Fig. 2.1
Mitral PVL assess using TTE (a) and TOE (b). It should be note that echocardiography artefacts, especially acoustic shadowing in mechanical prosthesis, may obscure the presence of PVL in TTE examination (yellow star). Thus, in the presence of clinical suspicion, TOE should be performed for an accurate assessment of PVL (yellow arrow)
For the detection of prosthetic mitral valve regurgitation, TTE assessment is less useful because the left atrium is veiled by the acoustic shadowing of the prosthesis (especially in mechanical prosthesis). The parasternal view may be helpful for the detection of prosthetic mitral regurgitation because the left atrium is not shadowed by the prosthesis. In contrast, apical views are limited because the left atrium is largely occluded by prosthetic artefact; however, PVLs can occasionally be detected. Even the most carefully and accurate TTE assessment have a low sensitivity for the detection of prosthetic mitral regurgitation. Hence, TOE should be performed in the presence of suggestive clinical presentation or pathological prosthetic mitral valve flow suspicion after TTE examination [19–21].
CW Doppler ultrasound signal may be useful for identifying prosthetic regurgitation even when regurgitation jet flows are not visible and pass undetected by TTE. Initially, it is recommended to align the CW Doppler ultrasound beam parallel to anterograde flow direction of the valve and then to scan the sewing ring to detect any potential abnormal regurgitation jet. In the mitral and tricuspid position, the regurgitation signal begins immediately after the closure of the prosthesis and continues during systole up to the onset of anterograde flow in diastole. However, in aortic and pulmonary position, the regurgitation signal is detected in diastole. The accurate analysis of the CW Doppler recording, with especial emphasis on the timing of different flow signals, is essential for correct identification of prosthetic valve regurgitation and its localization. Indirect signs in CW Doppler recording are also helpful for the evaluation of the severity (density and shape of signal compared with anterograde flow, regurgitation flow velocity, duration and morphology). Be aware that, despite the fact that the use of CW Doppler enhances the likelihood of detecting invisible PVLs over TTE colour Doppler, the eccentric nature of PVLs may make the correct alignment with CW Doppler ultrasound beam difficult, and occasionally PVLs can still go undetected (Fig. 2.2 ).
Fig. 2.2
Prosthetic mitral regurgitation. (a). TTE four-chamber view and (b) TOE four-chamber view. CW doppler recording of mechanical prosthetic mitral regurgitation. Dense, shape, regurgitation flow velocity, duration and morphology of CW doppler signal can be helpful for the estimation of the severity. In this case, CW doppler signal is not too dense and the outline is not well defined, suggesting regurgitation is not severe
It should be noted that even negative findings in a comprehensive examination using the combination of different TTE tools (2D-TTE imaging, TTE colour Doppler and CW Doppler signal) does not exclude the presence of prosthetic valve regurgitation and further studies should be performed.
2.3.3 Transesophageal Echocardiography
TOE is considered the mainstay tool for accurate assessment of PVLs, and it should be systematically performed in the presence of clinical suspicion, even when TTE findings do not identify any pathological prosthetic valve regurgitation.
The main technical limitation of TTE for the assessment of prosthetic valves are echocardiography artefacts, specifically in mechanical prosthesis in mitral position, because the left atrium and, accordingly, regurgitation jets are veiled by acoustic shadowing related to metallic components of the prosthesis. Although TOE provides excellent visualization of left atrial and mitral regurgitation jets, due to the acoustic shadowing which lengthens to the opposite direction, other technical problems such as reverberation and colour Doppler artefacts remain an important limitation with both approaches. Despite this, TOE has been proven to be an important complement to the transthoracic approach in technically difficult studies, and it has become the preferred tool for a more precise assessment of the location and quantification of severity in PVLs. Furthermore, TOE may be useful to identify related aetiological conditions such as the presence of valve endocarditis, prosthetic dehiscences, abscess or masses.
As mentioned above, TTE may often be sufficient and, in some cases, superior to TOE for the detection of aortic prosthetic regurgitation [22, 23]. However, TOE approach may be required in technically difficult TTE examinations or when TTE findings are contradictory. In addition, TOE may be helpful to identify the precise origin and to separate paravalvular from transvalvular leakage flows (Fig. 2.3 ). It is essential to obtain images in multiple views and multiple planes to ensure complete visualization of the valvular and paravalvular region. Colour Doppler examination should be performed carefully in long-axis view, short-axis view and transgastric views for the detection of PVLs in aortic position. Keep in mind that, in contrast to TTE studies, in TOE images, acoustic shadowing of prosthesis affects the anterior region and it may limit the correct evaluation of prosthetic aortic regurgitation at the midesophageal level. Additionally, the presence of concomitant mitral prosthesis may cause significant shadowing and obscure the left ventricular outflow tract, passing unnoticed abnormal flow signals [24–26].
Fig. 2.3
Mitral PVL assess using 2D-TOE and 3D-TOE colour images. It is essential to identify physiologic from pathologic flows and to separate intravalvular and paravalvular jets. In this case, severe paravalvular eccentric jet is visualized with regurgitation origin outside the prosthetic sewing ring
TOE has demonstrated to be superior to TTE in detecting prosthetic mitral regurgitation, and TOE examination is required for its accurate diagnosis [27]. TOE four-chamber view, two-chamber view and long chamber view permit an excellent visualization of the left atrium and the prosthetic sewing ring in order to identify PVLs. A systematic assessment with a detailed scanning of the sewing ring using colour Doppler in multiple angles should be performed to detect prosthetic mitral regurgitation and to distinguish physiologic from pathologic flows and paravalvular from intravalvular regurgitation jets. Typically, in mitral PVLs, when the jet goes through the regurgitant orifice outside the prosthetic ring from the left ventricle to left atrium, the flow tends to be eccentric and adopts unusual directions. Moreover, the role of TOE in mitral PVLs is essential to determine the precise origin and mechanism of the regurgitation jet and to evaluate indirect signs of severity. Among these, systolic flow reversal in pulmonary veins has been correlated with the severity of mitral PVLs, provided that the regurgitation jet is not directed into the interrogated vein.
TOE is also helpful in the good-quality acquisition of other parameters related with regurgitation severity. TOE examination and the use of off-axis views provide a better visualization of PVLs flow throughout its entire length, facilitating the alignment of CW Doppler ultrasound beam and improving the CW Doppler signal. In addition to other parameters, the analysis of CW Doppler recording allows estimation and quantification of the severity of the regurgitation [28].
Importantly, TOE is not only important to identify and define the degree of PVL. Selection of the appropriate treatment strategy in patients with haemodynamically significant PLVs requires an accurate identification of the shape and size of the regurgitant orifice. In light of this, TOE is not only fundamental for the evaluation and procedural planning of PVL, but it is also the key for guidance during the intervention of percutaneous PVL closure or open heart surgery.
2.3.4 3D Echocardiography
Over recent years, technical advancements in imaging have allowed the development of novel tools to enhance diagnostic accuracy and to overcome classic limitations of 2D-TTE and TOE, particularly in heart valvular disease. One of the most relevant contributions has been the emerging of three-dimensional transthoracic (3DTTE) and transesophageal echocardiography (3DTOE) [29, 30].
In the evaluation of prosthetic heart valves, 3D echocardiography, with or without colour Doppler, provides excellent results for diagnosis and characterization of all-type prosthetic valve dysfunction, even compared with direct surgical inspection. 3DTTE and more specifically 3D-TOE have been shown to be particularly accurate for the diagnosis of PVLs compared with 2D-TTE. The major advantage of 3DTOE is the capacity to analyse the entire valve in one full volume or 3D zoom instead of the thin slice visualized in 2D echocardiography, providing powerful information about the localization and the extent of regurgitation jets (Fig. 2.4). Also 3DTOE allows the assessment of prosthetic valve details, such as the sewing ring, the leaflet motion and the presence of any PVL etiological conditions (vegetations, abscess, dehiscences) [29–33].
Fig. 2.4
Prosthetic mitral regurgitation. Three-dimensional transesophageal echocardiography color image of mechanical prosthesis. En-face real-time three dimensional colour doppler TOE visualization of the prosthesis also enables to measure the circumferential extent of paravalvular regurgitation that has been associated with the severity of PVL (yellow arrow, severe PVL, more than 20% of sewing ring circumference)
Especially, 3DTOE has been demonstrated an enhancement in the diagnostic accuracy and quantification of regurgitant degree in patients with multiples PVL. The more accurate measurement of flow convergence, vena contracta and the extent of the jet in the receiving chamber permit an improvement of severity quantification. This tool has the ability to acquire a 3D colour full volume that can then be rotated and cropped for the identification and precise delimitation of the effective regurgitant orifice area.
Finally, 3DTEE has been increasingly recognized as invaluable for guidance of procedures for percutaneous PVL closure [34–37].
However, 3DTEE has some limitations indeed. A comprehensive assessment of prosthetic valves can be challenging and technically demanding because it requires high-quality image acquisition. Thus, a complete training process should be carried out by staff of echocardiography laboratories in order to optimize its acquisition.
2.3.5 Intracardiac Echocardiography
In recent years, intracardiac echocardiography (ICE) has become increasingly recognized as a valuable imaging tool for guiding structural heart disease and cardiac arrhythmias procedures. Unlike TOE, it does not require general anaesthesia, which may be especially useful for sick patients in whom local anaesthesia may be more desirable. At present, 2D and 3D intracardiac echocardiography (ICE) represents a complementary technique to other imaging modalities in the assessment of prosthetic valves and more specifically in evaluation of PVL. Its high-image resolution and detail definition provide additional information regarding the severity and the accurate localization and also enable the identification of related causes of PVL: vegetations, abscess or dehiscences [38–40].
Nevertheless, ICE is no stranger to inherent echocardiographic limitations, such as colour artefacts, acoustic shadowing and reverberations that may make an accurate assessment of PVL difficult. Moreover, its invasive nature, the additional costs and the need for specific operator skills remain limitations. For this reason, ICE is not recommended for the first approach in the assessment of PVL.
In current practice, the major role of ICE is the use as intraprocedural guidance of percutaneous PVL closure showing some advantages compared with routine imaging techniques (TOE and fluoroscopy): avoidance of general anaesthesia and reduction of radiation exposure [41].
2.3.6 Stress Echocardiography
Stress echocardiography is a well-established tool for the assessment of patients with valvular heart diseases and suspected prosthetic heart valve dysfunction [42]. Patients with mild or moderate PVL and incongruent exertional symptoms for which the clinical signification is unclear, stress echocardiography may be useful in confirming or excluding the haemodynamically significant repercussion of the paravalvular regurgitation. A symptom-limited grade exercise with supine bicycle and dobutamine stress echocardiography are the most commonly used in most laboratories. Treadmill exercise is occasionally used for the assessment of exercise capacity, but it is less helpful to quantify changes in valvular haemodynamics because the recording of the valve or prosthesis parameters is acquired after completion of exercise, when the haemodynamics may rapidly return to baseline level. In addition to the evaluation of the PVL, other haemodynamically significant findings like inducible ischemia, exercise-induced pulmonary hypertension, impaired left ventricular contractile reserve, dynamic left ventricle dyssynchrony and altered exercise capacity may be assessed [43–46].
A comprehensive assessment of Doppler echocardiographic qualitative or quantitative criteria for prosthetic valve regurgitation severity at rest and during stress echocardiography should be performed. An increase of systolic pulmonary artery pressure up to 60 mmHg during stress echocardiography has been related to the presence of haemodynamically significant mitral regurgitation (intra- or paravalvular) [42, 46, 47]. Occasionally, exercise testing is also helpful to unmask symptoms and to define the optimal timing of intervention in asymptomatic patients with PVL [48, 50].
2.3.7 Cardiac Computed Tomography
Over the last several years, cardiac computed tomography has rapidly emerged as a promising imaging technique for the assessment of prosthetic valves [51]. Recently, preliminary experience concerning the assessment of the role of cardiac CT for detection of complications associated with prosthetic valves, such as thrombosis, pannus formation, suture loosening and endocarditis, has been successfully evaluated with good results.
In recent years, electrocardiography-gated computed tomographic (CT) angiography with three-dimensional (3D) and four-dimensional (4D) reconstruction using volume-rendering techniques has established its usefulness as a reasonable tool for the assessment of PVL. The use of electrocardiography-gated with helicoidal CT acquisition in multiple phases that include the entire cardiac cycle, preferably with retrospective 4D imaging reconstruction, is the protocol recommended for the evaluation of prosthetic PVL; although, the protocol ultimately depends on patients’ characteristics, heart rate, CT scanner and CT workstation. In the CT assessment of prosthesis, the main goal is to minimize cardiac and prosthetic movement and to avoid motion artefacts. Hence, it is preferable to use retrospective ECG-gated reconstruction of helical CT acquisition sequences and 4D reconstruction in order to visualize the PVLs in greater detail [52, 55].
Additionally, CT imaging can be helpful in the assessment of the periprosthetic anatomy; structural prosthetic integrity and the surrounding anatomic landmarks, such as the left anterior descending coronary artery course; and the distance between the left ventricular apex and the chest wall (Fig. 2.5) [56, 57, 83].
Fig. 2.5
Computed tomography (CT) imaging in prosthetic aortic paravalvular regurgitation. CT imaging provides detailed localization, size and severity of PVL. CT imaging also can be helpful in the assessment of the periprosthetic anatomy, structural prosthetic integrity and the surrounding anatomic landmarks. In these images can be appreciated a PVL (yellow arrow) in patient with mechanical aortic prosthesis and ascending aortic dissection
However, this technique has some drawbacks. Particularly, artefacts from dense structures, such as a prosthetic valve or calcification, may limit PVL size estimation. Furthermore, exposure to radiation and the use of intravenous contrast increase the risks associated with the procedure. Thus, the benefits of high-quality images obtained with this imaging modality should be balanced with the associated risk of radiation, especially in young patients. For this reason, the role of cardiac CT in the evaluation of PVL is mainly to complement echocardiographic findings in order to plan the most suitable treatment rather than purely diagnostic studies.
Therefore, it is important to integrate CT and echocardiographic findings to delimit the detailed localization, size and severity of PVL. At present, both imaging techniques are well-recognized for guidance treatment of PVL [58].
2.3.8 Cardiac Magnetic Resonance Imaging
Cardiovascular magnetic resonance (CMR) is an attractive imaging technique for the assessment of cardiac valvular heart disease [59, 60]. CMR provides accurate and reproducible direct quantification of native valvular regurgitation and has been widely recognized as the non-invasive gold standard for quantification of regurgitant volumes. Recently, diverse small studies have demonstrated the feasibility of CMR for evaluation of prosthetic heart valves to complement echocardiography, especially PVL-related transcatheter aortic valve replacement (TAVR) [61–64]. CMR is able to perform accurate flow-imaging and volume-based measurements.
CMR allows direct measurement of regurgitant flow volume that is an important parameter for severity classification. Also, CMR plays an important role in evaluating accurate flow-imaging and volume-based measurements, irrespective of regurgitant jet number or morphology, and in quantifying regurgitant volumes for multiple valve types.
Different CMR sequences are required depending the clinical context and the purpose of the examination. For flow and velocity measurements, phase-contrast sequences can be appropriated, and motion-sensitized acquisitions can be helpful to assess turbulent flow. The development of CMR four-dimensional (4D) flow may provide a comprehensive characterization of flow patterns in the assessment of PVL [65].
CMR assessment of PVL is highly reproducible and complements echocardiographic semiquantitative and quantitative parameters for grading the severity of regurgitation. Importantly, some studies have reported that patients with greater than mild PVL assessed by CMR, with values of regurgitant fraction >20%, present with a higher incidence of adverse events and prognostic implications [66–68].
Although CMR consistently has demonstrated high reproducibility of measurements, this technique also has inherent technical limitations. CMR quantification of volumes requires high-quality images and an experienced operator. Basically, CMR valve-related artefacts depend on the amount of metal. Bileaflet and titanium-containing prosthetic valve cause fewer artefacts than monoleaflet valves or cobalt-chromium alloys. Biological valves containing a simple ring show no disturbing artefacts, unlike valves with metal struts. Additionally, some situations, such as arrhythmias and motion artefacts, may reduce the accuracy of measurement and significantly affect the quality of acquisition. These aspects, in addition to the increased costs and the irregular access to scanners, remain limitations for a widespread use in the assessment of PVL (Fig. 2.6 ).
Fig. 2.6
Magnetic resonance imaging in prosthetic mitral regurgitation. Note the presence of systolic flow in left atrium with regurgitant jet origin outside the sewing ring and Coanda effect suggesting significative mitral PVL (Courtesy Dra. Covadonga Fernández-Golfín, Ramón y Cajal University Hospital. Madrid. Spain)
2.4 Echocardiography Assessment of Specific Prosthetic PVL
2.4.1 Mitral Paravalvular Regurgitation
Basically, the same methods used for quantifying severity of native mitral valve regurgitation can be applied for prosthetic mitral regurgitation. Nevertheless, it should be noted that many parameters used routinely for quantification of native mitral regurgitation are not specifically validated for the assessment of mitral prosthetic regurgitation, and their application is extrapolated from quantitative parameters in native valve guidelines.
As mentioned, echocardiography is considered the mainstay tool for the diagnosis of mitral PVL. However, a comprehensive assessment of severity of prosthetic mitral regurgitation is frequently challenging. The major limitation in the evaluation of prosthetic mitral valve by echocardiography is the acoustic shadowing that usually obscures regurgitation jets, especially with mechanical prosthesis. This problem is minimized by the use of TOE, which commonly provides an excellent visualization of left atrial and mitral regurgitation jets. Therefore, TOE is the preferred tool for a more precise identification of PVL, and it should be systematically performed when there is TTE or clinical suspicion of pathologic mitral regurgitation.
First of all, it is essential to distinguish intraprosthetic from paraprosthetic regurgitation jets. A thorough evaluation of the entire sewing ring using colour Doppler and a multiple plane echocardiographic approach, sweeping the mitral prosthesis from 0° to 180°, is the key for an accurate identification of mitral PVL.
Following PVL identification it is necessary to define a detailed localization. In order to unify the nomenclature related with localization of PVL around the perimeter of the sewing ring, a clockwise format from a surgeon’s perspective is used (mitral valve or mitral prosthesis view from left atrium). In this perspective, the midpoint of the anterior side of the annulus is aligned at the “12 o’clock” position, and the midpoint of the posterior side of the annulus is seen at the “6 o’clock” position. This usually leaves the posterior-medial commissure and interatrial septum approximately at the “3 o’clock” position, while the anterior-lateral commissure and left atrial appendage are seen approximately at the “9 o’clock” position. Anterior location was defined for PVLs situated between 9 and 12 o’clock, septal location for PVLs between 12 and 3 o’clock, posterior location for PVLs between 3 and 6 o’clock and lateral location for PVLs between 6 and 9 o’clock. Some studies and surgical series have revealed that most common localization of mitral PVL is anterior-septal (between 10 and 11 o’clock) and posterior-lateral (between 5 and 6 o’clock) (Fig. 2.7 ).
Fig. 2.7
Clockwise format from a surgeon’s perspective (mitral valve or mitral prosthesis view from left atrium). In this perspective, the midpoint of the anterior side of the annulus is aligned at the “12 o’clock” position, and the midpoint of the posterior side of the annulus is seen at the “6 o’clock” position (Courtesy Dr. Eduardo Franco, Ramón y Cajal University Hospital. Madrid. Spain)
2.4.1.1 Quantification of the Severity of Mitral PVL
Commonly, PVLs in mitral position have a complex morphology, and assessment of the severity of prosthetic mitral paravalvular regurgitation can be difficult. Current recommendations for prosthetic mitral regurgitation assessment, either intra- or paravalvular, are derived from native mitral valvular regurgitation, integrating parameters obtained by different imaging modalities, mainly TTE and TOE. This multi-parametric approach includes findings related to prosthetic valve structure and motion, qualitative or semiquantitative parameters, quantitative parameters and indirect signs. Differentiation of mild from moderate or severe prosthetic PVL is usually easier than discriminating moderate form severe [43–45, 69, 70].
Prosthetic Valve Structure
PVLs are more common with mechanical valves than bioprosthetic valves. An accurate assessment of prosthetic valve structure and motion is required in order to identify abnormal findings related with the severity of mitral PVL. The presence of dehiscence or evidence of valve instability (rocking motion) is associated with significant paravalvular regurgitation. Other findings related with etiological PVL conditions, such as endocarditis, pseudoaneurysm or abscess, are frequently associated with severe mitral PVL and poor clinical prognosis.
Qualitative or Semiquantitative Parameters
Colour Doppler or CW/PW Doppler parameters can point out severity in mitral PVL. Regurgitant jet area can suggest severity of regurgitation. A small thin jet (jet area <4 cm2 ) in the left atrium usually reflects mild PVL, while a large, wide jet (>8 cm2 ) reflects a moderate or severe regurgitation. Although this parameter can be helpful for the assessment of central regurgitant jets, mitral PVL can be underestimated because regurgitant flow is commonly eccentric and with complex morphology.
The intensity and shape of the PVL CW Doppler signal may also be useful to estimate regurgitant severity. Triangular shape of CW Doppler signal is associated with severe regurgitation. Other qualitative parameters, such as pulmonary venous flow with systolic flow reversal, indicate severe mitral PVL.
The application of the Doppler velocity index (DVI), by using the ratio of the VTIs of the mitral prosthesis to the LV outflow tract (VTIPrMV/VTILVO ) is an indirect parameter of mechanical mitral prosthetic valve dysfunction. Although it has been widely used as an indirect parameter of prosthetic mitral valve stenosis, the Doppler velocity index may be equally elevated in paravalvular regurgitation (increased mitral inflow and decreased velocity in LVO). DVI values higher than 2.5 are associated with the presence of severe PVL.
Also, the proportion of circumferential extent area of paravalvular regurgitation in relation with the entire prosthetic sewing ring perimeter has been proposed as an appropriate method to estimate the degree of regurgitation, and its application is generally recommended in current guidelines.
Quantitative Parameters
The width of the vena contracta is the quantitative parameter that best relates with angiographic assessment of prosthetic mitral paravalvular regurgitation. Values less than 3 mm reflect mild mitral PVL, whereas values higher than >6 mm are associated with significant PVL. Moderate mitral PVLs are included in intermediate values of vena contracta width 3–6 mm. Other parameters like regurgitant volume and regurgitant fraction can be useful to separate severe from mild or moderate PVL.
In combination with PVL regurgitation velocity measured by CW Doppler, the radius of the proximal flow convergence can be used to estimate effective regurgitant orifice area (ERO). However, ERO is often over- or underestimated due to the eccentric nature of PVL and the presence of multiple regurgitant jets. Despite the fact that the proximal isovelocity surface area (PISA) has not been specifically validated for PVL quantification, the presence of a large PISA may indicate severe regurgitation.
It should be noted that most of the quantitative parameters used routinely for the assessment of native or prosthetic mitral regurgitation assume effective regurgitant offices (ERO) with spherical shapes. However, the ERO of mitral PVL usually are irregular, and they do not follow any conventional geometrical shape. Therefore, the precise definition of size and shape in mitral PVL are extremely enhanced by using a 3D colour echocardiographic assessment (Fig. 2.8 ).
Fig. 2.8
TOE Colour Doppler images and 3D TOE color echocardiographic assessment of mitral paravalvular regurgitation. Commonly, effective regurgitation orifice of mitral PVL is irregular and they do not follow any conventional geometrical shape. 3D colour echocardiographic images provide a high-definition of ERO and allows an accurate measurement of vena contracta (yellow arrow and green line)
Indirect Sign
Complementarily to direct imaging and Doppler assessment of PVL, additional indirect findings should be evaluated for an overall severity quantification. These indirect signs basically include the size and function of cardiac chambers (left ventricle and left atrial dilatation, left ventricle hypertrophy, systolic function) and the level of systolic pulmonary arterial pressure.
It is grossly important to compare these measurements with previous echocardiographic examination in order to identify slight variations that may reveal novel apparition or worsening of previous PVL (Table 2.1 ).
Table 2.1
Echocardiographic criteria for severity evaluation of prosthetic mitral valve regurgitation
Mitral | Mild | Moderate | Severe |
|---|---|---|---|
Valve structural parameters | |||
Mechanical or bioprosthesis | Usually normal | Usually abnormal | Usually abnormal |
Qualitative or semiquantitative parameters | |||
Colour flow jet area | Small, central jet (usually <4 cm2 or <20% of LA area) | Variable | Large central jet (usually >8 cm2 or >40% of LA area) or variable size wall-impinging jet swirling in LA |
Flow convergence | None or minimal | Intermediate | Large |
Jet density: CW Doppler | Incomplete or faint | Dense | Dense |
Jet Contour: CW Doppler | Parabolic | Usually parabolic | Early peaking, triangular |
Pulmonary venous flow: PW Doppler
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