, Zivile Valuckiene and Petros Nihoyannopoulos
(1)
Department of Cardiothoracic Surgery Hammersmith Hospital, Imperial College Healthcare NHS Trust, London, UK
Introduction
Echocardiography is a widely used non-invasive imaging modality which provides real-time dynamic information on cardiac structures of interest. Transoesophageal echocardiography (TOE) is remarkable for its superior image quality and has served the cardiac surgeons in the perioperative setting since the 1980s. Its initial role was monitoring of left ventricular (LV) function, which, over time has expanded to encompass the complex assessment of the anatomy and function of all heart chambers, valves and the great vessels [1]. Introduction of real time three dimensional (3D) echocardiography has made a revolutionised the history of echocardiography by transforming it into a highly competitive and comprehensive imaging modality.
Transthoracic echocardiographic (TTE) assessment is routinely performed before any cardiac surgical procedure. Preoperative TOE is recommended when TTE is non-diagnostic or more detailed evaluation of cardiac structures is needed. TOE has also secured its place in the perioperative setting and is recommend in:
All open heart (valvular) and thoracic aortic surgical procedures;
Some (high risk) coronary artery bypass graft cases;
Non-cardiac surgery when patients have known or suspected cardiovascular pathology which may negatively impact outcomes [2].
Standard Echocardiographic Assessment
Comprehensive echocardiographic assessment provides a surgeon with information on cardiac chambers, valves and the great vessels. In this chapter, we will highlight the applications of echocardiography on the following topics, most relevant for cardiothoracic surgeons:
Left ventricular (LV) function assessment
Right ventricular (RV) function assessment
Mitral valve (MV) assessment
Aortic valve assessment
Prosthetic valves
Myectomy
Postoperative Complications
LV Function Assessment
Evaluation of LV function is essential for the preoperative assessment of the patient. The degree of LV impairment and dilatation are important parameters when timing valvular surgery. Quick ‘eyeballing’ of the overall systolic function by an experienced observer in the operating room is a good correlate to quantitative measurements of LV ejection fraction which is performed by the Simpson method or recently introduced 3D LV volumetric reconstruction (Fig. 1.1). Assessment of LV regional wall motion abnormalities (RWMA) allows detection of areas of myocardial asynergy and identifies coronary territories in compromise. New RWMA in the perioperative setting may indicate native coronary artery (accidental ligation) or early graft failure, inadequate myocardial preservation during cardioplegia or off-pump surgery. This is particularly important in the right coronary artery territory as, due to its anterior and superior location, air embolism may occur. Occasionally, the left circumflex artery (supplying blood to the lateral wall) may become compromised as there is a risk of accidental ligation of the artery in the atrioventricular groove while applying sutures in the posterior mitral annular area. TOE assists the surgeon while weaning-off the patient from cardiopulmonary bypass (CPB) and helps ensure complete de-airing of the cardiac chambers by providing visualisation of residual air bubbles in the LV cavity, thus, reducing the risk of coronary air embolism and subsequent RV or LV dysfunction. Perioperative LV dimensions help to assess systemic volume status. While assessing the LV function in the operating room, it is useful to take the following tips into consideration:
Figure 1.1
Left ventricular volume and ejection fraction assessment by three-dimensional reconstruction on transthoracic echocardiography. There is evident left ventricular dilatation (end-diastolic and end-systolic volumes are 163 ml and 137 ml, respectively) and severely reduced global left ventricular systolic function (EF 16 %). A semiautomatic algorithm assesses both global (EF) as well as regional LV volumes with the LV segmented into 16 regions (colour coding of the LV)
CPB unloads both ventricles and LV function may appear better than it really is;
Systemic volume underfilling status may falsely ‘shrink’ the LV;
At a slow heart rate, the LV appears ‘sluggish’ and the increase in heart rate may improve the systolic function in such case;
Paradoxical anterior systolic motion of the interventricular septum is a common finding after pericardiotomy and, when observed in isolation, does not indicate new myocardial ischemia.
To avoid possible pitfalls in LV assessment, its volumes and function should be assessed, not only while coming off bypass, but also at the very end of the surgery (fully off-bypass).
RV Function
Right ventricular (RV) function is of particular concern, both before and after CPB surgery. Poor RV function may preclude the patients from undergoing any surgical procedure requiring general anaesthesia (GA) and CPB. the thin walls and crescent shape of the RV make it a highly compliant chamber, able to accommodate significant increases in volume; however, the ability to comply with a significant increase in pressure is limited. Decreased RV function is a recognized phenomenon after CPB and is associated with increased mortality rates [3]. It is important to recognize RV dilatation and free wall hypokinesis, which frequently occur post CPB; however, transient RV stunning needs to be distinguished from ongoing or established ischaemia that may hamper weaning-off the patient from CPB. the assessment of RV function in theatre is highly subjective and experienced operators are needed.
From the transthoracic approach, several parameters have been described to assess RV function (see recent ASE/EACVI guidelines [4]). Among many suggested quantitative parameters, tricuspid annular plane systolic excursion (TAPSE) is by far the most validated and easy to use at the echocardiography department or in a busy intraoperative theatre setting (Fig. 1.2). Current guidelines suggest the degree of RV systolic impairment is present when TAPSE is 16 mm or less. the assessment of RV function goes hand in hand with pulmonary artery (PA) pressure estimates. PA pressure is easily obtainable by echocardiography if there is a sufficient degree of measurable tricuspid regurgitation (TR). However, this measurement is unreliable in cases of severe TR. Evidence of RV failure, the presence of pulmonary arterial hypertension (PAH) and CPB is a ‘killer combination’, notorious for extremely high surgical risk. Therefore, RV dimensions, function (TAPSE) and PA systolic pressures should be carefully assessed before any open heart surgery.
Figure 1.2
(a) Normal (TAPSE 1.9 cm) obtained by transoesophageal echocardiography in mid-oesophageal 4 chamber view (note the difficulty in axial alignment of the cursor in this view, contributing to underestimation of measured parameters). (b) Impaired right ventricle as evidenced by moderately reduced TAPSE (1.07 cm) measured on TTE
Perioperative TOE allows prompt assessment of RV morphology and volume loading conditions. The interventricular septum becomes flattened during diastole in acute RV distension due to volume overload of the RV. Acute RV dilation shifts the interventricular septum towards the LV, resulting in LV compression, underfilling and reduced systemic cardiac output, leading to weaning-off CPB difficulties. Persistently hypokinetic RV and a small hyperdynamic LV cavity may direct the surgical team towards insertion of a RV assist device if adequate therapeutic support is ineffective.
Valve Assessment
Valvular function should be carefully evaluated for every patient as part of a standard preoperative assessment. If there is a valvular issue, it needs to be clarified before the surgery. Preoperative TOE may be needed if TTE is inconclusive. In valvular assessment, perioperative echocardiography is constrained by the following limitations:
Altered haemodynamic and loading conditions: reduced preload and afterload of the ventricles under GA accounts for substantially less valvular regurgitation in comparison to preoperative evaluation;
Risk of heart rate and rhythm alterations: reduced systemic blood pressure under GA causes reflective tachycardia and general anaesthetics may provoke atrial fibrillation, consequently, the estimation of valvular lesions may be difficult;
Reduced capacity to work up complex valve lesions: in a busy operating room, the time span for echocardiographic examination may be limited and, under altered LV loading conditions, the assessment of the pathology may not be straightforward.
No valvular case should be accepted to theatre without a high quality preoperative echocardiographic assessment and full understanding of the underlying pathology.
Mitral Valve (MV) Assessment
Anatomy
The mitral apparatus is a complex structure, composed from mitral annulus, two leaflets, chordae and two papillary muscles. The mitral annulus is a frequent surgical target in cardiac surgery and its unique saddle-shaped anatomy was first understood by the help of 3D echocardiography [4] (Fig. 1.3). Carpentier’s classification of mitral leaflet segments has been widely adopted and used in practice. Each of the two mitral valve leaflets are divided into 3 equal thirds, thus, avoiding the individual anatomic variations of the number and size of the leaflet scallops (Fig. 1.4). It also enables better communication among the cardiac sonographers, anaesthetists, cardiologists and cardiothoracic surgeons while addressing the underlying MV pathology. 3D TOE imaging of MV provides en face ‘surgical view’ of the valve, which is a good match of what the surgeon expects to see in theatre. The images can be rotated by 360° to visualize the valve from either left atrial or LV sides. 3D MV imaging allows comprehensive assessment of the anatomic lesion and its severity helps to estimate the potential success of valve repair or, alternatively, aid the surgeon to choose the valve replacement strategy.
Figure 1.3
(a) Normal MV with a saddle shape of the annulus, with anterior and posterior points being higher than the posteromedial and anterolateral; (b) incompetent MV with leaflet coaptation defect as a result of ischaemic heart disease. Note the annular distortion, loss of saddle shape, significant tenting and ventricular displacement of mitral valve leaflets. A anterior, P posterior, Ao aorta, AL anterolateral, PM posteromedial
Figure 1.4
Carpentier’s MV and scallop nomenclature in (a) reconstructed 3D MV model and (b) real-time 3D TOE ‘surgical’ en face view. A anterior, P posterior, Ao aorta, AL anterolateral, PM posteromedial, A1/A2/A3 anterior mitral leaflet scallops, P1/P2/P3 posterior mitral leaflet scallops
Mitral Valve Regurgitation (MR) (Table 1.1)
Aethiology of mitral regurgitation is presented in Table 1.1.
Table 1.1
Aetiology of mitral regurgitation
Organic (primary) mitral regurgitation | Fibroelastic deficiency (FED) of the MV tissue (also known as degenerative or myxomatous mitral valve disease); |
Mitral valve prolapse; | |
Infective endocarditis; | |
Mechanical trauma (ruptured chordae, leaflet perforation); | |
Rheumatic heart disease; | |
Congenital structural abnormalities (prominent leaflet cleft, parachute mitral valve); | |
Annular and leaflet calcification; | |
Serotoninergic pharmacological substances (ergotamine, methysergide, pergolide, cabergoline, 3,4-methylenedioxymethamphetamine). | |
Functional (secondary) mitral regurgitation | Ischaemic heart disease; |
Systolic LV dysfunction, conduction disturbances (dyssynchronous contraction); | |
Hypertrophic cardiomyopathy. Dilated cardiomyopathy; LV dilatation of other aethiology (e.g. due to long standing hypertensive heart disease). |
Echocardiography is indispensable in planning surgical interventions for MR and describing the anatomy and mechanism of regurgitant lesions:
1.
Leaflet morphology and mobility. Carpentier’s classification of leaflet lesion type and motion disturbances distinguishes three major types of causes of MR.
Type I: Normal leaflet motion. Mitral leaflet mobility is normal with no prolapse. MR is derived from a dilated mitral annulus, mitral cleft or leaflet perforation due to trauma or endocarditis (Fig. 1.5). This type also includes patients with dilated cardiomyopathy and functional MR in cases when the motion of the mitral valve leaflets is not restricted.
Figure 1.5
Mechanism of type I (Carpentier’s) mitral valve insufficiency: (a) Significant mitral annular dilatation secondary to severe LA enlargement resulting in significant leaflet malcoaptation most appreciated on 3D TOE reconstructed mitral annular model (b). Note, a flattened annular shape and secondary prolapse of A2 segment. Pictures (c, d) show mitral valve cleft at 5 o’clock and another coaptation defect at the posteromedial commissure (10 o’clock) in diastole and systole respectively. A anterior, Ao aorta, AL anterolateral, PM posteromedial, P posterior
Type II: MV is structurally abnormal with one or more prolapsing parts. It is characterised by excessive leaflet motion often secondary to fibroelastic deficiency (FED), ruptured chordae or papillary muscles (Fig. 1.6).
Figure 1.6
Type II (Carpentier’s) mitral regurgitation. (a, b) show 2D and 3D TOE images of extensive myxomatous valve disease. There is thickening of the anterior MV leaflet, affecting all three leaflet segments, prolapse of A2 segment, A3/P3 segments and posteromedial commissure, which is best visualised in 3D en face view. (c–e): degenerative MV disease with a flail A2 segment secondary to a ruptured chord (arrow). Severe mitral regurgitation directed posteriorly
Type III: The responsible mechanism of MR in this type is restricted leaflet motion. Based on the cardiac cycle in which leaflet restriction is observed, it is divided into two categories (Fig. 1.7).
Figure 1.7
Type III (Carpentier’s) MV regurgitation. (a): Type 3a. Rheumatic mitral valve with severely restricted posterior mitral valve leaflet (PML). The anterior leaflet is mobile and overrides the PML in systole, leading to a very eccentric and severe posteriorly directed MR jet (b). Both leaflets are thickened at the tips. (c) Type 3b. Dilated LV cavity due to ischaemic heart disease results in systolic and diastolic tenting and restriction of the MV leaflets, resulting in functional severe MR (d)
Type IIIa: Systolic and diastolic restriction of leaflet motion (rheumatic heart disease);
Type IIIb: LV dilatation/ischaemia with systolic leaflet restriction (tenting of the leaflets).
2.
Chordae level pathology. It includes chordae rupture, elongation (redundant chordae) and abnormal insertion, resulting in MV incompetence. Two papillary muscles provide chordae that attach to both mitral valve leaflets and suspend the mitral valve, ensuring equal tension of the leaflets bodies during cardiac systole. Based on the level of leaflet attachment, the chordae are divided into the three following types:
Primary chordae attach to the free edge of mitral valve leaflet;
Secondary chordae attach to the ventricular surface of the valve;
Tertiary chordae are attached to the basal region of the leaflets (Fig. 1.8).
Figure 1.8
3D image of the mitral valve chordae: 1 0 primary chordae attached to the tip of the mitral valve leaflet, 2 0 secondary chordae to the ventricular surface of the valve, 3 0 tertiary chordae, attached to the basal region of the leaflet. PM posteromedial papillary muscle
3.
Papillary muscle morphological and functional pathology. Two papillary muscles (anterolateral and posteromedial) serve as anatomical and functional links between the mitral valve, the subvalvular apparatus and the LV walls. They help to maintain optimal systolic tension of subvalvular structures, allowing adequate closure of the leaflets and preventing them from prolapsing above the annular plane. In structural abnormalities like papillary musclerupture, elongation, scarring, abnormal position or insertion, well balanced forces of the subvalvular apparatus are distorted, resulting in incompetent MV (Fig. 1.9). Functional papillary muscle pathology (dysfunction due to loss of contractility) interferes with timely closure of the valve and causes increased tenting of the valve, preventing adequate leaflet apposition and coaptation.
Figure 1.9
On the left – normal arrangement of papillary muscles (two arrows). On the right – abnormal arrangement of papillary muscles: several heads of papillary muscles, located anteriorly (multiple arrows)
4.
Myocardial pathology and dysfunction. the LV is the last, but not least, important element accounting for normal MV function and competence. LV dilatation causes displacement of papillary muscles, annular dilatation and increased systolic and diastolic tension of the valve, thus, impeding normal valve closure. Regional wall motion abnormalities, areas of thinning and ventricular aneurysms result in asymmetric tenting patterns of the MV apparatus and functional (ischemic) MR (Fig. 1.10).
Figure 1.10
Inferior LV aneurysm with thrombus evident on 2D echocardiographic image (a) and 3D LV reconstruction (b)
Function
The severity of MR can be quantified by various echocardiographic techniques: colour flow jet area, vena contracta width, proximal isovelocity surface area (PISA) and detection of flow reversal in the pulmonary veins (Table 1.2). Assessment of regurgitant orifice area (ROA) by the PISA method is a recommended approach for MR estimation by TTE (Fig. 1.11). 3D echocardiography allows overcoming many limitations of conventional 2D echocardiographic assessment. 3D TOE provides direct planimetry of regurgitant orifices in an en face projection (Fig. 1.12). This also illustrates that often ROA is not circular, which is an erroneous assumption that the PISA method is based upon and there may be multiple regurgitant orifices and jets present (Fig. 1.13). 3D images allow detailed and comprehensive visual assessment of underlying structural and functional abnormalities of the mitral valve [5].
Figure 1.11
3D-guided 2D reconstruction of severe mitral regurgitation colour flow Doppler images (a–d). The cursors are placed at the tips of mitral valve leaflets and the neck (vena contracta) of the regurgitant MV jet. Off-line reconstruction allows appreciation of elliptical vena contracta and regurgitant orifice shape in functional mitral regurgitation. (e) Proximal isovelocity surface area (PISA) measurement on TOE color flow Doppler image. (f) Systolic flow reversal in the pulmonary veins is in keeping with severe mitral regurgitation
Figure 1.12
(a, b) 3D TOE imaging allows direct visualization of the regurgitant orifice (a) and regurgitant flow (b). Note the presence of two regurgitant orifices which would be otherwise difficult to appreciate on 2D imaging. (c, d) Degenerative mitral valve disease with diffuse severe MR arising along the leaflet coaptation line. 3D colour flow imaging allows better appreciation of dynamic functional MR nature: more MR is seen in early systole (c) compared to mid systole (d). (e, f) 3D MV imaging allows clarification of complex MR mechanism: a combination of factors is responsible for MR in the presented images (e LV side, f LA side). There is dominating degenerative MV disease with flail tip of A2 with ruptured small primary chord. There is also PMVL restriction secondary to left circumflex artery infarct and a cleft between P2/P3
Figure 1.13
3D guided MV reconstruction and visualization of multiple MR jets: (a) 2D view of two MR jets; (b) 3D ‘en face’ MV reconstruction depicting two circular coaptation defects; (c) planar ‘en face’ visualization of regurgitant MV jets, allowing assessment of regurgitant orifice area; (d) 3D MV flow image allowing visualization of regurgitant jets and their origins. A anterior, Ao aorta, AL anterolateral, PM posteromedial, P posterior
Table 1.2
Grading the severity of MR
Mild | Moderate | Severe | |
|---|---|---|---|
Jet area/LA (%) | <20 | 20–40 | >40 |
Vena contracta (mm) | <3 | 3–6 | ≥7 |
PISA radius (Nyquist 40 cm/s) (mm) | <4 | 4–9 | >10 |
Regurgitant volume (ml) | <30 | 31–59 | ≥60 |
Regurgitant fraction (%) | <30 | 31–49 | ≥50 |
Regurgitant orifice area (cm2) | <0.2 | 0.21–0.39 | ≥0.4 |
Preoperative 3D TOE allows the estimation of MV reparability and its use in the perioperative setting has contributed greatly to increase the success of MV repair. However, pre-bypass TOE is not a substitute for a comprehensive preoperative TTE/TOE assessment of MR severity or underlying lesion, especially in functional MR, when loading conditions may significantly alter the degree of visible and measurable MR.
Whether a valve is suitable for repair depends on the pathology and the expertise of the surgeon (Table 1.3). Isolated repair of type 1 lesions or repairs of PML prolapse have excellent results [6]. The results of AML prolapse are less satisfactory; however, contemporary surgical techniques have shown to improve the results. The complexity of the repair increases with the increasing number of prolapsing scallops, commissural involvement and superimposed leaflet or annular calcification. Rheumatic MV disease is usually advanced and complex at the time of referral for surgery. A combination of thickened, calcified and deformed leaflets with commissural fusion, as well as subvalvular involvement, is generally unsuitable for MV repair. Chronic ischaemic MR is a result of LV remodelling: ischaemic injury and myocardial scarring leads to LV dilatation, increased papillary muscle separation and tenting of the valve leaflets, with restricted systolic motion and consequential MR. Generally, ischaemic MR is considered to be repairable. A careful assessment of the mechanism of mitral regurgitation will allow the surgeon to better select the type and extent of ischaemic MR repair. Different 3D TOE appearances of the mitral valve are depicted in Fig. 1.14.
Table 1.3
Criteria for determining MV suitability for repair
Location | Posterior location of MV lesion points towards a ‘simple repair’. Anterior location of MV lesion indicates increasing complexity of surgical correction. |
Number of segments involved | Lesions confined to a single MV segment (scallop) are the easiest to repair. Each added abnormal segment increases the technical difficulty of repair procedure. |
Commissural lesion | Intact commissures reduce the complexity of repair, while their involvement points towards the necessity of complex surgical techniques. |
Height of PML | Increased height of PML is a risk factor for postoperative SAM. |
Figure 1.14
Row 1: Type 1 repairable MV lesions. (a, b) Large mobile echogenic mass with mobile serpingenous (?) elements attached to LA surface of P2 and posterior MV annulus visible on 3D MV views. (c) Row 2: Lesions, requiring more complex surgical approach to MV repair. (d) Degenerative mitral valve disease with P2 prolapse, extending to P1. (e) Extensive myxomatousmitral valve disease and dilated annulus. Thickening of the anterior leaflet affecting all 3 segments, but A2 and A3 are more markedly affected. Prolapse of A2 segment and flail A3/P3 segments and posteromedial commissure. Flail cords seen attached to A3 and P3. (f) Degenerative/myxomatous mitral valve disease with extensive posterior leaflet prolapse mainly affecting the middle and lateral (P2 and P1) scallops. Row 3: Difficult to repair MV lesions: (g) degenerative mitral valve disease with bileaflet prolapse and loss of coaptation; (h) Elongated AML with a vegetation at the tip. There is prolapse of A2 and a flail A1 segment with a ruptured chord; (i) flail P1, prolapse of P3, degenerative MV disease
The role of TOE is established in guiding MV repair. TOE is now essential for the surgeon to select the surgical repair strategy and technique. Approximately 1 in 10 MV repairs result in obstruction of the LV outflow tract (LVOT) due to systolic anterior motion (SAM) of the anterior mitral valve leaflet (AML) [7]. SAM can be predicted by a small LVOT diameter and increased posterior mitral valve leaflet (PML) length [8], coaptation point to interventricular septum distance less than 2.5 cm and the ratio of AML length to PML length of 1.3 cm or less [9]. 3D TOE provides dynamic measurements of the mitral annulus on a beating heart in systole and diastole while sizing the mitral annuloplasty ring. Larger ring sizes are suggested for cases of higher likelihood of postoperative SAM, while smaller rings are used in correcting ischaemic MR. Limited triangular or quadrangular resection is sufficient to resolve MR in isolated one scallop prolapse. However, in the presence of predictors of post-repair SAM, a sliding annuloplasty technique in addition to quadrangular resection of the PML to reduce its length is known to be advantageous. Determination of the morphology of complex prolapse (commissural, bileaflet) requires more complex surgical techniques, e. g. commissural plication, Alfieri technique (stitching together the tips of A2 and P2, and converting MV into a double orifice valve). Identification of chordal rupture or elongation directs to chordal transfer/shortening or replacement techniques.
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