Imaging in Structural Heart Disease

Facilities

The cardiac catheterization lab was introduced in the 1970s, a time when fluoroscopy was the only imaging modality employed in routine practice. The fluoroscopic C -arm remains the centerpiece of most cardiac catheterization labs. Fluoroscopy is a vital component of any laboratory; however, integration of other imaging modalities into this space must be a consideration in today’s cardiac catheterization lab. SHD interventions often require real-time imaging guidance, often with TEE, ICE, or CT. Intravascular ultrasound, fractional flow reserve, and to a certain extent, ICE are conveniently designed as “plug and play” add-ons to the fluoroscopy system; however, this is not the case with the display and visualization components of TEE, CT, and CMR imaging. The modern cardiac catheterization lab should be large enough to accommodate the extra equipment and a team of sonographers and echocardiographers in addition to the interventional and anesthesia teams. The fluoroscopic C -arm is typically mounted at the head of the table where the echocardiographer and the anesthesiologist need access to the patient for their respective tasks. The room can often become crowded, and the various team members may not have an adequate view of the display monitors. When setting up an SHD laboratory of the future, the imaging components should be considered as important as the fluoroscopy unit.

The SHD lab or hybrid operating room should ideally be at least 800 square feet. The monitors should be large enough and mobile enough to provide adequate visualization for the interventionalist, as well as the echocardiographer, who usually is positioned at the opposite side of the table. The monitors should be capable of displaying a large number of inputs at a very high resolution. With the integration of advanced imaging techniques such as the importation of preprocedure CT and CMR images, there should be enough workstations with the appropriate software capabilities. Lastly there must be an integrated imaging archive system that can store intraprocedure imaging clips from several modalities in a composite “case” for postprocedure review.

Personnel, Core Knowledge, and Training

In addition to the facilities, there are considerations with regard to the expertise that is available within the institution. Reading and interpreting imaging studies for intervention is a markedly different task than reading studies for diagnostic purposes only. Preintervention studies focus on patient selection, device sizing and suitability, and intraprocedural strategy. For example, a preprocedural TEE for an atrial septal defect (ASD) closure is not simply to diagnose the ASD. Additional attention must be paid to size of the defect, the relationship and distance to surrounding structures, and adequate rims for seating of the closure device. These are not typically parameters recorded in a routine diagnostic study. A team of echocardiographers, imaging specialists, and radiologists who have a dedicated interest in SHD intervention is key to successful outcomes.

The increasing use of imaging in interventional cardiology may also change the paradigm of how future interventionalists are trained. The interventional cardiologist must be capable of interpreting imaging studies, including advanced modalities for which there may have been no formal training. The authors recommend that SHD training expand to include an imaging curriculum. At minimum, this would include instruction in ICE and TEE, including real-time 3D TEE (RT 3D TEE). Box 2–1 outlines the requirements for a successful integrated imaging and catheterization lab suite.

Preprocedural Imaging

Preprocedural planning often includes diagnostic imaging studies with a focus on interventional aspects of the procedure, including the type of defect, the vascular access, the navigation strategy, and any special equipment that may be required for the procedure. In advanced percutaneous valve interventions the preprocedural imaging is critical for patient selection and good outcomes. Preprocedural imaging often includes CT and CMR imaging as well as echocardiography. Nearly every patient who comes for a structural heart evaluation will have had some type of preprocedural imaging that includes baseline diagnostic studies. The key components of preprocedural imaging will be highlighted in several examples in this chapter.

Intraprocedural Imaging Guidance

Intraprocedural guidance refers to physically bringing the imaging modality to the catheterization lab and actively using the images to navigate catheters, position and deploy devices, and immediately assess for complications. Although fluoroscopy provides important intraprocedure guidance, including the visualization of hardware, wires, and devices, the lack of soft-tissue definition and visualization of cardiac chambers has limited this modality in SHD interventions.

Intraprocedure imaging modalities must be portable, must not interfere with the set-up of the catheterization lab, and importantly, must provide real-time imaging that can be updated and changed as the procedure dictates. Imaging guidance has predominantly been an echocardiography-based task with ICE being the most familiar modality for navigation in the interventional lab. 2D TEE and, increasingly, RT 3D TEE are the preferred imaging modalities for complex SHD interventions. RT 3D TEE has been used to successfully guide most common percutaneous SHD interventions. It provides the necessary soft-tissue definition and can be rapidly updated and repositioned for new views to optimize and tailor the image guidance.

An example of the emergence of image guidance is provided in Figure 2–1 depicting the transseptal puncture. This procedure was originally described by Ross, Braunwald, and Morrow over 50 years ago and has been commonly performed with fluoroscopy alone, without the addition of expensive imaging equipment. However, safety and confidence can be enhanced with the echocardiographic imaging of the interatrial septum either with ICE or with 2D TEE or RT 3D TEE. The interatrial septum is visualized in several planes, with care to puncture at the site of the fossa ovalis, which is easily visualized as the thin portion of the septum. The Brockenbrough needle is pulled back from the superior vena cava to the right atrium, and the site of puncture is directly visualized. Simultaneous pressure monitoring also confirms successful crossing to the left atrium. With the advent of complex navigation requirements for mitral valve interventions there is increasing reliance on not only a safe transseptal puncture but also a strategic placement of the transseptal puncture. Figure 2–2 shows the strategy of transseptal puncture for a MitraClip (Abbott Vascular Structural Heart, Menlo Park, Calif.) procedure. The correct alignment of the clip delivery system perpendicular to the plane of the mitral valve orifice is critical and requires adequate navigation room within the left atrium. A strategic transseptal puncture must be performed posterior and superior from what might be considered the standard target puncture site.

Although image guidance is usually associated with a real-time imaging technology, CT is increasingly becoming an intraprocedure modality as well. CT has the benefit of excellent soft-tissue characterization and provides a full field of view. The limitation, however, is cardiac motion artifact and the need for electrocardiography (ECG)-gated acquisitions. Preprocedure CT scans can be used to outline navigation strategies for complex procedures. The CT data set can be rotated into an orientation, mimicking the fluoroscopic C -arm projection and can provide a preplanned viewing angle for image guidance. Figure 2–3 is an example of preplanning the intraprocedural navigation strategy for a mitral paravalvular leak closure using TrueView software (Phillips Medical, Andover, Mass.). The gantry position was predetermined for optimal viewing, and a roadmap of the catheter navigation to the mitral paravalvular leak was created. These data can then be imported into the angiographic suite and registered with fluoroscopy. As a result, the CT image will rotate with the C -arm during the procedure, providing real-time image guidance. This type of technology may limit radiation time and contrast dose and enhance procedural success. Table 2–2 describes the modalities used for intraprocedural guidance. These techniques have fundamentally changed how SHD interventions are performed with an increased emphasis on safety and operator confidence.