Interventional Echocardiography

Echocardiographic Imaging Modalities

Echocardiography offers many advantages in guiding transcatheter procedures. The real-time aspect of visualizing cardiac motion and flow dynamics by echocardiography cannot be achieved by imaging modalities such as computed tomography (CT) or magnetic resonance imaging (MRI). Although fluoroscopy provides live imaging, most thin, pliable, and dynamically moving intracardiac structures are not visible. Precise locations of minute pathology such as paravalvular defects are also extremely difficult to determine solely by fluoroscopy. In a single-center retrospective study, the addition of intraprocedural transesophageal echocardiography (TEE) to standard fluoroscopy for transcatheter patent foramen ovale closure was associated with reductions in postprocedural residual shunt, need for reintervention, and overall radiation exposure.

Among echocardiographic imaging modalities, TEE has been the mainstay of procedural guidance because of its exceptional imaging quality. Its esophageal position allows concurrent fluoroscopy during the procedure because the TEE operator is often situated at the head or slightly to the side of the patient with his or her hands away from the chest and out of the fluoroscopic imaging field. In contrast, intraprocedural transthoracic echocardiography (TTE) often can be performed only intermittently because of the need to avoid interference with fluoroscopy. Nonetheless, successful transcatheter procedures guided by TTE instead of TEE have been reported.

Like TEE, intracardiac echocardiography (ICE) can be used simultaneously with fluoroscopy, and it has recently gained traction as a reasonable alternative. However, ICE requires additional vascular access, has a shallower imaging field, and provides inferior three-dimensional (3D) imaging resolution. The high cost for ICE-capable echocardiography platforms and disposable ICE transducers has prohibited its routine use for procedural guidance.

Another reason favoring TEE over ICE for procedural guidance is familiarity with TEE among the structural heart team. Properly trained interventional echocardiographers, including cardiologists and cardiac anesthesiologists, are experienced in performing and interpreting procedural TEE studies. Interventional proceduralists are also well accustomed to TEE images, and procedural flow is often based on a routine sequence of expected TEE images. In short, TEE acts as a common language that facilitates communication among all team members.

Even though some studies suggest that TTE and ICE are safe, efficacious, and potentially superior imaging modalities, ^, TEE is accepted as the gold standard for optimal guidance of transcatheter procedures. This chapter provides an overview of interventional echocardiography focused mainly on TEE-related topics. Various imaging modalities are not mutually exclusive but rather complementary to one another, all based on specific intraprocedural imaging needs. The pros and cons of TEE, TTE, and ICE for transcatheter imaging guidance are summarized in Table 10.1 .

Echocardiographic Imaging Modes

This section presents practical two-dimensional (2D) and 3D TEE imaging modes commonly used to guide transcatheter interventional procedures. Vendor-neutral terminology is used for description of specific 3D modes.

3D TEE

Real-time 3D TEE has played an essential role in the exponential growth and innovation of transcatheter heart procedures in recent years. With the added dimension of elevation in 3D TEE, complex delivery of transcatheter devices can be accurately tracked within the cardiac cavity. Most importantly, 3D TEE overcomes the major limitation of geometric assumptions often made during quantitative echocardiography. Like 2D TEE, 3D TEE imaging suffers from ultrasound artifacts such as dropout, blurring, blooming, reverberation, and shadowing artifacts. Stitch artifacts, exclusive to gated 3D echocardiography, have become less of a hindrance with improvements in ultrasound transducer technology and machine computational power.

Ideal intraprocedural 3D TEE imaging used for transcatheter procedural guidance should include properties such as single-beat acquisition, large volumetric data set, high volume rate, and superb spatial resolution. Current modes of 3D TEE include live narrow-sector imaging, focused zoom, multibeat gated full-volume acquisition, and simultaneous biplane or multiplane imaging. The most valuable 3D TEE modes specific for structural heart imaging are the focused zoom and simultaneous biplane modes. Interventional echocardiographers must be proficient in using and switching among these different imaging modes.

Zoom mode is achieved by adjusting orthogonal imaging sector sizes that focus on the region of interest. When a smaller volumetric data set is selected, the region of interest is visualized with increased spatial and temporal resolution. However, sufficient surrounding structures should be included in the imaging sector to serve as anatomic landmarks. In the absence of anatomic landmarks, the 3D structure of interest should be rotated and displayed in a conventional manner to facilitate communication ( Fig. 10.1 ). Real-time cropping of the 3D image is occasionally necessary to better appreciate the cardiac structure or pathology. Image cropping tools include fixed plane, flexible plane, multiplane, two-click crop, and box crop ( Fig. 10.2 ). Cropping of 3D data sets before acquisition may further improve overall image resolution.

Postacquisition analysis of a 3D data set can be performed on-cart or off-cart in vendor-specific multiplanar reconstruction (MPR) software packages. All 2D imaging cut planes can be tilted and moved to numerous angles and positions around the region of interest, permitting accurate quantitative measurements of 3D structures. However, measurements made directly on 3D images may be subject to parallax error and should be performed with caution ( Fig. 10.3 ).

Depending on the reason for using 3D TEE, multibeat gated and single-beat real-time imaging can be applied to 3D zoom mode. In situations in which optimal resolution is prioritized, such as confirming preprocedural pathology or grading postprocedural results, multibeat acquisition is more appropriate to maximize image quality and volume rate. However, when 3D zoom mode is used for real-time visualization and guidance of the procedure, single-beat live imaging is more appropriate to allow for instantaneous response of the 3D image to transducer manipulation.

Live 3D TEE images have been superimposed on fluoroscopic images to form so-called fusion images ( Fig. 10.4 ). Fiducial markers placed on TEE images are immediately integrated into the fluoroscopic fused data set, facilitating communication between the echocardiographer and the interventionalist. Easier identification of precise locations by fusion imaging may improve overall procedural safety and completion time.

Simultaneous biplane mode is another valuable 3D imaging mode for transcatheter procedural guidance. Its usefulness lies in the ability to concurrently visualize orthogonal sectors at various omniplane angles. Unlike other 3D TEE modes that require tremendous computational power to process large volumetric data sets, this mode obtains only two perpendicular imaging planes, producing exceptional overall resolution. As an additional feature, the imager can use a flexible tilt plane to interrogate a specific structure or determine the precise location of a catheter or wire based on an exact perpendicular image plane. Because the superior-inferior and anterior-posterior rims of the fossa ovalis can be visualized simultaneously by this imaging mode, a major application is for procedures performed on the interatrial septum (IAS), including transseptal punctures and device placement for occlusion of atrial septal defects. The optimal transseptal locations for various left-sided interventions are summarized in Table 10.2 .

TABLE 10.2

Transseptal Location for Transcatheter Interventions.

Transcatheter Procedure	ME Bicaval View (Superior/Inferior)	ME AoV SAX View (Anterior/Posterior)
Balloon mitral valvuloplasty	Mid	Posterior
Mitral valve edge-to-edge repair	Superior	Posterior
Mitral valve replacement (valve-in-valve, valve-in-ring, valve-in-calcified annulus)	Mid	Posterior
Mitral paravalvular defect occlusion	Mid	Posterior
Left atrial appendage closure	Inferior	Posterior
Percutaneous LV assist device	Mid	Mid
Atrial septal defect/patent foramen ovale repair	Through defect	Through defect

AoV , Aortic valve; ME , mid-esophageal; Mid , middle; SAX , short axis.

Intraprocedural TEE for Transcatheter Aortic Valve Replacement

The number of patients presenting for transcatheter aortic valve replacement (TAVR) has grown exponentially. Although there is a significant trend for TAVR patients to receive minimal sedation and TTE postprocedural assessment, general anesthesia with intraprocedural real-time TEE guidance remains essential in certain situations. This section focuses on practical aspects of intraprocedural TEE, such as sizing the aortic annulus, for TAVR in native and bioprosthetic valves.

Multiple studies have retrospectively associated undersized and oversized transcatheter heart valves (THVs) with postprocedural paravalvular leakage (PVL). ^, Accurate and reliable aortic annular measurements by appropriate imaging may reduce the overall incidence of these events. Contrast-enhanced multidetector computed tomography (MDCT) is considered the primary imaging modality for preprocedural characterization of valvular morphology and annular size. However, when contrast-enhanced MDCT is unavailable or contraindicated (e.g., emergent case, patient with advanced renal disease), 3D TEE is an appropriate alternative. Compared with 2D echocardiography, 3D TEE provides better appreciation of the noncircular annular plane. In a comparison with 3D TEE, 2D echocardiography was shown to consistently underestimate aortic annular dimensions, leading to a change in THV size selection in 23% of the patients. A meta-analysis of 13 observational studies examined the agreement between measurements of the aortic annulus obtained by 3D TEE and by MDCT. A significant linear correlation was established between the two imaging modalities, although annular area was found to be slightly smaller when measured by 3D TEE (mean difference, −2.22 mm ² ; 95% limits of agreement: −12.79 to 8.36). This finding did not alter THV size selection or likelihood of procedural success. Because of its eccentricity, the mean diameter of the aortic annulus is often calculated by the measured area or circumference instead of by direct linear measurements from one cusp insertion (hinge-point) to another. Circumference-derived diameters have been shown to result in a lower incidence of postprocedural PVL, compared with area-derived diameters. This could be a result of the larger diameter (23.4 ± 2.3 mm vs. 22.9 ± 2.3 mm; P < 0.001) calculated by measured circumference compared with area.

Commercial software, using MPR of the 3D TEE data set, is often used for off-line analysis of the complex aortic root anatomy ( Fig. 10.5 ). It is important to understand the concept of finding three aortic valve (AoV) anchoring sites, one from each cusp, to obtain an accurate cross-sectional plane of the aortic annulus (i.e., three points form a plane). This principle can be applied to any 3D volume, regardless of which TEE view is used to acquire the data set. A guide for attaining the aortic annulus cross-sectional plane, modified from the turnaround technique, is described in Table 10.3 .

The aortic annular area, circumference, and diameters can be measured manually on the transverse plane (see Fig. 10.5D ). Semi-automated and fully automated measurements of these parameters have also been described with excellent and reliable results. ^, As with any measurements, cyclic variation may occur with respiration or cardiac contraction. It may be necessary to average several results. If a patient presents with a previously placed bioprosthetic valve of unknown size, the internal valvular diameter can be measured with the same technique as described for sizing of the aortic annulus.

Immediately after THV deployment, intraprocedural TEE can be used to detect potential complications, including coronary artery occlusion, THV malposition, residual aortic regurgitation, mitral valve (MV) impingement, THV embolization, pericardial effusion, and aortic rupture and dissection. ^, If preprocedural imaging analysis suggests a potential risk of coronary obstruction, several preventive strategies may be considered, including the newly described b ioprosthetic or native a ortic s callop i ntentional l aceration to prevent i atrogenic c oronary a rtery obstruction (BASILICA) procedure.

The BASILICA procedure involves laceration of the AoV leaflet to create a triangular space in front of the coronary ostia, mitigating the risk of obstruction after TAVR. Intraprocedural TEE plays a vital role for the success of this technically demanding procedure ( Fig. 10.6 ). Simultaneous biplane mode is often used to guide the location, position, direction, and orientation of the leaflet traversal system in the aortic sinus ( Table 10.4 ). After leaflet puncture, a wire is advanced into the left ventricular outflow tract (LVOT) and captured by a transvalvular snare, forming a loop around the targeted leaflet. Distinguishing catheters from one another by TEE may be difficult due to shadowing from native calcification or prosthetic valve cages and stents. After the targeted leaflet is lacerated by electrocautery, significant hemodynamic instability may occur with transition from a stenotic physiology to that of regurgitation. If severe aortic regurgitation is not appreciated on TEE, the leaflet puncture site should be re-examined.

Intraprocedural TEE For Percutaneous Mitral Valve Edge-To-Edge Repair

Favorable outcome of surgical repair for degenerative MV disease has been well documented. Unfortunately, up to 49% of patients with symptomatic severe mitral regurgitation (MR) are denied surgical options due to unacceptable risk factors. In recent years, percutaneous approaches to MV repair have been proposed for these patients with high or prohibitive risk. Numerous large clinical trials have demonstrated a significant positive impact on clinical outcomes, such as reduced hospitalizations and reduced mortality. ^, Practical recommendations for intraprocedural TEE imaging of the most commonly used technology approved by the U.S. Food and Drug Administration, the MitraClip system (Abbott Vascular, Santa Clara, CA) are discussed later in this section. Improved real-time 3D TEE imaging technology has facilitated exponential growth in the use of this edge-to-edge clip (E-EC) system.

MV repair with E-EC therapy involves leaflet edge-to-edge approximation, drawing comparison to the surgical technique described by Alfieri et al. Differences between these two methods are summarized in Table 10.5 . In addition to improving leaflet coaptation, the E-EC system creates a tissue bridge that restricts mitral annular dilation and facilitates left ventricular (LV) remodeling. A reduction in mitral annular dimensions, including circumference and anteroposterior and bicommissural diameters, was documented by 3D TEE immediately after E-EC implantation. Patients with functional MR were also found to have a reduction in mitral annular sphericity index (ratio between anteroposterior and mediolateral distances) and in anatomic MV orifice area after E-EC. Interestingly, the mechanism of MR reduction by E-EC therapy in these patients seemed to depend on MR jet directionality. Those with central functional MR seemed to benefit most from the shortening of anteroposterior diameter and increase in coaptation area, whereas those with eccentric functional MR benefited from a decrease in average leaflet tethering angle. Further, patients who received the E-EC therapy were found to have significant biventricular volume reduction and functional improvement based on myocardial strain assessments after the procedure. ^, Because many of these beneficial effects are seen immediately or relatively soon after device implantation, some have proposed E-EC therapy as a reasonable solution to stabilize patients who are in acute cardiogenic shock from MR.

TEE plays a pivotal role in preprocedural patient selection, intraprocedural guidance, postprocedural assessment, and complication exclusion. Numerous articles have reviewed the procedural steps and corresponding imaging sequence.

Mitral Valve and Regurgitant Jet Evaluation

Compared with MR severity grading during preprocedural screening echocardiography, grading of MR severity by TEE is less important during the procedure because of the significant physiologic effects of general anesthesia and mechanical ventilation. However, intraprocedural quantitative assessment of MR at baseline and throughout the procedure still plays a role because it is necessary to objectively assess the relative impact that the intervention has on MR reduction. Importantly, intraprocedural TEE should focus on comprehensive understanding of the morphologic nature of valvular disease and structural components of the MV apparatus. With improvements in operator experience and device technology, many MV features that were previously considered contraindications are today seen as challenging yet acceptable ( Table 10.6 ).

TABLE 10.6

Optimal and Challenging Mitral Valve Morphologic Features for Edge-to-Edge Clip Intervention.

Adapted from Nyman CB, Mackensen GB, Jelacic S, Little SH, Smith TW, Mahmood F. Transcatheter mitral valve repair using the edge-to-edge clip. J Am Soc Echocardiogr . 2018;31(4):434–453.

Optimal Morphology	Challenging Morphology
Central A2/P2 lesion	Peripheral A1/P1, A3/P3, or commissural lesion
Posterior leaflet length >10 mm	Short posterior leaflet length 7–10 mm
Tenting height <11 mm	Tenting height ≥11 mm
Coaptation length >2 mm	Coaptation length ≤2 mm or noncoapting leaflets
Flail gap <10 mm	Flail gap ≥10 mm
Flail width <15 mm	Flail width ≥15 mm
Calcification absent	Calcification present in non-grasping zones
MV area >4 cm 2	MV area <4 cm 2 but >3 cm 2

A/P1–3 , Anterior and posterior mitral leaf segments; MV , mitral valve.

The mid-esophageal (ME) bicommissural view is extensively used for guidance during this procedure. It is of utmost importance to establish an accurate view that transects the commissures precisely. Because the 3D image obtained by narrow-angle real-time 3D mode with backward elevation tilt is rendered by adding 10 to 30 degrees of elevation angle to the 2D imaging plane, this unique 3D mode may help verify any 2D views ( Fig. 10.7 ). After the true ME bicommissural view is attained, simultaneous biplane mode imaging with color-flow Doppler (CFD) can be activated with the scan line systematically sweeping through the MV from medial to lateral. The origins of the MR jet or jets can be individually identified and interrogated by this method ( Fig. 10.8 ).

The MR jet width in the ME bicommissural view may shed light on the potential number of devices needed to treat the pathology. For instance, if the width of the MR jet is 15 mm or greater, two or more E-EC devices may be needed to facilitate leaflet approximation. With the scan line cutting through the MR jet, CFD is suppressed to reveal the underlying valvular pathology. On the corresponding long-axis view window, anterior and posterior leaflet length, coaptation defect, flail or prolapse gap, calcification, tenting angle, and ventricular chordae attachments can be closely examined ( Fig. 10.9 ). The overall MV anatomy and MR jet characteristics can be appreciated, with or without CFD, in 3D-rendered volume acquisition.

Transseptal Puncture

The ideal location for transseptal puncture for the E-EC system is in the superior and posterior portion of the thin fossa ovalis. This is best visualized in the ME bicaval view for superior-inferior positioning and in the ME AoV short-axis (SAX) view for anterior-posterior positioning. Simultaneous biplane mode is often used to display both views concurrently. Bear in mind that if this mode is activated in the ME bicaval view, the corresponding orthogonal view is the mirror image of the ME AoV SAX view, with left- and right-sided structures inverted ( Fig. 10.10 ). A fibrotic, lipomatous, aneurysmal, or defective septum may pose difficulties for the proceduralist and should be communicated if discovered. Once the ideal location is identified, the distance between the IAS tenting site and the MV leaflet coaptation is measured in the ME 4-chamber view or in the inverted ME 4-chamber view at a 180-degree omniplane angle. The optimal distance is approximately 4.5 to 5 cm but heavily depends on factors such as E-EC type, MR etiology, and jet origin location.

Positioning of Steerable Guide Catheter and Clip Delivery System

The steerable guide catheter and clip delivery system are crossed into the left atrium (LA) after the IAS is punctured. The trajectory of these devices needs to be visualized continuously to avoid injury to nearby structures such as the left atrial appendage (LAA) and the AoV. Single-beat 3D zoom mode with a large-volume sector encompassing the entire LA is often used for this step. As the clip and clip delivery system is being advanced, the TEE transducer is often rotated toward the patient’s left side to follow along ( Fig. 10.11 ).

The clip delivery system is then lowered and steered toward the MV, monitored by simultaneous biplane mode imaging of the ME bicommissural view and the corresponding ME long-axis (LAX) view to ensure that the device is positioned directly above the MR origin. The clip arms are then opened to check for orientation by 3D zoom mode. The perpendicularity of the E-EC device and the MV line of coaptation is confirmed. The omniplane angle may need to be adjusted in the bicommissural plane, depending on the laterality of the lesion, to maintain its parallel alignment to the coaptation line ( Fig. 10.12 ).