Version May 2024
INTRODUCTION — The advent of transcatheter aortic valve implantation (TAVI) has dramatically changed the care of patients with severe aortic stenosis (AS). The need for a multimodality imaging, team-based approach throughout the continuum of the care of TAVI patients makes this procedure unique for patients with aortic stenosis [1]. Preprocedural planning, intraprocedural implantation guidance, and long-term follow-up of patients undergoing TAVI require the expert use of multiple imaging modalities, each with its own strengths and limitations [2-5]. Multimodality imaging is an important aspect of each of these steps such that a team of skilled and knowledgeable cardiologists and radiologists able to perform and interpret a variety of imaging techniques are an important part of the care team for patients undergoing TAVI.
This topic will discuss how clinicians derive multimodality imaging information and integrate it into the decision-making process for patient care during the preprocedural, intraprocedural, and long-term follow-up assessments for TAVI using both balloon-expandable (eg, Edwards devices) and self-expanding (eg, Medtronic devices) transcatheter heart valves (THVs) (figure 1). When appropriate, we compare the utility of various modalities. In many instances, local expertise will dictate which modalities are employed at each stage. Preferred modalities vary according to the imaging goals at each stage.
Indications, outcomes, periprocedural management, and complications of TAVI are discussed separately. (See "Choice of intervention for severe calcific aortic stenosis" and "Transcatheter aortic valve implantation: Complications".)
PREPROCEDURAL ASSESSMENT
Preprocedural imaging goals — Overall goals of the preprocedural assessment include the following:
●To confirm patient suitability:
•To confirm presence of severe aortic stenosis with indication for valve replacement, and absence of other severe valve lesions. (See "Indications for valve replacement for high gradient aortic stenosis in adults".)
•To confirm suitability of TAVI as appropriate therapy and the absence of any contraindications. (See "Choice of intervention for severe calcific aortic stenosis".)
●To assess suitability of the proposed access site.
●To ensure that the proposed device can be safely and successfully implanted based on anatomic (aortic valve and root, left ventricle, and coronary ostia) and device characteristics.
●To help select the appropriate device type and size to optimize clinical outcomes dependent on imaging variables.
●To aid in the development of a procedural plan including determination of coplanar fluoroscopic angulation to be used at the time of the procedure.
Key steps — The following are common key preprocedural imaging steps, although imaging methods selected vary among institutions and for individual clinical settings. The sequence and timing of these steps will depend on whether any previous imaging is available, the likelihood of TAVI versus aortic valve surgery, and renal function. (See "Clinical manifestations and diagnosis of aortic stenosis in adults" and "Choice of intervention for severe calcific aortic stenosis".)
●Echocardiography
•Transthoracic echocardiography (TTE) will generally demonstrate severity and provide an initial assessment of aortic valve morphology, identify any concomitant valve lesions such as mitral regurgitation (MR), assess left and right ventricular function, and provide an estimate of pulmonary artery pressure. An approximation of aortic annular and sinus dimensions can also be obtained, although in current practice two-dimensional TTE plays a limited role in annular sizing.
•Preprocedural transesophageal echocardiography (TEE) is performed as needed, often with three-dimensional imaging to assess the aortic root as dictated by local practice. There is growing utilization of three-dimensional TEE for annular sizing, particularly in patients with contraindications to computed tomography (CT) such as renal dysfunction and known iodinated contrast allergies [6].
●Diagnostic cardiac catheterization
•Coronary angiography is generally performed to assess for coronary artery disease.
•Invasive transaortic pressure gradient measurement to assess severity of aortic stenosis is not generally required (and entails added risk) but is indicated if noninvasive data are nondiagnostic or if there is a discrepancy between the echocardiogram and clinical evaluation [7]. Continuous quality improvement approaches to increase echocardiographic data accuracy and reliability have been shown to decrease the proportion of patients referred for invasive valvular hemodynamic assessment from 47 to 19 percent [8].
•At some institutions, aortography and peripheral angiography are performed at the time of cardiac catheterization since invasive angiography provides information complimentary to that from the CT angiogram.
●Multidetector computed tomography (MDCT) angiography is considered essential for preprocedural planning to assess the aortic root (including aortic annulus and sinus dimensions), descending aorta, and iliofemoral vascular system. MDCT assessment of the annular dimensions has gained near universal acceptance as the standard of care as there is evidence suggesting that MDCT favorably influences clinical decision making [4,9-12] enabling clinical outcome optimization [13].
•The choice of modality must take into consideration comorbidities such as renal dysfunction, dye allergy, arrhythmias, and pulmonary disease, as these may limit the use of potentially nephrotoxic intravenous contrast, electrocardiogram gating, and breath holds for MDCT.
●Cardiac magnetic resonance (CMR) has a limited role in the assessment for TAVI, owing mostly to a lack of data demonstrating significant superiority compared to other modalities. Potential advantages of CMR include being a noninvasive imaging modality free of ionizing radiation that provides detailed visualization of cardiac structures and quantitative flow measurements [14]. Patients with renal dysfunction, significant arrhythmias or pulmonary disease may pose issues to safety and image quality. (See "Clinical utility of cardiovascular magnetic resonance imaging".)
Determining eligibility for peripheral vascular access — MDCT has become the imaging modality of choice for examination of the abdominal aorta and iliofemoral arteries, with optional angiography. Preprocedural assessment of the iliofemoral system and descending aorta enables detection of significant occlusive or aneurysmal disease of the proposed access site or catheter route. This assessment is undertaken to reduce the risk of complications related to vascular access with TAVI, with published rates ranging from 6.3 to 30.7 percent [15-18]. In the operable high-risk (cohort A) and inoperable (cohort B) cohorts of the Placement of Aortic Transcatheter Valve (PARTNER) randomized controlled trial, major vascular complications occurred in 15.3 percent of patients [19], with more contemporary data suggesting a lower rate of major vascular complications (7.9 percent) [5]. These rates are influenced by various clinical factors: sex (higher risk among women), screening protocols, and the diameter of the arterial sheaths used [19]. (See "Transcatheter aortic valve implantation: Complications".)
Multidetector computed tomography — A standardized approach includes three-dimensional volume-rendered imaging, curved multiplanar reformats, and maximum intensity projection images [20]. Incorporation of this approach into preprocedural screening, along with use of smaller sheaths and use of percutaneous vascular repair techniques, was associated with reduction in the risk of TAVI-associated vascular complications over time.
MDCT imaging identifies patients with unfavorable vasculature, which may impact the decision to use an alternative vascular approach (ie, transapical, transaxillary, or direct aortic) [21,22]. Multiple luminal measurements orthogonal to the vessel (rather than in a transverse axial plane) enable evaluation of vessel size, degree of calcification, minimal luminal diameter, plaque burden, and vessel tortuosity, and also identify high-risk features, including dissections and complex atheroma (image 1). In a prospective study of 130 patients undergoing TAVI, a sheath to femoral artery ratio (SFAR) of 1.05 or higher predicted vascular complications, as well as 30-day mortality [23]. However, the SFAR has subsequently undergone reappraisal with the thinking being that the historical value of 1.05 was too conservative, yielding high sensitivity but poor specificity, and 1.12 may be more appropriate [24]. Although minimal vessel diameters have been suggested [21], the optimal vessel diameter is likely to be a moving target as sheath size diminishes. Protocols have been published that employ direct power injection of diluted contrast in the infrarenal aorta to help reduce the risk of contrast-induced nephropathy [20,25].
Conventional angiography — Angiography is now generally used as an adjunctive modality since it provides a basic assessment of intraluminal characteristics but a very limited evaluation for atherosclerosis, plaque burden, or the degree of vessel tortuosity. However, it can in some circumstances provide additional information about the lumen and motion of calcium on fluoroscopy.
Ultrasound — Surface ultrasound of the access site is often used to guide vascular puncture [26]. Coronary intravascular ultrasound catheters can be used in the peripheral arteries to see the lumen in patients when there is blooming artifact from calcifications.
Principles of aortic root and aortic valve imaging
Components — Preprocedural imaging of the aortic root and associated structures is performed with the following goals:
●Measuring aortic annulus size (see 'Aortic annulus measurement' below)
●Assessing coronary ostial height (see 'Coronary ostia' below)
●Assessment of left ventricular outflow tract (LVOT) and subannular calcification (see 'Left ventricular outflow tract and septum' below)
●Sinus of Valsalva and sinotubular junction (STJ) mean diameter (see 'Sinotubular junction and proximal aorta' below)
●Morphological evaluation of the aortic valve (tricuspid versus bicuspid) (see 'Aortic leaflets' below)
●Identifying other features that may interfere with successful implantation
A thorough multimodality imaging preprocedural evaluation using TTE and MDCT, with or without TEE (which may be three-dimensional) and root angiography, will identify predictors of complications and may result in patient exclusion or other anticipatory action.
Aortic root anatomy — In all imaging modalities, standard aortic annulus measurements are performed at the lowest hinge point of the aortic valve leaflets at the virtual basal plane of the aortic root in systole at the time of maximal valve opening. The location and timing of measurement are important given variations in dimensions along the aortic root as well as fluctuations during the cardiac cycle.
The aortic root complex has been described as being composed of three elliptical rings and one crown-like ring: the virtual basal annulus, the anatomic annulus, the STJ, and a crown-like ring demarcated by the hinges of the leaflets (figure 2) [27]. From caudal to cranial, the virtual basal ring is what is measured routinely as the "aortic annulus" in all imaging modalities [2,28]. This ring is defined by the basal attachment points ("basal hinge points") of the aortic valve cusps within the LVOT. Next, the anatomic annulus is located where the muscular arterial aortic root joins the muscular interventricular septum anteriorly and the fibrous skeleton of the mitral valve apparatus posteriorly and leftward. The highest ring, the STJ, lies above the level of the sinuses of Valsalva and is the outlet of the aortic root into the ascending aorta. The crown-like ring structure is created by the shape of the aortic leaflets attached throughout the length of the aortic root. The leaflets and rings together form a three-dimensional, oval-shaped, three-pronged coronet, with three anchor points at the nadir of each aortic cusp.
Relevance of transcatheter heart valve characteristics — Transcatheter heart valve (THV) characteristics should also be considered (figure 1). The height of the valve prosthesis and the aspect of the prosthesis that is covered by fabric (the "skirt") impact device selection and placement. Specific valve characteristics are important because incorrect valve placement may interfere with coronary flow and future coronary access as well as increase the likelihood of significant paravalvular regurgitation. In addition, devices that are implanted deeper into the LVOT are more likely to result in heart block and the need for permanent pacemaker implantation.
Aortic annulus measurement — Preprocedural sizing of the annulus is now largely performed using MDCT-determined annular area and perimeter measures. Accurate aortic annulus measurement is critical for the success of TAVI because this size determines the size of the THV that should be used [27,29]. Inaccurate sizing has been consistently shown to be the most common cause of paravalvular aortic regurgitation (PAR) [30]. THV size choice based on aortic annulus perimeter [31] or cross-sectional area [13] is superior to annulus diameter for reducing the likelihood of postimplantation PAR. CT measurements guiding size selection of the Medtronic CoreValve were felt to be an important factor in minimizing PAR rates in the United States Pivotal Trial [3,32]. Subsequently, CT was used in the intermediate risk PARTNER 3 trial, which had the lowest rate of greater than mild PAR of any large scale trial to date [4].
Multidetector computed tomography scanning — MDCT-based measurements of the annulus have been shown to be highly reproducible and allow for a deeper understanding of annular geometry over two-dimensional measurements of the annulus. The goals of current CT sizing algorithms aim for prespecified degrees of annular oversizing such that the THV is larger than native aortic annulus. The degree and extent of "oversizing" depends on the structural design of the THV and the measurement used. Self-expandable devices require greater oversizing to mitigate the risk of paravalvular regurgitation than balloon-expandable devices. In contrast, severe oversizing with balloon-expandable devices increases the risk of annular injury. In addition, 10 percent perimeter oversizing does not translate to the same percentage area oversizing but is in fact closer to 20 percent area oversizing [33,34].
Current MDCT systems allow imaging of the aortic root with sufficiently minimal slice thickness (0.5 to 0.75 mm) to allow for oblique reconstruction without degradation of spatial resolution (0.5 mm in-plane and 0.5 mm through plane). Measurements are taken from systolic phase reconstructions of retrospective electrocardiographic gated images, using the phase with the maximum valve opening, as is performed in echocardiography. Typically, the annular size is largest in a late systolic phase with the best image quality. Identifying an accurate deployment coplanar fluoroscopic angulation (ie, the "3-coronary-sinus-alignment" plane) with MDCT a priori can help reduce the need for contrast dye injection during TAVI [35].
The general sizing principle for all valves is that a three-dimensional reconstruction of the annular plane is essential. For balloon-expandable valves that are circular after deployment, area-based measurements are most commonly used. The reasons for this are multiple fold. To start, area measurements have been shown to be highly reproducible across workstation platforms, unlike perimeter measurements, which rely on smoothing algorithms that are not available across all workstations. In addition, since aortic annuli are commonly elliptical, area-based measurements will yield more conservative sizing recommendations than perimeter measurements, which is prudent given the risk of annular injury with extreme annular oversizing with balloon-expandable valves [33]. For self-expanding valves where PAR is the greater risk and rupture is less of a concern, perimeter-based sizing is more commonly used. Either way, a principle of selecting a transcatheter valve that is somewhat larger than the native annulus is established, but the extent of "oversizing," the so-called "sizing ratio," will differ between specific technologies.
Oversizing the THV based on MDCT measurements reduces the risk of paravalvular regurgitation [31]. All transcatheter valves come in a range of sizes to account for a range of annular sizes, and these differ considerably between valves. Newer, MDCT-based approaches that employ three-dimensionally-derived, cross-sectional measurements of the aortic annulus affect device sizing and patient selection and reduce PAR for the SAPIEN THV and Medtronic CoreValve, compared with traditional, two-dimensional TEE [3,9,13,32].
Echocardiography — Biplane imaging or three-dimensional reconstruction has become the echocardiographic gold standard for preimplantation assessment of the aortic root. Echocardiographic measurements of the aortic annulus for selecting THV size have traditionally used the maximal diameter from a two-dimensional, parasternal, long-axis image (ie, a sagittal plane image) on TTE (image 2) or a midesophageal long-axis TEE image between 120 and 140 degrees (image 3). Care must be taken to measure at the virtual basal ring and not to measure too cranial into the aortic root.
An advantage of using zoomed, three-dimensional datasets is the ability to generate two orthogonal, long-axis views of the aortic root using multiplanar reconstruction mode. A third plane perpendicular to both of these long-axis views can be manipulated to obtain the transverse two-dimensional plane of the aortic annulus [36].
Three-dimensional TEE imaging allows for precise identification of the annular plane from orthogonal, long-axis views using adjacent anatomy to accurately identify the annular plane [6]. This approach minimizes the effect of acoustic shadowing on measurement of the annulus. TEE imaging of balloon aortic valvuloplasty may help define the annular dimension in difficult cases. The use of intracardiac echocardiography (ICE) in the preprocedural stage is nascent, but compares favorably with MDCT [37].
Aortic leaflets — The major implications of aortic leaflet morphology for TAVI are related to the number of cusps present, the degree of leaflet calcification, and the height of the leaflets with respect to the coronary ostia. Severe, asymmetric calcification of the aortic valve leaflets and asymmetric leaflet excursion may result in incomplete expansion of the THV and result in limited orifice size and/or paravalvular regurgitation. Valvular calcification poses a risk with either the SAPIEN or CoreValve THV; however, positioning of the CoreValve is more independent of valvular calcification, owing to its constrained waist and larger length. Bulky aortic valve calcification is a risk factor for left main coronary artery obstruction during THV deployment and, in rare cases, with creation of a membranous septal defect due to inferior displacement of extensive annular or basal leaflet calcifications during stent expansion [22]. MDCT and three-dimensional TEE are the favored modalities by the authors, each with their limitations as explained below [38].
The role of TAVI in managing patients with bicuspid aortic valve is uncertain since data on efficacy and safety are limited. Bicuspid aortic valves have been considered a contraindication to TAVI due to concerns of poor seating, asymmetrical stent expansion, and/or PAR due to severe distortion of the native valve leaflets [15,39]. There are, however, growing data from large multicenter registries that would suggest that these concerns may have been overstated and that outcomes following TAVI in bicuspid valvular aortic stenosis appear to be quite good [40]. (See "Bicuspid aortic valve: Intervention for valve disease or aortopathy in adults", section on 'Transcatheter aortic valve implantation' and "Bicuspid aortic valve: Intervention for valve disease or aortopathy in adults".)
Multidetector computed tomography scanning — Given the limitations of echocardiography with regard to acoustic shadowing from calcification and the high spatial resolution of MDCT, MDCT is currently the test of choice in quantifying severity and identifying the location of aortic cusp calcification (image 4). MDCT can be used to measure the distance from the annulus/leaflet hinge point to the left main ostium and the length of the corresponding coronary cusp, important parameters in planning strategies to reduce the risk of coronary obstruction [22]. Multiplanar, three-dimensional techniques allow for reconstruction of the plane of the coronary ostia, with corresponding better visualization and assessment of these complex structures and their relationships. In addition, there is growing awareness of the potential of MDCT to discriminate aortic valvular morphology in a fashion that is superior to TTE [41]. MDCT also allows imaging of the exact location and quantification of calcification, which may aid in prognosis of patients with aortic stenosis and planning for TAVI [42,43].
Echocardiography — One grading system used for surgical aortic valve replacement (SAVR) that discriminates calcium being confined to leaflet tips (mild), calcium extending from the leaflet tips to the leaflet bases (moderate), and bulky calcification that extended from tip to base in all three leaflets (severe) has shown modest correlation with the actual weight of the excised native valve [44]. Severe and bulky calcification of the aortic leaflets and annulus may render echocardiography unreliable, while less severe calcification may not pose as much limitation [45].
A traditional, long-axis, parasternal view of the LVOT and aorta by TTE is used to identify the severity of calcification and overall valve mobility. While the right coronary cusp and left noncoronary commissure are visible in the traditional, long-axis view, short-axis views of the aortic valve from the parasternal or subcostal window are often also necessary to identify the exact number of cusps, location of calcification, and commissural fusion, if present.
When significant aortic valve calcification limits further analysis by TTE due to acoustic shadowing, TEE may be helpful [46]. The role of three-dimensional TEE in the preprocedural assessment has mostly involved providing an accurate depiction of the annulus, measurement of the annular-coronary ostial distance, and, less often, providing an assessment of the aortic cusps when TTE is indeterminate.
Coronary ostia — Coronary artery compromise is an important, but fortunately infrequent, complication of TAVI, occurring in <1 percent of patients in clinical trials and single-center reports [47-49]. [11]Coronary occlusion most commonly affects the left coronary (88.6 percent) and occurs more commonly in women and following balloon-expandable TAVI [11]. Prior to this registry, anatomical predictors were largely anecdotal, but careful caliper-matched analysis confirmed the following as possible risk factors for coronary ostial obstruction [50]:
●A low-lying coronary ostium <10 to 12 mm from the basal leaflet insertion to the coronary ostium as measured by MDCT
●Mean sinus of Valsalva diameter of <30 mm
●Sinus of Valsalva diameter/annular diameter ratio of <1.25
These risk factors have been present in many of the reported cases of coronary ostial obstruction during TAVI [50-52], although no definite criteria exist to stratify patients on the basis of risk for coronary obstruction. Coronary obstruction appears to be more frequent in women, which may be related at least in part to smaller aortic root dimensions and lower coronary ostial height [50]. Coronary obstruction rates are higher with SAPIEN versus CoreValve THVs [50].
Potential mechanisms for coronary ostial obstruction have been proposed including:
●Displacement of native bulky aortic leaflets over the coronary ostium
●Impingement of the coronary ostia by the THV support structure
●Inappropriately high positioning of the sealing cuff of the THV
●Embolization of atheroma, calcium, thrombus, air, or vegetation
●A significantly oversized THV
●Aortic root dissection
Though there have been no trials comparing various noninvasive imaging modalities in assessing the relationship of measures of annular-ostial height with clinical outcomes, the authors favor MDCT and three-dimensional TEE for this assessment.
Echocardiography — Echocardiography can provide important preprocedural information regarding risk factors for coronary obstruction. It is crucial to know the distance from the basal aortic annulus to the ostia of the left and right coronary arteries and to compare this with the length of the cusps. TTE is inferior to TEE in this regard due to low resolution and limited views of the cusps and coronary ostia in the long axis. TEE is able to define the annular-ostial distance and length of the coronary cusps using two- and three-dimensional imaging to visualize the true vessel plane. Echocardiographic imaging of the left coronary ostium will typically require three-dimensional TEE [28].
Multidetector computed tomography scanning — MDCT can be used to measure the distance from the annulus/leaflet hinge point to the left main ostium and the length of the corresponding coronary cusp, important parameters in planning strategies to reduce the risk of coronary obstruction [22]. Multiplanar, three-dimensional techniques allow for reconstruction of the plane of the coronary ostia, with corresponding better visualization and assessment of these complex structures and their relationships.
Risk assessment is performed preprocedurally with MDCT as it is the only modality supported by meaningful multicenter data. Importantly, these measurements should be performed in a standardized fashion to ensure reproducibility. Coronary ostial height of <11 mm in a female and <12 mm in a male connote increased risk of coronary occlusion, but coronary ostial height is but one of a number of relevant measurements that are ascertained from a preprocedural CT scan. These include but are not limited to sinus of Valsalva (SOV) diameter, STJ diameter, and SOV/annular ratio [22,53].
Sinotubular junction and proximal aorta — For TAVI, STJ width and the presence and degree of calcification may be related to the incidence of prosthesis-patient mismatch (PPM) [54,55]. Small and heavily calcified STJs may also predispose patients to balloon migration, THV embolization, or aortic root rupture during implantation of the THV. STJ calcification is also associated with more severe atherosclerotic aortic arch disease [28,29,56,57]. In addition, with longer balloon-expandable valves that may extend up to the level of the STJ, care must be taken as with tapering of the STJ there are reported cases of STJ injury from the transcatheter device.
Echocardiography — Two-dimensional TTE images should be used to visualize the aortic root in different views in varying intercostal spaces and at different distances from the left sternal border. Right parasternal views, with the patient in a right lateral decubitus position, can also be useful to focus on the root including the STJ. In the parasternal, long-axis views (ie, corresponding to the sagittal plane by other noninvasive modalities), the STJ is measured in a similar manner to the aortic annulus (image 2). The thoracic aorta is generally better imaged using TEE as it lies in the near field of the transducer, and this should be considered in patients with poor acoustic windows due to large body habitus or lung hyperinflation.
Multidetector computed tomography scanning — The accuracy of MDCT imaging of the STJ depends on the method used to measure. Double-oblique imaging, compared with axial methods, yield smaller differences compared with planimetry, and measurements obtained by double-oblique imaging are generally smaller, as was demonstrated in a study of patients with thoracic aortic aneurysms [58].
Concomitant cardiac pathology
Mitral valve leaflets
Anatomy and pathology — The aortic annulus is in close proximity to the mitral valve apparatus, with the majority of the noncoronary leaflet and a portion of the left coronary leaflet in fibrous continuity with the anterior mitral valve leaflet. The two interleaflet triangles abutting the noncoronary leaflet are also in fibrous continuity with the anterior mitral valve annulus (the aortomitral curtain) (figure 3). Anterior mitral valve morphology is especially important to characterize in the preprocedural phase in order to avoid unintentional impingement of the anterior leaflet with placement of the THV too low within the ventricle [29]. Moreover, dense calcification within the aortomitral curtain or mitral annular calcification may increase the risk of paravalvular regurgitation due to asymmetric expansion of the THV [59].
Choice of imaging modalities — The anterior mitral valve leaflet can be visualized noninvasively by MDCT, CMR, fluoroscopy, and echocardiography. MDCT is probably the modality of choice for quantifying calcification, barring motion artifacts, significant arrhythmia, or other potential limitations of MDCT. Echocardiography offers the advantage of being able to obtain morphologic as well as hemodynamic information related to mitral valve function in real time, without the added time necessary for postprocessing. Similar to MDCT and CMR, TEE using multiplanar reconstruction of three-dimensional datasets allow for complete visualization and offline manipulation of the images to inform the anatomic relationships between the mitral leaflets and LVOT [60].
Mitral regurgitation
Spectrum of disease — Most (76 percent) patients with severe aortic stenosis (AS) have some degree of MR, with at least mild MR being found in 61 to 90 percent [61,62]. Moderate or severe MR is seen in 15 to 48 percent of patients undergoing TAVI [15,63,64]. Most of these patients have organic as opposed to functional MR [65]. During implantation, the guidewire or delivery catheter may interfere with the mitral subvalvular apparatus and worsen the degree of MR. Worsening MR is included in the differential diagnosis of acute hemodynamic instability during implantation, and, as such, the operator should be aware of any baseline mitral insufficiency. This is usually adequately assessed by two-dimensional TTE imaging of the left atrium, mitral valve, left ventricle, and pulmonary veins using two-dimensional, color, and spectral Doppler in standard manner to characterize MR [66]. During the procedure, TEE with biplane or full-volume three-dimensional image acquisition may be particularly helpful to identify guidewire entrapment within the mitral subvalvular apparatus.
Choice of imaging modalities — Echocardiography is the primary noninvasive imaging modality for evaluating valve defects including MR. TTE is adequate for qualitative and semiquantitative assessments of MR; however, when available, TEE is preferred, especially when planning interventions [67]. Two-dimensional TEE underestimates effective orifice area (by 0.13 cm2), regurgitant volume (by 21.6 percent), and overall severity of MR as compared with three-dimensional TEE [60]. Three-dimensional TEE minimally underestimates regurgitant volume, compared with CMR (by 1.2 percent), [60]. MDCT and CMR are unique, however, in that they both can provide high-precision measures of left ventricular volumes and quantifying total stroke volume, mitral regurgitant volume, and regurgitant fraction [68]. While CMR does allow for direct visualization of retrograde flow over the mitral valve, MDCT does not, and this limits its clinical acceptance in quantifying MR. Moreover, regurgitant flow data obtained by MDCT and CMR may be inconclusive when there is poor signal-to-noise ratio, false electrocardiogram triggering, or motion artifacts [68]. Echocardiographic assessments of MR may be limited by the patient’s body habitus or coexisting lung disease, resulting in suboptimal acoustic windows and technically limited studies [69]; however, semiquantitative, echocardiographically determined severity of MR remains the gold standard and predicts clinical events [70].
Left ventricular outflow tract and septum
Spectrum of disease — Both self-expandable and balloon-expandable THVs extend their lower edge into the LVOT. Abnormalities within this region should be identified during the preprocedural assessment in order for the operator to be able to anticipate and take steps to minimize complications. Marked upper septal hypertrophy, for example, protruding into the LVOT may create a significant challenge to the proper seating of the THV and may risk spontaneous repositioning after deployment [2]. Prominent septal hypertrophy has also been associated with atrioventricular (AV) block and need for pacemaker implantation post-TAVI [71,72]. Hemodynamically significant LVOT obstruction due to septal hypertrophy is a contraindication to TAVI; however, there are reports of successful implantations performed with modifications of the THV for such patients [73].
The focus on septal configuration and LVOT morphology as a predictor of device positioning has somewhat shifted over the years. With growing experience, positioning is less common a problem; however, there has been increasing awareness that subannular/LVOT calcification plays a significant role in paravalvular regurgitation and annular rupture. Bulky subannular calcification, particularly below the noncoronary cusp in the setting of annular area oversizing by greater than 20 percent with a balloon-expandable device, has been shown to be associated with a significant increased risk of annular rupture [10,74,75]. Subannular calcium has also been shown quite consistently to increase the risk and severity of PAR particularly with self-expandable valves.
Choice of imaging modalities — Morphology of the LVOT is usually adequately visualized with two-dimensional TTE imaging of the LVOT in the long axis from a parasternal window. Apical windows utilizing off-axis views can also further delineate the relationships between the LVOT, anterior mitral leaflet, and aortic root.
MDCT and echocardiographic-based measurements of septal thickness predict AV block post-TAVI [71,76]. Direct comparisons of various imaging modalities' performance for septal thickness in relation to TAVI clinical outcomes are lacking; however, studies of normal and athletic hearts show that echocardiography tends to overestimate interventricular septum thickness compared with MDCT (by up to 2.2 mm) [77,78]. One explanation for this discrepancy is that trabeculations, if present, are better excluded from the interventricular septal measurement by MDCT than by echocardiography and differences in spatial and temporal resolution [79,80].
Prediction of heart block — Pre-implant MDCT is used to measure the length of the membranous septum in a coronal fashion to enable identification of those at risk for developing heart block following TAVI. It is known that low THV implantation results in an increased risk of pacemaker implantation [81], but the role of pre-implant imaging in identifying patients at risk was previously underappreciated. Since the bundle of His penetrates the septum at the junction of the membranous and muscular septum, those with short membranous septae are more likely to develop heart block [12].
Ventricular thrombus
Clinical significance — Left ventricular thrombus is a contraindication to TAVI and thus should be excluded prior to the procedure. Management of left ventricular thrombus following myocardial infarction is discussed separately. (See "Left ventricular thrombus after acute myocardial infarction".)
Choice of imaging modalities — In clinical practice, TTE is most often used to detect left ventricular thrombus. Diagnostic yield is improved when the study is performed specifically to detect left ventricular thrombus and when sonographic intravenous contrast is used [82,83].
For the TAVI candidate in whom the detection of left ventricular thrombus determines eligibility for the procedure, the operator should not rely on suboptimal echocardiographic images but must perform another diagnostic test such as a contrast-enhanced echocardiogram, CMR, or MDCT when there is a suspicion for a left ventricular thrombus. While left ventricular thrombi can be detected by MDCT [84,85], there are more data comparing echocardiography with CMR [86-88]. A study comparing echocardiography and CMR (including delayed-enhancement or late gadolinium-enhanced CMR) found low sensitivity (33 percent) and high specificity (91 percent) for noncontrast echocardiography compared with CMR [88]. Among patients undergoing noncontrast echocardiography for the indication of suspicion of left ventricular thrombus, sensitivity was 60 percent.
IMAGING DURING TRANSCATHETER HEART VALVE IMPLANTATION
Intraprocedural imaging goals and strategy — Multimodality imaging during implantation of a transcatheter heart valve (THV) is done with the following goals in mind:
●Ensuring proper THV selection and sizing
●Assessing THV position and function immediately after deployment
●Immediate identification of intraprocedural complications
Fluoroscopy and angiography are used during all TAVI procedures. Standard practice is to combine intraprocedural angiography with pre-implant, three-dimensional angiographic or multidetector computed tomography (MDCT) reconstructions to identify the optimal deployment projection. The optimal coplanar view for the implant is usually selected on preprocedural computed tomography (CT) scanning [89-93]. In addition, approximately 50 percent of implanters utilize intraprocedural transesophageal echocardiography (TEE) and TTE is becoming more widely accepted as a sole echocardiographic modality during implantation [94,95].
Echocardiography offers the advantages of portability, excellent spatial resolution, and the ability to perform structural, functional, and hemodynamic assessments at the time of the procedure, and thus aids in imaging of deployment, alignment, and complications.
Ensuring proper transcatheter heart valve placement
Fluoroscopy and angiography — As noted in the 2012 expert consensus statement, fluoroscopy and angiography are the mainstays of imaging during the TAVI procedure [1]. Visualizing the native aortic valve in the optimal planes is crucial for the success of TAVI. With angiography, this is best achieved by using a fluoroscopic view perpendicular to the native valve, sometimes called the "coplanar" view. Precise positioning can be also be achieved by overlaying preprocedural angiography or MDCT images on the fluoroscopy screen (image 5) [96-98]. Newer techniques employing three-dimensional angiographic reconstructions obtained by rotational C-arm fluoroscopic imaging have been used for TAVI and appear to be safe, practical, and accurate [94]. Fluoroscopic visualization of balloon inflation and injection of contrast at the time of placement can also be helpful.
Optimal positioning of the CoreValve THV is determined by fluoroscopy prior to and during deployment. Optimal deployment is assessed by measuring the depth of the left ventricular edge of the stent frame in the left ventricular outflow tract (LVOT) relative to the annulus of the noncoronary cusp of the aortic valve. The optimal implant depth for CoreValve is 4 to 6 mm below the annular plane. A larger angle between the plane of the LVOT and the plane of the ascending aorta tends to result in more severe aortic regurgitation (AR) with the CoreValve [99].
Echocardiography — TEE or TTE provide continuous, real-time visualization of the aortic annulus, valve, and balloon, thus aiding device placement and both prediction and immediate detection of AR as well as other life-threatening complications.
Optimal positioning of the SAPIEN valve within the LVOT and aortic root ("50-50" positioning) depends on accurate identification of the hinge points of the native aortic valve leaflets and their relation to the extent of the THV above and below that point. Because the hinge points are not all at the same level within the oval-shaped annulus, single-plane imaging is not optimal. TEE can be used to assess whether the delivery system, including the THV, is coaxial to the LVOT. The tips of the native leaflets provide another echocardiographic landmark necessary to make sure that the distal end of the SAPIEN stent covers the tip of native aortic valve.
For CoreValve, optimal deployment can be assessed by echocardiography, but is more often done using fluoroscopy. (See 'Fluoroscopy and angiography' above.)
The use of TEE during THV implantation is not standard at all TAVI centers, but its use is strongly recommended to guide implantation, to confirm optimal deployment and final position, and to detect complications [100]. TEE can be used for both transfemoral and transapical deployment, but, with transfemoral procedures increasingly being performed under local anesthesia combined with moderate (formerly called conscious) sedation [101], TTE is gaining an evidence base as the sole echocardiographic modality during implantation [1,102,103].
Experience using intracardiac echocardiography (ICE) during TAVI is growing. ICE has been shown to require less repositioning and provide more frequent visualization of both coronary ostia than TEE while obtaining annular measurements that are similar to values obtained by preprocedural TEE [104].
Identifying complications
Aortic regurgitation — TEE is particularly useful in predicting, identifying, managing, and monitoring paravalvular aortic regurgitation (PAR), which occurs in approximately 85 percent of patients immediately post-TAVI [15,105]. Although minor AR is common following TAVI, moderate or severe AR is infrequent. For both types of THVs, the most important determinants of post-TAVI AR may be assessed by multimodality imaging: undersizing of the prosthesis, the extent of calcification of the valve, and the THV position in relation to the annulus [55]. Studies of the SAPIEN valve showed that a low cover index (calculated as the difference between the prosthesis diameter and annulus diameter, divided by the prosthesis diameter) is also an important predictor of post-TAVI AR [30,106,107]. (See "Transcatheter aortic valve implantation: Complications", section on 'Aortic regurgitation'.)
Immediately after deployment, the presence of AR can rapidly be assessed with TEE imaging in a single-plane short-axis view or biplane mode [21]. For paravalvular regurgitation, the short-axis plane of imaging is optimally positioned just below the THV stent and skirt and just within the LVOT to avoid mistaking flow within the sinuses of Valsalva for regurgitant jets into the LV. Confirmation of the severity of AR should always be performed from multiple echocardiographic views. Standard long-axis views (120 to 140 degrees) can show AR, while deep gastric views allow imaging of the LVOT without acoustic shadowing. Imaging the entire annulus is mandatory and requires rotating 180 degrees while centered on the valve. Small regurgitant jets are commonly seen and do not require intervention as these jets typically decrease over time [108,109]. Patients with more than mild paravalvular regurgitation, however, could be considered for a second balloon dilatation to reduce the degree of AR (image 6). TTE has been demonstrated in one center to be a reasonable alternative to TEE for assessing PAR after TAVI [103].
Other TAVI complications — Multimodality imaging by TEE, fluoroscopy or TTE also affords the opportunity to detect many of the causes of sudden hemodynamic compromise during TAVI. Findings of importance, by either TEE or fluoroscopy, include a new wall motion abnormality, large pericardial effusion, color flow signal of severe regurgitation, dissection of the ascending aorta, rupture of the annulus, and the location of the THV [2]. Embolization of the THV is the most frequent reason (41 percent) for emergency surgery in TAVI patients, which is easily imaged during TAVI with TEE [110].
Heart block has also been reported with the self-expanding THV and is thought to be due to the relatively low ventricular positioning of the THV and its proximity to the conduction pathway [72,111]. This complication is usually detected by cardiac rhythm monitoring, and corresponding imaging findings such as abnormal mitral inflow patterns, atrioventricular (AV) dyssynchrony, or diastolic MR may be noted.
Symptomatic or hemodynamically significant valve thrombosis is rare, occurring in <1 percent of patients undergoing TAVI. Limited evidence is available on the frequency and clinical significance of subclinical valve leaflet thrombosis. Post-implant MDCT has serendipitously identified leaflet thickening that was occult on postimplant echocardiography owing to normal gradients. Early postimplant CT have shown both symmetric and asymmetric leaflet thickening with varying degrees of leaflet restriction. These findings may represent subclinical valve thrombosis but have not been convincingly linked with symptoms or downstream events. Further investigation is required to determine the incidence, clinical significance, and appropriate management of subclinical bioprosthetic valve (including transcatheter valve) leaflet thrombosis. (See "Transcatheter aortic valve implantation: Complications", section on 'Valve thrombosis'.)
LONG-TERM FOLLOW-UP
Follow-up imaging goals and strategy — The goals of post-transcatheter heart valve (THV) implantation imaging include:
●Assessment of valve hemodynamics (ie, gradients and effective orifice area)
●Quantification of transvalvular, paravalvular, and total regurgitation
●Determining the effect of THV implantation on left ventricular hypertrophy, chamber remodeling, diastolic and systolic function
●Detection of long-term complications (ie, device migration, leaflet thrombus formation, mitral valve dysfunction, endocarditis, and valve degeneration)
●Ongoing assessment of concomitant pathology
The most common long-term follow-up strategy for patients post-TAVI involves periodic imaging with echocardiography. Both types of THVs approved for use in the United States have demonstrated good ultrasound imaging characteristics such that a transthoracic echocardiogram (TTE) can provide a detailed assessment of valve position, function, and structure without significant acoustic shadowing [2,112]. Expert consensus suggests more frequent imaging during the first year after TAVI [1]; however, there are no specific post-TAVI follow-up guidelines outside of those requested as part of clinical trials [15,39], and the recommended frequency of imaging is likely to decrease and approach that for surgical aortic valve replacement (SAVR) [113,114]. Cardiac magnetic resonance (CMR) can also demonstrate important THV characteristics and allow for a more quantitative assessment of regurgitant flow, if clinically indicated.
Transcatheter heart valve hemodynamics — The THV hemodynamic evaluation of the post-TAVI patient is similar to that for surgically replaced valves as guided by the published guidelines for prosthetic valves [114]. Continuous wave Doppler is used to derive peak and mean transvalvular pressure gradients, with the highest velocity signals across the left ventricular outflow tract (LVOT) often obtained in the suprasternal notch and right parasternal views. Indices of effective orifice area and Doppler velocity index (DVI) and transvalvular gradients should be followed, with the important caveat that the technique of measuring the pre-valvular velocity profile post-TAVI is unique.
Due to the flow acceleration within the THV proximal to the valve cusps as well as at the level of the THV cusps, it is critical to ensure that the sampling volume (pulsed-wave Doppler) be placed proximal to the stent when the pre-valvular velocity profile is being measured. Erroneously sampling too close to the THV into the area of flow acceleration will result in an overestimation of the effective orifice area or DVI [115]. Inconsistent sampling sites between different echocardiographic examinations will result in variable calculated valve areas that may be misinterpreted as changing valve hemodynamics [2]. The optimal position for measuring LVOT diameter and pre-valvular velocity profile for calculating effective orifice area is immediately proximal to the THV stent for the SAPIEN valve [116]. Although this site has also been used for left ventricular outflow measurements for the CoreValve, the optimal site for CoreValve measurements has not been reported.
An observational study found that mean transaortic gradient after TAVI with the SAPIEN THV was lower than that after SAVR with stented valves and similar to that after SAVR with stentless valves [117]. The three-year results from a balloon-expandable valve study suggest that a small increase in mean transvalvular gradient (3.8 percent per year) and a small reduction in valve area (0.06 cm2 per year) may occur over time [18].
Prosthesis-patient mismatch — Prosthesis-patient mismatch (PPM) occurs when the effective orifice area of the implanted THV is too small in relation to body size and is defined by an effective orifice area ≤0.65 cm2/m2. Individual observational studies and a systematic review suggest that PPM is less common after TAVI with the CoreValve or SAPIEN THVs than with SAVR (PPM incidence of 16 to 32 percent, 6 percent, and 20 to 70 percent, respectively) [54,55,117,118]. However, aortic regurgitation (AR; particularly paravalvular) is more frequent after TAVI than after SAVR [118]. The long-term implications of PPM for TAVI patients have not been described.
Aortic regurgitation — Both transvalvular and paravalvular AR (PAR) occur commonly after TAVI, with mild or less AR found in most patients [105,119]. AR is more frequent after TAVI (any postprocedural AR in 37 to 96 percent; postprocedural moderate to severe AR in 0 to 41 percent) than after SAVR (any postoperative AR in 5 to 54 percent; postoperative moderate to severe AR in 0 to 3 percent) [118]. In the CHOICE randomized trial, moderate or greater AR was more frequent with the self-expanding CoreValve compared with the balloon-expandable SAPIEN valve. Subsequent one-year follow-up data from the CHOICE trial showed persistently lower rates of greater than mild PAR (1.1 versus 12.1 percent) with the balloon-expandable device but no difference in one-year mortality [120]. In the SOLVE-TAVI randomized trial, the Corevalve Evolut R was shown to be equivalent to the Edwards Sapien 3 for the composite endpoint of all-cause mortality, stroke, permanent pacemaker implantations, and moderate or severe prosthetic valve regurgitation at 30 days. Longer-term comparative data are needed.
AR is generally assessed semiquantitatively using echocardiography. If clinically indicated, CMR or multidetector computed tomography (MDCT) can provide quantitative data on regurgitant volumes. A preliminary report suggested that CMR may be helpful in evaluating PAR following TAVI despite the presence of prosthesis-related artifact [121]. The study of 16 patients who had undergone TAVI found that follow-up quantitative CMR measurements of AR correlated strongly with postprocedure angiographic assessment of AR (r = 0.86), while the correlation between follow-up echocardiography and angiography was limited (r = 0.319). Further studies are needed to define the role of CMR in assessment of post-TAVI AR.
Follow-up echocardiograms should identify the presence, location, and severity of trans-, para- and total valvular regurgitation. A full characterization of the severity of regurgitation includes views from the parasternal long axis, short axis, the apical long axis, and the five-chamber views. Off-axis views should also be used to ensure accurate determination of the location and severity of eccentric regurgitant jets. Color and spectral Doppler techniques are applied in a manner similar to other prosthetic valves [114]. (See "Echocardiographic evaluation of prosthetic heart valves".)
Transvalvular aortic regurgitation — Significant transvalvular AR after TAVI is usually due to valvular damage during the implantation procedure, too large a prosthesis for a small annulus resulting in valve deformation, or severe calcification of the native valve leading to deformation of the frame of the THV [122]. Echocardiographic short-axis and off-axis views are especially helpful to characterize the origin of the jet passing through the prosthetic leaflets. With eccentric transvalvular AR jets, the vena contracta must be measured in the correct plane with care. Measurements of regurgitant jet width parallel to the LVOT measurement risk overestimating the degree of regurgitation. Clinical reporting guidelines follow those for other prosthetic valves in the aortic position, while standard trial endpoint definitions have also been published [123].
Paravalvular aortic regurgitation — PAR is synonymous with paravalvular leak, perivalvular leak, or paraprosthetic regurgitation. It is usually caused by incomplete THV apposition to the native annulus, too small a prosthesis for the annulus, or too low implantation of the valve, leading to leakage around uncovered portions of the prosthesis [122,124]. Because PAR jets travel along the natural curvature of the prosthesis-annular interface, it is often difficult to differentiate these jets from transvalvular AR, and imaging in multiple planes is necessary. The transthoracic short-axis view is usually the best view to demonstrate the true regurgitant orifice and helps to prevent the overestimation of PAR severity, which can occur when relying solely on apical views. The circumferential extent of PAR is used for grading severity (figure 4) [47]. As with all AR parameters, the approximation of circumferential extent should be weighed with all other available criteria for assessing the degree of regurgitation.
Total aortic regurgitation — While distinctions between transvalvular and PAR may have immediate impact on patient-care decisions, it is the total amount of AR that represents the volume load to the ventricle, thereby affecting chamber remodeling, left ventricular function, and the development of pulmonary hypertension [125].
Myocardial function — Important determinants of improved left ventricular function include left ventricular mass regression, improvement in ejection fraction, improved diastolic function, and reduction in mitral regurgitation (MR). Patients undergoing TAVI have beneficial changes in all of these parameters (mass regression [126], ejection fraction [127], diastolic function [126], MR, and myocardial strain [64,65,128,129]) and, in some cases, offer improvement greater than what is seen after SAVR [130]. Of these factors related to myocardial function, the least is known about the natural history and implications of MR and diastolic dysfunction after TAVI compared with SAVR [118].
CMR is helpful if echocardiographic results are uncertain since it offers a highly accurate measure of left ventricular systolic function and highly reproducible measure of left ventricular mass [131].
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Cardiac valve disease" and "Society guideline links: Transcatheter aortic valve implantation".)
SUMMARY AND RECOMMENDATIONS
●Multimodality imaging is a key aspect of the care of patients undergoing transcatheter aortic valve implantation (TAVI). The care team for patients undergoing TAVI should include cardiologists and radiologists skilled in various imaging modalities for each phase of care (ie, preprocedural, intraprocedural, and long-term follow-up). The goals and strategies of imaging combine to increase the likelihood of a successful procedure and decrease the risk of complications. (See 'Introduction' above and 'Preprocedural imaging goals' above.)
●Goals of preprocedural multimodality imaging for TAVI include ensuring patient suitability, ensuring suitability of the proposed access site, ensuring appropriate device type and size, and developing a procedural plan. (See 'Preprocedural imaging goals' above.)
●Key steps in TAVI preprocedural imaging include echocardiography for valve and aortic root assessment, multidetector computed tomography (MDCT) of the aorta and iliofemoral system, and coronary angiography with optional invasive angiography of the aorta and iliofemoral system. (See 'Key steps' above.)
●Goals of imaging during the TAVI procedure include ensuring proper device selection and sizing, providing immediate assessment of transcatheter heart valve (THV) position and function, and immediate identification of complications. (See 'Intraprocedural imaging goals and strategy' above.)
●The standard imaging during the TAVI procedure includes fluoroscopy and angiography with or without integration with preprocedural imaging (eg, MDCT images overlaid on fluoroscopy) and intraprocedural transesophageal echocardiography (TEE). (See 'Intraprocedural imaging goals and strategy' above.)
●Use of TEE during TAVI varies across centers but has superior ability to identify real-time deployment, alignment, and complications. The trend towards local anesthesia with moderate (conscious) sedation (rather than general anesthesia) during TAVI may limit the use of TEE in these cases. Intracardiac echocardiography (ICE) is an alternative. (See 'Intraprocedural imaging goals and strategy' above.)
●The differential diagnosis for sudden hemodynamic compromise during TAVI implantation is broad (eg, general anesthesia, arrhythmias, device deployment, hemorrhage, coronary artery obstruction, pericardial tamponade, severe mitral regurgitation [MR], aortic injury or dissection, left ventricular damage or perforation, embolization of the THV), and TEE aids in the rapid diagnosis of many of these conditions. (See 'Identifying complications' above.)
●Goals of long-term follow-up imaging following TAVI include assessment of valve hemodynamics, quantification of aortic regurgitation (AR; transvalvular, paravalvular, and total), determination of effects on left ventricular size and function, assessment of concurrent pathology, and detection of late complications. (See 'Follow-up imaging goals and strategy' above.)
●Echocardiography remains the standard for long-term evaluation of prosthetic valve structure and function, as well as the effects of TAVI on myocardial function and hemodynamics. (See 'Follow-up imaging goals and strategy' above.)
●Indices of effective orifice area and Doppler velocity index (DVI) and transvalvular gradients should be followed, with the important caveat that the technique of measuring the prevalvular velocity profile post-TAVI is unique. (See 'Transcatheter heart valve hemodynamics' above.)
●AR is common after TAVI, does not usually worsen, and should be reported as its components (transvalvular or paravalvular) as well as the total degree. (See 'Aortic regurgitation' above.)
●AR is generally assessed semiquantitatively using echocardiography. If clinically indicated, cardiac magnetic resonance (CMR) or MDCT can provide quantitative data on regurgitant volumes. (See 'Aortic regurgitation' above.)
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