Abstract
Echocardiography is an essential imaging tool for structural heart disease interventions. This imaging modality is ideal for preprocedural planning, intraprocedural guidance and postprocedural assessment of every transcatheter intervention. This chapter provides a detailed discussion of the use of echocardiography in transcatheter aortic and mitral valve replacement, mitral and tricuspid repair, and transcatheter approaches to the treatment of prosthetic valve dysfunction, including paravalvular leak closure and valve-in-valve replacement.
Keywords
echocardiography, transcatheter aortic valve replacement, transcatheter mitral valve repair/replacement, transcatheter paravalvular leak closure, transcatheter tricuspid valve replacement, valve in valve, 3D echocardiography
Introduction
Since the development and implantation of the first transcatheter pulmonic and aortic valves, there has been a rapid acceptance of transcatheter valve implantation as a solution to high-risk or inoperable patients with severe, symptomatic valve disease. Randomized trials have since supported the use of transcatheter aortic valve replacement (TAVR) for severe symptomatic aortic stenosis in these patient populations with evidence of efficacy and safety in the intermediate surgical risk population as well. These therapies have subsequently had an impact on the acceptance of percutaneous transcatheter therapies for multiple valvular heart disease pathologies. Transcatheter mitral valve repair devices have received the CE mark in Europe; however, the MitraClip remains the only commercially available device in the United States where transcatheter mitral valve replacements (TMVRs) are currently under investigation. Transcatheter tricuspid devices have been tested in animal models with some in their early feasibility stages in humans. In addition, transcatheter treatment of surgical valve failure with valve-in-valve (VIV) techniques has become widely accepted.
The preprocedural assessment of valvular heart disease severity utilizes echocardiography as the primary diagnostic imaging mode. However, this chapter will focus on the echocardiographic intraprocedural evaluation of valvular morphology and function, guidance of the transcatheter device implantation, and the postimplantation assessment for percutaneous valvular interventions.
Transcatheter Aortic Valve Replacement
TAVR has become an accepted alternative to surgical intervention in patients with severe, symptomatic aortic stenosis who are inoperable or at high risk for surgical valve replacement. Numerous consensus papers and guidelines suggest that echocardiography is important in the preprocedural, intraprocedural, and postprocedural evaluation of patients undergoing TAVR. As TAVR has become more routine, some centers have advocated the use of moderate sedation rather than general anesthesia for the procedure, limiting, but not eliminating, the ability to perform intraprocedural transesophageal echocardiography (TEE).
Transthoracic echocardiography (TTE) during TAVR faces multiple challenges due to both methodologic and patient-specific issues. Parasternal windows require direct placement of the probe within the fluoroscopic imaging plane with high exposure to radiation. The supine position and avoidance of the sterile field may prohibit proper transducer placement. The usual ultrasound interference rules still apply, such as chest wall deformities, emphysema, obesity, etc. Intraprocedural TTE can rule out the causes of acute hemodynamic compromise, such as pericardial effusions, underfilled or dysfunctional ventricles, and severe valvular regurgitation. However, the assessment of paravalvular regurgitation (PVR) remains challenging unless the imaging windows are ideal. Advantages and disadvantages of TTE and TEE for intraprocedural guidance during TAVR are summarized in Table 32.1 . In general, the risk-benefit analysis would favor TEE imaging in patients at low risk for either general anesthesia or monitored anesthetic care. In fact, studies have suggested that using TEE imaging during TAVR may reduce mortality. The final challenge to TTE imaging is the need for immediate and accurate interpretation of the images typically requiring the presence of a physician echocardiographer in a TAVR suite. If TTE images are acquired by such physicians, they need to have proper training and experience in performing TTEs. The following section will concentrate on intraprocedural TEE imaging for TAVR.
| Parameter | TTE | TEE |
|---|---|---|
| Sedation during TAVR |
|
|
| Imaging advantages |
|
|
| Imaging disadvantages |
|
|
| Other advantages |
|
|
| Other disadvantages |
|
|
Preimplantation Assessment
Prior to implantation of the valve, TEE is used to assess the entire “landing zone” of the transcatheter heart valve (THV) ( Box 32.1 ). This landing zone may differ depending on the type of valve implanted ( Fig. 32.1 ). The current commercially available balloon-expandable valve (SAPIEN 3) is short in height when fully deployed (15.5–22.5 mm depending on valve size), and the inflow (ventricular) edge is ideally positioned 1–2 mm below the level of the aortic annulus to allow the fabric skirt around the outside of the proximal portion of the valve to seal the annulus and prevent PVR. The current commercially available self-expanding THV (Evolut R) is much longer (∼50 mm), with the outflow end (aortic) within the ascending aorta, and the inflow end ideally positioned 2–5 mm below the annulus. Other valve designs used commercially in Europe are currently in trials in the United States.
Aortic Valve and Root
- •
Aortic valve morphology
- •
Number of cusps (unicuspid, bicuspid, tricuspid)
- •
Degree and location of calcium
- •
Presence of commissural fusion
- •
Planimetered valve area
- •
- •
Annular dimensions
- •
Minimum and maximum diameters
- •
Perimeter
- •
Area
- •
- •
Aortic valve hemodynamics
- •
Aortic valve peak velocity, peak and mean gradients, and calculated valve area
- •
Dimensionless index
- •
Stroke volume and stroke volume index
- •
Impedance
- •
- •
Left ventricular outflow tract
- •
Extent and distribution of calcium
- •
Presence of sigmoid septum and dynamic narrowing
- •
- •
Aortic root dimensions and calcification
- •
Sinus of Valsalva diameter and area
- •
Sinotubular junction diameter, area, and calcification
- •
Location of coronary ostia and risk of obstruction
- •
Mitral Valve
- •
Severity of mitral regurgitation
- •
Presence of mitral stenosis
- •
Severity of ectopic calcification of the anterior leaflet
Left Ventricular Size and Function
- •
Wall motion assessment
- •
Exclude intracardiac thrombus
- •
- •
Left ventricular mass
- •
Hypertrophy and septal morphology
- •
- •
Assessments of function
- •
Ejection fraction
- •
Strain and torsion
- •
Diastolic function
- •
Right Heart
- •
Right ventricular size and function
- •
Tricuspid valve morphology and function
- •
Estimate of pulmonary artery pressures
Despite higher rates of PVR with the self-expanding valve, clinical outcomes acutely, and at 1 year, do not differ significantly between the two valves. Often, the sizing of the annulus as well as the calcium location and burden, may help to determine the ideal type of THV to implant. However, as more valve types are available, other factors (i.e., bicuspid morphology, preexisting pacemaker, ease of deployment) may also influence the decision-making process.
The most important measurement currently used for THV sizing is the “annulus,” which is a virtual plane at the level of the hinge-point (lowest attachment site) of the three cusps. Because the annulus is often asymmetric and oval with annular diameters largest in the coronal plane and shortest in the sagittal plane, three-dimensional (3D) imaging is required. Although, typically, multislice computed tomography (MSCT) is used for assessing average diameter, the perimeter or area of the annulus may also be used. The 3D TEE has also been validated and may be as accurate as MSCT for these measurements.
It is important to understand the relationship between perimeter sizing and area sizing for TAVR and how this relates to the percent oversizing. The percent oversizing is defined as ((THV nominal measurement/native annular measurement) −1) × 100. For a circular orifice, the percent area oversizing is two times the perimeter oversizing. However, in the setting of an oval annulus, area oversizing will be less than two times the perimeter oversizing. The current balloon-expandable valve uses area oversizing, whereas the current self-expanding valve uses perimeter oversizing. All current devices use systolic measurements, which tend to be the largest measurement during the cardiac cycle, with the lowest risk of undersizing the valve. Advantages of the 3D TEE technique for preprocedural imaging include real-time imaging of the hinge-points of the cusps, and elimination of hand-tracing errors of direct planimetry. Nonetheless, 3D TEE techniques are still limited by ultrasound physics that create blooming and side-lobe artifacts as well as acoustic dropout. In addition, these techniques require expertise and practice. Advances in software packages are currently being developed and should automate many of the steps currently required to obtain 3D-derived measurements, and reduce interobserver variability of echocardiographic measurement of the aortic annulus. Two techniques have been used in the literature: direct planimetry of the short-axis (SAX) plane, and indirect planimetry. The steps for direct planimetry are outlined in Fig. 32.2 . The steps for indirect planimetry are outlined in Fig. 32.3 .
The aortic valve morphology has important implications for procedural success. The extent and distribution of calcium can impact procedural success and has been associated with excessive THV motion during deployment, and PVR. Bulky calcium increases the risk of calcific nodule displacement into the coronary ostia, annular rupture, root perforation, aortic wall hematoma, and aortic dissection ( Fig. 32.4 ). At this time, bicuspid aortic valve morphology is a relative contra-indication to TAVR. However, two reports of TAVR in a series of bicuspid aortic valve patients have shown that, compared to matched trileaflet aortic valve patients, there was no difference in acute procedural success, valve hemodynamics, or short-term survival. Numerous case reports of THV implantations in patients with congenitally abnormal aortic valves have limited the use of TAVR in this population because of reports of significant AR or suboptimal flow characteristics. In the setting of stenosis and limited leaflet motion, a trileaflet valve can be determined by color flow Doppler (CFD) in all three commissures ( Fig. 32.5A and 
) compared to a bicuspid valve with color Doppler in a single long commissure extending to the sinutubular junction (see Fig. 32.5B and 
).
Aortic root morphology is also important in preprocedural planning. The diastolic sinus of Valsalva diameter and height, the diastolic diameter of the sinutubular junction, and the systolic left main coronary artery ostium position may influence the size of THV selected as well as determine valve placement. The location of the coronary ostia is of primary importance since occlusion can lead to catastrophic left ventricular dysfunction. Complications associated with right coronary artery occlusion are significantly less frequent than with left coronary artery occlusion. A meta-analysis of 18 studies showed that coronary obstruction occurred from displacement of the calcified left coronary cusp (and not typically from the stented THV) and the factors associated with coronary obstruction following TAVR include: female sex, small aortic root diameter (mean diameter = 27.8 ± 2.8 mm), and low-lying coronary artery (mean height = 10.3 ± 1.6 mm). Although MSCT is often used for these measurements, 3D TEE imaging compares favorably and allows rapid acquisition of the coronal plane for measurement of the systolic annulus-to-left main distance as well as the length of the left coronary cusp during the procedure ( Fig. 32.6 ).
Intraprocedural Imaging
For most of the procedure, four key standard imaging views are used for basic procedural guidance and postprocedural assessment ( Fig. 32.7 ):
- 1.
Midesophageal SAX view of the left ventricular outflow tract (LVOT), aortic valve, and aortic root with and left main coronary (multiplane angle of 30–60 degrees)
- 2.
Midesophageal long axis (LVOT; multiplane angle of ∼120–150 degrees)
- 3.
Deep transgastric apical five-chamber view (multiplane angle 0–30 degrees) to image the aortic valve in long axis for hemodynamic assessment of the aortic valve (
)
- 4.
Transgastric (shallower than deep transgastric) long-axis view of the LVOT and aortic valve (multiplane angle 120–150 degrees) for hemodynamic assessment of the aortic valve (
).
For intraprocedural imaging, a 3D-capable TEE machine is strongly recommended, but not required; simultaneous biplane imaging and live, narrow volume 3D may be the most useful modalities with rapid image acquisition and, in general, higher volume rates compared to other 3D modalities. If a preprocedural TEE was not performed, then a comprehensive TEE protocol is completed with attention to the above measurements of the “landing zone.”
Multiple reviews have recently been published describing the importance of imaging throughout the TAVR procedure. A summary of important imaging recommendations is listed in Table 32.2 . A few caveats of imaging are discussed below.
| Procedural Step | Imaging Recommendations |
|---|---|
| Pacing wire position |
|
| Stiff wire position |
|
| Balloon aortic valvuloplasty (BAV) |
|
| Positioning of transcatheter valve |
|
| Transapical cannulation |
|
| Postdeployment |
|
Wire and Cannulation Position
Occasionally, the position of wires and cannulae must be confirmed. Following any wire placement into the heart, perforation and accumulation of pericardial effusion should be excluded. The right ventricular pacing wire tip is ideally in the right ventricular apex ( Fig. 32.8A and 
). The position of the retrograde stiff wire within the left ventricle (LV) can also easily be assessed by echocardiography (see Fig. 32.8B and 
) with the curve of the J-wire ideally positioned at the apex of the ventricle. The transapical TAVR approach requires additional imaging. Because of the small apical window generated by the limited thoracotomy, imaging of the left ventricular apex from a midesophageal view is useful to ensure optimal location of the apical puncture (see Fig. 32.8C ).
Balloon Aortic Valvuloplasty
Balloon aortic valvuloplasty (BAV) prior to TAVR is used to increase cusp excursion and to ensure adequate cardiac output during THV positioning. Although some studies have suggested preimplant BAV is not required for the implantation of some valve types, other THV types require BAV. A recent study has suggested that BAV prior to implantation of a balloon-expandable valve may reduce cerebral ischemic lesions. BAV can be used diagnostically for both the confirmation of annular sizing, and the prediction of calcium displacement (into the aorta, left main coronary or annular/subannular region) during final THV deployment. Therefore, imaging during and following BAV is important to assess the functional results of the dilatation and possible adverse events.
Ventricular and Baseline Valvular Function
A qualitative assessment of mitral regurgitation (MR), tricuspid regurgitation, and biventricular function should be made prior to implantation. Changes in the severity of MR may indicate mechanical compromise of the mitral apparatus from stiff wires, the THV, left ventricular dysfunction (particularly following pacing), systolic anterior motion following the abrupt reduction in afterload that occurs with valve deployment, increases in blood pressure, or severe aortic regurgitation (AR). An acute reduction in left ventricular or right ventricular function may be a clue to coronary artery compromise during the procedure. Quantitation of right ventricular stroke volume is attempted in order to aid in the final assessment of AR. Deep gastric views of the aortic valve are crucial, allowing accurate Doppler calculation of effective orifice area by continuity equation and assessment of the presence, location, and severity of AR.
Transcatheter Valve Positioning
It is critically important to precisely position the THV in order to prevent complications, such as embolization, coronary obstruction, PVR, and pacemaker implantation. Although fluoroscopy plays a central role, TEE, with its wide field of view, allows continuous imaging of not just the landing zone, but also of the ventricles and the mitral valve. TEE imaging can be used to confirm the THV location as well as the displacement of calcium during valve positioning, and may minimize the use of fluoroscopy and contrast.
For the third-generation balloon-expandable valve, precise positioning can be accomplished since the cell design of the stented valve results in foreshortening of the valve at the inflow portion of the valve with a stable position of the outflow portion of the valve throughout deployment. Thus echocardiographic positioning should focus on the long-axis view, optimizing the imaging of the entire stented valve and the supporting balloon catheter. In order to do this, small adjustments in image angulation or probe rotation should be used ( Fig. 32.9 and 
). This distal (i.e., aortic or outflow) edge of the THV stent should cover the native leaflets but remain below the sinotubular junction during the pacing run. Although simultaneous multiplane imaging is not required, it can be useful on occasion to image the orthogonal SAX, focusing on previously identified high-risk regions. For instance, bulky calcified leaflets may threaten the aorta ( Fig. 32.10A ) or coronary ostia (see Fig. 32.10B ), and early identification may help avoid a catastrophic complication.
For the second-generation, repositionable self-expanding valve, deployment is driven by fluoroscopic imaging. However, on occasion, simultaneous TEE imaging may diagnose an impingement of the mitral valve with resulting significant MR ( Fig. 32.11A ) or malpositioning that is poorly imaged by noncoaxial fluoroscopic views (see Fig. 32.11B ).
Postimplantation Assessment
A comprehensive evaluation of chamber and valvular morphology and function should be performed after TAVR. Table 32.3 summarizes the parameters that should be assessed. For hemodynamic evaluation of valve function, deep gastric views are imperative to align transaortic flow with the Doppler insonation beam ( Fig. 32.12 ).
| Chamber | Transcatheter Valve | |
|---|---|---|
| Structure |
|
|
| Function |
|
|
| Hemodynamics |
|
|
| Other |
|
|
Paravalvular Regurgitation
Multiple studies have shown a higher incidence of PVR in the TAVR population compared to the surgical aortic valve replacement population, with moderate or severe PVR seen in 0%–24% of TAVR patients. Studies also suggest that AR is an important predictor of mortality. The varying incidence of this complication, as well as the differences in prognostic significance for various grades of PVR, are likely attributed not only to differences in imaging modalities, but also to the absence of a unified grading scheme. A rapid assessment of PVR following TAVR is essential since this post-TAVR complication can be treated intraprocedurally with balloon dilatation, VIV salvage, or paravalvular device implantation. Although multiple modalities can be used to confirm severity, echocardiography remains a major modality that can determine location (central or paravalvular) and, thus, the need for and type of further intervention. Fortunately, with the newer iterations and types of THVs, this problem may become less significant.
Because of multiple grading schemes used for grading AR using both numerical scales and simple categories, a more granular 5-class grading scheme has been suggested : 0 = none or trace; 1 = mild; 2 = mild-to-moderate; 3 = moderate; 4 = moderate-to-severe; and 5 = severe. These five classes of grading can easily be collapsed into the 3-class scheme recommended by the American Society of Echocardiography (ASE)—European Association of Cardiovascular Imaging (EACVI) guidelines as follows: mild in a 3-class scheme = class 1 plus class 2 of a 5-class scheme; moderate in a 3-class scheme = class 3 plus class 4 of a 5-class scheme; and severe in a 3-class scheme = class 5 in a 5-class scheme. Unlike early reports of mortality associated with mild AR following TAVR, more recent studies utilizing this grading scheme have shown that mild and mild-moderate regurgitation do not affect the outcome.
There are a number of caveats to assessing PVR severity by echocardiography. First, while suboptimal stent shape and position may support Doppler findings of PVR, they lack sensitivity and specificity, particularly since valve design typically allows for a range of acceptable THV positions and shapes. Second, the use of ventricular size and remodeling as a clue to the severity of AR may not apply to this population with preexisting aortic stenosis and significant left ventricular hypertrophy. Third, the patient population of those preexisting severe, symptomatic aortic stenosis, as well as the atypical and irregular nature of the PVR jets, may limit the accuracy of qualitative, semiquantitative, and quantitative parameters used for native or surgical valve disease, and thus change the approach to grading severity. Also, there are imaging limitations that are similar to those encountered with surgical prostheses with acoustic shadowing of the far field (anterior paravalvular region for TEE and posterior paravalvular region for TTE) requiring an extensive search for jets by the use of multiple imaging windows (parasternal, apical, and subcostal for TTE, midesophageal, transgastric, and deep transgastric for TEE) as well as subtle angulation/translation of the transducer within each window.
Note that reduced compliance of both the ventricle and aorta will influence pressure halftime, making this particular parameter less useful. Similar issues exist for flow reversal in the aorta, which can occur in the setting of aortic noncompliance and hypertension, although true holodiastolic reversal may still be useful. Recent modeling has confirmed the limitation of using pressure halftime as a measure of regurgitant severity in this patient population, with shorter pressure halftime with both reduced LV and aortic compliance independent of aortic regurgitant severity.
Although THV shape and position may be clues to PVR severity, CFD imaging is the primary method of assessment. CFD imaging of PVR relies heavily on a multiwindow, multilevel approach, first documenting that the suspected PVR jet actually extends beyond the skirt into the LVOT. It is important to scan from distal (aortic) to proximal (ventricular) ends of the THV to identify jet locations and direction. The use of simultaneous multiplane imaging allows a rapid assessment of multiple SAX levels, using the long-axis image as the guide. Central prosthetic AR jets will occur at the level of leaflet coaptation, whereas PVR will be seen at the proximal (ventricular) edge of the THV. For grading severity of PVR, the imaging plane, which visualizes the smallest jet area or width, representative of the vena contracta of the jet, must be assessed. Although this region is typically near the proximal region of the THV stent, ensuring that the visualized jet reaches the ventricle (and is not sealed by the THV skirt) requires visualization of the sub-THV region as well. Multiple imaging planes are used to assess the entire circumference at the level of the vena contracta(e). Imaging of color flow around the THV within the sinuses of Valsalva should not be mistaken for PVR, since the THV skirt at the lowest inflow (ventricular) edge of the stented valve may prevent flow in the sinuses from reaching the ventricle.
Decisions about acute intraprocedural treatment (postdilatation, VIV salvage or paravalvular leak closure device) are typically made by assessment of color Doppler imaging from multiple views. Although quantitation is not typically performed, a qualitative assessment of jet location(s), number, and direction, as well as vena contracta(e) diameter or area, will allow a rapid decision to be made. Fig. 32.13 shows examples of various grades of PVR, with greater than mild regurgitation an indication for postdilatation in the absence of high-risk features. The high-risk features include bulky calcium that may occlude the left main or injure the aorta or aortic annulus, and hemodynamic issues that may be affected by a second pacing run. In addition, in the presence of severe calcification of the LVOT, the effectiveness of a postdilatation is reduced, and some paravalvular jets may be more appropriately treated with a closure device ( Fig. 32.14A ). Severe central regurgitation typically arises from malpositioning of the valve and can be treated with a second transcatheter valve (see Fig. 32.14B ).
Other complications of TAVR have been extensively reviewed for both the balloon-expandable and self-expanding valves. A summary of the types of complications that can be imaged are listed in Table 32.4 .
| Complication | Transesophageal Echo Assessment |
|---|---|
| Hemodynamic Instability | |
| Severe transvalvular or paravalvular aortic regurgitation |
|
| Severe mitral regurgitation |
|
| Pericardial effusion |
|
| Ventricular dysfunction |
|
| Aortic rupture or dissection |
|
| Major bleeding |
|
| Other Procedural Complications | |
| Balloon aortic valvuloplasty complication |
|
| Mal-positioning of the transcatheter heart valve |
|
| Fistula |
|
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