Interventional cardiologists have traditionally relied upon fluoroscopic imaging for percutaneous coronary interventions. Transcatheter structural heart interventions, however, require additional imaging modalities such as echocardiography and multislice computed tomography (MSCT) for pre-, intra- and post-procedural assistance. During transcatheter structural heart interventions, interventional cardiologists and non-invasive cardiovascular imagers may use different terminologies to describe a certain structure, thus causing misunderstandings within the team. Herein, we present a modality- independent terminology for understanding volumetric images in the context of transcatheter heart valve therapies. The goal of this system is to allow physicians to readily interpret the orientation of fluoroscopic, MSCT, echocardiographic and MRI images, thus generalising their understanding of cardiac anatomy to all imaging modalities.
引用本文： . Imaging modality-independent anatomy of the left heart: implications for left-sided transcatheter interventions. 華西醫學, 2018, 33(2): 145-149. doi: 10.7507/1002-0179.201712151 復制
Introduction
Since its beginnings, fluoroscopy has been and remains the main imaging modality used during percutaneous coronary interventions. However, with the development of structural heart interventions, several additional imaging modalities are required to achieve optimal clinical results. Indeed, echocardiography and computed tomography (CT) are used today for pre-procedural planning, intra-procedural guidance, and post-procedural follow-up of transcatheter structural interventions.[1-2] In the case of transcatheter valve replacement, interventional cardiologists rely on echocardiography and CT for patient selection, device sizing, and delivery.[3-4] Herein, we describe an imaging modality-independent terminology to describe the orientation of tomographic data for the specific purpose of left-sided transcatheter cardiac procedures.[5-7] This terminology is intended to be applied to fluoroscopy, CT, echocardiography, and magnetic resonance (MR) imaging, thus facilitating the translation between modalities.
1 Heart anatomy based on a unified terminology
While fluoroscopy, CT, echocardiography, and MR are all fundamentally different, they are used to image the same cardiac structures. Interventional cardiologists rely mostly on pattern recognition rather than three-dimensional anatomical understanding to perform transcatheter procedures. Noninvasive imagers on the other hand have developed a separate terminology to describe the orientation of tomographic images.[8-11] The reliance on multiple imaging modalities each with its own orientation system often results in a disconnect between each modality obfuscating the fact that the same anatomical information is being imaged.
We suggest that describing valve anatomy based on chambers of the heart may facilitate the translation of anatomical information between modalities. This system would enable members of the Heart Team to use the same language to describe common features independently of imaging modality. The concept of heart chamber anatomy originates from echocardiography but can readily be applied to fluoroscopy, CT, or MR.
Because of the mixed coordinate system defined during a CT, MR, or fluoroscopy exam, these modalities are ideal to describe anatomical structures in their attitudinal position.[5, 12-13] This system assumes that the patient is facing the observer. Structures lying closer to the head are superior, those lying closer the feet are inferior. Structures closer to the observer are anterior, while those that are further are called posterior. Finally, structures at the left of the observer are called right; those on the right of the observer are called left. This system is self-evident for CT, MR, and fluoroscopy, but it is not in the case of echocardiography. Indeed, this observation is particularly significant when considering left ventricle echocardiographic segments. The “anterior” segment lies opposite to the “inferior” segment, which contradicts the fact that two directions are separated by 90° in the attitudinal orientation.
From the standpoint of fluoroscopic c-arm angulations, one can describe specific angulations for each heart chamber view.[5-7] The two-chamber view is best appreciated in a shallow craniocaudal angulation at approximately right anterior oblique (RAO) 30°. This is the typical angulation where a left ventriculogram can be acquired. The three-chamber view can be achieved in a steep RAO caudal angulation or in a steep left anterior oblique (LAO) cranial angulation in some patients. The four-chamber view is located in a steep cranial angulation at approximately LAO 30°. Finally, a short-axis view can be appreciated in a moderate LAO-caudal angulation.
2 Three-chamber view
The three-chamber view (Fig. 1) maximally separates the aortic valve from the mitral valve. The minimum diameter of both the aortic and mitral valves is typically visualized in this view. It follows that measurement of each valve dimension in this view can lead to significant underestimation of the average diameter of the valve. In the three-chamber view, the left coronary cusp and non-coronary cusp of the aortic valve are overlapping along the aorto-mitral curtain. Furthermore, the anterior and posterior leaflets of the mitral valve are maximally separated but the subsegments of each leaflet are overlapping.
A three-chamber view can be generated during transthoracic echocardiography using a parasternal long-axis view or an apical view. During transesophageal echocardiography, a mid-esophageal long axis at 120–140° or a transgastric long axis at 100–130° can be used.
From an interventional perspective, the three-chamber view is the best view to direct a transapical guidewire from the left ventricle into the left atrium or the ascending aorta. The crossing of the mitral valve can be particularly challenging because of the funnel-like architecture of the left ventricular outflow tract (LVOT), which naturally guides the catheter toward the aortic valve. The LVOT can be avoided by directing the guidewire in the posterior and inferior direction. The three-chamber view is also ideal to direct catheters toward the anterior or posterior leaflet of the mitral valve. For atrial transseptal puncture, the atrial septum is viewed enface with the needle pointing toward the observer. This view can be used to minimize the risk of aortic root perforation during transseptal puncture.
Figure1
Three-chamber view
a. Shows a CT slice demonstrating the left atrium (LA), left ventricle (LV), and ascending aorta (Ao). The left atrial appendage is maximally separated from the left superior pulmonary vein. Note the separation of the anterior and posterior mitral valve leaflets and overlap of the mitral valve scallops of each leaflet. b. Shows a volume-rendered fluoroscopic image. The mitral valve annulus is overlaid in green.
3 Two-chamber view
The two-chamber view (Fig. 2) has the aortic valve overlapping the mitral valve on fluoroscopy. The maximum diameter of both the aortic and mitral valves is appreciated in this configuration. The anterior and posterior leaflets of the mitral valve are overlapping, thus maximally separating the three scallops of each leaflet; according to Carpentier’s classification, A1, A2, and A3 are separated but overlap with P1, P2, and P3. The scallops are ordered from 1 in the left and superior aspect to 3 in the inferior and right aspect relative to the mitral valve. The left atrial appendage is appreciated superior to the mitral valve and partially overlaps the ascending aorta. The two papillary muscle bundles are maximally separated in this view.
During transthoracic echocardiography, the two-chamber view can be generated from the apical window. On transesophageal echocardiography, this view is appreciated in mid-esophageal 60–90° or in transgastric long axis 90°.
From a historical perspective, it is interesting to note that prior to the advent of pre-procedural CT, echocardiography and fluoroscopy were used for transcatheter aortic valve replacement (TAVR) device sizing. Interestingly, an aortogram recorded in a nearly anterior-posterior orientation was used to measure the diameter of the aortic annulus. This procedure often resulted in the selection of a larger transcatheter device compared to that suggested by echocardiography in a three-chamber view. In the interventional context, the two-chamber view is important to direct catheters toward a mitral valve scallop but cannot differentiate between the anterior or posterior scallops. This is an important point for those performing mitral valve interventions that require the interaction with a specific segment of the valve. The two-chamber view is also important for the left atrial appendage closure since is demonstrates the ostium of the appendage perpendicularly and maximally separated from the left superior pulmonary vein. This allows catheters to be directed toward the appendage thus avoiding the pulmonary vein.
Figure2
Two-chamber view
a. Shows a CT slice demonstrating the left atrium (LA) and left ventricle (LV). The left atrial appendage (LAA) is maximally separated from the left superior pulmonary vein (PV). b. Shows a volume-rendered fluoroscopic image demonstrating the overlap of the mitral valve scallops A1 with P1, A2 with P2, and A3 with P3. Note the order of the mitral valve scallops, 1 being superior and lateral and 3 being inferior and posterior. The mitral valve annulus is overlaid in green.
4 Four-chamber view
The four-chamber view (Fig. 3) shows the left and right ventricles, as well as the left and right atria maximally separated. The interatrial and interventricular septa are perpendicular to the orientation of the screen. The aortic valve overlaps the anterior-inferior aspect of the mitral valve. The commissure of the mitral valve is appreciated in an oblique orientation where different leaflets and scallops are difficult to differentiate.
The four-chamber view can be achieved with transthoracic echocardiography using the apical window. During transesophageal echocardiography, a four-chamber view can be appreciated in a mid-esophageal 10–20° view. Note the tomographic imaging modalities can achieve a five-chamber view in nearly the same orientation as a four-chamber view by translating the imaging in the anterior and superior direction, which provides visualization of the aortic root, the fifth chamber.
From the interventional perspective, the four-chamber view is interesting to visualize atrial and ventricular septal defects. A catheter can thus be directed toward the defect as is done during transcatheter closure. During transseptal puncture, this view can be used to appreciate the needle perpendicularly as it crosses the atrial septum. However, it does not allow to differentiate the septum from the aortic root as those structures are nearly overlapped in this view.
Figure3
Four-chamber view
a. Shows a CT slice demonstrating the left atrium (LA), left ventricle (LV), right atrium (RA), and right ventricle (RV). b. Shows a volume-rendered fluoroscopic image. The mitral valve annulus is overlaid in green.
5 Short-axis view
The short-axis view (Fig. 4) of the heart shows the mitral valve and LVOT en face. Both the major and minor diameters of the mitral valve can be appreciated. The leaflets of the mitral valves as well as each of the leaflet scallops are maximally separated. This view is also perpendicular to the interatrial and interventricular septum. The aortic root lies anterior and superior to the mitral valve. The ostium of the left atrial appendage is appreciated perpendicularly and overlaps the left superior pulmonary vein in this orientation. The two bundles of papillary muscles are located opposite the LVOT, which is severely foreshortened in this view.
The short-axis view can be achieved using the parasternal or subcostal acoustic windows during transthoracic echocardiography. During transesophageal echocardiography, the short-axis view is obtained from a transgastric 0° configuration.
The short-axis view can be used to define the angulation of the left ventricular axis and the direction of the mitral valve during transapical puncture. For transseptal puncture, this view shows the needle perpendicularly. In the context of transcatheter aortic valve replacement or transcatheter mitral valve replacement, this view should not be used during deployment of the device at it provides no information on the depth of implantation in the aortic root or within the mitral annulus.
Figure4
Short-axis view
a. Shows a CT slice demonstrating the left ventricle (LV) and right ventricle (RV). Interestingly, the two papillary muscle bundles are in a superior–inferior configuration relative to each other. b. Shows a volume-rendered fluoroscopic image. The mitral valve annulus is overlaid in green. Note that the left ventricular outflow tract is severely foreshortened in this view and that it lies superior, right, and anterior relative to the two papillary muscle bundles.
6 Conclusion
We described standard imaging modality-independent view based on echocardiographic views of the heart. We described the relevance of these views for structural heart interventions. Using a common language between members of the Heart Team should facilitate translation of the wealth of information obtained from noninvasive imaging to the interventional cardiologist.
Introduction
Since its beginnings, fluoroscopy has been and remains the main imaging modality used during percutaneous coronary interventions. However, with the development of structural heart interventions, several additional imaging modalities are required to achieve optimal clinical results. Indeed, echocardiography and computed tomography (CT) are used today for pre-procedural planning, intra-procedural guidance, and post-procedural follow-up of transcatheter structural interventions.[1-2] In the case of transcatheter valve replacement, interventional cardiologists rely on echocardiography and CT for patient selection, device sizing, and delivery.[3-4] Herein, we describe an imaging modality-independent terminology to describe the orientation of tomographic data for the specific purpose of left-sided transcatheter cardiac procedures.[5-7] This terminology is intended to be applied to fluoroscopy, CT, echocardiography, and magnetic resonance (MR) imaging, thus facilitating the translation between modalities.
1 Heart anatomy based on a unified terminology
While fluoroscopy, CT, echocardiography, and MR are all fundamentally different, they are used to image the same cardiac structures. Interventional cardiologists rely mostly on pattern recognition rather than three-dimensional anatomical understanding to perform transcatheter procedures. Noninvasive imagers on the other hand have developed a separate terminology to describe the orientation of tomographic images.[8-11] The reliance on multiple imaging modalities each with its own orientation system often results in a disconnect between each modality obfuscating the fact that the same anatomical information is being imaged.
We suggest that describing valve anatomy based on chambers of the heart may facilitate the translation of anatomical information between modalities. This system would enable members of the Heart Team to use the same language to describe common features independently of imaging modality. The concept of heart chamber anatomy originates from echocardiography but can readily be applied to fluoroscopy, CT, or MR.
Because of the mixed coordinate system defined during a CT, MR, or fluoroscopy exam, these modalities are ideal to describe anatomical structures in their attitudinal position.[5, 12-13] This system assumes that the patient is facing the observer. Structures lying closer to the head are superior, those lying closer the feet are inferior. Structures closer to the observer are anterior, while those that are further are called posterior. Finally, structures at the left of the observer are called right; those on the right of the observer are called left. This system is self-evident for CT, MR, and fluoroscopy, but it is not in the case of echocardiography. Indeed, this observation is particularly significant when considering left ventricle echocardiographic segments. The “anterior” segment lies opposite to the “inferior” segment, which contradicts the fact that two directions are separated by 90° in the attitudinal orientation.
From the standpoint of fluoroscopic c-arm angulations, one can describe specific angulations for each heart chamber view.[5-7] The two-chamber view is best appreciated in a shallow craniocaudal angulation at approximately right anterior oblique (RAO) 30°. This is the typical angulation where a left ventriculogram can be acquired. The three-chamber view can be achieved in a steep RAO caudal angulation or in a steep left anterior oblique (LAO) cranial angulation in some patients. The four-chamber view is located in a steep cranial angulation at approximately LAO 30°. Finally, a short-axis view can be appreciated in a moderate LAO-caudal angulation.
2 Three-chamber view
The three-chamber view (Fig. 1) maximally separates the aortic valve from the mitral valve. The minimum diameter of both the aortic and mitral valves is typically visualized in this view. It follows that measurement of each valve dimension in this view can lead to significant underestimation of the average diameter of the valve. In the three-chamber view, the left coronary cusp and non-coronary cusp of the aortic valve are overlapping along the aorto-mitral curtain. Furthermore, the anterior and posterior leaflets of the mitral valve are maximally separated but the subsegments of each leaflet are overlapping.
A three-chamber view can be generated during transthoracic echocardiography using a parasternal long-axis view or an apical view. During transesophageal echocardiography, a mid-esophageal long axis at 120–140° or a transgastric long axis at 100–130° can be used.
From an interventional perspective, the three-chamber view is the best view to direct a transapical guidewire from the left ventricle into the left atrium or the ascending aorta. The crossing of the mitral valve can be particularly challenging because of the funnel-like architecture of the left ventricular outflow tract (LVOT), which naturally guides the catheter toward the aortic valve. The LVOT can be avoided by directing the guidewire in the posterior and inferior direction. The three-chamber view is also ideal to direct catheters toward the anterior or posterior leaflet of the mitral valve. For atrial transseptal puncture, the atrial septum is viewed enface with the needle pointing toward the observer. This view can be used to minimize the risk of aortic root perforation during transseptal puncture.
Figure1
Three-chamber view
a. Shows a CT slice demonstrating the left atrium (LA), left ventricle (LV), and ascending aorta (Ao). The left atrial appendage is maximally separated from the left superior pulmonary vein. Note the separation of the anterior and posterior mitral valve leaflets and overlap of the mitral valve scallops of each leaflet. b. Shows a volume-rendered fluoroscopic image. The mitral valve annulus is overlaid in green.
3 Two-chamber view
The two-chamber view (Fig. 2) has the aortic valve overlapping the mitral valve on fluoroscopy. The maximum diameter of both the aortic and mitral valves is appreciated in this configuration. The anterior and posterior leaflets of the mitral valve are overlapping, thus maximally separating the three scallops of each leaflet; according to Carpentier’s classification, A1, A2, and A3 are separated but overlap with P1, P2, and P3. The scallops are ordered from 1 in the left and superior aspect to 3 in the inferior and right aspect relative to the mitral valve. The left atrial appendage is appreciated superior to the mitral valve and partially overlaps the ascending aorta. The two papillary muscle bundles are maximally separated in this view.
During transthoracic echocardiography, the two-chamber view can be generated from the apical window. On transesophageal echocardiography, this view is appreciated in mid-esophageal 60–90° or in transgastric long axis 90°.
From a historical perspective, it is interesting to note that prior to the advent of pre-procedural CT, echocardiography and fluoroscopy were used for transcatheter aortic valve replacement (TAVR) device sizing. Interestingly, an aortogram recorded in a nearly anterior-posterior orientation was used to measure the diameter of the aortic annulus. This procedure often resulted in the selection of a larger transcatheter device compared to that suggested by echocardiography in a three-chamber view. In the interventional context, the two-chamber view is important to direct catheters toward a mitral valve scallop but cannot differentiate between the anterior or posterior scallops. This is an important point for those performing mitral valve interventions that require the interaction with a specific segment of the valve. The two-chamber view is also important for the left atrial appendage closure since is demonstrates the ostium of the appendage perpendicularly and maximally separated from the left superior pulmonary vein. This allows catheters to be directed toward the appendage thus avoiding the pulmonary vein.
Figure2
Two-chamber view
a. Shows a CT slice demonstrating the left atrium (LA) and left ventricle (LV). The left atrial appendage (LAA) is maximally separated from the left superior pulmonary vein (PV). b. Shows a volume-rendered fluoroscopic image demonstrating the overlap of the mitral valve scallops A1 with P1, A2 with P2, and A3 with P3. Note the order of the mitral valve scallops, 1 being superior and lateral and 3 being inferior and posterior. The mitral valve annulus is overlaid in green.
4 Four-chamber view
The four-chamber view (Fig. 3) shows the left and right ventricles, as well as the left and right atria maximally separated. The interatrial and interventricular septa are perpendicular to the orientation of the screen. The aortic valve overlaps the anterior-inferior aspect of the mitral valve. The commissure of the mitral valve is appreciated in an oblique orientation where different leaflets and scallops are difficult to differentiate.
The four-chamber view can be achieved with transthoracic echocardiography using the apical window. During transesophageal echocardiography, a four-chamber view can be appreciated in a mid-esophageal 10–20° view. Note the tomographic imaging modalities can achieve a five-chamber view in nearly the same orientation as a four-chamber view by translating the imaging in the anterior and superior direction, which provides visualization of the aortic root, the fifth chamber.
From the interventional perspective, the four-chamber view is interesting to visualize atrial and ventricular septal defects. A catheter can thus be directed toward the defect as is done during transcatheter closure. During transseptal puncture, this view can be used to appreciate the needle perpendicularly as it crosses the atrial septum. However, it does not allow to differentiate the septum from the aortic root as those structures are nearly overlapped in this view.
Figure3
Four-chamber view
a. Shows a CT slice demonstrating the left atrium (LA), left ventricle (LV), right atrium (RA), and right ventricle (RV). b. Shows a volume-rendered fluoroscopic image. The mitral valve annulus is overlaid in green.
5 Short-axis view
The short-axis view (Fig. 4) of the heart shows the mitral valve and LVOT en face. Both the major and minor diameters of the mitral valve can be appreciated. The leaflets of the mitral valves as well as each of the leaflet scallops are maximally separated. This view is also perpendicular to the interatrial and interventricular septum. The aortic root lies anterior and superior to the mitral valve. The ostium of the left atrial appendage is appreciated perpendicularly and overlaps the left superior pulmonary vein in this orientation. The two bundles of papillary muscles are located opposite the LVOT, which is severely foreshortened in this view.
The short-axis view can be achieved using the parasternal or subcostal acoustic windows during transthoracic echocardiography. During transesophageal echocardiography, the short-axis view is obtained from a transgastric 0° configuration.
The short-axis view can be used to define the angulation of the left ventricular axis and the direction of the mitral valve during transapical puncture. For transseptal puncture, this view shows the needle perpendicularly. In the context of transcatheter aortic valve replacement or transcatheter mitral valve replacement, this view should not be used during deployment of the device at it provides no information on the depth of implantation in the aortic root or within the mitral annulus.
Figure4
Short-axis view
a. Shows a CT slice demonstrating the left ventricle (LV) and right ventricle (RV). Interestingly, the two papillary muscle bundles are in a superior–inferior configuration relative to each other. b. Shows a volume-rendered fluoroscopic image. The mitral valve annulus is overlaid in green. Note that the left ventricular outflow tract is severely foreshortened in this view and that it lies superior, right, and anterior relative to the two papillary muscle bundles.
6 Conclusion
We described standard imaging modality-independent view based on echocardiographic views of the heart. We described the relevance of these views for structural heart interventions. Using a common language between members of the Heart Team should facilitate translation of the wealth of information obtained from noninvasive imaging to the interventional cardiologist.
