A decade of technical advances has established the feasibility of percutaneous strategies to treat SHD such as atrial septal defect (ASD), patent foramen ovale, as well as regurgitant
or stenotic cardiac valves18
utilizing the emergence of supportive image guidance. As more structural interventions are adopted, proceduralists are required to become adept at utilizing imaging technology that not only identifies vascular lumen or gross anatomy, but also images soft-tissue and adjacent structures. Future structural interventions hinge on the integration of imaging to navigate cardiac chambers, target different structures, and deploy a variety of therapeutic devices. Current methods such as x-ray fluoroscopy, 2D echocardiography, 3D echocardiography (3DE), cardiac MR, and cardiac CT have developed independently and merged into important adjuncts that enable the execution of complex structural interventions.8
In general, there are common elements to the process of executing structural interventions; however, individual procedures emphasize particular elements. The common elements include preprocedural planning, targeting, detection/positioning and tracking, mechanical biofeedback/ eye-hand coordination, precise repositioning and alignment, navigation, 3D localization, deployment surveillance, and postprocedure inspection (Figure 3.2
). These functions are discussed further in subsequent parts of the chapter and in the case-specific tasks.
Complex cardiac interventions occur in a dynamic and anatomically intense 3D environment requiring accurate characterization of structure and function. Ultrasound image generation is dependent upon either transmission or reflection of propagated sound waves and the return frequencies characteristically produced by different tissues. The frequencies used in medical imaging are tuned to both the target tissues and the depth needing to be imaged. These ultrasound images provide the anatomic landscape for interventional procedures. However, the interaction of highly reflective devices such as a “J” wire causes reverberation or signal dropout that must be mentally integrated with tissue effects when attempting to understand the anatomic landscape.7
Conversely, some catheters or wires such as a “glidewire” demonstrate very little ultrasound signature, thus making visibility almost impossible. Understanding the ultrasound characteristic of catheters, wires, and devices and their interaction within the anatomic landscape is critical for guidance of complex interventional procedures.
Traditionally, 2D TEE and intracardiac echocardiography (ICE) have assisted such interventions.27
2D TEE is capable of measuring structural defects, guiding navigation of catheters, and monitoring the delivery of devices. The safety and effectiveness of 2D TEE are well established in ASD/ventricular septal defect (VSD) device sizing, equipment navigation, device deployment, and assessment of postprocedural complications such as thrombus formation.29
Complementary use of echocardiography with x-ray imaging results in reduced radiation exposure when ultrasound guidance for navigation is performed in combination with an effort to reduce fluoroscopy. Despite these advantages, 2D TEE still requires mental integration of multiple imaging planes on the fly when tracking objects that are often in and out of plane.31
This is especially true when catheters, wires, and devices are variably echogenic. In ASDs for example, defect rims are not reliably imaged within one viewing plane possibly resulting in sizing errors and increasing the risk of device embolization if the incorrect device is deployed.33
This is equally true when assessing valvular structures, and when evaluating placement of devices near coronary arteries and their relationship to the annulus of the aortic valve and planes of orientation. Imaging of near structures such as inferior vena cava or pulmonary veins may be inadequate to assess safe navigation or structure obstruction. The advantage of enhanced guidance is balanced by the risk of long interventions that require general anesthesia.7
Development of 3DE has been slow but is now universally available with most vendors marketing 3D packages, and in some cases is acquired using a single cardiac beat. Processing is much
more user-friendly compared to prior platforms.34
Real-time 3D transthoracic echocardiography (RT3D TTE) has been clinically implemented to improve endomyocardial biopsy accuracy35
and off-pump mitral valve (MV) edge-to-edge repair in a pig model.36
This was expanded to successful percutaneous ASD closure.37
The development of real-time 3D imaging with both transthoracic (3D TTE) and transesophageal echocardiography (3D TEE) integrates moving structures with definition of depth in wide field of views providing superior structure resolution. This allows definition of cardiac defects, chambers, and valves while directly and simultaneously monitoring movements of interventional devices.
Figure 3.2 Graphic display of the volume images is shown by the three different 3D echocardiographic methods. RT3D TEE focused method is shown in panel A, which is at a focused depth that magnified 3D dataset (crème color). Shown in panel B is the narrow sector RT3D “live” method (blue color); note the larger FOV but, with less depth or thickness. Panel C, the steerable biplane technique shows the orthogonal nature of the planes (yellow lines).
Real-time 3DE obtained from the TEE probe has improved resolution of the atria, vena cava, and valves.38
The first available
RT3D TEE probe was released utilizing a matrix phase-array transducer (X7-2t, Philips, Andover, MA) that instantaneously acquires a 3D pyramidal dataset. Four different types of datasets may be acquired using this probe: complete volume gated dataset, real-time operator-focused 3D dataset, real-time zoomed 3D dataset, and simultaneous biplane adjustable 2D dataset (Figure 3.3
). Volume rendering and perspective are accomplished through color shading of the volume, thereby creating a sense of depth, but precise distances are not well validated within real-time 3D acquisitions.
Complete volume data gated acquisition takes advantage of the RT3D TEE’s wide field of view (FOV) by scanning and integrating a volumetric echosector, thereby displaying
moving cardiac structures. This is a summation of four adjacent wedge-shaped volumetric datasets acquired sequentially over four cardiac cycles, with subsequent fusion into a single large echosector (Figure 3.3C
The dataset may be viewed offline in operator-defined cropped planes in any axis and orientation, offering several visual vantage points ideal for preprocedural planning.
Figure 3.3 Steps for image guidance are shown. Using a mitral valve balloon valvuloplasty as an example, each key stage is shown: first, transseptal puncture; second, identification of the target; positioning and definition of trajectory; and target verification and precision adjustment. Each step is important for preplanning and procedural guidance.
Real-time 3D images may be acquired via two modes: (1) larger field of view (FOV) with focused thickness (Figure 3.3B
) volume that segments heart valves, complex defects, masses, and might allow visualization of the right ventricle (RV); (2) a high magnification mode, which acquires images using an obtuse view angle and a limited sector region of interest with less depth (Figure 3.3A
). The wider FOV and greater perspective are ideal for navigating catheters and interventional devices, while the thin sector 3D is better for determining edges of ASDs or leaflet insertion in valve clip procedure. Both volumetric datasets may be rotated or tilted to define desired structures and can be viewed in cropped planes of any axis and orientation. However, a systematic approach to movement of the volume is critical to avoid anatomic confusion. Thus, one could first tilt the image to gain a top view from which rotation like a clock can occur and then move toward key structures like the aortic valve positioned at 12 o’clock to provide standard perspectives such as the “surgeon’s view” of the left atrium (LA). These methods provide the advantage of online manipulation of the dataset, performed from different viewing angles or perspectives without probe repositioning or causing associated workflow interruptions.
While not a volumetric imaging mode, “X-plane” displays adjustable biplane images simultaneously. This unique feature allows operator’s definition of orthogonal specific views without movement of the probe or transducer (Figure 3.3D
The 2D orthogonal view method provides improved fine spatial and temporal resolution, acquired at a higher frame rate than those typically obtained employing 3D imaging. Biplane imaging also has the capability of color flow Doppler imaging that provides more precise 3D localization jets than standard 2D imaging for ASDs or regurgitant valvular lesions.
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