Reviews
Three-Dimensional Echocardiography ― Role in Clinical Practice and Future Directions ―
2020 年 84 巻 7 号 p. 1047-1054
詳細
2020 年 84 巻 7 号 p. 1047-1054
Echocardiography has become an extension of the physical examination in cardiovascular practice. Frequently, it is used to confirm a clinical diagnostic suspicion. Another important role is to detect the underlying cardiovascular lesion to explain a patient’s symptom complex or an abnormality found on chest radiography, electrocardiography, or cardiac enzyme tests. Patients are referred to the echocardiography laboratory because of their symptoms or due to non-specific laboratory abnormalities, and echocardiographers are expected to provide a definite diagnosis or a therapeutic clue. The introduction of the matrix array transducer into clinical practice allowed the acquisition of three-dimensional (3D) datasets. 3D echocardiography (3DE) has many advantages over 2-dimensional echocardiography, such as: (1) improved visualization of the complex shapes and spatial relations between cardiac structures; (2) improved quantification of the cardiac volumes and function; and (3) improved display and assessment of valve dysfunction. 3DE is increasingly utilized during routine clinical practice. This review article is aimed to examine the current clinical utility and future directions of 3DE.
Three-dimensional echocardiography (3DE) began with the cumbersome offline reconstruction of multiple 2-dimensional (2D) acquisition planes, first reported in the 1980 s. In the 1990 s, advancements in technology led to the development of a matrix-array transducer, which was capable of scanning a pyramidal volume instead of a single plane. In subsequent years, further advancements allowed the miniaturization of the matrix-array transducers, which improved the spatial and temporal resolution of the images. These pyramidal data sets are now analyzed with semiautomatic software facilitating the integration of this novel 3D imaging modality into the clinical setting.1 Recent studies have shown that when cardiac chamber sizes are quantified using 3DE, their volumes more closely approximate to those obtained with cardiac magnetic resonance imaging (CMR) than those obtained with 2-dimensional echocardiography (2DE).2,3 Therefore, the recent chamber quantification guidelines recommend the use of 3DE for cardiac chamber quantification.4 Echocardiography has become an extension of the physical examination in cardiovascular practice.5 This review article is aimed to examine the current clinical utility and future directions of 3DE.
Assessment of the left ventricular (LV) size and function is important in clinical practice. The accuracy of traditional 2D methodology for LV volume quantification is limited by the acquisition of foreshortened apical views and reliance on geometric assumptions.6,7 Foreshortening occurs when the imaging plane does not pass through the true LV apex resulting in an oblique view of the LV cavity.8 When these oblique views are used to calculate LV volumes, the resultant volumes are underestimated. In this regard, 3DE offers a number of advantages. It eliminates errors associated with ventricular foreshortening by allowing the user to select anatomically correct, non-foreshortened apical views from the pyramidal data set. In addition, 3DE eliminates the need for geometric assumptions when calculating ventricular volumes.
3D LV volumes correlate well with CMR-derived reference volumes, with smaller biases and narrow limits of agreement.2,3 This is important because 3DE can detect smaller volume and ejection fraction (EF) changes in patients requiring serial assessments. This is clinically useful in patients receiving potentially cardiotoxic chemotherapeutic agents or in those with valvular regurgitations, where small changes may prompt more frequent evaluations or changes in medical strategy.9,10 In laboratories with experience in 3DE, 3D measurement and reporting of LV volumes are recommended when good-quality 3D data sets are obtained. With the use of new adaptive analytic algorithms based on machine-learning technology, incorporating 3D quantification into daily clinical practice may become easier (Figure 1).11
Three-dimensional echocardiography-derived speckle strain analysis.
The normal 3DE LV end-diastolic volume (EDV) and end-systolic volume (ESV) in Japanese patients are 50±12 mL/m2 and 19±5 mL/m2 in men and 46±9 mL/m2 and 17±4 mL/m2 in women.12
In population-based studies, LV hypertrophy is an important predictor of cardiovascular events.13 Traditionally, LV mass has been quantified using M-mode or 2D measurements of wall thickness, together with end-diastolic LV cavity dimensions.4 3D LV mass can be determined using the 3D-guided biplane technique or the direct volumetric analysis method. Because 3DE is the only echocardiographic method that can directly measure LV volumes, it is an appropriate approach without geometric assumptions about cavity shape and hypertrophy distribution.14 3DE can assist in the diagnosis and avoid over detection of wall thickness, including tendons and right ventricular moderator band.
The normal 3DE LV mass values in Japanese men and women are 64±12 g/m2 and 56±11 g/m2, respectively.12
Speckle-tracking echocardiography (STE) allows quantification of LV deformation parameters (i.e., strain and strain rate) by tracking the motion of distinct acoustic markers throughout the cardiac cycle. The concept has been recently integrated into 3DE, enabling 3D deformation measurements. The main advantage of 3D STE over 2D STE is that speckles can be followed in all directions as they move within the thicker pyramidal imaging volume.15,16 With 2D tracking, speckles are lost when they move out of the imaging plane.17 Once full-volume datasets are obtained, 3DE images can be analyzed to quantify global longitudinal strain (GLS), global circumferential strain (GCS), global radial strain (GRS), and global area strain (GAS). 3D STE-derived LV strain has been shown to detect subclinical systolic LV impairment in a wide range of conditions.18–20 The reported 3DE normal mean values of GLS among the studies varied from 15.80% to 23.40% (mean, 19.05%); GCS varied from 15.50% to 39.50% (mean, 22.42%); GRS varied from 19.81% to 86.61% (mean, 47.48%); and GAS varied from 27.40% to 50.80% (mean, 35.03%).21
LV twist or torsion represents the mean longitudinal gradient of the net difference in clockwise and counterclockwise rotation of the LV apex and base, as viewed from the LV apex. Twist during ejection predominantly deforms the subendocardial fiber matrix, resulting in storage of potential energy. Subsequent recoil of twist deformation is associated with the release of restoring forces, which contributes to LV diastolic relaxation and early diastolic filling.22 3D STE has a theoretical advantage to overcome out-of-plane motion and is useful for understanding LV twist dynamics in clinical settings.17 The relationship between longitudinal and torsional mechanics of the LV provides insight into the transmural heterogeneity in myocardial contractile function. The presence of a subendocardial-to-subepicardial gradient in LV mechanics may provide a useful clinical measure for early recognition of a subclinical state of heart failure.
Non-invasive evaluation of LV filling pressure is important for the diagnosis and treatment of heart failure. The ratio of the early diastolic mitral inflow velocity to the early diastolic mitral annular velocity (E/e’) is used as a non-invasive parameter for estimating the LV filling pressure.23 However, its use in some conditions remains controversial, and the angle dependence of Doppler measurement and preload dependence of e’ in non-dilated hearts indicate major problems. The ratio of the early filling rate derived from the time derivative of LV volume to the early diastolic strain rate (FRe/SRe), similar to E/e’, by 3D STE, can address such limitations.24 The novel parameter can be simultaneously obtained with LVEF measurements, which would allow the quick and easy examination of the LV systolic and diastolic functions (Figure 2).
Measurement of the early diastolic strain rate by 3-dimensional speckle-tracking analysis.
The right ventricle (RV) has a crucial role in determining the functional status and prognosis of patients with a variety of diseases, including ischemic and non-ischemic cardiomyopathy, pulmonary arterial hypertension, and valvular heart diseases.25–27 Estimation of RV size and function using 2D imaging remains challenging due to its asymmetrical and complex crescent shape and retrosternal location, making it difficult to visualize the entire RV chamber from a single 2D echocardiographic view. The functional analysis of the RV from 2D echocardiography has therefore been limited to fractional change in RV areas and assessment of RV longitudinal motion using parameters such as tricuspid annular plane systolic excursion (TAPSE) and tissue Doppler S-wave velocity. Recently, 3DE has provided a unique opportunity for the quantification of RV volume and functional analyses. Several studies have made a comparison between 3DE and CMR for RVEF and RV volume measurements.28,29
Current published data suggest that the upper limits of 3DE RV EDV are 87 mL/m2 in men and 74 mL/m2 in women, while those of RV ESV are 44 mL/m2 in men and 36 mL/m2 in women.4 An RVEF of <45% indicates abnormal RV systolic function.
The newly developed RV 3D STE software provides RV volumes; 3 separate RV directional strain measurements, including global longitudinal, circumferential, and area strain; and regional inflow, apex, and outflow functions.30,31 This method allows the measurements of regional strain in the inflow, outflow, and apical portions of the RV. A recent report has demonstrated the detection of heterogeneous RV function abnormalities and improvement after treatment in a patient with pulmonary arterial hypertension.32
Left atrial (LA) enlargement has been suggested to represent long-term exposure to elevated pressures, and LA volume is a powerful predictor of adverse cardiovascular outcomes.33 LA volume measurements are preferred over the linear dimension because they allow a more accurate assessment of the asymmetric remodeling of the atrium.34 LA volume measured using 2DE is often underestimated compared with that measured using 3DE and CMR. The LA has the following functional roles: reservoir, conduit, and booster. The volumetric evaluation of the LA phasic function is derived from the measurements of maximum LA volume, minimum LA volume, and LA volume immediately before atrial contraction.
The normal LA maximum and minimum volumes in Japanese are 41±11 mL (23±6 mL/m2) and 17±5 mL (10±3 mL/m2) in men and 36±9 mL (24±6 mL/m2) and 15±4 mL (10±3 mL/m2) in women.12 The upper normal limit for maximum LA volume is 34 mL/m2 in both genders.4
More recently, an LA strain analysis has been applied to evaluate the LA phasic function (Figure 3), which may have prognostic implications.35,36 3DE allows calculation of time-volume curves, which may have prognostic implications in future. Some data suggest that with age, the LA reservoir function decreases and booster function augments.37
Left atrial volume and functional analysis by 3-dimensional echocardiography.
The morphology of the LA appendage (LAA) correlates with stroke in patients with atrial fibrillation.38 Even in patients with sinus rhythm, impaired LA and LAA functions are related to changes in the LAA. The WATCHMAN LAA closure device is a reasonable alternative to warfarin therapy for stroke prevention in patients with non-valvular atrial fibrillation.39 Understanding the 3D morphology of the LAA can help interventional cardiologists simulate operative procedures prior to LAA occlusion.40
The right atrium (RA) plays an integral role in cardiac performance by modulating RV function with its reservoir, conduit, and contractile functions.41,42 As with the LA volume, RA volume is likely to be more robust and accurate for the determination of RA size than linear dimensions. RA volumes are underestimated with 2DE compared with those measured using 3DE.
The upper limits of 3DE RA maximum and minimum volumes in men are 49 mL/m2 and 20 mL/m2, and in women, they are 38 mL/m2 and 16 mL/m2.42
The superiority of 3DE over 2DE lies in its realistic imaging of complex cardiac anatomy, visualization of their anatomical relationships, and geometry.43 With transthoracic 3DE, it is possible to quantify the mitral valve (MV) apparatus and LV characteristics that contribute to mitral regurgitation.44 3D transesophageal echocardiography (TEE) is increasingly utilized during routine clinical practice to evaluate patients who are good candidates for structural heart procedures, to guide a growing list of transcatheter heart procedures, and for echocardiographic quantification. 3D TEE is particularly suitable for evaluating complex MV anatomy, given the close proximity of the MV to the midesophageal imaging window. While 2DE provides a general understanding of the MV anatomy, 3DE provides a more comprehensive understanding of MV pathology and 3D spatial relationships (Figure 4). The en-face views of the MV provide incremental information on the mechanisms of valve dysfunction.45 This information is often critical for procedural and post-procedural of patients undergoing edge-to-edge plication using the MitraClip (Figure 5).46 3DE has also been used for characterizing mitral prosthesis paravalvular regurgitation and guiding transcatheter paravalvular leak closure procedures. 3DE measurements of the MV stenotic orifice area and MV regurgitant orifice area have already been validated in comparison to reference techniques.47,48
Two-dimensional transesophageal echocardiography (A,B) and 3-dimensional echocardiography (3DE) (C) in a patient with infectious endocarditis. 3DE provides spatial relationships of anatomy and vegetations (arrow heads). LA, left atrium; LV, left ventricle.
Two-dimensional orthogonal transesophageal echocardiographic views (A,B) and 3-dimensional en-face views of the mitral valve from the left atrial perspective (C) and the left ventricular perspective (D) during edge-to-edge plication with the MitraClip.
3DE affects the clinical evaluation of the aortic valve (AV) in the measurement of the aortic annulus and modeling of the AV and root.49,50 As the number of transcatheter AV implantation procedures continues to grow, transthoracic echocardiography has replaced TEE as the imaging modality of choice in many centers.51 When renal disease prohibits the use of computed tomography (CT) with iodinated contrast enhancement, the AV annulus can be measured accurately using 3D TEE in the periprocedural period.52
The tricuspid valve (TV) is a complex structure with 3 leaflets of varying sizes that are attached to the fibrous tricuspid annulus. Tricuspid regurgitation (TR) is an independent predictor of mortality. However, assessing the severity and mechanism of TR remains challenging. Unlike those of the MV, 3D images of the TV are best acquired from the transthoracic approach. The acquisition of 3DE datasets, including various components of the TV complex, by careful cropping and anatomical orientation of the cutting planes will allow the operator to obtain any desired view of the TV.53
Fusion of 3DE with other imaging modalities to evaluate patients with suspected or known coronary artery disease is promising. Recent studies on fusing 3DE strain with coronary CT angiography may ultimately obviate the need to induce hyperemia in order to detect hemodynamically significant coronary artery stenosis.54 3DE is important in the management of patients with congenital heart disease, particularly for pre-surgical planning, guidance of catheter intervention, and functional assessment of the heart.55 Fusion imaging allows direct visualization of the CT-derived coronary artery tree and myocardial function represented on the color-coded polar map (Figure 6).56 Catheter interventions for patients with structural heart diseases have been increasingly used in clinical practice. Echo-fluoroscopic fusion imaging provides better understanding of the 3D relationship of the anatomy and devices.57–59
Fusion imaging of a patient with coronary artery disease. Cardiac computed tomography shows coronary lesions (A, arrows). Three-dimensional speckle tracking echocardiography is integrated with the coronary artery tree (B). The degree of myocardial ischemia is indicated from green (no ischemia) to red (severe ischemia) on the color-coded polar map. LAD, left anterior descending artery; LCX, left circumflex artery; RCA, right coronary artery. Reproduced with permission from Takaya Y, et al.56
3DE has ushered in a new era of cardia imaging. Combining 3DE datasets with other imaging platforms (fusion imaging), 3D printing, virtual reality, and holography can be disruptive technologies in cardiology.60,61 Even with the development of new technologies (3DE, speckle-tracking, semi-automated analysis, etc.), the final interpretation of the analysis results is strongly dependent on the operator’s experience. Diagnostic errors are a major unresolved problem. Artificial intelligence (AI) can improve the analysis and interpretation of medical images. AI might help improve observer variation and provide accurate diagnosis with echocardiography, and cardiologists should have adequate and solid knowledge in this field.62
With current technologies, a full 3D examination in routine clinical practice is feasible. 3DE has many advantages over 2DE; (1) improved visualization of the complex shapes and spatial relations between cardiac structures; (2) improved quantification of the cardiac volumes and function; and (3) improved display and assessment of valve dysfunction. Innovative technologies are taking advantage of the enhanced spatial and temporal resolutions afforded by 3DE to improve diagnosis, communication, and patient management.
This study was supported by scholarship funds from Otsuka Pharmaceutical Co., Ltd. K.T. is a member of Circulation Journal Editorial Team.
