Multimodality Echocardiographic Imaging for a Novel Transcatheter Native Mitral Valve Replacement Procedure

Catheter-based treatments of structural heart diseases have been impressively expanding.^[1–7] This growth has been possible thanks to the developments of new percutaneous devices but also due to the innovations in imaging techniques. Mitral regurgitation (MR) treatment is still a challenge in the clinical arena. Mitral valve (MV) surgery plays a primary role on indications for intervention; however, transcatheter procedures have emerged as an alternative to treat inoperable and high-risk surgical patients.^[1–7] In patients with suitable anatomy, the transcatheter edge-to-edge mitral leaflet repair (TEER) is the most frequently applied procedure.^[1] Transcatheter native mitral valve replacement (TMVR) is a novel procedure that has the potential to overcome some of the current limitations associated with TEER.^[2–7] Nowadays, there is a wide range of TMVR devices at various stages of development.^[6,7] The TMVR device that is most used for native anatomy is the Tendyne system (Abbott, Menlo Park, CA).^[6–9]

Imaging is paramount in determining the procedural success, and many actors play a role in the imaging arena. Although angiography and fluoroscopy are performed by the implanter team, other multimodality semi- and noninvasive imaging, so-called “interventional imaging,” is performed by the structural heart disease interventional imagers.^[10] In this setting, computed tomography (CT), and two- (2D) and three-dimensional (3D) transesophageal echocardiography (TEE) have key roles in multimodality imaging and in the interaction between the implanting and interventional imaging teams.^[2–7,10] As its use is expanding into the clinical arena, a detailed description of the use of different imaging modalities is necessary for the interventional imager.^[2–7,10]

The aim of this technical note was to describe the key steps in periprocedural echocardiographic guidance of TMVR with the Tendyne system (Abbott), emphasizing potential caveats and areas of difficulty.

The Tendyne (Abbott) system consists of two self-expanding nitinol frames and a trileaflet porcine pericardial valve. The outer stent has a D-shape design to fit the mitral annulus; accordingly, the straight edge must be oriented anteriorly against the aortic-mitral continuity. The device is implanted under general anesthesia through a left mini-thoracotomy using a transapical approach; it is secured in a stable position after deployment by means of a polyethylene tether, which is attached to an apical epicardial pad. The valve is fully repositionable and retrievable intraoperatively by engaging the tether. Repositioning allows optimization of valve position following deployment. The access site and delivery sheath trajectory are planned from preprocedural cardiac CT (CCT). The matching of preprocedural planning is assessed by 2D TEE intraprocedural imaging guidance. A standard 0.035-inch wire is inserted into the left atrium (LA) and a balloon-tip catheter is advanced to the LA to ensure that the guidewire is not entangled in the mitral subvalvular apparatus. A 34-Fr sheath is then placed over the wire into the LA. The valve prosthesis is delivered through the sheath and partially deployed in the LA, until the outer valve expands up to approximately three-fourths of its final size. It allows the alignment of the D-shaped outer stent with the anterior straight edge against the aortomitral continuity; 2D and 3D TEE and fluoroscopy provide intraprocedural guidance. The delivery sheath is then retracted toward the left ventricle (LV) to completely deploy the remainder of the prosthesis in an intra-annular position. The prosthesis is connected to a braided fiber tether that is fastened to an apical pad on the epicardium. The length and tension of the tether are adjusted to optimize the sealing of the prosthesis for MR reduction and to minimize the risk of device displacement.^[2–4]

The periprocedural imaging pathway can be schematized in four fundamental steps: baseline evaluation of MR, preprocedural screening and planning, intraprocedural guidance, and follow-up. The imaging modalities used in each step are reported in Table 1.

Baseline evaluation of MR in TMVR includes the guidelines-recommended imaging pathway of MR assessment.^[1] It must carefully evaluate the etiology, mechanisms, and severity of MR, as well as the association of any other valvular abnormality and annular calcification and its extension.

A dedicated preprocedure cardiac multimodality imaging for TMVR is able to determine patient eligibility according to the anatomic characteristics and measurements, provide information for appropriate valve sizing, and detect features that can predispose to potential hazards or complications and contraindications.^[2–7]

In the preprocedural assessment, CCT plays a major role in allowing sizing of the LV and the MV annulus, detection and scoring of the MV apparatus calcification, and simulation of the prosthesis implantation and neo-left ventricular outflow tract (LVOT), hence predicting the risk of LVOT obstruction.^[2–7] Nevertheless echocardiography is useful in sizing the LV and MV annulus, in diagnosing contraindications (LA appendage or LV clot, endocarditis, thin or fragile apex not suitable for apical puncture), and in the assessment of the anatomic features that can help in predicting potential procedural complications.^[2–7]

Among the possible complications, the post-implantation neo-LVOT obstruction is one of the most important. In fact, implantation of a device can result in neo-LVOT obstruction as the Tendyne valve frame projects into the LV cavity and the LVOT. Considering that the neo-LVOT is a new dynamic structure in which the new device and the anterior mitral leaflet and the LVOT are interplaying, the detection of factors that predispose to LVOT obstruction include a focused assessment of all the previously mentioned structures. A long anterior leaflet, a hypertrophied interventricular septum, a small LV size, and an aortomitral angulation of less than 110° can predict potential risks. In addition, we must consider that LVOT obstruction can either be fixed or dynamic. Fixed LVOT obstruction occurs when the prosthetic MV pushes the anterior mitral leaflet toward the interventricular septum, thus determining a narrower neo-LVOT. Dynamic LVOT obstruction is determined by the dynamic systolic anterior movement of the anterior mitral leaflet toward the interventricular septum caused by Bernoulli forces generated in the neo-LVOT.^[2–7]

In addition to the baseline guidelines-recommended MR assessment,^[1,2–7] additional particular imaging features are required in the preprocedural screening and planning for TMVR to assess the anatomic suitability and the potential procedural risks.^[2–7] These additional echocardiographic features can be schematized as follows.

• For 2D image quality assessment, a good quality of the acoustic window and in particular of the long axis and commissural TEE view, key for the intraprocedural guidance, is fundamental.

• For sizing, the LV must be measured by TEE in the 3-chamber view or the short-axis view along the septolateral direction. It has been reported that LV end diastolic diameter of less than 3.5 cm or LV end systolic volume of less than 12 mL/m² body surface area may raise potential procedural problem dealing with positioning and stability of the bioprosthetic valve. Also, LV diastolic dimension more than 7 cm is a contraindication.

• For morpho-geometry with assessment of papillary muscle and chordae tendinae disposition, the location of the papillary muscles must be imaged to avoid their potential damaging in the access and their interference with the procedure. Apical location of the papillary muscle may interfere with the transapical access and the detection of an anterior displacement of the papillary muscle with consequent abnormal course of the chordae and/or aberrant chordae tendinae can make it more difficult to obtain the correct catheter trajectory and may increase the risk of LVOT obstruction.

• For thickness, an upper basal subaortic septal wall thickness greater than 2 cm may increase the risk of LVOT obstruction; also septal thickness greater than 1.5 cm can increase the risk of LVOT obstruction in the presence of long anterior mitral leaflet (AML) and if the calculation of basal septal thickness × anterior AML leaflet length is greater than 400 mm².

• An LVOT area of less than 1.8 cm² increases the risk of LVOT obstruction, particularly when associated with increased basal subaortic septal thickness and a long AML.

• An MV annulus-to-apex distance (diastole) of less than 100 mm is suggestive of potential procedural hazards. A distance of less than 8 mm between the AML and interventricular septum in diastole has also to be taken into account as an indicator of possible LVOT obstruction.

An LA size of less than 22 mL/m² is an indicator of potential procedural problems and suboptimal outcome.

• For annulus sizing, the septal-lateral (SL), intercommissural (IC), intertrigonal dimensions, as well as the entire and posterior perimeter of the mitral annulus are important to decide the size of the valve to be implanted. A TEE 3D enface view of the MV (surgeon's view) provides a reliable assessment also comparable to the CT annulus sizing. Using the standard annular segmentation method, acceptable ranges of size are as follows: SL dimension, 25 to 42 mm; IC dimension, 35 to 48 mm; entire perimeter, 100 to 145 mm.

• It has been reported that excessive length of the AML may determine the potential hazard for LVOT obstruction. TEE long axis is the view of choice in assessing the AML length. A length of greater than 2.5 cm increases the potential risk of LVOT obstruction.

• Calcium in the annulus and leaflets is evaluated for potential hazards. Excessive calcium in the leaflets may be prohibitive without adjunct procedures, such as balloon valvuloplasty, to permit an optimal placement of the prosthesis. Calcium is better assessed by CT scan that also allows its scoring.^[2–7]

• An aortomitral angle of less than 110° between LVOT or aortic annulus and mitral annular planes predisposes to LVOT obstruction.

Contrast-enhanced thin-sliced electrocardiography-gated CCT with 3D reconstruction is considered to be fundamental for TMVR planning.^[2–7]

CT reconstruction provides key information for the following:

• LV, LA, and MV annulus dimension for procedure feasibility and appropriate valve sizing,

• Assessment of anatomic features predicting neo-LVOT obstruction,

• MV apparatus calcium assessment and scoring,

• Chest and LV apical access,

• Implantation angles for best coaxiality,

• Simulation of prosthesis implantation and neo-LVOT.

Fluoroscopy, as well as 2D and 3D TEE, are key in the guidance of TMVR during the procedure.

The key step-by-step echocardiographic guidance for TMVR with the Tendyne system is illustrated in Table 2 and described as follows.

The site for optimal LV apical access that bisects the MV in both the commissural and SL planes as planned by preprocedural CT (Figs. 1A, B) is assessed during the procedure using 2D TEE. Echocardiography allows imaging of the finger poke while pushing the apex. This is visualized as an outpouching inside the LV cavity (Figs. 1C, D). Echocardiographic imaging also allows assessment to determine if the finger poke is matching the access point planned at preprocedural CT. It is important to use TEE X-plane imaging on simultaneous bicommissural and LVOT views to perform CT matching imaging.

Echocardiography can assess the appropriate advancement of the balloon-tip catheter from the LV into the LA, ensuring that the catheter and the guidewire are matching the planned trajectory in preprocedural CT and are not entangled in the mitral subvalvular apparatus. To this aim, the catheter with the balloon inflated is moved in and out through the MV apparatus (flossing). The task of the imager is to detect any distortion or traction of the chordae or the leaflets to detect any entanglement of the catheter. This assessment is performed using 2D TEE, though 3D imaging is also useful to visualize the catheter position.

The delivery sheath is inserted into the LV over the guidewire and it is positioned centrally into the LA between the A2 segment of the AML and the P2 scallop of the posterior mitral leaflet (Figs. 2A and 2B). The valve prosthesis is delivered through the sheath (Fig. 2C) and partially deployed in the LA, until the outer valve expands up to approximately three-fourths of its final size to allow its orientation (Figs. 3 and 4A). The D-shaped outer stent or atrial cuff of the Tendyne prosthesis is then rotated to fit the anatomic shape of the native MV (valve clocking). Valve clocking is paramount for guidance. The outer frame of the bioprosthesis, designed to fit the mitral annulus, must be aligned with the straight edge oriented anteriorly against the aorto–mitral continuity. The anterior straight edge is the highest in comparison with the other edges, and this feature allows the echocardiographers to detect it; the long cuff must be placed on the straight anterior part of the annulus with the short cuffs on medial, lateral, and posterior areas. Two-dimensional TEE X-plane imaging with simultaneous bicommissural and LVOT views can identify the higher anterior edge that, for an appropriately clocked valve, has only to be visualized on the long-axis view of the aorta (Figs. 3A, B). If the long cuff is visualized in the commissural view on the medial-lateral position, the valve is not appropriately oriented and is medially or laterally clocked (Figs. 3C, D). So, it makes the interventional imager able to guide the implanter to rotate the bioprosthesis in the correct position. Although 2D TEE allows visualization of valve clocking on the X-plane, in this phase, 3D TEE assessment is crucial. In fact, 3D TEE surgeon's view of the MV confirms the bioprosthesis radial orientation (Fig. 4A). After appropriate clocking, the valve prosthesis is withdrawn toward the LV and deployed intra-annularly (Fig. 4B).

As the prosthesis can be repositioned or fully retrieved, when the prosthesis is fully extruded, it is fundamental to assess the prosthesis functioning and sealing and the position of the device in the LV to avoid LVOT obstruction. Even though a prediction of the effect of the size of the prosthesis into the LV is planned and simulated by preprocedural CT, a dynamic intraprocedural assessment is mandatory. Two-dimensional TEE with Doppler is the modality of choice to detect LVOT obstruction. Imaging parameters and features to assess include the following: the prosthesis has correct clocking; hemodynamic parameters including Doppler gradients, pulmonary hypernsion, and valve prosthesis area; residual intravalvular regurgitation and perivalvular leakage; and presence and degree of LVOT obstruction.

The follow-up of the Tendyne device includes the guidelines-recommended imaging pathway of bioprosthesis. Transthoracic echocardiography and TEE are the techniques of choice.

The success of TMVR, a novel interventional procedure in the therapeutic armamentarium for MR whose use is expanding in the clinical arena, relies on the interaction between the implanter team and the imager team. The knowledge of multimodality integrated imaging in the different phases of TMVR is key for guiding interventional imagers and for procedural success.