Echocardiographic Imaging in Transcatheter Mitral and Tricuspid Valve Therapies
Essential tips, challenges, and future perspectives in imaging for transcatheter valve therapies.
Functional moderate and severe mitral regurgitation (MR) and tricuspid regurgitation (TR) have been associated with increased mortality.1 Over the past decade, transcatheter valve therapy (TVT) for patients with MR and, more recently, TR has increasingly gained importance as an alternative to more invasive and relatively higher-risk surgeries. TVT is complex and requires intense imaging preparation and guidance, so there is an increasing demand for comprehensive imaging to optimize success. Echocardiography is versatile, readily available, and easily repeated at bedside. Therefore, it plays a key role for TVT in preplanning, intraprocedural guidance, and postprocedural follow-up. In this article, we aim to highlight the general as well as tailored use of echocardiography for transcatheter mitral valve (TMV) and transcatheter tricuspid valve (TTV) therapy (see the Summary of Key Concepts in TVT Imaging sidebar).
THE NEED FOR ECHOCARDIOGRAPHY IN TVT
The mitral and tricuspid valves are three-dimensional (3D) apparatuses with complex geometry surrounded by important anatomic structures (Figure 1). The mitral annulus and tricuspid annulus are dynamic 3D structures. Three-dimensional transesophageal echocardiography (TEE) can provide better images of the annuli, but the reproducibility of multislice CT (MSCT) is higher. MSCT can be applied to evaluate the coronary artery, coronary sinus, and inferior vena cava, and it simulates neo-left ventricular outflow tract for TMV replacement.
A comprehensive imaging assessment is important for the treatment approach. Most TMV and TTV therapies replicate surgical procedures for valve repair.2,3 Valve repair can be performed at the level of the annulus (with annuloplasty), leaflets (with edge-to-edge repair), or subvalvular apparatus (neochordae implantation). If repair is not feasible, a nondedicated device, such as one built for the aortic position, or a device built for TMV or TTV replacement can be used.
Thus, the sonographer should have adequate step-by-step knowledge of the procedure and the appropriate devices, wires, and catheters. Before the procedure, the sonographer must confirm disease severity, patient eligibility, and appropriate device sizing. During the procedure, the sonographer must properly identify the device, wire, and catheter positions and properly communicate with the operator. Furthermore, anticipation and timely detection of procedural complications on echocardiography is a crucial role of sonographers. Both two-dimensional (2D) and 3D transthoracic echocardiography (TTE) and TEE have critical roles in the planning, guidance, and follow-up of TVT, and 3D TEE is indispensable for procedural guidance in current practice.
A GLOBAL APPROACH TO ECHOCARDIOGRAPHY IN TVT
Our clinical routine is to follow a stepwise approach when using echocardiography for patients with suspected or established functional MR or TR. We begin with comprehensive 2D and 3D echocardiography to assess valve regurgitation, morphology (annulus dilatation, leaflet coaptation, tethering), and the mechanism and etiology of regurgitation. Second, we confirm regurgitation severity via a semiquantitative approach including, at least, regurgitant jet vena contracta, proximal isovelocity surface area radius, effective regurgitant orifice area (EROA), and regurgitation fraction. Third, we assess the hemodynamic impact regarding volume and coexisting pressure overload. Fourth, we identify the presence and severity of other-sided valvular disease. Fifth, we assess the presence and severity of left- and right-sided heart chamber remodeling. Finally, we combine these data to allow for an optimal heart team decision.
ECHOCARDIOGRAPHY FOR TMV THERAPY
MitraClip (Abbott Structural Heart) is the only FDA-approved device for the treatment of native and, recently, functional MR.3 More than 80,000 MitraClips have been implanted worldwide,4 and thus, this article mainly focuses on the use of echocardiography during a MitraClip procedure. The first task is a comprehensive preprocedural assessment, which involves establishing the diagnosis, MR severity, and anatomic suitability for MitraClip repair (Table 1). Then, sonographers should follow mandatory steps to provide echocardiographic guidance during the procedure. The main steps for the MitraClip procedure include: (1) perform transseptal puncture; (2) introduce the guide catheter and clip delivery system into the left atrium (LA); (3) position the MitraClip above the mitral valve; (4) advance the MitraClip into the left ventricle (LV); and (5) grasp the mitral leaflet and deploy the MitraClip. The role of echocardiographic guidance for each step is presented in Table 2 and Figure 2.
Criteria for MitraClip Procedure Success
After MitraClip implantation, and in the absence of complication criteria on echocardiography, procedural success is characterized by reduction of MR by two or more grades in comparison to baseline, a residual mitral effective orifice area ≥ 1.5 cm2, and a mean transmitral gradient < 5 mm Hg. Additionally, residual MR jets are characterized by spraying nature and multiplicity after implantation. The 3D TEE planimetry of MitraClip EROA after implantation correlates well with cardiac magnetic resonance.5 Therefore, the use of 3D TEE is superior to 2D TEE and to quantitative Doppler interrogation of the residual MR, and it is preferred for planimetry of the mitral valve area.6
ECHOCARDIOGRAPHY FOR TTV THERAPY
Similar to TMV repair, transcatheter treatments of TR include techniques that replicate surgical repair procedures at the annulus, leaflet, and/or subvalvular levels. These TVTs are most often replicates of suture annuloplasty or ring annuloplasty. Currently, the most widely used technique in the tricuspid valve position is the off-label use of edge-to-edge repair with the MitraClip device.7,8 In general, most steps for mitral valve repair using the MitraClip device also apply to tricuspid valve repair, except for atrial-septal crossing.
Essential Differences: Tricuspid Versus Mitral Valve Imaging
Imaging of the tricuspid valve is more challenging than in patients with MR. The tricuspid valve is an anterior structure, and it lies in the field far from the TEE probe insonation beam. Therefore, TTE is more appropriate than TEE for imaging of the tricuspid valve. Consequently, TTE is important in preprocedural assessment of the tricuspid valve. Essential imaging concepts for patients with TR on echocardiography are listed in Table 3.9 TR severity is confirmed on multiple 2D TTE views using 2D with Doppler imaging of TR jet(s). Then, 3D dynamic measurements of the tricuspid valve annulus are performed, ideally on 3D TEE10 or simultaneous, multiplane, 2D imaging.11 The three leaflets of the tricuspid valve are difficult to simultaneously visualize on 2D echocardiography12; therefore, 3D echocardiography or a transgastric view is mandatory during procedural guidance, and a deep esophageal view with the TEE probe inferior to the LA and more directly behind the right atrium is more appropriate for tricuspid valve leaflet visualization.
Furthermore, standard transgastric and deep transgastric views are commonly used to guide tricuspid valve leaflet repair.13 These views are essential for the assessment of leaflet morphology, coaptation gap, device landing zone, and location of the main TR jet.13,14 Additionally, quantitative assessment of TR severity before and after TTV therapy has less established cut-off values in comparison with MR severity assessment,6,15 although a new TR severity grading scheme that differs from MR has been proposed to include massive and torrential TR.16
TTV procedures are more challenging than TMV procedures because patients with significant TR have several anatomic and pathophysiologic constraints. Most patients undergoing early TTV repair/replacement device feasibility studies have extensive right heart remodeling with loss of anatomic landmarks, which complicates catheter navigation and interferes with proper positioning of repair/replacement devices. The sonographer has to identify preexisting device leads that might interfere with device delivery and deployment. Furthermore, imaging views and quality will depend on numerous patient characteristics (eg, mechanical valves in place, chest deformation, esophageal anatomy/pathologies) but also on the device used for repair.
Data from TTV therapy studies are scarce. Most patients enrolled are currently inoperable or at “high surgical risk” with chronic functional TR. Due to the fact that patients with TR who are in need of intervention represent a very heterogeneous population, the role of imaging in patient selection is paramount to optimize clinical results and the effectiveness of TTV therapy. In general, key concepts include characterization of the annulus and leaflets (including coaptation distance and tethering), local and global right heart remodeling, and hemodynamic assessment of right-sided volumes and pressures.17
Echocardiography for Proper Sizing
The most important step in device sizing for TTV repair or replacement is the proper quantification of the tricuspid valve annulus. This step is challenging because the tricuspid valve annulus diameter is significantly larger than other valves and is highly influenced by volume status, which might preclude appropriate sizing and device selection. In addition, the landing zone that includes the tricuspid valve annulus and surrounding myocardium is more fragile. Therefore, TTV devices are at increased risk of dehiscence. There is also a risk of injuring adjacent structures. Multimodality imaging—including echocardiography, CT, and fluoroscopy—is needed for proper device implantation and to avoid devastating complications such as cardiac tamponade or injury to the right coronary artery or atrioventricular node.
Echocardiographic Guidance of the MitraClip Procedure for TR Repair
Similar to MR repair, the most frequently used device to repair TR is the off-label use of the MitraClip device. Two-dimensional TEE is a mandatory imaging modality for evaluating the suitability for TR edge-to-edge repair. Two-dimensional TEE biplane imaging with the primary view displaying the right ventricular inflow-outflow view is paramount to identify the tricuspid leaflets and visualize the coaptation of the septal-anterior and septal-posterior commissure with the secondary perpendicular plane.17 A stepwise approach for TR edge-to-edge repair is summarized in Table 4 and Figure 3.
Echocardiographic Determinants of Successful Repair
Ideally, success of TTV repair should be defined on echocardiography in the immediate postoperative period as reduction to mild or less regurgitation severity, associated with significant reduction of valve annulus diameter if previously dilated. Long-term success is reflected by reverse ventricular remodeling as well as reduction of ventricular afterload. Successful TTV repair is often coupled with patients’ symptomatic and functional improvement. In contrast, device failure could be reflected as patient death or a need for reintervention. Currently, most candidates for TVT repair are patients with advanced TR, which is often associated with right ventricular dysfunction. Most of these patients are beyond the point of complete repair. The definition of successful repair is yet to be determined.
According to data on tricuspid valve surgery, a higher grade of preoperative TR, larger tricuspid valve annuloplasty ring, presence of pacemaker leads through the tricuspid valve, combined mitral valve replacement rather than repair, depressed LV function, and advanced LV remodeling are associated with TR recurrence after surgery.18 Likewise, tethering distance has been associated with recurrent TR after annuloplasty.19 Patients with significant tricuspid valve leaflet tethering are nonsurgical candidates, and they are typically the first target population for transcatheter devices. On principle, annuloplasty alone will be insufficient in these patients. Thus, TVT devices should ideally also be able to address tethering. The Overview of Contemporary Devices for MR and TR sidebar summarizes transcatheter devices that are either currently available or under investigation for TVT.
OTHER COMPLIMENTARY IMAGING MODALITIES
There is no stand-alone imaging modality for TVT. MSCT could aid in preplanning for TVT that mimics surgical annuloplasty, spacer devices, and transcatheter valve replacement. It provides accurate 3D measurement and assessment of the annulus, device landing zone, relationship between the annulus and surrounding left circumflex (for TMV therapy) and right coronary artery (for TTV therapy), and annular tissue quantity and quality, as well as access selection and guidance. A stepwise approach is often used to assess suitability for a certain device, device sizing, vascular access, and the relationship of the tricuspid valve annulus to critical anatomic structures. Cardiac magnetic resonance provides accurate regurgitation fraction and could be used as an alternative to both echocardiography and CT for morphologic and functional assessment. The recent advent of fusion imaging allows superimposition of echocardiographic images to fluoroscopic images, which allows for better understanding of anatomic relationships and facilitates transcatheter procedures.
Transcatheter devices evolve rapidly, which could provide therapeutic alternatives to surgery in selected patients with significant MR or TR. Echocardiography plays a fundamental role in patients’ screening, selection, procedure guidance, and postprocedural follow-up. Standardized echocardiographic imaging protocols could provide effective communication among the heart team members during the procedure and potentially optimize therapeutic outcomes.
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Osama Soliman, MD, PhD, FACC, FESC
Department of Cardiology
Thoraxcenter, Erasmus University Medical Center
Rotterdam, the Netherlands
The Euro Heart Foundation
Amsterdam, the Netherlands
Chun Chin Chang, MD
Division of Cardiology
Department of Medicine
Taipei Veterans General Hospital
Thomas Modine, MD, PhD, MBA
Jiao Tong University
Heart Valve Center, Institut Coeur Poumon