (Table 1). In patients with a suboptimal transthoracic acoustic window, during cardiac surgery or interventional procedures, the 3D transesophageal (3DTEE) approach is usually used.
How to Use 3DTTE to Acquire the TV
3DTTE acquisitions of datasets including the TV can be performed from any of the conventional acoustic windows (parasternal, apical, and subcostal). There is not a specific acoustic window from which to acquire a 3DTTE dataset of the TV. The acoustic window from which the TV is best visualized by conventional 2DE is usually used to acquire a 3D dataset of the TV. However, due to the close proximity of the TV and the right ventricle (RV) to the chest wall, and the spatial orientation of the leaflets perpendicular to the direction of ultrasonography beams, an optimal 3DTTE acquisition of the TV is often best achieved from the apical approach, using an RV focused or a foreshortened 4-chamber view, which allows inclusion of the entire TV in the dataset (Central Illustration). Often, a parasternal long-axis view of the right chambers (with the transducer angled toward the right hip) or a parasternal short-axis view can also be used to obtain good quality 3D images of the TV. With the parasternal approach, the TV is situated in the near field, and the resulting 3DE images may have a better spatial resolution than images acquired from the apical approach; however, because the quality of the apical window is usually better than that of the parasternal window in many adult patients, both approaches are valid as long as all 3 TV leaflets are completely visualized.
To achieve the best spatial resolution, it is important that the TV is located in the center of the pyramidal volume acquisition. The acquisition volume, size, and shape will be adjusted in order to encompass the entire TV complex in the dataset, including the leaflets and their attachments to the septum and to the anterior wall and the annulus. The initial step for a good 3DE acquisition is to optimize, first, the 2DE image of the TV to ensure clear delineation of the valve structures with high tissue-blood contrast and absent or minimal noise (Central Illustration). The next step is to ensure that the TV complex is encompassed within the smallest possible acquisition volume during the entire cardiac cycle. Because of the complex anatomy of the valve, it is recommended that the acquisition volume also encompasses surrounding anatomical landmarks to help recognize the individual TV leaflets: the anterior leaflet is located close to the RV outflow tract, left ventricular outflow tract, and aortic valve; the septal leaflet is located close to the septum separating TV from the mitral valve; and the posterior leaflet is close to the RV inferior wall. Accordingly, the region of interest is usually sized and positioned using 2 orthogonal cut planes (Central Illustration).
Important limitations of the use of 3DE in imaging the cardiac valves are the difficulties to appreciate tissue characteristics (i.e., presence of calcifications, fibrosis, or vegetations and so forth) and to evaluate leaflet thickness. In 3DE, color maps are used to code the position (depth) of the voxels and not tissue texture abnormality. Moreover, 3DE usually shows leaflets thicker than they actually are (5). This phenomenon is caused by blurring or amplification artifacts. The different levels of resolution in axial, lateral, and elevation direction of the 3D volumetric dataset (with the axial resolution being higher than lateral and lateral higher than elevation) actually produces 3D ‘‘non-isotropic voxels.’’ In the assembly process, if the system uses, in 1 specific perspective predominantly the elevation resolution (i.e., en face view of the valves obtained from 3D datasets acquired using transthoracic approach and apical position), thin and long structures, such as tricuspid leaflets, may appear with increased thickness.
How to Use 3DTEE to Acquire the TV
The right heart and TV are located in the anterior mediastinum, quite far from the standard mid-esophageal position of the probe, with the left heart structures interposed between the probe and the TV. Because images in the far field may be subject to beam widening and attenuation, often 3DTEE datasets from this position are of lower quality than 3DTTE datasets obtained in patients by using a good transthoracic acoustic window. Because the right heart structures in part rest on the diaphragm, the distance between the transducer and TV can be reduced by advancing the probe to the distal esophagus, proximal to the gastroesophageal junction to obtain unobstructed views of the TV and acquire an optimal 3DTEE dataset. From this position, there is no left atrium in the near field, and only the right heart structures are visualized (Figure 2). However, this acquisition may provide good 3DE images of the valve leaflets only when they are in the closed position (during systole), when leaflets are perpendicular to the insonation beam, whereas the leaflets may be poorly visualized in the open position (during diastole), when they are parallel to the insonation beam. Conversely, acquisitions from the transgastric approach frequently allow good visualization of the TV leaflets in diastole, because they will be perpendicular to the insonation beam but not in systole (Figure 3). Accordingly, it is often necessary to obtain multiple 3DTEE datasets from different probe positions in order to fully assess the TV and the tricuspid annulus.
Limitations of 3D TEE Imaging of the TV
There are a number of limitations to 3D TEE imaging of the tricuspid valve. First, the position of the esophagus in relation to the plane of the tricuspid annulus typically places the annular plane from 0° to 45° to the insonation beam from every imaging plane. Differences in resolution in axial, lateral, and elevation directions of the 3D volumetric dataset (with the axial resolution being higher than lateral, and lateral higher than elevation) actually produces 3D ‘‘non-isotropic voxels.” When the leaflets are more parallel to the insonation beam (i.e., at 0°), lateral and elevation gain resolution will limit structural definition. Patients with an annular plane perpendicular to the insonation beam (i.e., at 90°) may provide better imaging of the tricuspid leaflets in systole, whereas the reverse is true for imaging leaflets in diastole. Second, the tricuspid leaflets are much thinner than the mitral leaflets, resulting in poor echocardiographic definition of the body of the leaflets and significant echo dropout. The thin leaflets and their oblique orientation with respect to the ultrasonography beam produce echoes that are weaker and scattered rather than strong and specular. The assembly algorithms therefore are unable to reconstruct valve leaflet surfaces without dropout artifacts (5).
If, however, the system optimizes the elevational plane, then thin and long structures, such as tricuspid leaflets, may appear with indistinct edges and increased thickness. Third, the fibrous body of the heart as well as any prosthetic material in the left heart (i.e., prosthetic valves) may cause acoustic shadowing or reverberations in the far field of imaging, commonly masking the TV. Although this can frequently be overcome by inserting the probe farther into the esophagus (thus removing the near field left-heart structure causing the artifact), this also changes the angle of insonation resulting in the problems already mentioned. All of these issues become even more problematic for 3D color Doppler imaging.
3DE Acquisition Modes for the TV
The 2 most commonly used 3DE acquisition modes are real-time and multibeat full-volume (6). The trade-offs between the 2 modes should be considered according to each patient and according to the objectives of the 3D scan.
Real-time 3DE acquisition of TV
Real-time 3DE refers to a volume of information acquired over a single or multiple heart beats. Real-time single-beat 3DE acquisition is not limited by motion artifacts (i.e., respirophasic or patient movement) or electrocardiographic cyclic variability (i.e., arrhythmia). Because the TV in the parasternal views is in the near field, the scan sector can be increased with less reduction of volume rate due to the minimal depth required for the acquisition, and it is sometimes possible to visualize the complete TV with a single-beat real-time 3DTTE acquisition. Real-time single-beat 3DTEE, with and without color Doppler, may be most useful when assessing respiratory variations of the regurgitant orifice size and for intraprocedural guidance of interventional procedures on the TV.
Multibeat 3DE acquisition of TV
Multibeat full-volume datasets are composed of several subvolumes that are then stitched together to create a single, larger volumetric dataset with higher temporal and spatial resolution than the same volume acquired using single-beat real-time acquisitions. Multi-beat 3DE datasets may be acquired with or without color Doppler. The 3DE color Doppler acquisition is usually performed to obtain an assessment of the severity of tricuspid regurgitation independent of the geometric assumptions about the shape of the regurgitant orifice affecting the measurements of the diameter of the vena contracta or the calculation of the effective regurgitant orifice area by proximal isovelocity surface area (7). However, multibeat acquisitions could be limited by stitching artifacts due to respiration, arrhythmia, or the patient’s movements. Stitching artifacts could be an issue that precludes accurate interpretation of the 3DE dataset and can be avoided by acquiring the dataset during relatively stable R-R intervals on the electrocardiographic (ECG) breath-holding, with the patient immobile and without moving the probe (6). The number of cardiac cycles to acquire depends on the patient’s characteristics (cardiac rhythm, ability to cooperate, and so forth), the size of the TV complex, and the acquisition depth. However, for quantitative analyses, a dataset should have a minimum temporal resolution of 20 volumes/s, with higher frame rates needed for assessing normal annular dynamics or in presence of tachycardia. To capture the volume with minimal stitched artifacts, imaging the elevational plane (either by 2D or 3D en face view) can be used (Figure 3).
3DE display and quantitative analysis of the TV
To assess the anatomy of the TV, 3DE datasets are typically displayed in volume rendering mode, visualizing the valve en face from both the ventricular and the atrial perspectives (Figure 4). Usually, the atrial perspective (also called the “surgical view” because it resembles the view of the surgeon when the right atrium is opened) is used to assess patients with primary TR (degenerative, traumatic, and others). The ventricular perspective is mainly used to evaluate the commissures and the regurgitant or stenotic orifice in patients with functional TR or stenotic tricuspid valves. Additional longitudinal cut planes can be used to evaluate the motion of single leaflets, the chordae tendineae and the papillary muscle position (Figure 5).
Despite the fact that current recommendations (6) advocate orienting the 3D en face view with the TV septal leaflet placed inferiorly (at the 6-o’clock position), regardless of the atrial or ventricular perspective, these recommendations were written at the end of the last decade, when interventional procedures for the TV were not available, and the proposed orientation of the TV was aimed to replicate the surgical view. Today, when 3DE is used mainly to guide interventional procedures in the catheterization laboratory, the present authors propose a more anatomically oriented display of the TV (Figure 4). Alternatively, Hausleiter et al. (8) recently proposed orienting the en face volumes in a way similar to the orientation of a 2D transgastric image; with the septal leaflet between 12- and 5-o’clock and the aorta at 5-o’clock. This orientation eliminates the third step (rotation of the image) that is always required by current guidelines because the anterior leaflet (not the septal leaflet) is in the far field of imaging from all imaging planes.
Because there is no commercially available, dedicated software with which to perform an echocardiographic quantitative analysis of either TV leaflets’ size and position or annulus geometry, measurements are obtained from dedicated cut-planes obtained by slicing the 3DE dataset.
A transversal cut plane positioned at the level of the tricuspid annulus and oriented in order to cross the junction with TV leaflets in 2 orthogonal planes, will allow the planimetry of tricuspid annulus area and perimeter, and to obtain anatomically sound measurements of its major and minor axes (Figure 6). These measurements are likely to be relatively accurate in patients with severe functional TR in whom the tricuspid annulus is flattened (9). Conversely, in normal subjects and in patients in whom the 3D geometry of the tricuspid annulus is preserved, measurements obtained by 3D reconstruction of the annulus are significantly different from those obtained by direct planimetry of tomographic cut planes (10). Software dedicated to the 3D reconstruction of the tricuspid annulus will allow initialization of the annulus in a series of rotated planes around it to factor the nonplanar nature of the TV into the tricuspid annulus measurements. This feature is not possible with the commercially available slicing method of tricuspid annulus assessment, which provides only planar tomographic views (11). When performing annular measurements using the slicing method, the position of the annular plane is chosen by the operator. However, the choice of the position of this plane is difficult because of the nonplanarity of the annulus. If the chosen annular plane is located at the hinge points of the annulus in 1 longitudinal view, it may not be possible to ensure that it is at the hinge points in the orthogonal plane. As a compromise, the plane is often placed above the annulus, toward the right atrium. As a result: 1) the operator measures a projected or planar area instead of the actual annular area; and 2) part of the right atrial wall will be incorrectly identified as tricuspid annular boundary, resulting in smaller end-diastolic measurements, because at this time the right atrium is the smallest (10,11). These findings explain why there is a need for dedicated software that accounts for the nonplanarity of the TV annulus to provide a more reliable and semiautomated quantification of tricuspid annulus size and dynamics.
In addition, dedicated longitudinal cut planes positioned in the center of each leaflet will allow measurements of the length of the leaflets, the leaflet-to-annular plane tethering angle of each leaflet, and of the coaptation depth of TV leaflets (Figure 7). The tenting volume of TV leaflets by 3DE, accounting for both annulus dilation and leaflet tethering, is a predictor of residual TR following surgical tricuspid annuloplasty (12).
Normal values of TV complex components and right heart chambers
European recommendations report a normal 2DE diameter of the tricuspid annulus in adults of 28 ± 5 mm when measured in diastole, using an apical 4-chamber view (13); however, no reference has been reported to support this value. Both European Association of Cardiovascular Imaging and American Society of Echocardiography agree that significant tricuspid annulus dilation should be defined by a diastolic diameter >40 mm or >21 mm/mm2 in the apical 4-chamber view (13,14). These numbers have limited scientific evidence and have been cited from a paper by Dreyfus et al. (15) in which the only measurements were the intraoperative, stretched annular diameters. Moreover, due to the noncircularity of tricuspid annulus, its dimensions inherently depend on the view used to obtain the measurement (parasternal long- and short axes, apical 4-chamber or subcostal) (9,11), with the apical 4-chamber view showing the highest feasibility (76%) and the highest reproducibility (9). Three recent studies in healthy subjects have reported that the end-diastolic diameter of the normal tricuspid annulus in 4-chamber view is larger than 3.0 cm and that it depends on sex, body size, and view (i.e., standard vs. RV-focused 4-chamber) and also on the diastolic frame in which the measurement is performed (10,11,16). Addetia et al. (2) reported that measurements of tricuspid annulus obtained from RV-focused view in healthy subjects (maximal diameter 35 ± 6 mm at late diastole) correlated more closely with right-heart chamber volumes than the same measurements taken from the standard 4-chamber view (maximal diameter 34 ± 6 mm at late diastole), implying that the former may be more representative of maximal TA size (10). Of note, it has been demonstrated that, regardless of the view, 2DE still underestimates significantly the maximal dimension of tricuspid annulus in comparison with 3DE, cardiac magnetic resonance, and multidetector computed tomography measurements (9,17,18). Thus, tricuspid annulus diameter measured in apical 4-chamber view is smaller than the maximal diameter obtained from 3DTTE (11) or 3DTEE (9) datasets, but 2DTTE and 3DE measurements are closely correlated (r = 0.84) with a systematic 4-mm underestimation by 2DTTE (9).
Furthermore, in healthy subjects, tricuspid annulus size and shape change significantly during the cardiac cycle (10,11). On average, tricuspid annulus linear dimensions and perimeter show >20% systolic shortening, whereas tricuspid annulus area shrinks by 35% during the cardiac cycle. Of this, 49 ± 29% occurs during atrial systole (between late- and end-diastole) (10). Tricuspid annulus area reaches a minimum in mid-to-late systole then increases during isovolumic relaxation and diastole reaching a maximum value in late diastole after the onset of atrial contraction (end of P-wave) (19,20). At late diastole (after atrial systole), normal maximal and minimal linear dimensions of normal tricuspid annulus were 40 ± 5 mm (23 ± 3 mm/m2) and 33 ± 5 mm (19 ± 3 mm/m2). Tricuspid annulus circularity (minimum/maximum diameters) is approximately 0.84 in late diastole, reflecting its elliptical shape. Furthermore, normal values of tricuspid annulus geometry are 11 ± 3 cm2 (6 ± 1 cm2/m2) for maximal area at late diastole, 12 ± 1 cm (7 ± 1 cm/m2) for maximal perimeter, whereas annular height between the highest and lowest point is approximately 7 mm (10,21).
Of note, the most significant reduction in tricuspid annulus size occurs in the pre-systolic phase of the cardiac cycle (after right atrial contraction and during isovolumic RV contraction), with subsequent shortening during the first part of systole. As seen in cross-section, tricuspid annulus shape becomes more circular during systole, and returns to more elliptical shape during diastole due to a relatively greater increase in antero-posterior dimension than in septolateral dimension.
Tricuspid annulus size and function depend also on gender, women having smaller and more dynamic tricuspid annuli than men, and body size (i.e., body surface area) (10).
Finally, tricuspid annulus size depends on the dimensions of right heart chambers, being more closely correlated with right atrial, than with RV volumes (10,11).
In addition to the annulus size and the extent of leaflet tethering, another parameter has recently been reported to be associated with the severity of TR in patients with pulmonary hypertension: the ability of the TV leaflets to grow in order to match the total leaflet area to the closure area (the minimal leaflet area separating the RV and the right atrium necessary to occlude the tricuspid orifice, as required by annular dilatation and ventricular tethering) (22). Afilalo et al. (22) reported that tricuspid leaflet area played a significant role in determining which patient with pulmonary hypertension developed significant TR. The tricuspid leaflet area-to-closure area ratio was the main determinant of the severity of the regurgitation in those patients (22). Accordingly, normal values of TV total leaflet area (the sum of the areas of the 3 leaflets measured at mid-diastole, in the open position) may be of interest to distinguish those patients who develop effective remodeling of the leaflets from those who do not. The authors report a median value of 14.4 cm2 of total leaflet area in healthy controls, which increased by 49% (21.4 cm2) in patients. However, the way the controls were selected was not described in the paper, and healthy controls had a median tricuspid annulus area of 6.9 cm2, which seems quite small compared to other studies reporting reference values of tricuspid annulus size (10,11,21). Therefore, these data and their pathophysiological significance need confirmation.
Finally, the extent of the distortion of the TV complex, leading to TR, is also related to the size of right heart chambers: the RV and the right atrium (23,24).
Incremental value of 3DE over 2DE to define abnormal TV morphology
The complex and variable morphology of the TV complex (25,26) and the difficulty to visualize all 3 TV leaflets in the same tomographic view make 2DE (either transthoracic or transesophageal) a suboptimal imaging technique for evaluating the mechanisms and the severity of pathologies affecting the TV.
Conversely, the acquisition of 3DE datasets including the various components of the TV complex, by careful cropping and anatomic orientation of the cutting planes, will allow the user to obtain any desired view to optimally appreciate the morphology of the TV components in the beating heart and perform a quantitative assessment of its geometry. The en face TV views from the right atrial or RV perspectives will provide a simultaneous display of all TV leaflets and their attachment to the tricuspid annulus to assess the morphology of each individual leaflet (native or prosthetic in case of bioprosthesis dysfunction), presence of leaflet structural abnormalities (such as prolapse, flail, ruptured chords or vegetations attached on leaflets), pacemaker lead interference, coaptation defects or commissural fusion, with the possibility of measuring the anatomical regurgitant or stenotic tricuspid orifice area, respectively (Figure 8). Longitudinal cut planes will allow assessment of the thickness and/or the extent of the tethering of the leaflets, and the status of the subvalvular apparatus (ruptured chordae, position of papillary muscles, and others). Slicing the 3D datasets will allow the quantitative analysis of tricuspid annulus shape and size, extent of the global tethering of the valve (tenting volume), and length and tethering angle of each leaflet (Figure 7, Table 2).
Role of 3D printing and fusion imaging in TV Diseases
Recently, both the increased awareness of cardiologists and cardiac surgeons about the negative impact of TR on patients’ outcome (27) and the currently reported perioperative mortality for tricuspid surgery of 8% to 15% (28), have fueled the development of transcatheter procedures that could potentially treat high surgical risk patients (29). Despite a large array of transcatheter-based devices designed to treat severe functional TR, significant controversy still remains about how, when and in whom to intervene. A more robust understanding of the anatomy and pathophysiology of TR in various clinical settings is needed to improve clinical management and selection of the most appropriate device for the appropriate patient.
Despite the technical advancements and the incremental clinical use of 3DE that has definitely improved our understanding of pathophysiology and functional anatomy of the regurgitant TV (4,24,30), the effectiveness of displaying 3DE datasets as projections on 2D, flat screens has been questioned (31). 3D printing of the TV (32) (Figure 9) has the potential to allow cardiac imagers and interventional cardiologists to move a step forward in understanding and quantifying tricuspid annulus geometry, elevating their impressions from textured flat-screen colored perspectives to actual exploration of the complex geometry of the TV, with the potential to guide personalized care of patients with severe TR (33,34).
The tissues of the various components of TV apparatus are soft and transparent to radiography. In patients with severe TR, only exceptionally there are calcium deposits on the TV and usually these patients are considered unsuitable for transcatheter procedures. Accordingly, the interventional cardiologist cannot rely on fluoroscopic imaging only to guide and monitor procedures on the TV. However, fluoroscopy has its own strengths in the catheterization laboratory: interventional cardiologists are more familiar with fluoroscopy than with other imaging modalities; wires, guide catheters, and devices have been designed to be radiopaque in order to optimize fluoroscopic guidance (conversely, they create artifacts when imaged with echocardiography); the system has a large field of view allowing the operator to follow long segments of catheters; the temporal resolution (up to 30 fps) is adequate to maneuver the catheters. On the other end, 2DE and 3DE can offer detailed anatomical assessment of the TV structures and are pivotal for guiding catheter navigation during transcatheter procedures (35). However, when images obtained from fluoroscopy (to manipulate catheters and devices) and echocardiography (to visualize the components of the TV apparatus) are shown on separate screens, the anatomical relationships between the position/orientation of the wires and catheters and the anatomy of the TV can be lost (also because, particularly for the TV, the projections of the fluoroscopy seldom mimic the views of echocardiography). Advances in the management of digital images have allowed to merge patient-specific imaging data from both fluoroscopic projections and either 2DE views or 3DE cut planes, and align them in the 3D space and time in order to obtain a fusion between 2 imaging modalities that can be displayed in a single monitor and used by the interventional cardiologist to obtain: 1) an easier localization of the anatomical structures of interest; 2) an improved localization of devices and an easier navigation inside the right-heart chambers; 3) a facilitated assessment of trajectories and axial alignment of catheter and devices; and 4) a more precise localization of the landing zone of devices (36) (Figure 10).
Further advances in digital imaging manipulation have recently allowed the fusion of data/images obtained 3 imaging modalities (3DE, angiography and computed tomography) to provide a multimodality imaging reconstruction of the stereoscopic anatomy of the TV and surrounding structures (i.e., the right coronary artery) with the possibility of a quantitative analysis of their spatial relationships (Figure 11).
Because echocardiography is the primary noninvasive imaging modality for assessing the patient with TV disease, 3DE is becoming essential for assessing the anatomy and function of TV complex, as a mandatory tool for better understanding of the TR mechanism, for more precise quantification of abnormal valve geometry, for guiding patient selection and the development of effective and durable TV repair procedures.
Dr. Muraru has received research support and speaker fees from and consults for GE Healthcare; and has received research support from TomTec Imaging Systems. Dr. Badano has received research support from GE Healthcare, Siemens, and TomTec Imaging systems; and is a member of the GE Healthcare Speakers Bureau. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.
- Abbreviations and Acronyms
- 2D echocardiography
- proximal isovelocity surface area
- right ventricle/ventricular
- transesophageal echocardiography
- tricuspid regurgitation
- transthoracic echocardiography
- tricuspid valve
- Received June 11, 2018.
- Revision received September 13, 2018.
- Accepted October 19, 2018.
- 2019 American College of Cardiology Foundation
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