|Year : 2022 | Volume
| Issue : 3 | Page : 236-247
Role of Echocardiography in Guiding Transcatheter Aortic and Mitral Valve Replacement
Manish Bansal, Ravi R Kasliwal
Department of Cardiology, Medanta - The Medicity, Gurgaon, Haryana, India
|Date of Submission||19-Sep-2022|
|Date of Acceptance||20-Sep-2022|
|Date of Web Publication||12-Nov-2022|
Dr. Manish Bansal
Department of Clinical and Preventive Cardiology, Medanta Heart Institute, Medanta - The Medicity, Gurgaon - 122 001, Haryana
Source of Support: None, Conflict of Interest: None
The recent technical advances have revolutionized the field of percutaneous structural heart disease interventions. Multimodality imaging is pivotal to the success of these procedures and echocardiography is an integral part of this imaging. Echocardiography is essential for preprocedural evaluation as well as postprocedure assessment and follow-up of all such patients. In addition, for mitral valve interventions, echocardiography is also indispensable for intra-procedural guidance, although its role in guiding transcatheter aortic valve replacement (TAVR) has diminished lately. A thorough understanding of echocardiography, especially for valvular assessment, and a high level of expertise in intraprocedural imaging are necessary for facilitating these procedures. This review describes the role of echocardiography in guiding TAVR and transcatheter mitral valve-in-valve replacement- the two most commonly performed percutaneous valve replacement procedures at present.
Keywords: Neo-left ventricular outflow tract, paravalvular leak, transcatheter aortic valve replacement, transcatheter mitral valve-in-valve replacement
|How to cite this article:|
Bansal M, Kasliwal RR. Role of Echocardiography in Guiding Transcatheter Aortic and Mitral Valve Replacement. J Indian Acad Echocardiogr Cardiovasc Imaging 2022;6:236-47
|How to cite this URL:|
Bansal M, Kasliwal RR. Role of Echocardiography in Guiding Transcatheter Aortic and Mitral Valve Replacement. J Indian Acad Echocardiogr Cardiovasc Imaging [serial online] 2022 [cited 2023 Feb 4];6:236-47. Available from: https://jiaecho.org/text.asp?2022/6/3/236/361064
| Introduction|| |
Over the past 10–15 years, transcatheter aortic valve replacement (TAVR) has emerged as an excellent alternative to surgical aortic valve replacement (SAVR) for patients with symptomatic severe aortic stenosis (AS) who require a bioprosthetic heart valve (BPHV). In patients at high surgical risk, TAVR has been demonstrated to be superior to SAVR, whereas in those at intermediate or low surgical risk, TAVR is at least noninferior to SAVR. A meta-analysis of several randomized clinical trials has shown that the overall mortality risk with transfemoral TAVR is lower than that with SAVR, with a hazard ratio of 0.88 (95% confidence interval 0.78–0.99). The success of TAVR has resulted in the expansion of this therapy to several other valve lesions. Failed surgically implanted BPHVs have emerged as another important indication for transcatheter valve replacement, and this approach has now become the preferred strategy for treating degenerated BPHVs.
Imaging plays a pivotal role in the successful performance of these procedures. Echocardiography and multidetector computed tomography (MDCT) are the main modalities used for preprocedure evaluation while echocardiography is the mainstay for postprocedure evaluation and follow-up. The choice of imaging for intraprocedure guidance varies according to the procedure. TAVR is now mostly performed under conscious sedation, and hence, echocardiography is generally not needed during the procedure, but it is required for immediate postprocedure assessment once the valve is deployed. In contrast, for transcatheter mitral valve replacement procedures, echocardiography is essential even for intraprocedure guidance.
| Transcatheter Aortic Valve Replacement|| |
Initial assessment of aortic stenosis
Echocardiography is the primary modality used for the assessment of aortic valve morphology and AS severity. It also permits a comprehensive cardiac assessment, including the assessment of concomitant valve lesions (if present), left ventricular (LV) systolic function, LV diastolic function, pulmonary pressures, and right heart function.
For the successful performance of TAVR, extensive calcification of the aortic valve is a prerequisite. TAVR can be performed for a heavily calcified valve even if aortic regurgitation (AR) is the dominant lesion and not AS. A trileaflet valve is the most suitable valve morphology for TAVR, but with increasing experience, TAVR is now being routinely performed for bicuspid aortic valves and even for unicuspid aortic valves.
The severity of AS is quantified based on aortic valve area (AVA) and transvalvular velocity and gradient. AS is considered severe if AVA is <1 cm2 (<0.6 cm/m2) and the peak aortic valve velocity >4 m/s or mean aortic valve gradient >40 mmHg. However, it is now well recognized that nearly one-third of all patients with severe AS (AVA <1 cm2) have relatively low valve gradients (i.e. mean aortic valve gradient <40 mmHg). This is known as low-gradient severe AS. Reduced LV stroke volume is the most common mechanism underlying low-gradient severe AS. When low stroke volume is caused by reduced LV systolic function, this is known as classical low-flow low-gradient severe AS. However, low stroke volume may also occur even in patients with preserved LV ejection fraction, an entity known as paradoxical low-flow low-gradient severe AS. In these patients who present with apparently low-gradient severe AS, a multimodality assessment including speckle-tracking echocardiography, dobutamine echocardiography, and aortic valve calcium score estimation with MDCT is required for accurate determination of the AS severity. A detailed discussion on this topic is beyond the scope of this review.
Evaluation specific for transcatheter aortic valve replacement
Once it has been decided that the patient needs to undergo TAVR, a lot of additional information needs to be collected to confirm the patient suitability for TAVR and for exact procedural planning. This includes accurate sizing of the aortic annulus, extent, and location of the aortic valve calcification, status of the aortic root (size, orientation, and any localized pathology), LV outflow tract (LVOT) anatomy (shape of the LVOT and any basal septal hypertrophy), coronary anatomy, especially the coronary ostial height, and the status of the rest of the aorta and the vascular access route. Most of this information is currently derived using MDCT. However, in patients in whom MDCT is not feasible for some reason (e.g. advanced renal dysfunction), three-dimensional (3D) transesophageal echocardiography (TEE) may be a reasonable alternative for the assessment of aortic valve and aortic root anatomy.
Aortic annulus size
Accurate measurement of the aortic annulus size is crucial for a successful TAVR.,, Oversizing the device may result in inadequate expansion of the prosthetic heart valve (PHV) with resultant valve malfunction, whereas under-sizing carries the risk of postprocedure paravalvular leak (PVL) and valve embolization.
Conventional two-dimensional (2D) echocardiography almost invariably underestimates the aortic annulus size., This is because the aortic annulus is oval in shape and the annulus diameter measured in 2D echocardiography (transthoracic or transesophageal) is the minor diameter [Figure 1]. 3D TEE, by enabling en face visualization of the aortic annulus, permits a more accurate sizing., For 3D echocardiographic measurement of the aortic annulus size, first a good-quality zoom-mode 3D dataset encompassing the entire aortic valve apparatus is acquired. The dataset is then cropped in multiplanar reconstruction mode (MPR) to visualize the aortic root in the cross section. The image plane is cut exactly at the level of the aortic annulus, which is identified as the level where the aortic leaflets are inserted. Once this cross-sectional image is obtained, aortic annulus can be directly planimetered to obtain all the relevant measurements [Figure 2]. For self-expanding TAVR devices, aortic annulus perimeter is used for valve sizing, whereas for balloon-expandable valves, major and minor diameters are preferred. The measurements are performed during mid-systole when the annulus is largest and most circular.
|Figure 1: Underestimation of aortic annulus size by two-dimensional echocardiography. (a) Annular measurement in the parasternal long-axis view during transthoracic echocardiography. (b) The corresponding computed tomography images show that the aortic annulus is oval in shape and the measurement obtained from echocardiography is actually the minor diameter|
Click here to view
|Figure 2: Direct planimetry of left ventricular outflow area using three-dimensional echocardiography|
Click here to view
Coronary ostial height
Adequate coronary ostial height safeguards against the risk of coronary occlusion by the native aortic valve leaflets once the TAVR is done and the implanted valve displaces the native leaflets toward the aortic wall.
While MDCT is the best modality for the assessment of coronary ostial height, these measurements can also be obtained using 3D TEE [Figure 3]. The same dataset as used for annulus sizing can be used for this purpose also, provided the coronary ostia are included in the dataset at the time of image acquisition. MPR mode is used to identify each coronary ostium in different views and the distance from the corresponding side of the aortic annulus is measured.
|Figure 3: Three-dimensional transesophageal echocardiography with multiplanar reconstruction for measurement of coronary ostial height. (a) Right coronary ostium, (b) Left coronary ostium|
Click here to view
Some of the latest echocardiography equipment have artificial intelligence enabled automated tools for analyzing the aortic root anatomy. Once the 3D TEE dataset is acquired, the analysis software automatically reconstructs the aortic anatomy, with some inputs from the operator. Once the reconstruction is done, all the necessary measurements are automatically provided by the software [Figure 4] and [Video 1]. Although this may simplify the analysis process, the operator must manually confirm the veracity of the reconstruction and the accuracy of the measurements.
|Figure 4: Role of artificial intelligence based automated software in delineating aortic root anatomy during 3D TEE. A 3D TEE dataset is acquired first (a) Using which the automated software creates a virtual model of the aortic root (b). Also see Video 1. 3D: Three-dimensional, TEE: Transesophageal echocardiography|
Click here to view
[Additional file 1]
Video 1: Role of artificial intelligence based automated software in delineating aortic root anatomy during 3D TEE. A 3D TEE dataset is acquired first, using which the automated software creates a virtual model of the aortic root. 3D: Three-dimensional, TEE: Transesophageal echocardiography
As mentioned above, TAVR procedures are now mostly performed under conscious sedation with fluoroscopic guidance. In such cases, transthoracic echocardiography (TTE) is used only at the end of the procedure to look for any PVL, rule out procedural complications and to confirm the overall success of the procedure. However, when the procedure is performed under general anesthesia, TEE can be used for providing additional intra-procedure guidance.
Correct placement of the valve
For TAVR, the valve is typically deployed such that the lower edge of the valve is 4–5 mm below the level of the aortic annulus. A too deep deployment may result in residual PVL, valve embolization into the LV, interference with the mitral valve function, and valve obstruction due to folding of the native valve leaflets over the transcatheter valve (in case of balloon-expandable valves). Conversely, a too high deployment is associated with the risk of coronary occlusion, valve embolization into the aorta, and residual PVL.
Real-time 3D TEE may help in confirming the exact location of the lower edge of the PHV during deployment. Conventionally, the edge toward the mitral valve is positioned slightly higher up before deployment and as the valve is deployed, it reorients to become coaxial with the aortic root.
Adequate valve expansion and normal valve functioning
Echocardiography, esp. 3D TEE, can confirm proper valve deployment with adequate valve expansion. The leaflets and their excursion can be visualized and the flow across the valve can be quantified. Not only it helps confirm successful valve deployment but also the gradients measured at this stage serve as the reference for subsequent comparison. Apical five-chamber view in TTE and deep transgastric LV outflow view in TEE are utilized for measuring the valve gradient. Following are the criteria to define the normal functioning of a transcatheter aortic valve:
- Peak aortic velocity <3 m/s
- Mean gradient <20 mmHg
- Ratio of LVOT velocity time integral (VTI) to aortic valve VTI ≥0.35
- Effective orifice area >1.1 cm2 for body surface area >1.6 and >0.9 cm2 for those with body surface area <1.6 cm2.
It is also very important to rule out any AR. AR may be valvular or paravalvular. Valvular AR usually occurs due to the presence of guidewire and/or catheter across the valve and disappears when the same is removed. Persistence of valvular AR even after removing the guidewires/catheters indicates valve malfunction, usually secondary to inadequate expansion, but is uncommon.
A PVL, in contrast, is a common complication after TAVR and is discussed below.
PVL is one of the most important complications of TAVR and has significant prognostic and therapeutic implications [Figure 5], [Figure 6] and [Video 2]a, [Video 2]b, [Video 2]c, [Video 3]a, [Video 3]b, [Video 3]c. The incidence of PVL varies depending on the extent and location of the aortic annular calcification and the type of valve used. In the largest meta-analysis of TAVR outcomes, the incidence of residual moderate or severe PVL after TAVR was reported to be 7.4%–11%. The incidence has since declined appreciably due to ongoing improvements in TAVR technology and increasing operator expertise. Currently, the incidence of moderate or severe PVL is expected to be < 5% at any good TAVR center.,
|Figure 5: Paravalvular aortic regurgitation in a patient who underwent transcatheter aortic valve replacement using a self-expandable valve. (a) The aortic valve short-axis view obtained immediately after the valve deployment shows that the leak is small, occupying hardly 10% of the valve circumference. (b) The same leak in the long-axis view. (c) The leak spontaneously diminishes significantly as the transcatheter valve underwent further self-expansion. The red arrows point to the aortic regurgitation jet in all the three images. Also see Video 2a-c|
Click here to view
|Figure 6: Another patient with a much larger paravalvular leak after transcatheter aortic valve replacement. (a) The short-axis view shows the leak to be much broader. (b) Deep transgastric left ventricular outflow view for better visualization of the jet extent (arrow). (c) Since the leak did not resolve even with repeat balloon dilatation, a percutaneous closure device (arrow) was deployed to seal the leak. Also see Video 3a-c|
Click here to view
Video 2: Paravalvular aortic regurgitation in a patient who underwent transcatheter aortic valve replacement using a self-expandable valve. [Additional file 2](a) The aortic valve short-axis view obtained immediately after the valve deployment shows that the leak is small, occupying hardly 10% of the valve circumference. [Additional file 3] (b) The same leak in the long-axis view. [Additional file 4](c) The leak spontaneously diminishes significantly as the transcatheter valve underwent further self-expansion
Video 3: Another patient with a much larger paravalvular leak after transcatheter aortic valve replacement . [Additional file 5](a) The short-axis view shows the leak to be much broader. [Additional file 6](b) Deep transgastric left ventricular outflow view for better visualization of the jet extent. [Additional file 7](c) Since the leak did not resolve even with repeat balloon dilatation, a percutaneous closure device was deployed to seal the leak
A significant PVL is usually poorly tolerated in patients undergoing TAVR for severe AS, because the hypertrophied stiff LV is unable to accommodate the sudden volume overload unless there was preexisting moderate or severe AR., Besides this immediate impact, moderate or severe PVL is also associated with worse long-term survival.,, However, the clinical significance of mild PVL is less clear. Although in the initial PARTNER 1 (Placement of AoRTic TraNscathetER Valve 1) trial, even mild PVL was associated with worse outcomes and increased mortality,, the subsequent evidence has been less consistent.
Aortic root angiogram can easily demonstrate AR but it only provides a rough assessment and may not be able to distinguish between valvular and paravalvular AR. Echocardiography is currently the best modality for diagnosing and quantifying PVL. TEE is much superior to TTE for this purpose, as the latter often underestimates PVL severity. Imaging in multiple windows is necessary to delineate the location, number, and size of PVLs. During TTE, parasternal long-axis view, parasternal short-axis view, apical five-chamber view, and the apical long-axis view permit good assessment of AR, whereas in TEE, mid-esophageal aortic valve short-axis view, mid-esophageal long-axis view, and the deep transgastric LV outflow view are the most helpful. The deep transgastric LV outflow view provides excellent visualization of PVL because the direction of the jet is parallel to the ultrasound beam, and therefore, this view is essential before concluding that there is no PVL [Video 3]b.
Several different methods exist for quantifying PVL severity., These include qualitative/semi-quantitative assessment using aortic root angiogram, indirect estimation based on hemodynamic parameters (aortic diastolic pressure, ratio of the difference between aortic and LV diastolic pressure to aortic systolic pressure, etc.), and a more objective assessment using echocardiography.
Several different echocardiographic parameters and schemes have been proposed to quantify the severity of TAVR-related PVL. Of these, the most accepted grading system is based on quantifying the circumferential extent of the PVL. A jet occupying <10% of the valve circumference is considered mild, 10%–30% moderate, and >30% severe. When multiple jets are present, their combined width is used to quantify the PVL severity.,
The other echocardiographic criteria used for assessing PVL severity include abnormal leaflet motion, vena contracta width and area, jet width in relation to the LVOT width, jet density and contour, pressure half-time, flow reversal in descending thoracic aorta, and more quantitative methods such as regurgitant orifice area, regurgitant volume, and regurgitant fraction.
If a significant PVL is found, it may require repeat balloon dilatation of the valve, implantation of another transcatheter heart valve (THV), percutaneous device closure of the leak, or very rarely, surgery [Video 3]c.
Excluding other complications
Echocardiography is very useful for ruling out several other post-TAVR complications. Interference of the mitral valve function due to low deployed THV; LV myocardial stunning; mitral regurgitation due to myocardial stunning, intraventricular conduction disturbance, or mitral leaflet impingement [Figure 7] and [Video 4]a, [Video 4]b, [Video 4]c, [Video 4]d; development of new wall motion abnormality; and aortic root injury manifesting as peri-aortic hematoma or aortic dissection can all be easily recognized with the help of echocardiography.
|Figure 7: (a) A tilting disc mechanical valve in the mitral position with the disc seen in open position (arrow). (b) The patient underwent transcatheter aortic valve replacement but unfortunately, the valve got deployed too low (arrow) in the left ventricular outflow tract so that it blocked the opening of the mitral valve leaflet. Also see Video 4a-d|
Click here to view
Video 4: [Additional file 8](a and [Additional file 9]b) A tilting disc mechanical valve in mitral position with normal disc excursion. Seen in open position. ([Additional file 10]c and [Additional file 11]d) The patient underwent transcatheter aortic valve replacement but unfortunately, the valve got deployed too low in the left ventricular outflow tract so that it blocked the opening of the mitral valve leaflet
A baseline echocardiogram should be performed before discharge and then at 3 and 6 months. Subsequent follow-up interval varies depending on the clinical status of the patient and the findings on the earlier scans but surveillance echocardiography at every 6 months is generally considered appropriate. TTE is the standard modality for this purpose. However, a TEE may be needed if TTE reveals any PHV malfunction, prompting a more detailed assessment of the valve structure and function.
At each follow-up examination, the leaflet mobility and the overall valve function should be assessed, aortic valve gradients measured and any valvular or paravalvular regurgitation ruled out.
If there is a significant increase in the valve gradient, a thorough evaluation is needed to define the underlying mechanism of the same. Leaflet thrombosis has been described as one of the important mechanisms of increased valve gradients after TAVR.,, The leaflet thrombosis may just appear as leaflet thickening, with or without restriction of the mobility and therefore, absence of any localized echogenic deposit does not rule out leaflet thrombosis. In case of significant AR, valve thrombosis, endocarditis, or structural degeneration should be ruled out.
| Transcatheter Mitral Valve-in-Valve Replacement|| |
Structural valve degeneration (SVD) is the most common complication associated with surgically implanted BPHVs. Overall, the incidence of SVD rises 7–8 years after the valve replacement surgery and varies according to the age of the patient (more common in younger individuals), site of implantation (more common in mitral position), and BPHV design and models. Other risk factors for SVD include patient-prosthesis mismatch, smoking, diabetes mellitus, end-stage renal disease, and hyperparathyroidism.[26-28] Apart from SVD, there are other conditions that may also lead to BPHV failure such as infective endocarditis and valve thrombosis.
Although reoperation has been a traditional treatment strategy for failed BPHVs, the advent of transcatheter valve-in-valve replacement has offered an attractive alternative. Because of the lower morbidity and mortality associated with a percutaneous valve-in-valve replacement than a redo surgery, the former is being increasingly adopted nowadays.,
In case of mitral valve lesions, percutaneous valve implantation may be performed for a variety of indications, including failed BPHVs, failed previous mitral annuloplasty ring repair, extensive mitral annular calcification, and native valve regurgitation. Of these, transcatheter mitral valve-in-valve replacement (i.e. TMViVR) for failed BPHVs is the most well-established indication at present. TMViVR can be performed regardless of whether stenosis is the dominant abnormality or regurgitation or a combination of the two. Previous registries have shown a higher technical success rate, lower incidence of residual regurgitation, and lower 30 days to 1-year all-cause mortality with TMViVR as compared to when transcatheter valve implantation is performed for failed mitral valve repair or mitral annular calcification.,
Preprocedure assessment for transcatheter mitral valve-in-valve replacement
The goals of preprocedure assessment in a patient undergoing TMViVR include- (1) to assess the severity of valve dysfunction, (2) to determine the mechanism of valve dysfunction, (3) to recognize potential contraindications to or anticipated complications with TMViVR, (4) to select appropriate valve size, and (5) to assess the transseptal and vascular access routes. Multimodality imaging with echocardiography and MDCT is used for obtaining this information.,, Echocardiography is used predominantly for assessing the mechanism and severity of valve dysfunction, ruling out contraindications such as left atrial clot, and evaluating the interatrial septal anatomy. In comparison, MDCT is the primary modality used for valve sizing, predicting neo-LVOT size and the risk of LVOT obstruction, and for the assessment of vascular access routes.
Severity of valve dysfunction
Evaluation of PHV function is often challenging. A combination of qualitative assessment of the valve leaflets and quantitative assessment of flow dynamics is required to determine the exact severity of the valve lesion. No single quantitative parameter is sufficiently accurate, and hence, several different parameters need to be combined to have an accurate assessment of the lesion severity.,
In case of mitral PHV stenosis, visible thickening of the valve leaflets and reduced opening provide important clues to the presence of significant stenosis. TEE permits excellent visualization of the mitral PHV leaflets and is the preferred imaging modality for the assessment of mitral PHVs. The quantitative assessment of mitral stenosis severity relies on several parameters including peak transvalvular velocity, mean mitral valve gradient, pressure-half time, ratio of VTI of mitral inflow to LVOT forward flow, and the effective orifice area derived using the continuity equation [Table 1]., Of these, transvalvular flow velocity, gradient, and the pressure-half time are affected by flow rate and loading conditions and are therefore less reliable. In comparison, VTI ratio and the effective orifice area are less load-dependent. However, they have their own limitations. They are not applicable if there is significant aortic or mitral regurgitation and are also inherently susceptible to errors because of the need to integrate information from different cardiac cycles and the challenges in accurately measuring LVOT VTI.
|Table 1: Quantitative parameters for assessment of the severity of prosthetic mitral valve obstruction*|
Click here to view
The assessment of prosthetic mitral regurgitation severity is even more challenging., A number of qualitative, semi-quantitative, and quantitative parameters have been described. These include color flow jet area, jet density and contour, pulmonary venous flow pattern, LA/LV dilatation, vena contracta size, effective regurgitant orifice area derived using proximal isovelocity surface area method, and regurgitant volume and fraction. 3D echocardiography has the advantage of allowing direct planimetry of jet vena contracta and may be more accurate in the presence of eccentric, noncircular jets. However, in clinical practice, the decision-making is largely governed by the symptomatic status of the patient, morphological appearance of the valve leaflets, visual assessment of the regurgitation jet, and the presence and severity of pulmonary hypertension.
Mechanism of valve dysfunction
SVD of a BPHV may result either in thickening and/or calcification of the valve leaflets with reduced mobility or weakening/disruption of the valve leaflets leading to prolapse or flail segment with significant regurgitation [Figure 8] and [Video 5], [Video 6]a, [Video 6]b, [Video 6]c, [Video 7]a, [Video 7]b. Careful inspection of the valve structure helps in recognizing these abnormalities. A TMViVR can be performed for any of these conditions.
|Figure 8: A few examples of structural valve degeneration of bioprosthetic heart valves in mitral position. (a and b) The valve leaflets (arrow) are markedly thickened and rigid, resulting in significant valve obstruction [Video 5]. (c and d) The valve leaflets are thickened with one of the leaflets being flail (arrow), resulting in both severe stenosis and regurgitation of the prosthetic mitral valve [Video 6a-c]. (e and f) The valve leaflets are thin, but one leaflet has become flail (arrow) resulting in severe mitral regurgitation [Video 7a and b].|
Click here to view
[Additional file 12]
Video 5: Three-dimensional transesophageal echocardiography with en face visualization of the mitral prosthetic heart valve. The valve leaflets are thickened and rigid with markedly reduced mobility
Video 6: [Additional file 13](a) A bioprosthetic heart valve at mitral position with thickened leaflets. One leaflet is flail also, resulting in both severe stenosis and regurgitation of the prosthetic mitral valve [Additional file 14](b). [Additional file 15](c) Three-dimensional transesophageal echocardiography with en face visualization of the prosthetic valve. Reduced mobility of the two leaflets and flail third leaflet can be easily appreciated. Also seen is guidewire positioned in the left atrium
Video 7: [Additional file 16](a) A bioprosthetic heart valve at mitral position with thin leaflets, but one leaflet has become flail. [Additional file 17](b) Color doppler showing severe mitral valve regurgitation
Apart from the above, BPHV failure can also occur due to infective endocarditis, valve thrombosis, or pannus formation. Identifying these abnormalities is important because active infective endocarditis is a contraindication to percutaneous valve replacement, whereas BPHV thrombosis may be treated with intensified anticoagulation or even fibrinolysis, obviating the need for repeat valve intervention.
In patients with significant PHV regurgitation, it is also essential to confirm that the regurgitation is valvular and not paravalvular because the latter would require a different form of intervention and would not benefit from valve-in-valve implantation.
Predicting the risk of left ventricular outflow tract obstruction
Iatrogenic LVOT obstruction is the most feared complication of TMViVR procedure. It is defined as an increase in the LVOT gradient by 10 mmHg or more from the baseline. The risk of this complication is much lower (0.7%–2.2%) with TMViVR than when the valve is implanted in a native valve (5% with valve-in-ring and 10%–40% with valve-in-MAC).,
A number of factors predispose to the risk of LVOT obstruction with TMViVR, including orientation of the surgically implanted PHV toward the ventricular septum [Figure 9] and [Video 8], larger size of the THV, deeper deployment of the THV, ventricular septal hypertrophy, small size LV cavity, and preserved LV ejection fraction. [35,38-40] Since the frame of the surgical valve confines the leaflets of the surgical valve, the redundancy of the valve leaflets is a less important mechanism of LVOT obstruction in case of TMViVR.
|Figure 9: Parasternal long-axis view showing a bioprosthetic mitral valve oriented towards the interventricular septum leaving only a narrow passage for left ventricular outflow. Also see Video 8. LA: Left atrial, LV: Left ventricle, RV: Right ventricle|
Click here to view
[Additional file 18]
Video 8: Parasternal long-axis view showing a bioprosthetic mitral valve oriented towards the interventricular septum leaving only a narrow passage for left ventricular outflow
Predicting the likelihood of LVOT obstruction after TMViVR requires careful assessment of the LVOT anatomy and estimating the anticipated neo-LVOT size after the implantation of THV. MDCT is the primary modality use for this purpose. Using dedicated postprocessing software, a virtual neo-LVOT can be created for the given technical specifications of the planned TMViVR procedure. From this, the neo-LVOT area can be planimetered directly. A predicted neo-LVOT area <200 mm2 indicates increased risk of LVOT obstruction, whereas an area <170 mm2 predicts LVOT obstruction with 96.2% sensitivity and 92.3% specificity. Although it is not feasible to predict the neo-LVOT size with TEE, TEE can still provide other valuable information. The orientation of the surgical valve, size of the LV cavity, septal thickness and contour, and existing LVOT size can all be assessed using TEE and can help alert the interventional team about the possibility of postprocedure LVOT obstruction. TEE is also used for measuring baseline LVOT gradient, which serves as the reference for comparing the gradients obtained immediately after the procedure.
Interatrial septal anatomy and other potential contraindications
TMViVR is now mostly performed through transseptal approach. Hence, a careful assessment of the interatrial septum (IAS) anatomy is essential before proceeding with this procedure. The presence of IAS aneurysm, patent foramen ovale or an atrial septal defect (ASD), previous surgically or percutaneously closed ASD, and lipomatous hypertrophy of IAS may all pose challenges during TMViVR, and therefore, the interventional team should be informed about the same.
TEE is also used for excluding other contraindications for TMViVR such as an LA/LA appendage or LV thrombus and the presence of another valve lesion requiring surgical intervention. A careful assessment of the right ventricular function and pulmonary pressures should also be performed to anticipate the need for closing the iatrogenic ASD which will be created during the procedure.
The TMViVR procedure is done under combined fluoroscopic and TEE guidance.,,,, Once the TEE probe is inserted after induction of general anesthesia, a quick reassessment of the preprocedure findings should be done. The mitral PHV structure and function, IAS anatomy, LV size and systolic function, the status of LVOT and the baseline LVOT gradient, RV systolic function, pulmonary pressures, etc., should be checked. Any intracardiac thrombus should be ruled out. Pericardial effusion, if present, should be noted. Pulmonary venous flow should be recorded, for comparison with the postprocedure findings. Only after reconfirming the suitability of TMViVR and excluding any obvious contraindication, the procedure is initiated.
A proper transseptal puncture is crucial for facilitating a successful TMViVR procedure. The ideal site for transseptal puncture is infero-posterior to the mid-part of the septum, at roughly 3–4 cm from the mitral annulus. To guide this, simultaneous biplane imaging is used [Figure 10] and [Video 9]. The mid-esophageal bicaval view (90°–120°) is used for confirming superior-inferior location, whereas the short-axis view (45°–60°) is used for anteroposterior orientation. The septal puncture needle is first advanced into the superior vena cava and is then gradually withdrawn while causing visible tenting of the IAS. The tenting site is continuously followed in the biplane mode as the needle is withdrawn. Once the desired location of the tenting is achieved in superior-inferior and anteroposterior directions, the imaging plane is quickly changed to display the four-chamber view in which the distance from the mitral annulus is measured. After ensuring a proper site for septal puncture in all the three views, the needle along with the sheath is advanced into the LA under real-time TEE guidance.
|Figure 10: Transseptal puncture under transesophageal echocardiographic guidance. Simultaneous biplane imaging is used with bicaval view (left image) providing superior-inferior orientation and the aortic valve short-axis view (right image) providing anterior-posterior orientation [Video 9]. IVC: Inferior vena cava, SVC: Superior vena cava|
Click here to view
[Additional file 19]
Video 9: Transseptal puncture under transesophageal echocardiographic guidance. Simultaneous biplane imaging is used with bicaval view (left image) providing superior-inferior orientation and the aortic valve short-axis view (right image) providing anterior-posterior orientation
After entering the LA, the puncture needle is removed and replaced with a coiled wire. Over this coiled wire, an Agilis catheter (St. Jude Medical, St. Paul, Minnesota) is advanced into the LA and the coiled wire is then exchanged with a J-tip wire which is used for crossing the mitral valve. In patients with severely degenerated mitral BPHV, crossing the valve may be problematic. In such cases, 3D TEE can help by providing the spatial location of the guidewire in relation to the PHV [Video 6]c.
After crossing the PHV, a pigtail catheter is advanced over the guidewire and positioned at the LV apex. The guidewire is then removed and exchanged with a curved stiff wire and then the pigtail catheter is also removed. This is followed by balloon dilation of the septal puncture, which is needed to allow an easy passage for the THV across the IAS. For this, an atrial septostomy balloon is advanced over the stiff wire, positioned across the IAS, and inflated under fluoroscopic and TEE guidance [Figure 11] and [Video 10].
|Figure 11: Balloon dilatation of the interatrial septal puncture. The inflated balloon (arrow) is seen across the interatrial septum [Video 10].|
Click here to view
[Additional file 20]
Video 10: Balloon dilatation of the interatrial septal puncture. The inflated balloon is seen across the interatrial septum
Valve positioning and deployment
After achieving satisfactory atrial septostomy and ensuring proper trajectory of the guidewire into the LV, the THV is advance over the wire, into the LA, and then across the existing BPHV. The exact positioning of the THV is confirmed with fluoroscopy and TEE [Figure 12] and [Video 11]. In general, the valve is deployed in such a manner that 80% of the valve frame is on the LV side and 20% on the LA side. Deployment deeper into the LV cavity improves the hemodynamic performance of the valve but increases the risk of LVOT obstruction. Conversely, deployment more toward the LA minimizes the risk of LVOT obstruction but increases the risk of PVL and device embolization into the LA.,
|Figure 12: Real-time three-dimensional echocardiography to confirm positioning of the percutaneous valve (arrow) across the surgically-implanted prosthetic mitral valve (arrowheads point towards the sewing ring) [Video 11]|
Click here to view
[Additional file 21]
Video 11: Real-time Three-dimensional echocardiography to confirm positioning of the percutaneous valve across the surgically-implanted prosthetic mitral valve
Once the proper device positioning is confirmed, the valve is deployed using slow balloon inflation under rapid ventricular pacing with ventilation briefly paused. The deployment is done under fluoroscopic and real-time TEE guidance. After ensuring full expansion, the balloon is rapidly deflated and ventricular pacing stopped to resume normal transmitral flow.
Postprocedure outcome and complications
Immediately after valve deployment, the valve is assessed for proper positioning, expansion, and stability. The excursion of the valve leaflets is checked and the transmitral flow and gradient are assessed. Good excursion of the valve leaflets with laminar flow and low gradient indicate proper expansion of the valve [Figure 13] and [Video 12]a, [Video 12]b. Improvement in the pulmonary vein flow pattern also provides an indirect clue toward the successful deployment of the THV.
|Figure 13: (a and b) Same patient as in Figure 8a and b after the deployment of transcatheter valve across the degenerated surgical valve. Good valve opening is seen with good forward flow [Video 12a and b]. (c and d) Same patient as in Figure 8c and d after the deployment of transcatheter valve across the degenerated surgical valve. Good valve opening is seen with low transmitral gradient|
Click here to view
Video 12: ([Additional file 22]a and [Additional file 23]b) Same patient as in Video 5 after the deployment of transcatheter valve across the degenerated surgical valve. Good valve opening is seen with good forward flow
Any PVL between the surgically and percutaneously implanted valves should be ruled out [Video 13]a and [Video 13]b. Any valvular regurgitation should also be looked for. 3D TEE is very helpful in assessing the size and location of the paravalvular defect if present. A repeat balloon dilatation may be needed if there is an inadequate expansion of the valve with significant PVL and/or transmitral gradient. If there is a significant PVL which is not resolved even after a repeat balloon dilatation, device closure of the PVL may be needed.
Video 13: [Additional file 24](a) A paravalvular leak between the percutaneously implanted and the existing surgical bioprosthetic heart valve at mitral position. [Additional file 25](b) No residual leak is seen after repeat balloon dilatation of the valve
The next step is to assess the status of neo-LVOT. Imaging in multiple views is required, including the mid-esophageal long-axis view and the deep transgastric LVOT view [Video 14]. The latter is ideal for measuring LVOT gradient because it allows proper alignment of the Doppler beam with the LVOT flow. Any significant increase in the LVOT gradient should be immediately communicated to the interventionist.
[Additional file 26]
Video 14: Deep transgastric view showing the neo-left ventricular outflow tract after the performance of transcatheter mitral valve-in-valve implantation
Other procedural complications should also be ruled out. Any new wall motion abnormality should be looked for because the left circumflex artery may get compressed during the valve deployment. The appearance of new pericardial effusion or increase in the preexisting pericardial effusion indicates cardiac perforation and is another serious finding.
Lastly, the size of the residual ASD and the magnitude of the left-to-right shunt should be assessed. If there is a significant left-to-right shunt with underlying pulmonary hypertension and compromised RV systolic function or if there is right-to-left shunt resulting in hypoxemia, percutaneous closure of the iatrogenic ASD may be needed [Figure 14]. The decision may not be straightforward because if the ASD is closed, it will preclude, or at least complicate any subsequent transseptal transcatheter procedure. However, if the device closure is deemed necessary, the same is performed under TEE guidance, in the same manner as for any congenital ostium secundum ASD.
|Figure 14: (a) Residual interatrial septal defect after transcatheter mitral valve-in-valve implantation. (b) The defect is closed with an amplatzer closure device|
Click here to view
In some patients in whom there is a high risk of LVOT obstruction after TMViVR, percutaneous laceration of the surgical BPHV leaflet may be performed as a prophylactic step. This procedure is known as Laceration of the Anterior Mitral valve leaflet to Prevent LV Outlet ObstructioN (LAMPOON) and is more commonly required when transcatheter valve implantation is done in a native mitral valve than in a preexisting BPHV.[42-44] TEE guidance is essential for this procedure.
When LAMPOON is performed for TMViVR, the surgical valve leaflet facing the LVOT is lacerated. For this, a guide catheter with a guidewire is positioned in the LA, via transeptal approach. The surgical BPHV is crossed with the guidewire which is then snared in the LVOT through another guide catheter positioned in the ascending aorta. This connects the two guide catheters. The guidewire is then positioned against the PHV leaflet that is to be lacerated, exactly at the center of the leaflet. This can be confirmed with TEE, esp. 3D TEE. Once appropriate positioning is confirmed, traction is applied on both the catheters to lacerate the BPHV leaflet from its tip to the base. Adequate laceration greatly minimizes the risk of LVOT obstruction after TMViVR. The procedure is generally quite safe since the BPHV sewing ring prevents the extension of the laceration into the surrounding structures.
| Conclusions|| |
The recent technical advances have revolutionized the field of percutaneous structural heart disease interventions. Multimodality imaging is pivotal to the success of these procedures and echocardiography is an integral part of this imaging. Echocardiography is essential for preprocedural evaluation as well as postprocedure assessment and follow-up of all such patients. In addition, for mitral valve interventions, echocardiography is also indispensable for intra-procedural guidance, although its role in guiding TAVR has diminished lately. A thorough understanding of echocardiography, especially for valvular assessment, and a high level of expertise in intraprocedural imaging are necessary for facilitating these procedures.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
Siontis GC, Overtchouk P, Cahill TJ, Modine T, Prendergast B, Praz F, et al
. Transcatheter aortic valve implantation versus Surgical aortic valve replacement for treatment of symptomatic severe aortic stenosis: An updated meta-analysis. Eur Heart J 2019;40:3143-53.
Bax JJ, Delgado V, Hahn RT, Leipsic J, Min JK, Grayburn P, et al.
Transcatheter aortic valve replacement: Role of multimodality imaging in common and complex clinical scenarios. JACC Cardiovasc Imaging 2020;13:124-39.
Baumgartner H, Hung J, Bermejo J, Chambers JB, Edvardsen T, Goldstein S, et al
. Recommendations on the echocardiographic assessment of aortic valve stenosis: A focused update from the European association of cardiovascular imaging and the American society of echocardiography. J Am Soc Echocardiogr 2017;30:372-92.
Guzzetti E, Annabi MS, Pibarot P, Clavel MA. Multimodality imaging for discordant low-gradient aortic stenosis: Assessing the valve and the myocardium. Front Cardiovasc Med 2020;7:570689.
Saadi RP, Tagliari AP, Saadi EK, Miglioranza MH, Polanczyck CA. Preoperative TAVR planning: How to do it. J Clin Med 2022;11:2582.
Perry TE, George SA, Lee B, Wahr J, Randle D, Sigurðsson G. A guide for pre-procedural imaging for transcatheter aortic valve replacement patients. Perioper Med (Lond) 2020;9:36.
Altiok E, Koos R, Schröder J, Brehmer K, Hamada S, Becker M, et al.
Comparison of two-dimensional and three-dimensional imaging techniques for measurement of aortic annulus diameters before transcatheter aortic valve implantation. Heart 2011;97:1578-84.
Elkaryoni A, Nanda NC, Baweja P, Arisha MJ, Zamir H, Elgebaly A, et al
. Three-dimensional transesophageal echocardiography is an attractive alternative to cardiac multi-detector computed tomography for aortic annular sizing: Systematic review and meta-analysis. Echocardiography 2018;35:1626-34.
Rong LQ, Hameed I, Salemi A, Rahouma M, Khan FM, Wijeysundera HC, et al
. Three-dimensional echocardiography for transcatheter aortic valve replacement sizing: A systematic review and meta-analysis. J Am Heart Assoc 2019;8:e013463.
Bleakley C, Monaghan M. 3D transesophageal echocardiography in TAVR. Echocardiography 2020;37:1654-64.
Ribeiro HB, Nombela-Franco L, Urena M, Mok M, Pasian S, Doyle D, et al
. Coronary obstruction following transcatheter aortic valve implantation: A systematic review. JACC Cardiovasc Interv 2013;6:452-61.
Kappetein AP, Head SJ, Généreux P, Piazza N, van Mieghem NM, Blackstone EH, et al
. Updated standardized endpoint definitions for transcatheter aortic valve implantation: The valve academic research consortium-2 consensus document. Eur Heart J 2012;33:2403-18.
Lerakis S, Hayek SS, Douglas PS. Paravalvular aortic leak after transcatheter aortic valve replacement: Current knowledge. Circulation 2013;127:397-407.
Vahl TP, Kodali SK, Leon MB. Transcatheter aortic valve replacement 2016: A modern-day “Through the Looking-Glass” adventure. J Am Coll Cardiol 2016;67:1472-87.
O'Sullivan CJ, Wenaweser P. A glimpse into the future: In 2020, which patients will undergo TAVI or SAVR? Interv Cardiol 2017;12:44-50.
Jerez-Valero M, Urena M, Webb JG, Tamburino C, Munoz-Garcia AJ, Cheema A, et al
. Clinical impact of aortic regurgitation after transcatheter aortic valve replacement: Insights into the degree and acuteness of presentation. JACC Cardiovasc Interv 2014;7:1022-32.
Van Belle E, Juthier F, Susen S, Vincentelli A, Iung B, Dallongeville J, et al
. Postprocedural aortic regurgitation in balloon-expandable and self-expandable transcatheter aortic valve replacement procedures: Analysis of predictors and impact on long-term mortality: Insights from the FRANCE2 Registry. Circulation 2014;129:1415-27.
Leon MB, Smith CR, Mack MJ, Makkar RR, Svensson LG, Kodali SK, et al
. Transcatheter or surgical aortic-valve replacement in intermediate-risk patients. N Engl J Med 2016;374:1609-20.
Kodali SK, Williams MR, Smith CR, Svensson LG, Webb JG, Makkar RR, et al
. Two-year outcomes after transcatheter or surgical aortic-valve replacement. N Engl J Med 2012;366:1686-95.
Généreux P, Head SJ, Hahn R, Daneault B, Kodali S, Williams MR, et al
. Paravalvular leak after transcatheter aortic valve replacement: The new Achilles' heel? A comprehensive review of the literature. J Am Coll Cardiol 2013;61:1125-36.
Zoghbi WA, Asch FM, Bruce C, Gillam LD, Grayburn PA, Hahn RT, et al
. Guidelines for the evaluation of valvular regurgitation after percutaneous valve repair or replacement: A report from the American society of echocardiography developed in collaboration with the society for cardiovascular angiography and interventions, Japanese society of echocardiography, and society for cardiovascular magnetic resonance. J Am Soc Echocardiogr 2019;32:431-75.
Kitamura M, Von Roeder M, Abdel-Wahab M. Quantitative assessment of aortic regurgitation following transcatheter aortic valve replacement. Expert Rev Cardiovasc Ther 2021;19:633-45.
Fanous EJ, Mukku RB, Dave P, Aksoy O, Yang EH, Benharash P, et al
. Paravalvular leak assessment: Challenges in assessing severity and interventional approaches. Curr Cardiol Rep 2020;22:166.
Hansson NC, Grove EL, Andersen HR, Leipsic J, Mathiassen ON, Jensen JM, et al
. Transcatheter aortic valve thrombosis: Incidence, predisposing factors, and clinical implications. J Am Coll Cardiol 2016;68:2059-69.
Chakravarty T, Søndergaard L, Friedman J, De Backer O, Berman D, Kofoed KF, et al
. Subclinical leaflet thrombosis in surgical and transcatheter bioprosthetic aortic valves: An observational study. Lancet 2017;389:2383-92.
Côté N, Pibarot P, Clavel MA. Incidence, risk factors, clinical impact, and management of bioprosthesis structural valve degeneration. Curr Opin Cardiol 2017;32:123-9.
Kostyunin AE, Yuzhalin AE, Rezvova MA, Ovcharenko EA, Glushkova TV, Kutikhin AG. Degeneration of bioprosthetic heart valves: Update 2020. J Am Heart Assoc 2020;9:e018506.
Eric Jamieson WR, Marchand MA, Pelletier CL, Norton R, Pellerin M, Dubiel TW, et al
. Structural valve deterioration in mitral replacement surgery: Comparison of Carpentier-Edwards supra-annular porcine and perimount pericardial bioprostheses. J Thorac Cardiovasc Surg 1999;118:297-304.
Vahanian A, Beyersdorf F, Praz F, Milojevic M, Baldus S, Bauersachs J, et al
. 2021 ESC/EACTS Guidelines for the management of valvular heart disease. Eur Heart J 2022;43:561-632.
Writing Committee Members, Otto CM, Nishimura RA, Bonow RO, Carabello BA, Erwin JP 3rd
, et al.
2020 ACC/AHA guideline for the management of patients with valvular heart disease: A report of the American college of cardiology/American heart association joint committee on clinical practice guidelines. J Am Coll Cardiol 2021;77:e25-197.
Guerrero M, Vemulapalli S, Xiang Q, Wang DD, Eleid M, Cabalka AK, et al.
Thirty-day outcomes of transcatheter mitral valve replacement for degenerated mitral bioprostheses (valve-in-valve), failed surgical rings (valve-in-ring), and native valve with severe mitral annular calcification (valve-in-mitral annular calcification) in the United States: Data from the society of thoracic surgeons/American college of cardiology/transcatheter valve therapy registry. Circ Cardiovasc Interv 2020;13:e008425.
Yoon SH, Whisenant BK, Bleiziffer S, Delgado V, Dhoble A, Schofer N, et al
. Outcomes of transcatheter mitral valve replacement for degenerated bioprostheses, failed annuloplasty rings, and mitral annular calcification. Eur Heart J 2019;40:441-51.
Bhargava AA, Shekiladze N, Xie J, Kini A, Gleason PT, Lerakis S. Use of transesophageal echocardiography for transcatheter valve-in-valve implantation for patients with prior bioprosthetic surgical aortic, mitral, tricuspid, and pulmonic valves. Ann Cardiothorac Surg 2021;10:605-20.
Garcia-Sayan E, Chen T, Khalique OK. Multimodality cardiac imaging for procedural planning and guidance of transcatheter mitral valve replacement and mitral paravalvular leak closure. Front Cardiovasc Med 2021;8:582925.
Barreiro-Perez M, Caneiro-Queija B, Puga L, Gonzalez-Ferreiro R, Alarcon R, Parada JA, et al
. Imaging in transcatheter mitral valve replacement: State-of-art review. J Clin Med 2021;10:5973.
Zoghbi WA, Chambers JB, Dumesnil JG, Foster E, Gottdiener JS, Grayburn PA, et al.
Recommendations for evaluation of prosthetic valves with echocardiography and Doppler ultrasound: A report From the American society of echocardiography's guidelines and standards committee and the task force on prosthetic valves, developed in conjunction with the American college of cardiology cardiovascular imaging committee, cardiac imaging committee of the American heart association, the European association of echocardiography, a registered branch of the European society of cardiology, the Japanese society of echocardiography and the Canadian society of echocardiography, endorsed by the American college of cardiology foundation, American heart association, European association of echocardiography, a registered branch of the European society of cardiology, the Japanese society of echocardiography, and Canadian society of echocardiography. J Am Soc Echocardiogr 2009;22:975-1014.
Lancellotti P, Pibarot P, Chambers J, Edvardsen T, Delgado V, Dulgheru R, et al
. Recommendations for the imaging assessment of prosthetic heart valves: A report from the European association of cardiovascular imaging endorsed by the Chinese society of echocardiography, the Inter-American society of echocardiography, and the Brazilian department of cardiovascular imaging. Eur Heart J Cardiovasc Imaging 2016;17:589-90.
Yoon SH, Bleiziffer S, Latib A, Eschenbach L, Ancona M, Vincent F, et al
. Predictors of left ventricular outflow tract obstruction after transcatheter mitral valve replacement. JACC Cardiovasc Interv 2019;12:182-93.
Reid A, Ben Zekry S, Turaga M, Tarazi S, Bax JJ, Wang DD, et al
. Neo-LVOT and transcatheter mitral valve replacement: Expert recommendations. JACC Cardiovasc Imaging 2021;14:854-66.
Urena M, Himbert D, Brochet E, Carrasco JL, Iung B, Nataf P, et al
. Transseptal transcatheter mitral valve replacement using balloon-expandable transcatheter heart valves: A step-by-step approach. JACC Cardiovasc Interv 2017;10:1905-19.
Harloff MT, Chowdhury M, Hirji SA, Percy ED, Yazdchi F, Shim H, et al
. A step-by-step guide to transseptal valve-in-valve transcatheter mitral valve replacement. Ann Cardiothorac Surg 2021;10:113-21.
Babaliaros VC, Greenbaum AB, Khan JM, Rogers T, Wang DD, Eng MH, et al
. Intentional percutaneous laceration of the anterior mitral leaflet to prevent outflow obstruction during transcatheter mitral valve replacement: First-in-human experience. JACC Cardiovasc Interv 2017;10:798-809.
Khan JM, Babaliaros VC, Greenbaum AB, Foerst JR, Yazdani S, McCabe JM, et al
. Anterior leaflet laceration to prevent ventricular outflow tract obstruction during transcatheter mitral valve replacement. J Am Coll Cardiol 2019;73:2521-34.
Case BC, Khan JM, Satler LF, Ben-Dor I, Lederman RJ, Babaliaros VC, et al
. Tip-to-base lampoon to prevent left ventricular outflow tract obstruction in valve-in-valve transcatheter mitral valve replacement. JACC Cardiovasc Interv 2020;13:1126-8.
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13], [Figure 14]