Mitral regurgitation (MR) is one of the most common valvular heart diseases, second only to aortic valve stenosis.1 According to international guidelines, acute MR may occur due to papillary muscle rupture during myocardial infarction and generally requires urgent surgery because of the severity of hemodynamic impairment. Chronic MR requires surgical treatment in symptomatic patients, whereas asymptomatic patients should be evaluated individually for surgery.2,3 Despite the lack of consensus regarding the timing of intervention, asymptomatic patients with chronic MR can be recommended for surgery when it is associated with depressed left ventricular (LV) function, LV enlargement, atrial fibrillation, or pulmonary hypertension.2,4–6 It has been established that, when feasible, mitral valve (MV) repair is preferable to valve replacement due to fewer perioperative complications and better clinical outcome.7–9 Recently, percutaneous MV repair has been increasingly recognized as a valid option for high surgical risk patients with symptomatic MR.10,11 The EVEREST (Endovascular Valve Edge-to-Edge Repair Study) trials have convincingly demonstrated that percutaneous MV repair with the MitraClip® delivery system (Evalve Inc., Menlo Park, CA) effectively reduces MR.12,13 Data from EVEREST I suggested that percutaneous repair with the MitraClip® system significantly reduced MR (≤ 2+) in most patients, thereby reducing rates of recurrent MR, additional surgery, and death.14
In addition, the percutaneous procedure is generally well tolerated by high-risk patients with LV dysfunction and major comorbidities.15 In the EVEREST II Trial, percutaneous MV repair was compared with surgery and showed superior safety but less reduction in MR at 1-year overall (MR moderate to severe at 1-year follow-up: 21% vs 3% percutaneous vs surgery group, respectively).16–19 Recently, the United States Food and Drug Administration has approved the premarket approval application for the MitraClip® Clip Delivery System (MitraClip® CDS) for percutaneous reduction of significant (≥3+) symptomatic degenerative MR in patients for whom a heart team has determined the surgical risk to be prohibitive.20
Etiology of Mitral Valve Regurgitation
The MV complex consists of the leaflets, mitral annulus, the subvalvular apparatus (chordae tendineae and papillary muscles), and their connections to the LV. The mitral annulus is a complex saddle-shaped structure with peaks anteriorly and posteriorly, and nadirs medially and laterally. Valvular competency depends on the correct interaction among the different components of the MV apparatus, and for this reason, MR can result from the impairment of any single element of the system.21,22 Thus, MR can be distinguished as primary or secondary. Primary MR is related to structural alterations of any of the MV apparatus components. Primary MR is most commonly caused by rheumatic and degenerative diseases. Due to the progressive reduction in the prevalence of rheumatic disease in developed countries, degenerative MR is now the most common type of primary MR. Secondary MR results from functional disturbance of the MV apparatus due to the changes in the LV geometry such as dilated cardiomyopathy or acute myocardial infarction.
The recommendations for surgery in patients with symptoms of either primary or secondary chronic MR are presented in Table 1.2
The MitraClip® System is a percutaneous approach that has been introduced into clinical practice.23,24 This approach results in permanent apposition of the 2 MV leaflets by a clip that is placed between the anterior middle scallop (A2) and posterior middle segment (P2) of the anterior mitral leaflet (AML) and the posterior mitral leaflet (PML), respectively.12,25,26 The iatrogenic coaptation of the AML and PML leads to the creation of a double-orifice MV that mimics the surgical edge-to-edge procedure introduced by Alfieri27 in 2001.
The clip is deployed between the 2 MV leaflets by a transeptal approach. The system comprises: (1) a 24-F steerable guide catheter that is advanced to the left atrium (LA) by a previously performed transeptal puncture; (2) a CDS, with the clip located on its distal tip, introduced through the catheter to the MV orifice; (3) the MitraClip® device comprises a mechanical clip with 2 arms that can be opened or closed by a handle mechanism positioned at the proximal end of the delivery catheter.12,28,29
A “grasping” system is located on the internal side of the clip’s 2 arms that stabilizes the clip after its deployment and attaches it to the LV side of the AML and PML. The system is steered by the 2-knob coaxial mechanism that allows medial–lateral and anteroposterior movements of the delivery system’s distal tip. The external handle navigates the CDS through the cardiac chambers: opening, orienting, deploying, and eventually detaching the clip from the MV14 (Fig. 1).
Echocardiography in MitraClip® Candidates
Echocardiography is an important diagnostic tool for the evaluation of MV in patients undergoing percutaneous MV repair. Transesophageal echocardiography (TEE) evaluation of MV anatomy and LV function provide useful information regarding the feasibility of percutaneous MV repair (Table 2).30–36 In EVEREST I, key anatomic inclusion criteria included a regurgitant jet origin associated with the A2 to P2 segments of the MV12. For patients with functional MR, to have sufficient tissue to grasp with the clip arms, a coaptation length of at least 2 mm and a coaptation depth <11 mm are needed. The coaptation length is measured as the vertical length of leaflet tissue in contact during midsystole in the atrial to ventricular direction (Fig. 2A). Coaptation depth is defined as the shortest distance between the coaptation and the annular planes (Fig. 2B). The 2 TEE views for measurement of coaptation length and coaptation depth are the 4-chamber long-axis (LAX) view and the midesophageal (ME) LAX view.
For patients with a flail mitral leaflet, a flail gap <10 mm and a flail width <15 mm are also important anatomic features to allow proper grasping. Flail gap is defined as the greatest distance between the ventricular side of the flail segment to the atrial side of the opposing leaflet edge in either the 4-chamber LAX or ME LAX view (Fig. 2C). Flail width is defined as the width of the flail leaflet segment as measured along the coaptation line in the transgastric short-axis (SAX) view (Fig. 2D).
Real-time 3-dimensional (D) TEE may have increasing value, compared with that of 2D TEE, providing higher quality visualization of MV anatomy.37 En face visualization of the MV segments, both from the atrial and ventricular orientations, allows detailed detection of MV pathology38–41 with particular emphasis on tissue defects such as clefts that can impact the feasibility of a Mitraclip® and are more difficult to recognize by 2D TEE.
MitraClip® Procedure and Intraprocedural Echocardiography
The MitraClip® procedure is usually performed in anesthestized patients to avoid movement and to facilitate TEE evaluation. Invasive hemodynamic monitoring is generally implemented to continuously evaluate hemodynamic status of these high-risk patients.
The delivery catheter is inserted through a femoral vein, using TEE and fluoroscopic guidance in the cardiac catheterization laboratory, as previously described.12,42 Intraprocedural TEE,14,42–44 preferably using real-time 3D to better evaluate the spatial interaction between the cardiac structures and the intracardiac devices by visualizing them from both atrial and ventricular perspectives, is instituted.45–47 Fluoroscopy is used primarily for assessing the opening angle of the clip arms, whereas it has a limited role in the steering and positioning of the clip. The latter are appropriately accomplished by TEE, so it is used as the primary imaging modality to guide the procedure and is reported to be essential to its success.48 TEE guidance is needed to implement the phases of the percutaneous procedure as follows: transseptal catheterization, axial alignment of the clip delivery system, leaflet grasping, assessment of leaflet capture, clip deployment, post–clip deployment assessment, and withdrawal of the clip delivery system.
These are the steps for the procedure:
Step 1: Transseptal Puncture
Proper localization of the septal puncture site is important.49 The septal puncture must be performed in the posterior–superior portion of the interatrial septum to assure sufficient movement of the CDS into the LA and to provide optimal orientation of the clip with respect to the MV annular plane.
The TEE views that help guide the transseptal catheterization follow (Fig. 3):
- The ME SAX view (approximately 40°) shows the anterior–posterior portion of the interatrial septum and the junction of septum primum with septum secundum at the edge of the fossa ovalis. This view allows visualization of the aorta in a transverse orientation and is used for anterior–posterior (anterior towards the aorta) adjustments of the needle position and direction during transeptal puncture.
- The ME bicaval view (approximately 90°) shows the superior–inferior portion of the interatrial septum. This view is used for inferior–superior orientation with tenting of the fossa (superior toward superior vena cava).
The ME 4-chamber view (approximately at 0°–30°) allows for the evaluation of the distance from the point where the septum is punctured to the mitral annular plane (Fig. 3).
- Avoidance of accidental puncture of the aortic valve and/or the aortic root during this phase of the procedure is important.29,43 The puncture site is determined by creating tenting on the interatrial septum. The ideal site of transseptal puncture is localized across the fossa ovalis in a posterior trajectory toward the line of mitral leaflet coaptation at least 30 to 35 mm away from the valve, to allow the guide and device catheter a perpendicular approach to the MV and facilitate optimal movement and orientation through the distal portion of the guide catheter in the LA.
The linear distance between the tenting point on the septum and the MV annular plane can be easily measured at the beginning of the procedure using 2D TEE views.
Step 2: Axial Alignment of the Clip Delivery System
Once the transseptal puncture has been performed, the 24-F guide catheter is advanced into the LA and oriented perpendicular to the coaptation line and near the A2–P2 segments. The acquisition of the following views allows for navigation of the tip of the device across the MV, guidance of the clip orthogonal axial alignment with the plane of the MV annulus, and navigation parallel to the direction of anterograde mitral flow:
- ME commissural view (approximately 60°) is used to display the medial–lateral plane of the MV.
- ME LAX view (approximately 120°) identifies the anteroposterior plane of the MV.
Three-dimensional TEE is particularly helpful in guiding the medial, lateral, anterior, and posterior adjustments of the clip delivery system (Fig. 4). Once the clip’s arms are opened, 3D TEE is also useful for the evaluation of the adequacy of the clip arms alignment with respect to the MV’s line of coaptation. The atrial perspective of the MV and the accurate leaflets visualization provided by 3D TEE images suggest the proper rotation of the clip to achieve a perpendicular position to the mitral leaflets at the origin of the regurgitation jet (Video 1, see Supplemental Digital Content 1, http://links.lww.com/AA/A891).
Step 3: Leaflet Grasping
The clip’s arms are now opened into the grasping position and oriented perpendicularly with respect to the MV leaflets’ coaptation line (Fig. 5). The device is now advanced into the LV through the MV and the arms of the clip grasp the mitral leaflets (Video 2, see Supplemental Digital Content 2, http://links.lww.com/AA/A892). The ME LAX view is generally used to guide this crucial phase of the procedure (Fig. 6). Three-dimensional TEE can adequately evaluate the positioning and orientation of the clip by providing images of the MV and the clip from both the atrial and ventricular site (Fig. 7). The residual MR jet estimate, the diastolic transmitral peak velocity measurement, and mean mitral gradient should be performed to confirm adequacy of clip implantation and ensure the lack of MV stenosis.36 When the grasp is not optimal or a partial clip detachment occurs, the clip can be opened, removed from the initial position (Video 3, see Supplemental Digital Content 3, http://links.lww.com/AA/A893), and redeployed (Video 4, see Supplemental Digital Content 4, http://links.lww.com/AA/A894). The location of the MitraClip® device can be changed to achieve the best apposition of the mitral leaflets to optimize reduction of MR. The echocardiographer’s acquisition of real-time information regarding the position of the clip and the severity of the MR can successfully guide the procedure.
Step 4: Assessment of Leaflet Capture and Clip Deployment
The adequacy of leaflet capture and clip deployment is confirmed by TEE assessment of combined grasped tissue stability and MR reduction, in the presence of a double-orifice MV. Color flow Doppler is used to analyze the origin, vena contracta, size, and direction of the residual jets.50 Although both 2D and 3D TEE views can adequately visualize the double-orifice image (Figs. 8–9), 3D TEE, in live 3D or wide zoom modality, better evaluates the efficacy of the MV repair by visualizing the MV orifices either from the atrial or the ventricular site (Video 5, see Supplemental Digital Content 5, http://links.lww.com/AA/A895).27 TEE provides information about the need for a second clip when the first clip is not positioned optimally and when severe residual MR is detected. Once efficacy of the percutaneous MV repair is demonstrated on TEE, the clip is closed and released.
Step 5: Post–Clip Deployment Assessment and Withdrawal of the Clip Delivery System
A comprehensive TEE examination is required after clip deployment to confirm reduction of MR, adequate position of the clip, evaluation of gradients (in particular after 2 clip implantation), and to detect any new findings (Video 6, see Supplemental Digital Content 6, http://links.lww.com/AA/A896).
The MV area should be measured by planimetry in the basal transgastric SAX. After percutaneous MV repair, each of the 2 orifices is planimetred at the level of the clip and summed (Fig. 10). Neither pulsed or continuous wave Doppler mitral velocity have been validated for use with a double-orifice valve after percutaneous MV repair.
Once the positioning of the clip is deemed adequate, the system is removed. TEE guidance is used to carefully withdraw the clip delivery system into the right atrium and out of the patient.
Detection of Complications
TEE provides a method for early detection of potential complications of clip placement including perforation of the atrial wall that may cause pericardial effusion/tamponade or partial detachment of the clip defined as detachment of a single leaflet from the clip (Video 7, see Supplemental Digital Content 7, http://links.lww.com/AA/A897). In the EVEREST I study, partial clip detachment occurred in 10 patients (9%) without the need for urgent intervention.12 TEE is used to check for iatrogenic atrial septal defect after the procedure51 (Fig. 11).
THE ROLE OF 3D TEE IN PERCUTANEOUS MITRAL VALVE REPAIR
Real-time 3D TEE significantly contributes to performance adequacy and to evaluating the individual steps of Mitraclip® device implantation.52
In addition, 3D TEE allows for complete visualization of the MV apparatus by providing images from both the atrial and the ventricular perspective.37–41 The 3D views of the intracardiac devices’ position with respect to the heart structures help the operator to guide the clip delivery system through the heart and to deliver the clip correctly. With the recent introduction of real-time 3D TEE, we should consider the real advantage of this modality in the operative management of percutaneous MV repair. Clinical experience and evidence from the literature suggest that real-time 3D TEE improves visualization of the MV through the display of the whole valve from a single image. This means that consulting off-line sources or relying on one’s memory is not needed and that even physicians who are not expert in ultrasound imaging, such as surgeons and interventional cardiologists, can easily interpret the echo view. As a consequence, 3D TEE ameliorates communication between operator and echocardiographer, possibly reducing the duration of the procedure. However, 3D TEE has limitations that need to be considered. This modality is strongly dependent on spatial resolution and frame rate; a good 3D image is always the result of good 2D image quality.
TEE not only plays a major role in the MitraClip® procedure, but also it is an indispensable tool. Real-time 3D TEE can improve echocardiographic performance during the MitraClip® procedure. Cardiac anesthesiologists, who combine expertise in intraoperative echocardiography with skill in hemodynamic management, may play a pivotal role in the new MitraClip® procedure.
Name: Fabio Guarracino, MD.
Contribution: This author prepared the manuscript.
Attestation: Fabio Guarracino approved the final manuscript.
Name: Rubia Baldassarri, MD.
Contribution: This author helped preparing the manuscript.
Attestation: Rubia Baldassarri approved the final manuscript.
Name: Baldassare Ferro, MD.
Contribution: This author helped preparing the manuscript.
Attestation: Baldassare Ferro approved the final manuscript.
Name: Cristina Giannini, MD, PhD.
Contribution: This author helped preparing the manuscript and collecting the figures.
Attestation: Cristina Giannini approved the final manuscript.
Name: Pietro Bertini, MD.
Contribution: This author helped preparing and reviewing the manuscript and editing the movies.
Attestation: Pietro Bertini approved the final manuscript.
Name: Anna Sonia Petronio, MD.
Contribution: This author helped preparing and reviewed the manuscript.
Attestation: Anna Sonia Petronio approved the final manuscript.
Name: Vitantonio Di Bello, MD.
Contribution: This author helped preparing and reviewed the manuscript.
Attestation: Vitantonio Di Bello approved the final manuscript.
Name: Giovanni Landoni, MD.
Contribution: This author reviewed the manuscript.
Attestation: Giovanni Landoni approved the final manuscript.
Name: Ottavio Alfieri, MD.
Contribution: This author reviewed the manuscript and the figures.
Attestation: Ottavio Alfieri approved the final manuscript.
This manuscript was handled by: Martin J. London, MD.
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