Version May 2024
INTRODUCTION — Echocardiography is the major noninvasive diagnostic tool for real-time imaging of cardiac structure and function. One of the significant advances in this field has been the development and refinement of three-dimensional (3D) imaging. Since the potential of 3D echocardiographic imaging to overcome many of the limitations of two-dimensional (2D) echocardiography has been fully recognized, ultrasound imaging has gone through multiple phases of development, gradually bringing this imaging technology into the realm of clinical imaging. Real-time 3D echocardiography allows single- or multi-beat acquisition of pyramidal datasets during a breath-hold without the need for off-line reconstruction. One major advantage of 3D echocardiography is the improvement in the accuracy and reproducibility of the evaluation of cardiac chamber volumes by eliminating the need for geometric modeling and the errors caused by foreshortened apical views. Another benefit of 3D imaging is the visualization of cardiac valves and congenital abnormalities, providing guidance of interventions for structural heart disease.
This topic will review the scientific basis for and the clinical use of 3D ultrasound imaging of the heart.
CLINICAL APPLICATIONS — The usefulness of 3D echocardiography has been demonstrated in a number of areas:
●Direct and automated evaluation of cardiac chamber volumes without the need for geometric modeling and without the detrimental effects of foreshortened apical views, resulting in more accurate and more reproducible left ventricular (LV) and right ventricular (RV) volume and ejection fraction (EF) measurements than 2D echocardiography compared with cardiac magnetic resonance (CMR) imaging reference values [1-19]. Also, 3D measurements of myocardial function and strain have been shown to have added prognostic value [20].
●New "surgical" views of the mitral, tricuspid, and aortic valves, adjacent structures, and intracardiac masses [21-43].
●Assessment of regional LV wall motion aimed at objective detection of ischemic heart disease at rest and during stress testing, as well as quantification of systolic dyssynchrony to guide ventricular resynchronization therapy in patients with heart failure [10,44-48].
●Direct evaluation of the size and morphology of the vena contracta along with volumetric quantification of mitral and tricuspid valve lesions [49-54].
●Guidance of interventional procedures in structural heart disease, including 3D printing to enhance personalized presurgical planning [55-60].
Assessment of left ventricular volume and function — Among the principal reasons for requesting an echocardiogram in clinical practice is the assessment of LV chamber size and systolic function. This assessment is predominantly performed using qualitative visual interpretation, or "eye-balling," of dynamic ultrasound images of the beating heart to estimate LV ejection fraction (LVEF), which requires adequate training and experience. Quantification of LVEF from 2D echocardiographic data requires assumptions regarding geometric modeling of the LV.
Limitations of this subjective qualitative interpretation have been long recognized, and consequently, the use of quantitative techniques has been recommended [61,62]. Additional limitations of 2D imaging include:
●The "missing third dimension" has been considered the main source of the relatively wide inter-measurement variability of 2D echocardiographic estimates of ventricular size and function.
●The frequently encountered limitations of endocardial visualization, particularly in the LV apical-lateral segments, are commonly compensated for by tilting the transducer. This maneuver generally improves endocardial visualization but also generates oblique or "foreshortened" views of the ventricle, resulting in less accurate and less reproducible measurements.
The advantage of 3D echocardiography is that it does not require image plane positioning to avoid foreshortening or geometric modeling, thus providing more accurate chamber quantification.
3D technology allows frame-by-frame detection of the 3D endocardial surface from real-time 3D datasets [13]. Most studies that have directly compared the accuracy of 3D measurements of LV volumes and LVEF have demonstrated the superiority of the 3D approach over the 2D methodology, which consistently underestimates LV volumes. This superiority was demonstrated in both accuracy and reproducibility when compared against independent reference techniques, such as CMR [7,8,13,63-66]. In a study in patients post-myocardial infarction, serial real-time 3D echocardiographic measurements had low test-retest variability and were thus able to detect with confidence subtle changes in LV volumes that were not detectable by 2D echocardiography [67]. This is of particular importance in situations that require serial follow-up evaluations of LV function, such as monitoring of cardiotoxic effects of chemotherapy [68]. Similar findings were described by other investigators who used real-time 3D echocardiography-derived measurements for risk stratification in patients post myocardial infarction and in patients with heart failure [69].
However, despite high correlation with CMR reference values and high reproducibility, several studies have reported that real-time 3D echocardiography still underestimates LV volumes, albeit less than 2D echocardiography [9,67,70-75]. For both 2D and 3D measurements, the magnitude of the differences varied widely among studies, suggesting that measurement methodology played an important role. Indeed, in a multicenter study designed to identify the potential sources of error, the major sources of volume underestimation were the tracing methodology and the limited spatial resolution of real-time 3D echocardiographic imaging, which in many patients hindered the differentiation between the myocardium and endocardial trabeculae (image 1) [76]. The results of this study underscored the need for unified guidelines for tracing LV endocardial boundary in order to obtain measurements of LV volumes that are comparable to the current standard reference CMR technique.
In a later study, accurate 3D echocardiography derived LV volumes and LVEF were reproducibly obtained using fully automated endocardial contouring algorithms [15]. This fully automated technique, which decreases the measurement time, yielded results that correlated well with CMR measurements of LV end-diastolic volume, LV end-systolic volume, and LVEF (r-values greater than 0.9). Importantly, the technique was also shown to be highly accurate in a variety of patient groups, including those with atrial fibrillation [15]. Newer techniques for fully automated segmentation of the heart based on machine learning have been more recently developed and tested. A computer algorithm capable of calculating volume data simultaneously for left heart chambers (figure 1) has been developed and found to allow accurate and reproducible volumetric measurements suitable for clinical use [77,78].
Importantly, reference values for 3D echocardiography-derived LV volumes and LVEF have been published from a large cohort of normal subjects [79,80] and were incorporated into the 2015 American Society of Echocardiography/European Association of Cardiovascular Imaging (ASE/EACVI) chamber quantification guidelines, which recommended the use of this methodology in laboratories with sufficient experience [62]. Because these normal values were obtained from a predominantly White population, a large-scale, multicenter study is underway to determine interracial differences in these parameters.
Three-dimensional measurements of myocardial strain are available, and a number of studies focused on 3D strain measurements as an alternative to 2D strain measurements that are fraught by the out-of-plane motion of the speckles throughout the cardiac cycle. One study reported that 3D global longitudinal LV strain was associated with long-term mortality more strongly than 2D EF and even 3D EF, supporting the use of this parameter for prognostic and not only diagnostic purposes [20].
Assessment of right ventricular volumes — Due to the complex crescent shape of the RV, estimation of its volume based on geometric modeling from 2D images has been challenging. The intrinsic ability of 3D imaging to directly measure RV volumes without the need for geometric modeling has resulted in significant improvements in accuracy and reproducibility of RV volume quantification [1,16-19,81].
RV volume measurements can be affected by multiple factors, including gain settings as well as the thickness and orientation of disks used by the disk summation technique [82,83]. However, studies using new software designed specifically for volumetric analysis of RV quantification reported high levels of agreement with CMR values with small underestimation in RV volumes [84-87]. Several studies reported normal age- and sex-specific reference values for RV size and function obtained in a large group of healthy volunteers [88,89]. Based on these studies, the 2015 ASE/EACVI chamber quantification guidelines have provided normal 3D echocardiography-derived values for RV volumes and recommended the use of this methodology in laboratories with sufficient experience [62].
Assessment of atrial volumes — Improved accuracy and reproducibility of the 3D approach have been demonstrated in studies that compared 2D and 3D echocardiographic measurements of left and right atrial volumes against an independent gold standard such as CMR imaging [12,90-93]. These findings may have important clinical implications for the diagnosis and management of patients with atrial fibrillation, diastolic dysfunction, and acute myocardial infarction [94-98]. For example, one study showed that 3D echocardiography classified enlarged left atria more accurately than 2D echocardiography, resulting in fewer patients with undetected atrial enlargement and potentially undiagnosed diastolic dysfunction [92]. 3D assessment of left atrial volume was not included in the 2015 ASE/EACVI guidelines because normal values of left atrial volume have yet to be established across a wide age range.
Assessment of left ventricular mass — Another clinically important variable that is frequently assessed by 2D echocardiography is LV mass. Measurement of LV mass relies on both endocardial and epicardial visualization, with the latter being more difficult because of problems in identifying the epicardial border. As with measurements of LV volumes, there are also other limitations such as inaccurate modeling due to foreshortening. The use of 3D imaging appears to overcome these limitations, as several studies have reported significant improvements in the accuracy and reproducibility of 3D estimates of LV mass compared with their traditional M-mode and 2D counterparts [74,99-104]. This has clinical implications for the serial assessments of the severity of LV hypertrophy in patients with systemic hypertension.
Contrast-enhanced 3D echocardiography — The feasibility of applying volumetric analysis to contrast-enhanced real-time 3D echocardiography datasets obtained in patients with suboptimal image quality has been tested. This approach allows quantification of global as well as regional LV function, when used with selective dual triggering at end-systole and end-diastole to reduce the destructive effects of ultrasound on contrast-enhancing microbubble agents [105,106]. In one study, power modulation with low mechanical indices was shown to successfully reduce microbubble destruction, resulting in continuous contrast-enhanced 3D imaging suitable for accurate and reproducible analysis of LV size and function in patients with suboptimal image quality [107]. One study demonstrated the feasibility and confirmed the accuracy of quantification of RV size and function from contrast-enhanced 3D echocardiographic images [108].
Valvular heart disease — 3D echocardiography plays an increasingly important role in the management of valvular heart disease due to developments in ultrasound and computer technologies, which have resulted in improved on-line 3D displays and sophisticated off-line volumetric valve quantification. The superiority of 3D echocardiography over 2D imaging lies in its realistic "surgical" views of native valves and their anatomic relationships, as well as improved quantification of valve geometry and severity of regurgitation [109].
Mitral valve — Most reports of the evaluation of valvular heart disease using 3D echocardiography have focused on the mitral valve. Volume-rendered 3D displays of the mitral valve acquired with transesophageal echocardiography (TEE) enable improved evaluation of the anatomy (figure 2 and image 2 and movie 1) and its supporting structures [54]. 3D echocardiographic studies have played a crucial role in describing and quantifying the geometry of the mitral annulus, leaflet and coaptation surfaces, tethering and tenting volumes. As an example, 3D visualization of the mitral valve was instrumental in describing the saddle shape of the mitral annulus and redefining the diagnostic criteria for mitral valve prolapse [21,39]. Computer software has also defined the relationship between the mitral apparatus and the position of the papillary muscles thereby providing insight into the pathophysiology of mitral regurgitation. (See "Echocardiographic evaluation of the mitral valve".)
The development of a fully-sampled matrix array transducer has enabled real-time volumetric imaging of the mitral valve from the transthoracic and transesophageal approach (image 3) [110].
The utility of real-time 3D echocardiography in the evaluation of patients with mitral stenosis, and in particular the assessment of mitral valve area, has been established in multiple studies [26,31,37,55,111-113]. The main advantage of 3DE is the ability to achieve a perpendicular en-face cut-plane of the mitral valve orifice enabling accurate mitral valve area measurements. When compared with traditional 2D and Doppler measurements, such as 2D planimetry, pressure half-time and flow convergence, 3DE best agreed with mitral orifice area calculations derived using the Gorlin formula during cardiac catheterization (image 4) [31,37,113]. The 3D measurements had the additional advantage of having lower intra- and inter-observer variability [31,37,113]. (See "Rheumatic mitral stenosis: Clinical manifestations and diagnosis", section on 'Echocardiography'.)
The ease of acquisition and on-line review of real-time 3D echocardiography facilitates immediate assessment of the mitral valve commissural splitting, stretching or tearing after percutaneous balloon mitral valvuloplasty in the cardiac catheterization laboratory. Immediately following balloon valvuloplasty, changes in left atrial and ventricular compliance together with irregularities of the mitral valve orifice limit the utility of the pressure half-time method and 2D planimetry. The high accuracy and reproducibility of 3D echocardiography before and after balloon valvuloplasty compared with the pressure half-time method and 2DE planimetry were demonstrated in a study using invasively determined (Gorlin formula) mitral valve area as the standard [55].
Characterization of the mitral valve apparatus using 3DE has shed new light on the pathophysiology of mitral regurgitation in patients with nonischemic and ischemic cardiomyopathy. Functional mitral regurgitation is associated with annular dilatation and reduced cyclic variations in annular shape and area [32]. Further investigations revealed differences in patients with ischemic mitral regurgitation compared with normal subjects in mitral annular shape with increased inter-commissural and antero-posterior diameters along with increased leaflet tenting indicating chordal tethering (image 5) [3,27,38,114]. Also, patients with anterior wall myocardial infarction have flattened mitral annulus, which is more pronounced than in patients with posterior myocardial infarction [115].
Several studies have reported that mitral regurgitation due to ischemia occurs in conjunction with remodeling of the ischemic region leading to LV dilatation with subsequent papillary muscle displacement (previously known as papillary muscle dysfunction) [116,117]. This results in increased chordal tethering and leaflet tenting, which in turn leads to mitral regurgitation due to decreased leaflet apposition. The insights provided by 3D echocardiography have demonstrated that the presence of mitral regurgitation in patients with dilated or ischemic cardiomyopathy is a disease of the remodeled myocardium rather than secondary to an intrinsic valvular abnormality.
Other studies demonstrated that analysis of 3D echocardiographic images of the mitral valve can provide information on dynamic changes in mitral valve annular surface area and annular longitudinal displacement throughout the cardiac cycle, as well as define the position of the papillary muscles in 3D space [118-120]. Specifically, in patients with dilated cardiomyopathy and mitral regurgitation, symmetric papillary muscle displacement with simultaneous enlargement of the mitral annulus leads to progressive chordal tethering and leaflet tenting, resulting in predominantly central mitral regurgitation, as a result of decreased leaflet coaptation [118-120]. These changes were associated with a relatively non-pulsatile mitral annulus, which displaces minimally towards the apex during systole. In contrast, in patients with ischemic mitral regurgitation, LV remodeling caused by abnormal inferior wall motion results in uneven papillary muscle displacement and asymmetric localized tethering associated with eccentric mitral regurgitation [118,121].
In addition, the characteristics of the mitral annular function were compared between patients with hypertrophic cardiomyopathy and LV hypertrophy secondary to hypertension or aortic stenosis [122]. Annular function in the LV hypertrophy group was similar to that of normal subjects, whereas annular apical-basal motion and annular area changes were reduced in hypertrophic cardiomyopathy [122]. All of these observations carry important implications for the planning of mitral valve repair.
One study demonstrated the usefulness of real-time 3D echocardiography in the evaluation of degenerative mitral valve disease, since quantitative analysis of real-time 3D echocardiographic images allowed accurate classification of the etiology of mitral valve prolapse and determination of the complexity of mitral valve repair [123]. Another study showed the value of 3D parametric maps of the mitral valve for the localization of MV pathology (figure 3) [124]. The role of 3D echocardiography in assessing mitral valve anatomy prior to surgical repair of mitral valve prolapse is discussed in detail separately. (See "Echocardiographic evaluation of the mitral valve", section on 'Mitral valve lesions causing mitral regurgitation'.)
Aortic valve — Real-time 3D echocardiography of the aortic valve using either the transthoracic or TEE approaches is challenging probably due to the oblique angle of incidence of the ultrasound beam and relatively small leaflet size. Real-time 3D echocardiography has been used to improve the accuracy of the quantification of aortic stenosis. Planimetry of the aortic valve using real-time 3D echocardiography has shown good agreement with the standard 2D TEE technique, flow derived methods and cardiac catheterization data, with the advantage of improved reproducibility [125].
Analysis of real-time 3D echocardiography in a small group of normal subjects revealed that the shape of LV outflow tract cross-section was not round but rather elliptical in half of the subjects. Incorrectly assuming a round LV outflow tract geometry during assessment of aortic stenosis may lead to significant underestimation of aortic valve area [126]. This hypothesis was confirmed in an animal model of upper septal hypertrophy, the severity of which correlated with the discrepancy between the traditional 2DE and real-time 3D echocardiography measurements of aortic valve area [127]. Calculations based on real-time 3D echocardiography color Doppler derived estimates of stroke volume correlated with invasive outflow tract flow measurements better than 2D echocardiographic measurements.
An alternative approach based on direct volumetric measurements of stroke volume using semi-automated LV endocardial border detection was compared with Doppler continuity equation and 2D Simpson's technique against invasive Gorlin formula results in patients with aortic stenosis [128]. This study showed that volumetric evaluation from real-time 3Dechocardiography was more accurate than traditional noninvasive techniques.
Tricuspid valve — Relatively limited data are available on the utility of 3D echocardiography in the evaluation of tricuspid valve disease. However, it is increasingly recognized that 3D echocardiography (image 6 and movie 1) allows the visualization of tricuspid leaflet morphology, level of leaflet attachment and coaptation, sub-chordal anatomy, and accurate quantification of the vena contracta of regurgitant jets [40,129].
Characterization of the tricuspid annulus and leaflets in patients with rheumatic heart disease with mitral stenosis and severe tricuspid regurgitation was performed using gated 3D TEE, which demonstrated thickened leaflets with restricted motion, together with annular dilatation [130]. Another study found that real-time 3D echocardiographic measurements of the tricuspid annulus were comparable to those obtained from magnetic resonance images and thus may be helpful for tricuspid valve surgical planning [131]. Several studies have explored the 3D geometry of the normal tricuspid annulus and found it to have round or oval shape that is more planar than the saddle shape of the mitral annulus [41,132].
In patients with functional tricuspid regurgitation, the annulus is even larger, more planar and more circular [133]. In patients with tricuspid regurgitation secondary to pulmonary hypertension, in addition to annular dilatation, an increase in tenting volume has been reported [134]. The severity of tricuspid regurgitation was found to be mainly determined by septal leaflet tethering, septal-lateral annular dilatation, and the severity of pulmonary hypertension [135]. 3D echocardiography has also improved the assessment of tricuspid regurgitation in the presence of pacemaker leads, confirming that it is frequently caused by impingement of the septal leaflet [42,43].
Characterization of the tricuspid annulus and leaflets in patients with rheumatic heart disease with mitral stenosis and severe tricuspid regurgitation was performed using real-time 3DE imaging, which enabled tricuspid valve planimetry, separate evaluation of each tricuspid valve leaflet with regard to thickness, mobility and calcification, as well as assessment of the commissural width at the time of maximal tricuspid valve opening [136].
3D transesophageal echocardiography — Advances in ultrasound transducer technology have allowed the miniaturization of matrix-array transducers, which was achieved by fitting thousands of piezoelectric elements into the tip of a TEE transducer and using integrated circuits for most of the beam forming. These technological advances have simplified the connection between the transducer and the imaging system, resulting in a reduction of the size of the connecting cable and significantly lowering power consumption, thus allowing real-time 3D TEE imaging.
The initial experience with this technology, its feasibility, and its clinical utility for real-time 3D imaging of different cardiac structures, including mitral, aortic, and tricuspid valves, inter-atrial septum, left atrial appendage, and pulmonic veins, was first reported in 2008 [137]. One of the major findings of this study was that real-time 3D TEE consistently provided excellent quality volume-rendered images of the mitral valve apparatus including the anterior and posterior leaflets, as well as annulus and subvalvular structures. Subsequently, imaging using matrix array TEE transducers has become the modality of choice for perioperative planning of mitral valve surgery as well as guidance of structural heart disease procedures [138,139].
Similar to previous 3D TEE acquisition methods, the views of the mitral valve from both left atrial and LV perspectives are unique to 3D imaging; but what distinguishes matrix TEE from rotational 3D acquisition is the consistency of superb quality of visualization of the mitral valve, the absence of rotational artifacts, and immediate on-line display of volume-rendered views. With the unparalleled level of anatomic detail, these volume renderings allow detailed volumetric analysis of the geometry and dynamics of the mitral valve.
Real-time 3D TEE can be employed in any of the usual clinical settings in which TEE is performed. Additionally, real-time 3D TEE can be utilized in the evaluation of the interatrial septum as well as during interventional cardiology procedures (eg, percutaneous valvuloplasty, percutaneous septal defect closure, etc).
Prosthetic valves — 3D TEE has improved visualization and assessment of prosthetic valves, as well as their associated complications, including endocarditis and paravalvular regurgitation. For mitral mechanical and bioprosthetic valves, the ring, leaflets, and struts can be clearly visualized in the majority of patients [140,141]. Although aortic mechanical and bioprosthetic valve leaflets are poorly visualized regardless of perspective, the aortic valve prosthetic rings can be well visualized from the LV outflow and aortic perspective. Similarly, with tricuspid prosthetic valves, the prosthetic ring can be consistently visualized, whereas the leaflets are poorly visualized. The common difficulties in adequately visualizing both the aortic and tricuspid prosthetic valve leaflets are because these valves lie far from the transducer, and their position is oblique with respect to the angle of incidence of the ultrasound beam.
Importantly, the en-face view is useful in the assessment of prosthetic valve endocarditis [140,142-144]. It allows identification of not only vegetations but also discrete valvular dehiscences and their associated regurgitation jets [142-144]. 3D echocardiography can also assist in differentiating vegetations from loose suture material, and the rocking motion of a partially dehisced valve is better appreciated on 3D images.
Volumetric color Doppler imaging — Many noninvasive methods for measuring cardiac output and stroke volume are limited by dependence on geometric assumptions, which can be overcome by the use of quantitative volumetric color flow imaging. This approach was initially validated in an in-vitro setup and in open-chest animals then evaluated in human subjects [20,145-147].
The feasibility of visualizing valvular regurgitant jets using real-time 3D echocardiography color flow imaging has also been demonstrated, and the quantification of mitral and tricuspid regurgitation jet volumes was shown to correlate well with 2D flow convergence methods [148,149]. 3D echocardiography-derived ratio of mitral regurgitant jet volume over left atrial volume has been proposed as a new method to assess the severity of regurgitant lesions, although these ratios were smaller than those measured using 2D echocardiography [148,149].
Having the advantage of volumetric imaging of the geometry of the flow convergence surface, without the assumption of rotational symmetry, real-time 3D echocardiography color flow imaging can quantify mitral regurgitation more reliably than 2D echocardiography [150-152]. Of note, one study has demonstrated this using automated analysis of 3D color Doppler images [151-153].
Indeed, it was shown that the true proximal flow convergence region is more hemielliptical than hemispherical, as previously believed [154]. Based on these observations, a hemielliptic approach was proposed for improved 2DE quantification of mitral regurgitation [154]. More recently, similar to mitral regurgitation, 3D color flow imaging has led to the recognition that the vena contracta in tricuspid regurgitation is not circular but rather elliptical [155,156].
Direct assessment of the vena contracta area using real-time 3D echocardiography revealed significant asymmetry of the vena contracta with functional versus organic mitral regurgitation [157,158]. Effective regurgitant orifice area correlated more strongly with 3D vena contracta area than 2D measures of vena contracta width.
3D echocardiographic guidance of interventional procedures — Because of the real-time nature of 3D echocardiography, it is increasingly used as the primary imaging modality for guidance of catheter-based cardiac interventions. The advantage of 3D echocardiographic images in this context is that they allow the visualization of the entire catheter length [138,139]. Also, 3D echocardiographic imaging provides en-face views of cardiac structures, which contribute to better understanding of the lesion undergoing intervention. This additional information leads to safer and shorter procedures with higher technical success, decreased radiation exposure, and improved outcomes. In addition, echocardiographic equipment is highly mobile and can therefore be performed at the site of care, including the cardiac catheterization laboratory or surgical suite.
Mitral valvuloplasty — The ease of acquisition and online review of real-time 3D echocardiography facilitates immediate assessment of the mitral valve commissural splitting, stretching, or tearing after percutaneous balloon mitral valvuloplasty in the cardiac catheterization laboratory. Immediately following balloon valvuloplasty, changes in left atrial and ventricular compliance, together with irregularities of the mitral valve orifice, limit the utility of the pressure half-time method and 2D planimetry. The high accuracy and reproducibility of 3D echocardiography before and after balloon valvuloplasty compared with the pressure half-time method and 2D planimetry were demonstrated in a study using invasively determined (Gorlin formula) mitral valve area as the standard [55].
Catheter based mitral valve repair for mitral regurgitation — This procedure is an advancement in the non-surgical repair of mitral regurgitation in selected patients. Using a catheter based system, a clip can be delivered percutaneously to grab the tips of the mitral leaflets, creating an edge-to-edge repair [159,160]. This results in two mitral orifices, with significant reduction in the total regurgitant orifice and improvement in the patient's symptoms and functional capacity. During the procedure, live 3D TEE is helpful in the accurate selection of the trans-septal puncture site and is essential for guiding the catheter to position the clip as they are advanced across the atrial septum into the left atrium and placed just proximal to the center of the mitral orifice. Importantly, after the procedure, 3D echocardiography can identify complications, such as pericardial effusion or larger-than-expected atrial septal defects. Occasionally, based on the echocardiographic assessment of the result of the procedure, placement of a second clip may be required [56,160].
Transcatheter closure of ventricular septal defect — 3D echocardiography has proven useful in the diagnosis and catheter-based treatment of ventricular septal defects. 3D TTE can provide en-face images of the defect from both RV and LV perspectives. The shape and the area of the defect can be accurately assessed in combination with the calculation of shunt velocity time integral by spectral Doppler, leading to better estimation of shunt volume [57]. 3D TEE has also been used to guide the procedure and to evaluate its results [58,161].
Percutaneous aortic valve implantation — Percutaneous AV replacement is quickly gaining popularity as a less invasive option for AV replacement. 3D TEE allows accurate assessment of the LV outflow tract (LVOT) and aortic annulus dimensions, which are important in valve size selection [162,163]. An undersized device may result in paravalvular insufficiency or detachment and embolization of the prosthesis. In contrast, oversized devices may result in damage or rupture of the aortic annulus. During the procedure, 3D TEE helps guide the catheter with the prosthetic valve into an optimal position. The exact spatial orientation of the device is crucial, as the valve and the catheter should be aligned coaxially in the LVOT. Advancing the device too far into the aorta may result in occlusion of the coronary ostia, while retraction toward the LVOT may interfere with the motion of the anterior mitral leaflet, resulting in mitral regurgitation [59]. Post-procedure, 3D TEE is useful in evaluating results and identifying potential complications, including paravalvular and transvalvular regurgitation, new wall motion abnormalities, mitral regurgitation, aortic dissection, pericardial effusion, and cardiac tamponade. (See "Choice of intervention for severe calcific aortic stenosis".)
Closure of congenital defects and paravalvular leaks — 3D TEE guidance is instrumental in identifying the site and size of paravalvular leaks. This technique is also useful in guiding the procedure for leak closure (image 7). During this procedure, the RT 3D TEE images of the cardiac structures, catheters, and occlusion devices are displayed together with the fluoroscopic images and are used to guide the operator during the various stages of the procedure.
LIMITATIONS AND FUTURE DIRECTIONS — 3D echocardiography continues to rapidly advance in terms of its technical capabilities, but is still limited in some regards. As discussed above, fully automated endocardial border detection performed as part of real-time 3D echocardiography offers the promise of improved accuracy and reproducibility of LV volume and ejection fraction measurements as well as improved workflow due to shorter examination times. (See 'Assessment of left ventricular volume and function' above.)
The assessment of valvular function and pathology with real-time 3D echocardiography offers some notable improvements over 2D echocardiography. However, the temporal resolution of 3D echocardiography is limited to the sampling rates of commercially available software (10 to 20 volumes per second). Investigators have proposed a technique of acquiring sample volumes over several heart beats and then using the simultaneously obtained electrocardiographic signal to "reorder" the samples [164]. This technique achieves higher frame rates using the currently available technology but relies on assumptions of periodicity of heart motion from beat to beat, which limits the applicability of the technique in patients with variable R-R intervals (eg, those with atrial fibrillation, frequent ventricular or premature atrial complex [PAC; also referred to a premature atrial beat, premature supraventricular complex, or premature supraventricular beat], etc). While this appears to be a promising way to improve the dynamic real-time 3D echocardiographic assessment of valvular function, the technique needs to be validated in additional studies.
Future advances in 3D echocardiography hardware (transducer, computer processing speed) and software should allow wider angle acquisition and color flow imaging to be completed in a single cardiac cycle, which will shorten data acquisition and eliminate stitching artifacts. The transducers will have smaller footprints and weight with higher spatial and temporal resolution. In addition, transducers capable of 2D imaging only will be gradually phased out and replaced by new probes that will be versatile in their capability of imaging in different modes, including 2D, 3D, color, and tissue Doppler. With these multi-tasking transducers, it may be possible to significantly reduce the number of steps required to complete an echocardiographic examination, and thus reduce the time of the test. For example, the standard 2D views could theoretically be obtained from a single volumetric dataset and used for diagnostic purposes assuming that both spatial and temporal resolutions are sufficiently high.
Significant improvements are needed in temporal and spatial resolution in the far field. We also anticipate that the quantification of all cardiac chambers, including flow dynamics, will be performed on the imaging system in an increasingly automated fashion, thus gradually eliminating the need for off-line analysis. This is of crucial importance, in particular, in the interventional settings of the catheterization laboratory and the operating room, where immediate visual and quantitative feedback is important.
It is anticipated that with the ability of real-time acquisition, on-line adjustments of rendering, and cropping capabilities, real-time 3D TEE will be used routinely in perioperative planning of mitral valve surgery as well as guidance of percutaneous interventions. The ease and speed of data acquisition coupled with the ability to display cardiac structures using unique 3D views has led to the rapid integration of this imaging modality into clinical practice and is making an impact on echocardiographic diagnosis of valve disease. In addition, the new 3D printing technology offers opportunities for customized manufacturing of rings and prosthetic valves [60].
SUMMARY AND RECOMMENDATIONS
●Real-time three-dimensional (3D) echocardiography allows for rapid acquisition of images and datasets during a single breath-hold without the need for off-line reconstruction. Major advantages of 3D echocardiography compared with traditional two-dimensional (2D) echocardiography are the improved accuracy of evaluation of cardiac chamber volumes (by eliminating the need for geometric modeling as well as a reduction in errors caused by foreshortened views) and more realistic visualization of cardiac valves and congenital abnormalities. (See 'Introduction' above.)
●Principal reasons for requesting an echocardiogram in clinical practice include the assessment of left ventricular (LV) chamber size and systolic function. 3D technology permits frame-by-frame detection of the 3D endocardial surface from real-time 3D datasets. Nearly all studies that have directly compared the accuracy of 3D measurements of LV volumes and LV ejection fraction have demonstrated the superiority of the 3D approach over the traditional 2D methodology. (See 'Assessment of left ventricular volume and function' above.)
●Due to the complex crescent shape of the right ventricle (RV), estimation of its volume based on geometric modeling from 2D images has been challenging. The intrinsic ability of 3D imaging to directly measure RV volumes without the need for geometric modeling has resulted in significant improvements in accuracy and reproducibility in RV volume quantification. (See 'Assessment of right ventricular volumes' above.)
●Volume-rendered 3D displays of transthoracic or transesophageal images enable improved evaluation of the anatomy of the heart valves and their supporting structures. Accordingly, 3D imaging is particularly helpful to the cardiac surgeon or interventional cardiologist to provide the most detailed anatomic and functional information when planning a variety of interventions and evaluating their results. (See 'Valvular heart disease' above.)
●3D echocardiography is widely incorporated into clinical practice. However, transthoracic 3D imaging is limited by its less than optimal frame rates and spatial and temporal resolution. Improvements in single beat acquisition and in 3D color Doppler quantification have aided integration into routine practice. The ease of data acquisition, decreased reliance on expertise-driven interpretation, and reproducible quantitative analysis provide a foundation for the use of 3D echocardiography in the evaluation, intervention, and management of heart disease. (See 'Limitations and future directions' above.)
ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Lissa Sugeng, MD, MPH, who contributed to earlier versions of this topic review.
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