Mitral Valve Repair

Maurice Hogan and Jörg Ender

INDICATIONS

Mitral valve (MV) regurgitation is the most prevalent isolated heart valve disease (1), and valve repair or replacement remains the only effective treatment for chronic severe disease (2,3).

MV regurgitation results from either structural or functional disorder (2,3). Structural (or primary) MV regurgitation is most commonly caused by degenerative MV disease and implies pathology of the architecture of the MV apparatus, that is, the valve leaflets, chordae tendineae, or papillary muscles. Functional (or secondary) MV regurgitation implies that the mitral apparatus itself is structurally normal, and regurgitation is then typically caused by ischemic or dilated cardiomyopathy. In these cases of functional mitral disease, regurgitation results from displacement of the papillary muscles consequent to left ventricular (LV) dilatation often in combination with mitral annular dilatation. The displacement of the papillary muscles causes tethering of the valve leaflets and restricts their motion, thereby preventing coaptation (4).

MV repair improves long-term survival if patients are operated on early and in centers which have both low operative mortality (<1%) and high rates of repair (80% to 90%), as opposed to valve replacement (5,6). Patients who undergo MV repair rather than valve replacement clearly demonstrate lower operative mortality, better recovery of left ventricular ejection fraction (LVEF), and better long-term survival (7,8). This improvement in outcome for patients treated with repair versus replacement is intuitive considering that they have lower rates of endocarditis, fewer thromboembolic events, and do not require long-term anticoagulation (unless otherwise indicated).

Chronic severe mitral regurgitation (MR) ultimately leads to LV dilatation. To maintain forward stroke volume in the face of significant regurgitant fraction, the LV chamber necessarily becomes more compliant and develops eccentric cardiac hypertrophy. Pulmonary congestion then decreases also, as the now dilated left atrium and ventricle can accommodate the regurgitant volume at lower filling pressure. These early responses are therefore adaptive and during this phase the patient may remain asymptomatic. Over time, however, the progressive LV enlargement and increasing LV end-diastolic pressures lead to a reduction in LVEF. With progressive left atrial dilatation, the onset of atrial fibrillation and/or pulmonary hypertension can develop, and their occurrence in patients with chronic severe MR constitutes an indication for surgery, even in patients with preserved LVEF and LV end-systolic diameter less than 40 mm (2,3).

The recommendations for the timing of surgery in patients with chronic severe MR rely on patient symptoms and also on echocardiographic evaluation of LV function and size (Fig. 10.1) (2,3). It is noteworthy that patients with chronic severe MR, who are symptom free, have normal LV dimensions and function, and do not have atrial fibrillation or pulmonary hypertension, are only recommended to undergo valve surgery if it is likely that the valve can be repaired rather than replaced. The current recommendations also suggest medical therapy for symptomatic patients who have depressed LV function and/or LV dilatation, in whom chordal preservation is unlikely with conventional surgery; the option of percutaneous repair is not yet considered in these guidelines. Although the percutaneous mitral clip procedure is less effective in reducing MR than conventional repair surgery, it is associated with fewer major adverse events than conventional repair and does improve patients’ clinical condition (9). Long-term results are not yet available for the percutaneous mitral clip procedure but it may prove to be a valid alternative to medical therapy for this cohort.

ECHOCARDIOGRAPHIC EVALUATION

Intraoperative transesophageal echocardiography (TEE) is a class I indication for patients undergoing MV repair (10), meaning that its use improves patient outcome. The role of intraoperative echocardiography can be considered as two components: Pre- and postrepair.

THE PREREPAIR EVALUATION

The prerepair examination should evaluate the following:

1. Structure of the MV apparatus

2. Function of the MV leaflets according to the Carpentier classification

3. Severity of the MV regurgitation

4. Circumflex artery and its relationship to the MV annulus

5. Cardiac structures for secondary or coexisting abnormalities

This information is then summarized and the likelihood of successful repair discussed with the surgical team so to be of use in planning the surgical procedure.

1. Evaluation of the Structure of the Mitral Valve Apparatus

The MV apparatus consists of the MV annulus, the MV leaflets (anterior and posterior), chordae tendineae, papillary muscles, and left ventricle. The nomenclature proposed by Carpentier to describe the segments of the mitral leaflets (11) is the most commonly used and is widely accepted as standard (Fig. 10.2). The anatomy of the mitral apparatus is detailed in Chapter 8, Mitral Regurgitation. To visualize all the structures of the MV apparatus and to elucidate fully the mechanism of MR and any associated pathology, several views are necessary (12).

Midesophageal (ME) four-chamber view: Normally shows the A2 and P2 segments of the MV (Fig. 10.3). From there, slight withdrawal of the probe will show the A1 and P1 segments, whereas slight advancement of the probe will show the A3 and P3 segments (Fig. 10.4). LV systolic function can also be assessed in this view by measuring LVEF. Interpretation of LVEF must take account of the patient’s loading conditions, and patients with MR who have normal LV function demonstrate LVEF greater than or equal to 60% (3). Patients with reduced LVEF preoperatively also have reduced postoperative LVEF, higher perioperative mortality, and poorer long-term survival (13,14).

ME mitral commissural view: From the ME four-chamber view, the MV should also be scanned by forward rotation to show the P3, A2, and P1 segments (Fig. 10.5). Continued forward rotation produces the ME two-chamber view with P3, A3, A2, and A1 segments (Fig. 10.6) and ME LAX views with the P2 and A2 segments (Fig. 10.7).

From the ME position, the probe is advanced into the stomach to obtain the transgastric (TG) views.

TG mid-SAX view: Regional wall motion abnormalities as well as global LV function can be assessed by measuring fractional shortening or fractional area change. This view serves as the reference view for possible new regional wall motion abnormalities which may arise due to complications of the MV repair in the postrepair examination (see postrepair examination).

TG two-chamber view: The ultrasound beam travels perpendicular to both the papillary muscles and chordae so that these two structures are often very clearly visualized (Fig. 10.8). LV diameters are measured in this view (15).

TG basal SAX view: Shows all segments of the MV leaflets together with both commissures (Fig. 10.9). This view allows for planimetric measurement of the MV orifice area. An existing cleft pathology in one of the leaflets can often be diagnosed in this view during diastole (Video 10.1, cleft anterior mitral leaflet). The use of color flow Doppler (CFD) helps to confirm the diagnosis (Video 10.2, CFD cleft anterior mitral leaflet), and with real-time (RT) 3D TEE the cleft can often be better elucidated (Video 10.3, cleft posterior mitral leaflet).

Three-dimensional assessment of the MV: The additional value of RT 3D TEE for the evaluation of MV pathology is still a matter of debate (16,17). There is a high level of consistency between RT 3D TEE assessment of MV pathology and the findings of macroscopic surgical inspection (18). The most important potential advantages of RT 3D TEE are that it is capable of providing several unique views and images which are intuitively more understandable. RT 3D TEE is probably the method of choice when available as it can complement the standard 2D examination (19).

The guidelines for image acquisition and display using 3D echocardiography (20) recommend that the MV be displayed with the aortic valve placed superiorly, regardless if the MV is oriented as viewed from the left atrium or left ventricle. This brings the advantage that the anterior leaflet is readily identifiable inferior to the aortic valve; the posterior leaflet must then be further inferior in this view. Viewed from the atrial side, then the valve segments are named 1, 2, and 3, from left to right (Fig. 10.10). The view from the left atrium is the most intuitively understandable and helpful 3D view of the MV (also referred to as the “en face” or “surgical” view). This view is often particularly helpful in translating the TEE findings to the surgeon, as in this single view all segments of the MV can be seen and pathology can often be clearly localized, especially in cases of excessive leaflet motion (Fig. 10.11, Video 10. 4). Cleft defects, indentations, or leaflet perforations are often distinctly better viewed in this view compared to standard 2D images.

In examining the structure of the mitral apparatus it is important to identify and quantify the presence and severity of calcification of the mitral apparatus, especially on the annulus and leaflets. Calcification has a characteristic echodense appearance on echo and is not difficult to identify (Fig. 10.12). Because of shadowing artifacts, however, it may impede visualization of other structures.

Quantitative measurements: In the preoperative structural assessment of the mitral apparatus, a number of echocardiographic measurements should be made, as these are important firstly in assessing whether the valve is amenable to repair and secondly in helping to determine the correct repair technique.

Size of Mitral Annulus

The normal mitral annulus is not round, rather it is described as saddle-shaped, and the ratio between the transverse and anteroposterior diameters is approximately 4:3. When the annulus dilates, however, it expands predominantly in the anteroposterior direction, thus reducing the normal 4:3 ratio, as its fibroelastic skeleton is weakest around the posterior annulus. To assess for mitral annular dilatation the annulus is therefore measured in its anteroposterior diameter between the base of the A2 and P2 segments at the level of the mitral annulus. This is done in diastole using the ME LAX view (21), (Fig. 10.13).

Length of Anterior Mitral Leaflet

This is a particularly important measurement to make in the setting of mitral repair and is used to determine the size of the annuloplasty ring to be implanted. The length is best measured during diastole using the ME LAX view with the measurement made from the base of the anterior leaflet (at the annulus) to its leaflet tip (21), (Fig. 10.13). Because of the semicircular shape of the anterior leaflet, the measurement along the A2 segment in this image plane will be the longest. Care should be taken not to include the primary chordae in the measurement, which attach to the tip of the leaflet.

Length of Posterior Mitral Leaflet

This can be measured using the same ME LAX image used for the annulus and anterior leaflet (21), (Fig. 10.13). Measurement is made from the base of the leaflet at the annulus to the tip of the posterior leaflet. The main significance of this measurement is in predicting the likelihood of systolic anterior motion (SAM) of the anterior leaflet occurring postoperatively, as discussed later.

C-sept Distance

The distance from the coaptation point of the mitral leaflets to the septum is also useful in the risk assessment for SAM postrepair. This measurement should be made again in the ME LAX view, this time in systole, so that the leaflets have coapted. The shortest direct distance from the coaptation point to the septum is measured (Fig. 10.14).

Left Ventricular End-systolic Internal Diameter

This is best measured using the TG two-chamber view, with systole timed according to MV closure. The long axis of the LV should be horizontal in the image and measurement is made at the level of the chordae from endocardial edge to endocardial edge (Fig. 10.15). For improved accuracy an average measurement from a number of cardiac cycles should be obtained, especially in the case of arrhythmia. A measurement greater than 40 mm defines LV dilatation. The ME two-chamber view can also be used (15).

Left Ventricular End-diastolic Internal Diameter:

Left ventricular end-diastolic internal diameter can also be measured using either the TG or ME two-chamber view, this time at end-diastole. Measurements are made at the level of the chordae, and greater than 55 mm represents LV dilatation (15).

Tenting Height

Also referred to as coaptation depth, this is a very important measurement to make, as a preoperative tenting height of 11 mm or higher is associated with poor repair results, and so is usually taken as an indication for MV replacement rather than repair (22,23). This usually occurs in the setting of Carpentier type IIIb pathology, where the left ventricle is dilated and the consequent restriction of the MV leaflets in systole means that they coapt below the level of the mitral annulus. The measurement should be made in the ME LAX or ME four-chamber views in systole. Using the zoom function over the MV or reducing the image depth reduces the percentage error of the measurement. To make this measurement, the level of the mitral annulus is first identified by marking the annular plane. The tenting height is the perpendicular distance from this line marking the annulus level to the coaptation point (Fig. 10.16).

Tenting Area

Similar to tenting height this is measured using the ME LAX view in systole. Tenting area is that area which is enclosed by the line drawn between anterior and posterior annulus and the valve leaflets (Fig. 10.17). An area of >2.5 cm² is unfavorable for MV repair in functional MR (19).

Coaptation Length

This represents the extent to which both leaflets come to oppose each other during systole. It is measured at end systole in ME LAX views (Fig. 10.18). It is perhaps more important to measure postrepair, as it is one of the fundamental goals of repair, and good coaptation length is associated with better repair durability and long-term results. Usually the coaptation length is longer following implantation of artificial chords as compared to leaflet resection (24).

2. Carpentier Classification System

Functional classification of the leaflets has implications in determining the likelihood of valve repair as will be discussed later. The functional classification of the MV is based on leaflet motion. In type I dysfunction the motion of the leaflets is normal, in type II it is excessive, and in type III it is restrictive (Fig. 10.19). Type III is further subclassified as type IIIa (structural) with restricted motion during both systole and diastole due to leaflet damage (calcification or rheumatic disease) and type IIIb (functional) where the restriction is limited to systole and is due to tethering of the leaflets (ischemic or dilated cardiomyopathy).

Application of CFD is helpful in determining the functional classification. In type I the regurgitant jet is usually central. In type II with one leaflet involved the regurgitant jet is eccentric and directed over the noninvolved leaflet (Fig. 10.20, Videos 10.5–10.11). However, if both leaflets are involved the regurgitant jet can be central. In type III dysfunction, usually, the regurgitant jet is central because most often both leaflets are affected (Videos 10.12–10.16). With only one leaflet involved the regurgitant jet is eccentric and directed over the affected leaflet (Fig. 10.21). In addition, in type II dysfunction, one has to discriminate between billowing, prolapse, and flail (19,21).

1. Billowing is defined as motion of the body of the leaflets above the mitral annulus plane (Fig. 10.22). To some degree it is a normal finding. It is abnormal when >2 mm in ME LAX view or >5 mm in ME four-chamber view. It is generally associated with excessive tissue, chordal elongation, and possibly later occurrence of leaflet prolapse (Videos 10.17, 10.18).

2. Prolapse describes displacement of one or both leaflet edges above the plane of the mitral annulus where the free margin is directed to the LV (Fig. 10.23). It is often associated with chordal elongation but can also be associated with chordal rupture (Videos 10.5–10.11). The regurgitant jet seen with CFD is always directed over the noninvolved segments in patients with type II dysfunction (Fig. 10.20, Videos 10.6, 10.7, 10.9).

3. Flail is defined as displacement of the free edge of one or both leaflets above the mitral annular plane, where the free edge of the leaflet is also directed into the left atrium (Fig. 10.24, Videos 10.19–10.21). It is often associated with chordal rupture but can also be associated with extreme elongation of the chords.

3. Assessment of the Severity of the Mitral Valve Regurgitation

The severity of the MV regurgitation is practically best assessed using the vena contracta width, the flow convergence (or PISA) method, and the pattern of pulmonary venous flow, as described in Chapter 8, Mitral Regurgitation.

4. Visualization of the Circumflex Coronary Artery and its Relationship to the Mitral Valve Annulus

Damage or distortion of the circumflex coronary artery caused by the annuloplasty ring or prosthetic valve sutures is a well recognized and potentially devastating complication which occurs in up to 1.8% of patients undergoing MV surgery (25–27). Visualization of the circumflex coronary artery by TEE can be accomplished in most patients by starting from the ME LAX view of the aortic valve and gradually turning the probe to the left (28). From the origin of the left main coronary artery, one can follow the course to the bifurcation into the left anterior descending artery and the circumflex coronary artery by turning the probe to the patient’s left. Further turning of the probe will visualize the course of the circumflex along the mitral annulus (Fig. 10.25, Video 10.22). The circumflex coronary artery must be distinguished from the coronary sinus, a venous structure that runs in a parallel direction to it, and noting that the circumflex coronary artery decreases in diameter along its course from its point of origin, while the coronary sinus increases in diameter, will help to differentiate the two (29). The distance of the circumflex coronary artery from the mitral annulus can also be measured and this information may directly help the surgeon. The preoperative visualization of the circumflex coronary artery acts as a reference for the postrepair visualization.

5. Define Secondary and Coexisting Abnormalities of Other Cardiac Structures

It is recommended that a comprehensive TEE examination be performed both pre- and post bypass in patients undergoing MV repair. In addition to defining the pathology and severity of the MV regurgitation, it is important to examine for echocardiographic evidence of secondary features of MR and also to identify any other coexisting cardiac pathology.

Assessment of LV global and regional systolic function and chamber size has been discussed already and is important to quantify prebypass as a reference for the postoperative examination. Attention should also be paid to the aorta, specifically looking for the presence of atherosclerotic plaque which, if present, increases the risk of postoperative cerebrovascular events. Ascending aortic plaque or calcification increases the risk of complications arising from aortic cannulation and cross-clamping, and if present, these may warrant alteration of surgical technique (30). Plaque in the descending aorta becomes more relevant if a retrograde perfusion technique is used, as in some minimally invasive techniques.

Related posts:

A Practical Approach to the Echocardiographic Evaluation of Ventricular Diastolic Function Diagnosis of Myocardial Ischemia Echocardiography for Percutaneous Aortic Valve and Mitral Clip Implantation Mitral Valve Stenosis Transesophageal Echocardiography for Coronary Revascularization Prosthetic Valves

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