Author + information
- Received February 26, 2018
- Revision received March 15, 2018
- Accepted March 15, 2018
- Published online August 20, 2018.
- Michele Pighi, MDa,
- Pascal Thériault-Lauzier, MD, PhDa,
- Hind Alosaimi, MDa,
- Marco Spaziano, MDa,
- Giuseppe Martucci, MDa,
- Tian-Yuan Xiong, MBBSa,b,
- Jean Buithieu, MDa,
- Luiz Fernando Ybarra, MDa,
- Jonathan Afilalo, MD, MScc,
- Jonathon Leipsic, MDd,
- Ozge Ozden Tok, MDe,
- Negareh Mousavi, MDa,
- Andrea Mangiameli, MDf,
- Thomas Pilgrim, MDg,
- Fabien Praz, MDg,
- Stephan Windecker, MDg and
- Nicolo Piazza, MD, PhDa,g,∗ ()
- aDepartment of Medicine, Division of Cardiology, McGill University Health Centre, Montreal, Quebec, Canada
- bDepartment of Cardiology, West China Hospital, Sichuan University, China
- cDivision of Cardiology and Centre for Clinical Epidemiology, Jewish General Hospital, McGill University, Montreal, Quebec, Canada
- dDepartment of Medicine and Radiology, University of British Columbia, Vancouver, British Columbia, Canada
- eDepartment of Cardiology, Memorial Hospital, Istanbul, Turkey
- fInterventional Cardiology Department, Ramsay Générale de Santé, Institut Cardiovasculaire Paris Sud, Massy, France
- gDepartment of Cardiology, Bern University Hospital, University of Bern, Bern, Switzerland
- ↵∗Address for correspondence:
Dr. Nicolo Piazza, Division of Cardiology, Department of Medicine, McGill University Health Centre, The Royal Victoria Hospital, 1001 Boulevard Décarie, Montréal, Quebec H4A 3J1, Canada.
Performing transcatheter tricuspid valve interventions requires a thorough knowledge of right-heart imaging. Integration of chamber views across the spectrum of imaging modalities (i.e., multislice computed tomography, fluoroscopy, and echocardiography) can facilitate transcatheter interventions on the right heart. Optimal fluoroscopic viewing angles for guiding interventional procedures can be obtained using pre-procedural multislice computed tomography scans. The present paper describes fluoroscopic viewing angles necessary to appreciate right-heart chamber anatomy and their relationship to echocardiography using multislice computed tomography.
Multislice computed tomography (MSCT) multiplanar reconstruction has enhanced patient selection and procedural planning for transcatheter aortic and mitral valve interventions (1,2). Recent publications have described how optimal fluoroscopic viewing angles of left-sided heart structures (e.g., aortic and mitral valve complex, left atrial appendage, atrial septum, and pulmonary veins) can be obtained using MSCT (3,4). Optimizing fluoroscopic viewing angles may decrease procedural times, radiation exposure, contrast volume, and rates of acute kidney injury, and avoid device malpositioning, among other complications.
More recently, interest is shifting toward transcatheter tricuspid valve (TV) interventions (5). Even though the anatomic and functional components of the right heart have been the topic of numerous publications, little consideration has been given to understanding their fluoroscopic configuration. Due to a lack of standardized fluoroscopic viewing angles, interventions on the right heart can be technically challenging. A better understanding of right heart fluoroscopic anatomy can lead to increased operator confidence while reducing procedural time, radiation dose, contrast volume, and complications during transcatheter TV interventions.
Similar to our previous work on left-sided heart structures, this paper aims to describe the fluoroscopic anatomy of right-sided heart structures using MSCT (3). Furthermore, we discuss how fluoroscopic chamber views can mimic standard echocardiographic views (6).
In this article, cardiac structures will be described according to their attitudinal orientation, as detailed in a previous publication by Thériault-Lauzier et al. (3). This approach will be useful to build a consistent nomenclature for both fluoroscopic and MSCT imaging of the right heart. As such, if the subject is facing the observer and standing upright, structures closer to the observer are described as anterior and those relatively farther away as posterior. Components lying closer to the head are superior (i.e., cranial [CRA]) and those toward the feet are said to be inferior (i.e., caudal [CAU]). Structures on the right-hand side of the subject are right-sided, and vice-versa for the left. Describing heart structures in their attitudinal position allows for a common nomenclature between fluoroscopy and MSCT; this approach, however, may require a modification to conventional echocardiographic nomenclature that tends to label structures according to their relative position within the heart (e.g., septal, lateral) while ignoring their attitudinal orientation.
Fluoroscopy is a 2-dimensional planar imaging modality. This technique is affected by parallax, and therefore requires the operator to select multiple viewing angles to provide accurate 3-dimensional spatial information. By contrast, MSCT is not affected by parallax due to its 3-dimensional volume acquisition nature with isotropic voxels allowing the preserved spatial resolution in all imaging planes. It leads to fewer positioning errors and allows the calculation of optimal fluoroscopic viewing angles. For any particular structure, an optimal fluoroscopic viewing angle should minimize positioning errors due to parallax. This fluoroscopic projection is such that the source-to-detector direction is orthogonal to the axis of symmetry of the anatomic feature of interest. MSCT images can be used to define the direction of structures and yield an optimal projection curve (7,8). On the basis of this optimal projection curve (i.e., S-curve), it is possible to select an optimal fluoroscopic angle for a given anatomic structure of interest. In addressing structural procedures, different cardiac structures must be distinguished to accurately implant specific devices. Therefore, it is crucial to understand which fluoroscopic angulations provide maximal separation between structures of interest.
Importantly, fluoroscopy and MSCT rely on x-ray attenuation for contrast resolution. Through this mechanism, it is possible to use MSCT volumetric data to simulate fluoroscopic images, as presented in our report.
In the current paper, we aim to provide general fluoroscopic angulations to describe specific right-sided heart structures. The fluoroscopic images shown in the present paper are obtained from a MSCT scan belonging to a 70-year-old man with severe functional TV regurgitation. Although cardiac structures across patients are similar in orientation, exact fluoroscopic views vary on a patient-by-patient basis (4). Precise angulations for procedural planning can be obtained using MSCT software packages that offer double-oblique multiplanar reconstructions while providing corresponding fluoroscopic viewing angles. FluoroCT version 3.2 (Circle CVI, Calgary, Alberta, Canada) was used to perform the analysis presented in this article.
Overview of the right-sided structures of the heart
Right atrium and venae cavae
The right atrium can be identified within the superior and anterior portion of the right heart. It consists of 2 parts: a smooth-walled posterior portion known as sinus venosus and a pectinated muscular anterolateral portion known as the right atrial appendage. The right atrial appendage is a triangular anterior structure with its apex pointing superiorly and lying over the anterosuperior aspect of the right atrioventricular groove (9) and the aortic root. The superior (SVC) and inferior vena cava (IVC) connect to the right atrium through its superior and inferior aspects, respectively, with the crista terminalis extending on the margin of the right atrium and demarcating the junction of the right atrium and the appendage.
Fossa ovalis and interatrial septum
The fossa ovalis is a depression in the right atrial aspect of the interatrial septum. In the normal heart, the interatrial septum extends from a right posteroinferior to left anterosuperior direction, resulting in a right anterior oblique (RAO)/CAU “en face” view. Structures surrounding the atrial septum include: 1) the inferior vena cava (right inferior-posterior); 2) the infolding of the atrial septum (right superior-posterior); 3) the coronary sinus (left anterior-inferior); and 4) the noncoronary cusp of the aortic valve (left superior-anterior) (10).
The coronary sinus (CS) extends along the posterior rim of the atrioventricular groove (i.e., inferior-posterior surface of the heart). The coronary sinus relieves the great cardiac vein and terminates within the right atrium; the ostium is located left anterior-inferior to the atrial septum, posterior to the TV annulus, and immediately to the left of the inferior vena cava. The coronary sinus ostium is adjacent to the septal component of the TV leaflet and slightly more superior anterior is the membranous septum; together these structures allow identification of the Triangle of Koch and atrioventricular node.
The advent of advanced interventional cardiac techniques and devices for the management of mitral regurgitation (11), heart failure, and chronic angina (12) confirms the importance of understanding the relative location of the coronary sinus.
The TV is the largest and most apically positioned valve; its plane is vertically oriented. Its functional anatomy, similar to that of the mitral valve, can be divided into 4 components: 1) the fibrous annulus (with attached atrium and ventricle); 2) the 3 leaflets; 3) the papillary muscles; and the 4) chordal attachments. Considering the attitudinal orientation of the heart, the TV leaflets classically designated as septal, anterior, and posterior (13) can be designated posterior, anterior, and inferior, respectively. To avoid confusion, the current paper adopts the “traditional” nomenclature; interventional cardiologists, however, should realize the attitudinal orientation of the leaflets so as to better manipulate catheters around the TV. The leaflets are separated by commissures (anteroseptal, anteroposterior, and posteroseptal) and occasionally TV can be quadri-leaflet. The 3 TV leaflets vary in both circumferential (annular) and radial size. The relative circumferential or annular ratios of the anterior-to-septal-to-posterior leaflets in normal patients are 1:1:0.75 (14). The anterior leaflet is the longest with the largest area and the greatest motion. The septal leaflet is the shortest in radial direction and the least mobile. The posterior leaflet is most frequently the smallest of the 3 and may present with multiple scallops. Anatomic landmarks for each leaflet may vary depending on the size and shape of the annulus. For example, in the presence of severe tricuspid regurgitation, the annulus dilates in an septal-lateral direction (13) (or anteroposterior direction with attitudinal orientation). The commissure between the septal and posterior leaflets, however, is usually located adjacent to the coronary sinus ostium.
Various transcatheter interventions targeting the TV require accurate positioning of delivery catheters in relationship with components of the TV (e.g., clips or screws). A clear understanding of fluoroscopic leaflet configuration is important to complement echocardiography during transcatheter procedures targeting the TV. The fluoroscopic anatomy of the leaflets will be a topic of further discussion.
Right ventricle and papillary muscles
The right ventricle lies anterior to the left ventricle. It forms nearly the entire sternocostal surface of the heart and the inferior border of the cardiac profile. It consists of 3 “chambers”: inlet, apical body, and outlet (15). Because the position of the heart in situ is oblique, the apex of the right ventricle is located inferiorly compared with the left ventricle. The TV apparatus includes 2 distinct papillary muscles (anterior and posterior) and a variable third papillary muscle. The largest is typically the anterior papillary muscle with chords supporting the anterior and posterior leaflets. The posterior papillary muscle supports the posterior and septal leaflets. The septal papillary muscle is variable: small, multiple, or absent in up to 20% of normal patients with chords arising directly from the septum to the anterior and septal leaflets (16). Due to its high variability, the fluoroscopic anatomy of the septal papillary muscle will not be described in the present study. The apical portion of the right ventricle is considered a potential target for interventions for tricuspid regurgitation (5). Accurate positioning of devices and their fixation to the right ventricular apex can be facilitated by optimal fluoroscopic viewing angles that avoid parallax and overlap of cardiac structures. Understanding the spatial orientation of the papillary muscles can avoid entanglement with delivery catheters and enhance correct placement of devices.
Pulmonary valve and right ventricle-to-pulmonary artery tract
The pulmonary valve is a semilunar valve located anterior and superior relative to the aortic valve and comprises 3 leaflets. Considering the attitudinal orientation of the heart, the pulmonic cusps designated as left, right, and anterior (12) are in fact posterior, right anterior, and left anterior, respectively. The classic anatomic landmarks described in the aortic root are less evident in the pulmonary trunk and valve, including the sinotubular junction. The leaflets have no annulus in the sense of a fibrous ring. The crown-shaped insertion of the pulmonary leaflets crosses the anatomic ventriculoarterial junction, and the interleaflet triangles are incorporated within the muscular right ventricular outflow tract (RVOT).
Fluoroscopic anatomy of the right heart and its structures
Right-sided heart structures can be described by a set of fluoroscopic chamber views (1-, 2-, 3-, and 4-chamber views). Table 1 summarizes the differentiating characteristics between fluoroscopic right- and left-sided heart chamber views (3).
Tricuspid valve and chamber views
The TV represents a main focus of interest among right-sided heart structures. Important fluoroscopic angulations of the TV annulus include its en face view and perpendicular “in-plane” views described by the optimal projection curve (i.e., S-curve). The optimal projection curve plots the set of all fluoroscopic angulations in which a given structure would be shown perpendicularly in plane. Similar to the mitral valve, the optimal projection curve of the TV annulus demonstrates a steep slope in the RAO region and resultant en face view in a left anterior oblique (LAO)/CAU view. By exploring the optimal projection curve, it is possible to visualize the plane of the TV annulus in different chamber views (Figure 1). This approach provides a framework for understanding the relative position of right-sided heart structures (Figure 2). In the next sections, we review 4 important fluoroscopic angulations for right-sided heart structures and describe their relevance for transcatheter interventions.
One-chamber (short-axis) view
This view can be obtained by orienting the C-arm in an LAO projection with a variable degree of CAU angulation. In our example (Figure 3), an LAO 52°/CAU 14° angulation displays the en face view of the TV and short axis of the RV. In this view, it is possible to appreciate the trajectory of the CS. This view is potentially useful for targeting the structures of interest by matching the anatomic disposition of the leaflets of the fluoroscopic view with a modified (upside down) transgastric transesophageal echocardiography (TEE) view, seen from the ventricular side (17). The short-axis view is useful to differentiate the 3 leaflets of the TV and potentially helpful in guiding procedures targeting these structures, providing the operator with the necessary information to navigate the right atrium and ventricle through the valve. The en face view of the TV also allows the operator to identify the trajectory of the right coronary artery and its distance from the TV annulus. During TEE, the 1-chamber view can be appreciated using a basal transgastric window (0° to 20°) or by using 3-dimensional acquisitions during transthoracic echocardiography or TEE (18).
Right-heart 2-chamber or right ventricle inflow view
This view can be obtained by placing the C-arm in an RAO projection with a variable degree of CAU angulation. This view can help identify the attachments of the anterior and posterior leaflets of the TV to the atrioventricular junction. In the current example, the 2-chamber view was obtained with an RAO 42°/CAU 21° angulation (Figure 4).
The anterior and posterior papillary muscles can be maximally separated in the 2-chamber view (Figure 5). This projection corresponds to a parasternal long-axis 2-chamber view of the right ventricle.
In the RAO fluoroscopic view with mild CAU angulations, both the orifice of the IVC and the TV are in plane. This view may help to better understand the precise angle between the planes of the IVC and TV, and guide delivery catheters from the IVC across the TV and into the right ventricular inflow tract. During attempts to enter the right ventricle, caution is needed to avoid entering and/or injuring the coronary sinus, whose orifice looks inferior and posterior in this projection. The positioning of a device at the right ventricular apex can also be safely achieved using the 2-chamber view in order to avoid entrapment in the subvalvular structures while the papillary muscles are maximally separated. The right-heart 2-chamber view (RAO 35°/CAU 35°) shows the interatrial septum (Figure 6). Furthermore, this is an optimal view to rule-out overlap with the aortic root during transseptal puncture. An RAO projection with extreme CAU angulation (RAO 66°/CAU 61°) shows the CS and the TV both in plane while achieving maximal separation between the 2 structures. In some cases, achieving optimal fluoroscopic angulations may be impractical; a slight compromise in fluoroscopic viewing angles, however, may provide enough visual cues to properly direct catheters.
TEE can demonstrate a 2-chamber view using a mid-esophageal right ventricular inflow view at 100° to 120° (bicaval angle, rotated toward the right), a low-esophageal right atrial view, or a transgastric right ventricular inflow (long-axis) view at 110° to 130°.
Right-heart 3-chamber view
This view is obtained by placing the C-arm in an RAO projection with a variable degree of CRA angulation. A mild CRA angulation (RAO 30°/CRA 24°) with the TV in plane allows visualization of the attachments of the posterior and septal leaflets (Figure 4). In this specific example, a mild RAO projection with a mild-to-moderate CRA angulation (RAO 18°/CRA 30°) creates an overlap between the anterior and posterior tricuspid papillary muscles (Figure 5). In this view, it is possible to appreciate the ostium of the coronary sinus en face (Figure 7). The right-heart 3-chamber view can be obtained during TEE using a transgastric view at 60° to 90°.
This view can be obtained by placing the C-arm in an LAO (or a minimal RAO) projection with cranial angulation. An extreme cranial angulation (RAO 6°/CRA 63°) with the TV in plane allows visualization of the attachments of the anterior and septal leaflets (Figure 4). The 4-chamber view can appreciate the TV annulus and atrial septum both in plane (i.e., the intersection of their respective optimal projection curves). The fluoroscopic 4-chamber view corresponds to the classical apical 4-chamber view on transthoracic echocardiography or mid-to-low esophageal view at 0° to 20° on TEE.
Bicaval or RVOT–pulmonary artery view
This view can be obtained by placing the C-arm in an LAO moderate-to-extreme (lateral) projection with a variable degree of CRA/CAU angulation. Two adjacent tomographic views can be superimposed on this fluoroscopic view, that is, the RVOT–pulmonary artery (PA) view (medially) and the bicaval view (more laterally). Likewise, this structure is best appreciated on the mid-esophageal bicaval view on TEE (19) where it is identified from the confluence of the SVC and the body of the right atrium (Figure 8).
During transcatheter pulmonary valve replacements, physicians often select a lateral projection with shallow CRA angulation to obtain the best views of the right ventricle-to-PA tract (Figure 9). Similar TEE views can be obtained from a high transesophageal window at 0° or from a deep transgastric window at 70° to 90°. Oriented more to the right, the bicaval view can be appreciated from a modified subcostal transthoracic view or from the classical mid-transesophageal bicaval view at 90° to 110°.
Numerous papers have previously described the prominent role of MSCT in the planning of left-sided heart interventions (e.g., transcatheter aortic valve replacement and mitral valve repair) (20). There is currently an increasing interest toward right-sided structures as possible targets for transcatheter interventions in treating both acquired and congenital cardiovascular disease. Although the fluoroscopic right-heart anatomy has been previously described to guide electrophysiological interventions (21), no systematic fluoroscopic descriptions are available for structural heart interventions.
Given the low volumes of right-sided transcatheter structural interventions, imaging right-sided heart structures can be challenging for the interventional cardiologist. Although specific MSCT-derived fluoroscopic viewing angles may differ between patients, the common orientation of the human heart allows generalizations to be made about fluoroscopic chamber views. In the current paper, we have demonstrated that the right-heart 1-chamber view can be obtained in an LAO/CAU angulation, 2-chamber in RAO/CAU, 3-chamber in RAO/CRA, and 4-chamber in an LAO/CRA view. In essence, we have covered the 4 quadrants of the fluoroscopic viewing grid. These standardized views provide a framework for better understanding the 3-dimensional anatomy of the right heart. These standardized views can then be matched to echocardiography thereby improving the communication and creating a similar “language” between interventional cardiologists and invasive/noninvasive imaging specialists (Central Illustration).
In the present paper, a single patient’s MSCT scan was used to generate the fluoroscopic views and explains why we chose to provide approximate angulations. In a previous paper, our group described the modest interindividual variability of fluoroscopic viewing angles for left-sided heart structures (4). It is likely that right-sided structures show similar variability in orientation and allow generalizations to be made with respect to fluoroscopic chamber views and orientation of cardiac structures; the same can be said for coronary imaging during percutaneous interventions. Furthermore, variability between patients in fluoroscopic viewing angles can result from changes in cardiac chamber dimensions from hypertrophy or dilation, comorbidities such as pulmonary obstructive disease or obesity, and normal aging. Similar to our previous work on left-sided fluoroscopic chamber views, future studies should address the interindividual variability of right-sided fluoroscopic chamber views. The objective of the current paper was not to provide the operator with rigid pre-established procedural views, but rather to describe general C-arm positions to obtain the 1-, 2-, 3-, 4- and bicaval/RVOT-PA chamber views while providing guidance to the relative position of cardiac structures in these views. Precise angulations should be obtained on a case-by-case basis.
Although matching views could be demonstrated across imaging modalities, the echocardiographer may have to invert the image (up/down and/or left/right) and/or rotate the image display 90° from the traditional echocardiographic views to match the fluoroscopic windows as we have demonstrated in the figures. Although manipulating echocardiographic windows is more laborious, it allows for the interventional cardiologist and invasive imaging specialist to seemingly “fuse imaging in the mind.”
Performing transcatheter tricuspid valve interventions requires a thorough knowledge of right-heart imaging. Integration of chamber views across the spectrum of imaging modalities can facilitate transcatheter interventions on the right side of the heart. Chamber view anatomy is imaging modality independent and may provide a foundation for a common language that is rapidly understood among the players involved in structural heart disease interventions.
Dr. Thériault-Lauzier has been a consultant for CircleCV and Cephea Valve Technology. Dr. Buithieu has been a consultant for HighLife SAS, Medtronic, and Shanghai MicroPort Medical Group Co. Dr. Leipsic has had institutional core laboratory agreements with Edwards Lifesciences, Medtronic, Tendyne, and Neovasc; and has been a consultant for Edwards Lifesciences and Circle CVI. Dr. Pilgrim has received research grants to the institution from Biotronik, Boston Scientific, and Edwards Lifesciences; and has received speaker fees from Biotronik and Boston Scientific. Dr. Praz has been a consultant for Edwards Lifesciences. Dr. Windecker has received research grants to the institution from Abbott, Amgen, Boston Scientific, Biotronik, and St. Jude Medical. Dr. Piazza has been a consultant/proctor for HighLife, Medtronic, and MicroPort; and a consultant for Cephea. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.
- Abbreviations and Acronyms
- coronary sinus
- inferior vena cava
- left anterior oblique
- multislice computed tomography
- pulmonary artery
- right anterior oblique
- right ventricular outflow tract
- superior vena cava
- transesophageal echocardiography
- tricuspid valve
- Received February 26, 2018.
- Revision received March 15, 2018.
- Accepted March 15, 2018.
- 2018 American College of Cardiology Foundation
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