Role of Echocardiography in the Assessment of Right ...

Curr Cardiovasc Imaging Rep (2013) 6:486–497 DOI 10.1007/s12410-013-9235-z

ECHOCARDIOGRAPHY (T BUCK, SECTION EDITOR)

Role of Echocardiography in the Assessment of Right Heart Disease: Update 2013 Timothy C. Tan & Judy Hung

Published online: 26 October 2013 # Springer Science+Business Media New York 2013

Abstract The right heart plays a significant role in overall cardiac function, with right heart diseases shown to have similar clinical impact as left heart diseases. Despite the availability of a number of imaging modalities for the assessment of the right heart, echocardiography remains the first line imaging modality of choice based on its advantages of being safe, readily accessible and cost effective. Currently, echocardiography whether by the transthoracic or transesophageal approach, plays an important role in the diagnosis and ongoing management of patients with right heart disease. While two dimensional imaging is the mainstay of echocardiographic assessment of the right heart, the availability of more advanced echocardiographic techniques has improved our ability to assess right heart function and a range of right heart pathologies. These techniques apart from overcoming some of the inherent challenges associated with two dimensional imaging of the right heart, have also provided invaluable insights into the physiology of the right heart and pathophysiology of a range of right heart related diseases. Keywords Echocardiography . Right heart . 3D imaging, Strain . Tissue Doppler

Introduction The role of the right heart and its contribution to overall cardiac physiology and function has been traditionally underestimated. This was because the right heart was believed to only serve as a conduit and its contractile function of little T. C. Tan : J. Hung (*) Cardiac Ultrasound Laboratory, Blake 256 Division of Cardiology, Massachusetts General Hospital and Harvard Medical School, 55 Fruit Street, Boston, MA 02114-2696, USA e-mail: [email protected]

hemodynamic significance. Therefore, the development of tools for the assessment of the right heart and its study lagged behind that of the left ventricle, despite right heart diseases having the same poor clinical outcomes as that of left heart dysfunction [1, 2]. Over the past decade, considerable evidence has emerged supporting an essential role for the right heart in normal cardiac function and in maintaining adequate pulmonary perfusion pressures under various conditions. This growing body of evidence includes data demonstrating that RV hemodynamic function is physiologically different to the LV and has clinical significance for patient outcomes in a spectrum of conditions [3•, 4, 5]. Additionally a close relationship between right and left ventricular function has been established [6] with evidence showing that impaired right ventricular function can significantly impact left ventricular function due to the adverse systolic and diastolic interactions via the interventricular septum and the pericardium [7, 8]. Current evidence linking right ventricular dysfunction with increased morbidity and mortality in patients with congenital heart disease, valvular disease, coronary artery disease, pulmonary hypertension and heart failure highlights the value and need for routine imaging of the right heart, particularly in the context of assessing its function and for diagnosis of pathology. Imaging of the right heart can yield potentially useful clinical information, which can be extremely helpful for clinical diagnosis and management. While there is now a number of imaging modalities capable of effectively imaging the right heart and any associated pathology, echocardiography has always been the first line imaging modality due to its ability to provide dynamic structural and hemodynamic information on the right heart. It also has the added advantages of being a readily accessible, non-invasive and cost effective imaging modality, which can be performed at the bedside without the risk of any radiation exposure to the patient. While the mainstay of current echocardiographic assessment of the right heart

Curr Cardiovasc Imaging Rep (2013) 6:486–497

is based predominantly on conventional 2 dimensional (2D) echocardiography, recent advances in echocardiographic imaging such as the use of echocardiographic contrast, 3 dimensional echocardiography, Doppler tissue imaging and myocardial deformation indices, have provided valuable insights into the physiology of the right heart and further improved the utility and application of this imaging modality for the assessment of the right heart. This review aims to discuss the use of these more advanced echocardiographic techniques and to provide an update on their role in assessing right heart function and pathology.

Right Heart Anatomy The right ventricle (RV) is a unique structure with an asymmetrical shape and complex wall motion. It has thin walls and a muscle mass approximately one-sixth that of the left ventricle (LV). Even though it pumps against approximately one-sixth the resistance of the LV, it is able to eject the same rate and volume of blood as the thicker walled LV [9]. Anatomically, the RV can be categorized into three distinct parts, i.e., 1) the inflow tract comprising of the tricuspid valve, chordae tendinae, papillary muscle; 2) apex with the trabeculated myocardium; and 3) the outflow tract also known as the infundibulum which is smooth walled, based on the different structural and functional features of each part (see Fig. 1) [10, 11]. However, the prominent features of the RV that can be visualized on standard 2D echocardiographic imaging are the tricuspid valve, thin walls (3–4 mm), heavy trabeculation and the moderator band, an intracavitary muscle, which runs from the septum to the anterior RV wall (see Fig. 2A). Contractile function on echocardiography can also be visualized to be most active along the longitudinal axis with a less prominent radial motion toward the common septum [12].

Two Dimensional Echocardiography Guidelines The current American Society for Echocardiography (ASE), European Association of Echocardiography (EAE) and the Canadian Society of Echocardiography (CSE) guidelines for the assessment of the right heart advocates a comprehensive 2D echocardiographic examination of the right heart which entails imaging from multiple acoustic windows, and a final assessment drawn from a combination of qualitative and quantitative parameters [3•]. In terms of a qualitative evaluation of the RV, the current guidelines include a visual evaluation of wall thickness, shape, ventricular cavity size and regional function relative to the LV and for the quantitative assessment a range of echocardiographic measures including RV wall thickness, RV and right atrial size, RV diastolic and systolic function by fractional area change (FAC), S’, tricuspid

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Pulmonary Valve

Tricuspid Valve

Outflow tract Inflow tract

Body and apex with trabeculated myocardium

Fig. 1 Schematic diagram of the right ventricle showing the different anatomical features and functional segments of the right ventricle. The inflow tract comprises of the tricuspid valve, associated chordae and papillary muscles. The body and apex consists of heavily trabeculated myocardium and the outflow tract, is usually free of trabeculations and encompasses the pulmonary valve. Image adapted from Schattke et al. 2012 [80]

annular plane systolic excursion (TAPSE), RV index of myocardial performance (RIMPI), pulmonary circulatory pressures, i.e., systolic pulmonary artery pressure (SPAP), estimation of right atrial pressure based on inferior vena cava size and collapse and pulmonary arterial diastolic pressure (PADP). These guidelines also provide a range of reference values for the proposed measures, which have been drawn from population studies or pooled values from several studies (refer to guidelines [3•] for recommended detailed methodology for assessing these parameters and the relevant reference values). The right heart chambers typically develop pertinent characteristics in response to pathological conditions, such as hypertrophy of the walls of the RV outflow tract (precordial views), free wall (apical views) or diaphragmatic wall (subcostal views) and/or dilation of right heart chambers in response to volume or pressure overload from a variety of etiologies, allowing qualitative and quantitative differentiation by 2D echocardiography [13]. Primary myopathic processes or right heart masses can also be detected effectively using 2D echocardiography. However, the main challenge with using standard 2D echocardiography is the accuracy and reproducibility of the imaging due to 1) the asymmetric shape of the RV, 2) limited number of well-defined landmarks, 3) the anterior position of the RV relative to the LV, 4) location of the RV within the thoracic cavity beneath the sternum (which makes imaging from the standard available windows on the human chest difficult), and 5) the non-symmetrical crescent shape (thereby making it impractical to image by echocardiography the irregular shaped organ in a single encompassing

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Fig. 2 Standard apical 4 chamber 2D transthoracic echocardiography images of the right ventricle showing the thin walls, apical trabeculation and moderator band (A). The real shape of the right ventricular can be visualized with 3D imaging. 3D multiplanar reconstruction of the right ventricle demonstrates its conical structure which is not obvious with 2D imaging (B)

plane) [11]. Hence obtaining the necessary information required for a complete and comprehensive assessment may not be possible from a single view or imaging plane or

Fig. 3 2D transthoracic echo images (apical 4 chamber and subcostal views) with (C & D respectively) and without (A & B respectively) echocardiographic contrast illustrating how echocardiographic contrast can be used to highlight and distinguish between an intramyocardial lesion as opposed to an aneurysm in the right ventricular free wall (arrows). LA = Left atrium, LV = Left ventricle, RA = Right atrium, RV = Right ventricle

applicable in the case of the RV. Some of these limitations with 2D imaging may be overcome with the use of more advanced echocardiographic techniques.


Advanced Echocardiographic Techniques 3D Echocardiography Three dimensional echocardiography involves the acquisition and processing of three spatial dimensions allowing better visualization and analysis of cardiac structures as they move through space and time [14]. This technique also allows volume rendered reconstruction of intra-cardiac structures beyond the plane of imaging, making it possible to study the size, shape and motion of specific intra-cardiac structures from any perspective [15–18]. Due to the complex shape of the RV, 2D echocardiography based assessments of the RV can be inaccurate as segments of the RV such as the outflow tract or infundibulum is easily overlooked even though it contributes up to 25-30 % of the RV volume [19]. Early 3D imaging by echocardiography was focused on imaging the left ventricle and was developed based on technology which utilized the reconstruction of 2D images. Limitations of this technology significantly affected image quality and acquisition/analysis times making 3D imaging in the early days, cumbersome, time consuming and impractical for use in routine clinical practice. Subsequent improvements in 3D ultrasound technology have given rise to 3D imaging applications that now make it possible for practical and routine application of this imaging technique in the clinical setting. The development of a full matrix array transducer led to significantly improved resolution, higher penetration and harmonic capabilities that can be applied to both gray scale and contrast imaging, thus allowing 3D volume rendering of images and the simultaneous display of two orthogonal 2D imaging planes. The subsequent development of real-time 3D echocardiography (RT-3DE) enabled images to be obtained in just one cardiac cycle allowing a more realistic visualization of the heart (see Fig. 2B) and its structural dynamics. Additional improvements to the 3D echocardiographic imaging technology has given rise to the currently available applications including real time biplane or triplane imaging with a steerable orthogonal plane (allowing immediate simultaneous visualization of orthogonal 2D imaging planes from traditional transducer acoustic windows), real time or live narrow angle imaging for visualizing structure and function, full volume datasets derived from either a single capture or successive narrow angle volumes, which are digitally reconstructed or ‘stitched’ together and multiplanar or 2D cut plane views that are reconstructed from a full volume dataset [20]. The ability to perform multi-beat acquisitions at higher frame rates has significantly improved image quality [21] with dynamic 3D imaging allowing the opening and closing of valves (see Figs. 4 and 5) and the intra-atrial and –ventricular septa to be examined en face to gain a more accurate perception of their spatial relationship with adjacent structures and the characterization of anatomical defects or

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pathology if present [22]. The advent of new technological advances in 3D echocardiography have improved its applicability for assessing the RV. The assessment of RV function is of particular relevance in patients potentially requiring cardiovascular surgery as right-sided heart failure is one of the most frequent causes of morbidity and mortality after valvular and congenital surgery, coronary bypass or heart transplantation. Hence the accurate assessment of RV function in the preoperative setting is important for accurate risk stratification and postoperative management. Additionally, 3D echocardiography plays an important role in the assessment of right heart valvular structures as it provides views of the valve structure that is not available using standard 2D echocardiography [23•]. Current Clinical Applications of 3D Echocardiography in Right Heart Disease An important benefit of 3D over 2D echocardiography for RV volume quantification is that all three components of the RVare incorporated, without need for geometric assumptions for volume calculation. This is significant as the asymmetric shape of the RV is poorly adapted for geometric assumptions. In vitro and clinical evidence have shown 3D to be more accurate and reproducible than 2D methods [24–26]. Reference values for RV volumes and ejection fractions with real time 3D echocardiography have been published [27•] with data demonstrating excellent correlation between 3D RV volumes and ejection fraction measured using echocardiography compared to cardiac magnetic resonance in both children and adults [28–30]. The ability of 3D echocardiography to accurately accurate three-dimensional volumes of the RV is also dependent on the image quality thus dependent on scanning abilities of the sonographer as the three standard planes of the RV need to be visualized in their entirety and a large enough volume size obtained [31]. Furthermore, 3D RV volume measurements and image reconstruction, which can be performed online or offline on a 3D echo workstation once the 3D datasets have been acquired, requires special RV volume software which is frequently vendor-specific. Essentially each volume data set has to be imported into the vendor specific application and manipulated by rotating, angulating and slicing in any of the three displayed orthogonal planes to obtain an optimal 3D image. Three dimensional RV volumes are then calculated using the method of discs summation where the volume of the RV cavity is computed by usually adding the known areas of seven to eight discs (10 mm high but of varying lengths and widths) spanning the RV from base to apex. Most currently available algorithms for RV volume calculation are able to provide Beutel (mathematic dynamic three-dimensional model) analysis which generates a casting of the right ventricular volume filling and squeezing, generating a volumetric curve and allowing calculation of right ventricular ejection fraction

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Fig. 4 2D (A & B) and 3D transthoracic echocardiographic images of the tricuspid valve en face at the level of the parasternal short axis view highlighting the additional detail of the tricuspid valve leaflets visualized using 3D echocardiography compared to 2D echocardiography in the same patient

[23•, 31]. Segmental analysis of the three main sections of the RV (inlet, apex and outflow segments) can also be performed to generate global and regional RV function. Most currently available softwares for the quantification of RV volumes are semi-automated for ease of use in the clinical setting. A recent Fig. 5 2D (A, B & C) and 3D transesophageal images (D) of a complex fenestrated secundum ASD demonstrating the additional detail that can be obtained using 3D echocardiography which allows an appreciation of the spatial and anatomical construction of the ASD in relation to the surrounding structures

study demonstrated that manual correction of semi-automatic delineation was still necessary to obtain accurate 3D RV volumes and function and to decrease the bias [32]. A recent meta-analysis of 23 studies including 807 subjects revealed underestimation of RV volumes (P90 % for detecting ASDs, additional useful information can be obtained from 3D imaging pertaining to the size, morphology and location of the ASD, which may be very relevant for the surgeon (Fig. 5), as well as to provide guidance during percutaneous closure of such defects (Fig. 6). There are also increasing numbers of patients with congenital cardiac malformations, many of whom have previously undergone corrective surgery where 3D echocardiography can be helpful in visualizing complex anatomy. Three-dimensional color Doppler echocardiography has also been used to obtain more accurate quantification of the severity of regurgitation as it does not require geometric assumptions or reliance on the distant jet for quantification and to provide a direct measured vena contracta area. However there is very limited data on 3D Doppler assessment of tricuspid valve regurgitation or its efficacy for measuring the vena contracta. A recent study involving 92 patients with mild or greater tricuspid regurgitation who prospectively underwent 2D and 3D transthoracic echocardiography demonstrated good correlation between 3D vena contracta area (VCA) with effective regurgitant orifice area (r = 0.62, P