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Monitoring of procedures: peri-interventional echo assessment for transcatheter aortic valve implantation

Lindsay A. Smith, Mark J. Monaghan
DOI: http://dx.doi.org/10.1093/ehjci/jet042 840-850 First published online: 11 April 2013

Abstract

Transcatheter aortic valve implantation (TAVI) provides an effective, less-invasive alternative treatment for patients with symptomatic severe aortic stenosis at high surgical risk. Echocardiography plays a central role in patient selection, procedural guidance, and evaluation, and in the detection of complications. This review describes the peri-interventional role of echocardiography during TAVI, outlines current limitations, and identifies future implications.

  • Echocardiography
  • Transoesophageal echocardiography
  • Intracardiac echocardiography
  • three-dimensional echocardiography
  • Valvular heart disease
  • Transcatheter aortic valve implantation

Introduction

Transcatheter aortic valve implantation (TAVI) is a relatively new technique that provides an alternative, less-invasive treatment option for patients with aortic stenosis (AS) with conventional indications for aortic valve (AV) surgery but who have unacceptably high surgical risk.1,2 While TAVI can be performed with favourable outcomes in selected patients by skilled multidisciplinary teams, the technique remains challenging and associated with potentially serious complications.35 Echocardiography plays a central role in the assessment of patient suitability, in procedural guidance and evaluation, and in subsequent follow-up.69 Initial evaluation is performed by transthoracic echocardiography (TTE) with more detailed imaging by transoesophageal echocardiography (TEE) either prior to, particularly, if there are concerns regarding potential suitability, or at the time of TAVI. Multiple factors, readily assessed by echocardiography, should be considered when assessing patient suitability for TAVI, access route and selection of transcatheter heart valve (THV) type and size, all of which are important in determining the likelihood of successful outcome. During the TAVI procedure, two-dimensional (2D) and three-dimensional (3D) TEE and, in some centres, intracardiac echocardiography (ICE), may be used to provide real-time imaging to assist guidewire and delivery system placement, to assess the effects of balloon aortic valvuloplasty (BAV) and to ensure correct positioning of the AV prosthesis, to assess for aortic regurgitation (AR) immediately following implantation, and to evaluate any procedural complications.10,11 TTE is typically performed prior to discharge and subsequently at regular intervals to monitor AV prosthetic function. We provide a detailed review of the peri-interventional role of echocardiography during TAVI and identify future implications.

TAVI procedure

The echocardiographer requires detailed knowledge of the various transcatheter AV prostheses and delivery systems used during TAVI, as well as a clear understanding of the actual interventional procedure and its particular technical challenges. While there are several transcatheter AV prostheses under development or clinical evaluation, there are two families of prostheses currently available for clinical use and supported by the largest body of evidence, the Medtronic CoreValve (Medtronic, Minneapolis, MN, USA) and the Edwards SAPIEN/SAPIEN XT valves (Edwards Lifesciences, Irvine, CA, USA).1214 They have differing characteristics, anatomical requirements, and echocardiographic appearances and are described in Table 1 and extensively elsewhere. In brief, the Medtronic CoreValve is a self-expanding, trileaflet, porcine pericardial valve mounted on a nitinol frame that is implanted retrogradely via transfemoral, transsubclavian, or transaortic route. The Edwards SAPIEN valve is a balloon-expandable, trileaflet, bovine pericardial valve mounted on a stainless steel cylindrical frame, with a fabric skirt designed to reduce paravalvular regurgitation that may be implanted anterogradely via transapical approach or retrogradely via transfemoral or transaortic approach. The newer generation Edwards SAPIEN XT valve differs in that it has a smaller delivery system, is less bulky, and comprises a cobalt-chromium frame.

View this table:
Table 1

Current transcatheter AV prostheses—anatomical requirements assessed by echocardiography

Valve typeValve sizeAnnulus dimension (mm)AV annulus-coronary ostial height (mm)SoV height (mm)SoV diameter (mm)Ascending aortic diameter
Medtronic CoreValve Evolut2318–20≥15≥25≤34 mm (30 mm from annulus)
Medtronic CoreValve2620–23≥15≥27≤40 mm (40 mm from annulus)
2923–27≥15≥29≤43 mm (40 mm from annulus)
3126–29≥15≥29≤43 mm (40 mm from annulus)
Edwards SAPIEN XT2318–2110
2622–2511
2926–27.511
  • Source: manufacturers' product information.

  • AV, aortic valve; SoV, sinus of Valsalva.

A multidisciplinary team performs the TAVI procedure in either a hybrid operating room or an adapted cardiac catheterization laboratory depending on local facilities and preference. The CoreValve may be implanted with local anaesthesia, mild sedation, and analgesia, and as such, the procedure is often performed without the TEE guidance. However, the SAPIEN valves are typically implanted with TEE guidance and general anaesthesia, although some have reported TEE-guided transfemoral TAVI using sedation. General anaesthesia, however, is always required for transapical or transaortic cases where a mini-thoracotomy is performed.

Peri-interventional echo assessment

Immediate pre-TAVI

Transthoracic echocardiography

TTE is used to identify and mark the left ventricular apex during transapical TAVI cases. It is important that the cardiothoracic surgeon is present for this, that the patient is in the final position, thus, avoiding movement of the skin relative to the ribs after marking, and that two views, potentially with simultaneous biplane imaging, are used to locate the true left ventricular apex (Figure 1).

Figure 1

Marking the LV apex prior to transapical TAVI (TTE).

Transoesophageal echocardiography

2D and 3D TEE enable detailed imaging of AV and aortic root anatomy, measurement of AV annulus dimensions, and review of other cardiac and aortic structures. The exact role of TEE, however, varies depending on the type of THV implanted, as well as on local procedures and preferences; for example, in centres where annulus dimensions are routinely measured using pre-procedural multislice computed tomography (MSCT), and THV selection is based upon these measurements, detailed annulus evaluation by TEE may not be required. The relative advantages and disadvantages of TEE during TAVI, as well as the benefits of 3D over 2D are presented in Table 2. TEE may be performed as a comprehensive study immediately pre-TAVI or, where performed as a part of pre-procedure workup, as an abbreviated and confirmatory study. Some centres report the successful use of ICE to guide TAVI, although there is currently no 3D capability and challenges with both catheter handling and adequate image quality exist, and also transnasal TEE, which similarly has no 3D capability at present, but may be used in patients unsuitable for general anaesthesia.15,16

View this table:
Table 2

Procedural guidance during TAVI—advantage and disadvantages of TEE

AdvantagesDisadvantages
Real-time procedural monitoring to complement fluoroscopyTypically requires general anaesthesia
Early detection and rapid evaluation of procedural complicationsAdditional operator and training (3D, interventional TEE)
Superior visualization of guidewires, catheters, balloons, and THVs (3D)Recognized contraindications
Superior anatomical and spatial orientation (3D)Additional space required for machine and echocardiographer
Aids communication within the multidisciplinary team (3D)May partially obstruct fluoroscopic view (can be overcome by probe repositioning/manipulation)
Reduced temporal resolution, tissue dropout, and artefacts (3D)
  • TAVI, transcatheter aortic valve implantation; TEE, transoesophageal echocardiography; THV, transcatheter heart valve.

AV annulus dimensions guide the selection of THV size, irrespective of THV type, and current guidelines are based upon the echocardiography measurements (Table 1). The aortic root is well visualized in the mid-oesophageal long-axis view between 120° and 140° plane rotation using 2D TEE. AV annulus dimension is measured from the hinge point of the non-coronary cusp with the posterior aortic wall to the hinge point of the right coronary cusp and the anterior aortic wall, perpendicular to the long axis of the root, using a zoomed image frozen in mid-systole (Figure 2). Poor visualization due to acoustic shadowing from calcified deposits can usually be overcome by probe manipulation. However, 2D TEE annulus dimension may underestimate or overestimate the true anteroposterior dimension, due to off-axis imaging, and underestimate the maximum annulus dimension, as the annulus is often elliptical rather than circular. 3D TEE, with online multiplanar reconstruction taking only a few minutes, facilitates measurement of the anatomically correct anteroposterior dimension, as well as maximum and minimum AV annulus dimensions, perimeter, and cross-sectional area (Figure 2). Indeed, prosthesis–annulus discongruence has emerged as a predictor of paravalvular AR following TAVI.1719 AV annulus dimensions may also be measured using other imaging modalities such as MSCT and cardiac magnetic resonance.2022 While TTE and 2D TEE AV annulus dimensions are consistently smaller, 3D TEE dimensions show excellent agreement with those obtained by MSCT.21,23,24 At present, there is no consensus regarding the gold standard technique for annulus sizing.8 In addition to assessment of the AV annulus, the morphology, absolute and relative dimensions of the left ventricular outflow tract (LVOT), and aortic root should be examined carefully.25

Figure 2

Measurement of AV annulus dimensions (3D TEE zoom mode with multiplanar reconstruction). The anatomically correct anteroposterior dimension is indicated in the upper right image and the medial–lateral dimension in the lower left image (arrows). The latter can only be measured using 3D TEE techniques.

The location, severity, and eccentricity of calcification within the AV annulus and cusps should also be noted. These factors are emerging as important determinants of the presence and severity of post-procedural paravalvular regurgitation, as such calcification may prevent adequate apposition of the valve skirt.2628 This may be visualized using 2D TEE mid-oesophageal AV long-axis and short-axis views and also with 3D TEE. The number of cusps should be determined as bicuspid AV is considered a relative contraindication to TAVI. With advanced degenerative disease, however, this is sometimes difficult to do with certainty. Some centres have reported successful outcomes in patients with bicuspid AV and severe AS but, where there is an eccentric orifice and eccentric calcification, the risk of malposition and THV embolization is high (Figure 3).29 It is important to consider the ability of the sinuses to accommodate the calcified valve cusps when crushed against the aortic wall by the THV, in order to reduce the risk of potentially life-threatening complications such as aortic rupture or coronary obstruction.12 The presence of small sinuses relative to annulus size and a narrow, heavily calcified sinotubular junction may further increase the risk of aortic rupture. The presence of calcification elsewhere within the LVOT and aortic root should be noted, as should mobile masses, as potential sources of embolic complications. The position of the coronary ostia and AV annulus-coronary ostial height should be assessed, to minimize the risk of coronary occlusion (Table 1). While AV annulus-right coronary ostial height can be measured in a 2D TEE modified mid-oesophageal long-axis view, AV annulus-left coronary ostial height can only be measured using 3D techniques with reconstruction of the coronal plane (Figures 4 and 5).

Figure 3

Unsuitable anatomy: bicuspid AV (real-time 3D TEE, AV viewed en face from the aortic aspect). While the valve orifice is relatively central, note the severe, eccentric leaflet calcification precluding TAVI.

Figure 4

Measurement of AV annulus—left coronary artery ostial height (3D TEE zoom mode with multiplanar reconstruction). This measurement (arrow) can only be made using 3D TEE techniques.

Figure 5

Measurement of AV annulus—right coronary artery ostial height (2D TEE mid-oesophageal modified long-axis view). This measurement can also be made using 3D TEE and multiplanar reconstruction.

The aetiology and severity of AR is determined using standard 2D TEE techniques according to current guidelines; 3D zoom and full-volume colour modes may also be useful. It is important to define the baseline AR severity as it may be significantly increased by BAV, potentially leading to haemodynamic instability and necessitating prompt THV implantation. Baseline AV gradients are best assessed with TTE but may be recorded from the 2D TEE transgastric views, assuming Doppler alignment is acceptable.

A baseline study systematically examining mitral valve anatomy, aetiology, and severity of mitral regurgitation, LV size and systolic function, regional wall motion abnormalities, right heart size and right ventricular systolic function, and pericardial effusion should be performed routinely in all cases. This is enables the echocardiographer to anticipate potential procedural difficulties as well as enabling direct comparison should complications be encountered. The presence of left ventricular thrombus, a contraindication to TAVI, should be excluded, as should significant LVOT obstruction due to basal septal hypertrophy as this may lead to THV displacement either during or after implantation (Figure 6).

Figure 6

Unsuitable anatomy: severe basal interventricular septal hypertrophy (2D TEE mid-oesophageal long-axis view with colour Doppler). Note insufficient space within the LVOT to accommodate the THV prosthesis and likely upward migration or embolization should deployment be attempted.

Intra-procedural guidance

Standard 2D TEE techniques, with complementary 3D TEE imaging, are used in addition to fluoroscopy for intra-procedural guidance, which itself can be considered in three stages: guidewire and delivery system positioning, BAV and THV positioning, and deployment.9 3D TEE typically provides superior visualization of guide wire, delivery catheter, balloon, and THV, compared with 2D TEE where movement out of plane leads to incomplete and inadequate visualization. It also enables images to be presented in a way that is more easily understood by the non-echocardiographer, therefore, aiding communication within the multidisciplinary team. 3D TEE, therefore, has an important role in guiding all stages of the TAVI procedure.7,3032 Ideally, the echocardiography images should be slaved to a monitor enabling side-by-side display with X-ray images and haemodynamic data and so facilitating review by the other members of the multidisciplinary team.

Guidewire/delivery system positioning

The echocardiographer helps facilitate approach to or crossing of the native AV; real-time 3D imaging with manipulation to show the approach of the guidewire to the AV en face, or, alternatively, simultaneous display of orthogonal views with 3D TEE, may be helpful. Any damage to the interventricular septum should be identified, the passage of the guidewire clearly visualized to exclude entrapment of the mitral valve chordae and the degree of mitral regurgitation re-evaluated; catheter advancement in these circumstances risks mitral valve injury and acute mitral regurgitation. The superior visualization achieved with 3D TEE, particularly, facilitates avoidance of the mitral valve apparatus during guidewire and delivery catheter introduction and placement (Figure 7).

Figure 7

Guidewire passing through the LVOT and crossing the AV (real-time 3D TEE).

Balloon aortic valvuloplasty

TEE is used to guide the balloon positioning prior to BAV and is, particularly, useful in cases where the valve is less calcified and, thus, less well identified fluoroscopically, and in valve-in-valve procedures. Real-time 3D TEE imaging during BAV, with simultaneous display of long- and short-axis views and long-loop acquisition, enables immediate review and evaluation of sizing, behaviour of the native AV leaflets and calcified material during inflation, as well as confirming balloon stability and optimal inflation and deflation (Figure 8). Upwards migration of the balloon may occur despite rapid ventricular pacing to reduce cardiac output. Following BAV, native cusp mobility and AR severity should be reassessed.

Figure 8

Monitoring BAV (real-time 3D TEE with simultaneous display of long- and short-axis views).

THV positioning and deployment

Positioning and deployment of the THV, and subsequent delivery system and guidewire removal, is similarly guided using TEE, again with long-loop acquisition (Figure 9). Real-time 3D TEE typically enables excellent visualization of the proximal and distal margins of the balloon-mounted THV, in contrast to 2D TEE where this may be challenging. The THV should only be implanted when there is an agreement between the operators and echocardiographer that positioning is correct, using a combination of fluoroscopy and TEE (Table 1). Too low a position risks prosthesis embolization into the left ventricle and impingement on the anterior mitral valve leaflet; the latter may disrupt the mitral valve function or potentially result in leaflet perforation in the longer term. Furthermore, failure to cover the native AV cusps with the THV enables them to fold over the top of the prosthesis disrupting function and causing transvalvular regurgitation. In contrast, too high a position risks upwards migration into the aorta, coronary ostial occlusion leading to the myocardial infarction and paravalvular regurgitation. THV malposition or embolization rates of 1.2–4% are reported and successful management of these complications may require conversion to open surgery or deployment of the THV in the aorta, avoiding important branch vessels, and implantation of a second prosthesis. Minor adjustment in THV positioning may be required during early deployment, due to a tendency for prosthesis migration upwards.

Figure 9

THV positioning (A) and deployment (B) during rapid ventricular pacing (real-time 3D TEE). Note the superior visualization of the proximal and distal margins of the balloon-mounted prosthesis with 3D TEE.

Following THV deployment, the echocardiographer confirms satisfactory THV position, circular appearance, and normal prosthetic function, taking into consideration normal leaflet mobility, the presence, aetiology and severity of AR and transvalvular gradients. Multiple TEE views are employed enabling comprehensive assessment of the THV post-deployment, including mid-oesophageal long-axis, short-axis, and five-chamber, as well as transgastric long-axis and deep transgastric views. It can be difficult post-TAVI to determine the severity and precise location of AR. Conventional parameters for AR severity, such as colour jet dimensions, vena contracta width, and quantitative measures, are helpful in the evaluation of transvalvular regurgitation but less so in paravalvular regurgitation, that is, typically eccentric and with multiple jets where it is uncertain how these should be summated.33,34 Severity of paravalvular AR, described by the circumferential extent of the jet in short axis at the level of the sewing ring, is helpful in determining severity. Current guidance suggests that circumferential extent <10% suggests mild, 10–20% moderate, and >20% severe regurgitation.35 This may be achieved using the 2D TEE mid-oesophageal short-axis view (Figure 10); however, it may be difficult to obtain an imaging plane directly beneath the implanted THV that is not oblique, potentially leading to misinterpretation. 3D TEE colour Doppler imaging with simultaneous visualization of long- and short-axis views or with full volume (gated) or zoom (non-gated) acquisition may also provide additional information (Figure 11).8,36 Online cropping of the 3D datasets to the level of jet origin, avoiding an oblique plane, and enabling planimetry of regurgitant orifice area, is possible and may be helpful; however, this is more time-consuming and initial assessment of post-TAVI AR is performed using 2D TEE colour Doppler.

Figure 10

Paravalvular AR immediately post-THV implantation (2D TEE mid-oesophageal view).

Figure 11

Transvalvular and paravalvular AR immediately post-THV implantation (3D TEE with colour Doppler). Note the clearly visualized small central transvalvular (solid arrow) and posterior paravalvular (dashed arrow) jets of regurgitation.

Mild transvalvular regurgitation is common, especially, while the catheter or guide wire remain across the valve, and often improves as the leaflets recover from crimping, as is trace or mild paravalvular regurgitation. Severe transvalvular regurgitation is rare, and may be due to incorrect prosthesis sizing or positioning, incomplete expansion or restricted leaflets, as is severe paravalvular regurgitation, which may also be the result of incorrect prosthesis sizing or positioning or severe asymmetric calcification (Figure 12).9,17 Depending on the mechanism, significant regurgitation may be an indication for balloon dilatation or implantation of a second THV.

Figure 12

Free transvalvular AR due to intrinsic THV failure (2D TEE mid-oesophageal long-axis view). Note the dense spontaneous echo contrast due to very low cardiac output state.

Detection of complications

Continuous real-time 2D and 3D TEE imaging enables the prompt detection, assessment, and management of complications.37 Where the presentation is with acute haemodynamic compromise, the echocardiographer should rapidly evaluate potential causes (Table 3, Figures 13 and 14).

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Table 3

Potential causes of acute haemodynamic collapse during TAVI assessed by TEE

Potential causeTEE assessment
THV embolization (towards aorta or LV), malposition (too high or too low) or malfunction (secondary to above or intrinsic THV failure)Assess THV position and function
Severe ARAssess whether transvalvular or paravalvular and identify aetiology
Severe mitral regurgitationAssess for THV impingement on AMVL, damage to mitral subvalvular apparatus, LV asynchrony (induced by RV apical pacing)
Acute coronary artery ostial occlusionAssess for new regional LV wall motion abnormalities
LV or RV perforationAssess for pericardial effusion and haemodynamic effects
Aortic rupture or dissectionAssess aortic root and ascending aorta systematically
HypovolaemiaAssess filling state and potential causes
  • TAVI, transcatheter aortic valve implantation; TEE, transoesophageal echocardiography; THV, transcatheter heart valve; AMVL, anterior mitral valve leaflet; LV, left ventricle; RV, right ventricle.

Figure 13

Aortic root to RA and RV fistulae post-THV implantation. (A) 2D TEE mid-oesophageal short-axis view. (B) 3D TEE full volume with colour Doppler. LA, left atrium; RA, right atrium; RVOT, right ventricular outflow tract; TV, tricuspid valve.

Figure 14

Acute pericardial effusion (arrows) and haemodynamic compromise complicating the THV implantation. (A) 2D TEE mid-oesophageal modified four-chamber view. (B) 2D TEE transgastric left ventricular short-axis view. Note the severe concentric left ventricular hypertrophy and small left ventricular cavity.

Immediate post-TAVI

Comprehensive TEE evaluation is performed following the initial confirmation of satisfactory THV position and function. Mitral valve anatomy, aetiology and severity of mitral regurgitation, left ventricular and right heart size and function, and pericardial effusion should all be re-evaluated post-procedure to enable the prompt detection of complications and to enable the comparison in the recovery period.

Future implications

Echocardiography provides an excellent real-time 2D and 3D imaging of the heart, making it the imaging modality of choice immediately before, during, and after TAVI.8 The exciting field of TAVI continues to evolve and expand, supported by increasingly robust clinical data. New valves and deployment systems are under development, a greater range of valve sizes is becoming available and it is likely that the indications for, and the availability of, TAVI will increase.

Further work is required to establish the optimum approach to annulus sizing and THV selection. It is apparent that a 3D imaging technique is required to establish annular dimensions, but it can be seen that THV sizing is based upon many more factors than annulus size alone. However, quite how these factors impact upon accurate prosthesis deployment and the presence of post-procedural paravalvular regurgitation, and how they are to be best integrated to determine the THV sizing, remains uncertain. More work is required to understand both the patient and procedural factors leading to the post-procedural AR, and its longer term clinical relevance, as well as improved echocardiography techniques for the quantitative assessment of paravalvular regurgitation. The role of 3D TEE in TAVI, and in catheter-based cardiac interventions, in general, will become better defined with the potential for improvements in decision-making and procedure duration and radiation exposure, as well as in short- and longer-term outcomes.38 There is, however, a need for specific training in interventional, and also 3D, echocardiography in order to address the additional demands of this form of imaging.

Conflict of interest

M.J.M is on the speakers' bureau and an advisor for Edwards LifeSciences (Irvine, CA) and is also on the speakers' bureau and receives equipment support from Philips Medical Systems (Best, The Netherlands). L.A.S: none declared.

References

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