Mitral Valve Diseases

2 Mitral Valve Diseases



A. Stephane Lambert



Introduction: The Role of Intraoperative Transesophageal Echocardiography In Mitral Valve Surgery




Key Points


The major roles of intraoperative transesophageal echocardiography (TEE) in mitral valve (MV) surgery are as follows:


• Confirm the preoperative diagnosis.

• Evaluate the progression of MV disease since the last preoperative investigation.

• Evaluate the valve in its dynamic state.

• Assist in planning surgical intervention.

• Evaluate associated cardiac dysfunction that may need attention (specifically tricuspid regurgitation).

• Rarely, detect unsuspected MV disease, which may require intervention.

• Evaluate repair in the operating room before chest closure, allowing further intervention if required.

When used in that fashion, intraoperative TEE has been shown to improve outcome.



Indications


The 2003 ACC/AHA/ASE (American College of Cardiology/American Heart Association/American Society of Echocardiography) Guideline Update for the Clinical Application of Echocardiography lists the various indications for TEE.1 Several of them apply specifically to the MV and they are listed in Table 2-1.


TABLE 2-1 INDICATIONS FOR MITRAL VALVE ASSESSMENT BY TRANSESOPHAGEAL ECHOCARDIOGRAPHY


















Class I
• Surgical repair of valvular lesions

• “Complex” valve replacement (e.g., homograft)

• Surgical repair of congenital lesions (including mitral valve lesions)

• Surgery for endocarditis

• Placement of intracardiac devices (which may affect mitral valve function)
Conditions for which there is evidence for and/or general agreement that a procedure be performed or a treatment is of benefit.
Class IIa
• Surgery in patients at high risk of myocardial ischemia/infarction or hemodynamic disturbances (often includes ischemic MR)

• Routine valve replacement

• Cardiac aneurysm repair (may affect mitral valve and/or papillary muscle geometry/function)

• Resection of cardiac tumors (LA myxomas can disrupt mitral valve function)
Conditions for which there is a divergence of evidence and/or opinion about the treatment.
Weight of evidence/opinion is in favor of usefulness or efficacy.
Class IIb
• Evaluation of suspected cardiac trauma

• Evaluation of regional myocardial function during off-pump coronary artery bypass (includes the diagnosis of acute ischemic mitral regurgitation)
Conditions for which there is a divergence of evidence and/or opinion about the treatment.
Usefulness/efficacy is less well established by evidence or opinion.

LA, left atrium; LA, left atrial; MR, mitral regurgitation.


From the 2003 ACC/AHA/ASE Guideline Update for the Clinical Application of Echocardiography.



Mitral Valve Anatomy (Figure 2-1)



• The mitral apparatus consists of
• Left atrial (LA) walls

• Mitral annulus

• Mitral leaflets

• Chordae tendinae

• Papillary muscles

• Left ventricular (LV) walls, which support the papillary muscles.

• Mitral annulus
• It is saddle shaped.

• It is a dynamic structure that changes its shape and diameter during the cardiac cycle.

• It plays a crucial role in proper MV coaptation.

• Dilatation of the annulus also leads to a loss of its saddle shape, which contributes to mitral dysfunction.

• Mitral leaflets (Figure 2-2)
• The anterior leaflet is larger and covers two thirds of the surface area of the MV.

• The posterior leaflet is smaller but it accounts for two thirds of the circumference of the MV.

• The two leaflets join at the anterolateral and posteromedial commissures.

• Coaptation between the two leaflets is curvilinear.

• The posterior leaflet has distinct scallops, separated anatomically by little indentations at the leaflet edges.

• The anterior leaflet does not have scallops, but is divided into segments for purposes of description.

• Chordae tendinae
• There are three types
• Primary: attach to the edges of the leaflets

• Secondary: attach to the body of the leaflets

• Tertiary: attach to the base of the posterior leaflet

• (Some authors describe quaternary chordae, which attach to the LV wall, not the valve, and they play a role in maintaining LV geometry.)

• Papillary muscles
• The LV has two: anterolateral and posteromedial, roughly aligned with the mitral commissures.

• Each papillary muscle supplies both leaflets with chordae tendinae.

• By contracting in systole, they play an important role in MV competence.

• Papillary muscle ischemia, infarct, or rupture may lead to acute mitral regurgitation (MR).

• The posterior papillary muscle is more prone to infarction/rupture owing to its single blood supply (right coronary artery [RCA]) in most patients.

• Chronic LV dysfunction leads to posterior and apical displacement of the papillary muscles, which also can lead to MR (see section on “Functional MR”)

image

Figure 2-1 MV anatomy.


Adapted from Otto CM. Evaluation and management of chronic mitral regurgitation. N Engl J Med. 2001;345:740-746. Reproduced with permission.


image

Figure 2-2 Cross section through the base of the heart shows the MV from the surgeon’s perspective in the LA. It demonstrates the relationship of the valve with other major cardiac structures. The MV segments are labeled according to the Carpentier nomenclature (see text for details). LAD, left anterior descending.


Modified from Otto CM. Textbook of Clinical Echocardiography. 4th ed. Philadelphia: Elsevier/Saunders; 2009:40. With permission.



Mitral Valve Nomenclature



• Three nomenclatures of the MV exist in the literature.

• It is important to know which nomenclature is used by the surgical team to avoid confusion
1 Classic anatomic
• The posterior leaflet scallops are identified as anterolateral, middle, and posteromedial according to their anatomic location.

• The anterior leaflet has no subdivisions.

2 Carpentier’s nomenclature (this is the most commonly used and was adopted by the ASE/Society of Cardiovascular Anesthesiologists)
• The three posterior leaflet scallops are named P1, P2, and P3, from anterolateral to posteromedial.

• The corresponding segments of the anterior leaflet are named A1, A2, and A3, respectively (note that the anterior leaflet does not have scallops and the various areas are referred to as segments).

3 Duran’s nomenclature
• Used in some centers.

• The three posterior leaflet scallops are named P1 (anterolaterally), P2 (posteromedially), and PM (middle). PM is further divided into PM1 (lateral half) and PM2 (medial half).

• The anterior leaflet is divided into two segments, A1 laterally and A2 medially.

• The commissural areas are named C1 (anterolateral) and C2 (posteromedial).

• All segments of the MV that attach to the anterolateral papillary muscle receive the number 1 and all segments that attach to the posteromedial papillary muscle receive the number 2


Systematic Examination of the Mitral Valve


Regardless of the type of MV disease, the TEE assessment always begins with a systematic two-dimensional (2D) examination of the valve. Using an organized sequence of cross sections, each scallop/segment of the MV is carefully examined for structure and function. The next section describes one sequence of views of the MV. It is important to remember that only the basic views are described here. With increasing experience, echocardiographers make great use of transition images, or images between standard views.



Sequence of Views (Table 2-2 and Figure 2-3)



• The examination begins in the mid-esophageal (ME) four-chamber view at 0 degrees. Identify the MV and zoom in on it by decreasing the depth of scanning.
• Slight anteflexion/withdrawal of the probe will reveal anterior aspects of the valve (A1-P1 and A2-P2).

• Slight retroflexion/insertion of the probe will reveal the posterior aspects of the valve (A2-A3 and P2-P3).

• Rotation of the transducer to about 60 degrees reveals the ME commissural view: P3-A2-P1 are seen from left to right.

• Further rotation of the transducer to about 90 degrees reveals the ME two-chamber view. In this view, the plane of the scan passes through the posteromedial commissure and provides a good view of P3. Slight rotation of the probe to the left demonstrates increasing amounts of the posterior leaflet, mostly the base of P2.

• Finally, rotation of the transducer to about 130 to 150 degrees reveals the ME long axis view: If lined up with the center of the valve, the plane of this view should cut through the middle of A2 and P2.

TABLE 2-2 The Systematic Mitral Valve Examination


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Figure 2-3 A-H, The systematic MV examination.



Key Points



• Pitfall: As a general rule, angles of rotation are reliable only if the scanning plane is in the center of the valve. In the long axis view, one can ensure that the scan passes through the center of the valve by turning the probe slightly from left to right. Only then can one be certain that one is looking at A2-P2.

• Intentionally “scanning” the valve from lateral to medial is an advanced technique that can be very useful to pinpoint the location of a lesion. This technique can be applied to the commissural view, two-chamber view, and long axis view.

• Returning to 0 degrees and advancing the probe into the stomach demonstrates the transgastric (TG) short axis view of the MV. In this projection, the anterior leaflet appears on the left of the screen and the posterior leaflet appears on the right (as if the observer were looking at the MV from the LV apex). This view is useful to diagnose mitral clefts. Color flow Doppler in this view also helps to localize the origin of the regurgitant jet.

• Finally, rotating the transducer to 90 degrees demonstrates the TG basal long axis view. This view is particularly useful to examine the subvalvular apparatus.


Three-Dimensional Echocardiography


Three-dimensional (3D) TEE provides exceptional images of the heart. Instead of a plane of information, the computer acquires a volume of data, which can then be reconstructed and viewed from any angle (Figure 2-4). Moreover, the data set can be sliced in any desired plane, much like a computed tomography (CT) scan, in order to re-create 2D images sometimes impossible to obtain by standard 2D echocardiography (Figure 2-5).


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Figure 2-4 Real-time 3D TEE image of an MV prolapse from the LA perspective. Note the prolapsed area of the posterior leaflet, involving P2 and P3 (arrows).


image

Figure 2-5 Multiplane reconstruction. This is a 3D data set of the heart, focusing on the MV. Once the data set is acquired, multiple planes can be displayed simultaneously and the scan lines can be adjusted to show any 2D cross section of the heart.


The MV, because of its proximity to the TEE transducer, lends itself particularly well to 3D imaging. At this time, 3D remains an adjunct to 2D, but as more centers gain experience with this technology, 3D imaging will become an integral part of intraoperative MV assessment.


The mechanism of MR is usually readily apparent on 3D imaging. Furthermore, off-line MV analysis software packages allow detailed quantification of MV disease, including dimensions, prolapses, and restriction (Figure 2-6). This is very useful in planning the surgical management of MR and may help to identify patients who require specialized surgical care. Moreover, the development of leaflet stress analysis packages opens the door to the possibility of predicting, in the immediate post-bypass stage, the durability of some MV repairs.


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Figure 2-6 3D MV analysis. Off-line analysis software allows detailed quantitative measurements of the MV, like annular dimensions, leaflet area and elevation, and tenting volumes.



Mitral Regurgitation


MR can be due to a structural problem in the valve itself or it may be due to distortion of the valve by external factors, described in Table 2-3.


TABLE 2-3 ETIOLOGY OF MITRAL REGURGITATION












Structural MR
• Congenital disease

• Fibroelastic disease

• Myxomatous degeneration

• Rheumatic disease

• Infectious disease
Functional MR
• Ischemic heart disease

• Non-ischemic dilated cardiomyopathy
MR due to LVOT obstruction
• In association with HOCM

• As a result of underfilled/hyperdynamic LV (rare without HOCM)

• Post-mitral valve repair (usually in the setting of underfilling/hyperdynamic states)

HOCM, hypertrophic obstructive cardiomyopathy; LV, left ventricle; LVOT, left ventricular outflow tract; MR, mitral regurgitation.



Classification of Mitral Regurgitation




Key Points



• The three categories of MR as enunciated by Carpentier are normal, excessive, and restricted leaflet motion.

• Pitfall: Some mechanisms of MR do not fall in any specific category. This is the case of MR resulting from systolic anterior motion (SAM) of the anterior leaflet. Other conditions may span more than one mechanism, as is true for many cases of ischemic MR: those patients usually have some degree of annular dilatation (type 1) and some tethering of the leaflets (type 3b).

• Note that the differentiation between severe prolapse and flail is often academic and depends on whether ruptured chordae tendinae can be visualized or not. The surgical treatment is often the same.

• Chronic MR of any type almost always leads to some degree of secondary annular dilatation. However, pure annular dilatation without any other pathology is relatively infrequent.

• Popularized by Carpentier

• Based on leaflet motion: normal, excessive or restricted (Figure 2-7).
• Type 1: normal leaflet motion. In type 1 lesions, the MR is usually due to pure annular dilatation or leaflet perforation.

• Type 2: excessive leaflet motion. In type 2 lesions, part or all of a mitral leaflet extends past the plane of the mitral annulus (into the left atrium [LA]) in systole. There are different degrees of severity of type 2 lesions:
• Billowing or scalloping: refers to a situation in which the body of the leaflet protrudes above the annular plane in systole but the point of coaptation remains below the annular plane. Often this is not associated with significant MR.

• Prolapse: refers to a state in which the tip of the leaflet extends above the annular plane during systole, leading to failure of coaptation and MR. This is usually the result of redundant leaflet tissue or elongated chordae tendinae.

• Flail: when the edge of the mitral leaflet flows freely into the LA during systole. This is usually the result of one or many ruptured chordae tendinae, which may be visible in the LA.

• Type 3: restricted leaflet motion. In type 3 lesions, part of one or both mitral leaflets is prevented from reaching the proper coaptation point, resulting in MR. Two subtypes exist:
• Type 3a: the restriction occurs in systole and diastole, meaning that the leaflet does not close properly and does not open fully. This is often the result of a structural leaflet problem, most commonly rheumatic valve disease. It may also be associated with some degree of mitral stenosis.

• Type 3b: the leaflet restriction occurs in systole only. The leaflet opening is not affected. Most commonly in type 3b lesions, the leaflets are structurally normal, but are tethered, hence the term “functional” MR. The mechanism is usually multifactorial and it is discussed in a later section of this chapter.

image

Figure 2-7 Carpentier’s classification of MR based on leaflet motion. A and B, In type 1, the leaflet motion is normal and the jet tends to be central. The cause of MR is usually annular dilatation (A) or leaflet perforation (B). C and D, In type 2, there is excessive leaflet motion and the jet is directed away from the diseased leaflet. E and F, In type 3 lesions, the leaflet motion is restricted. Type 3 lesions are further subdivided into 3A and 3B. The jet can be directed toward the affected leaflet or it can be central if both leaflets are equally affected.


Modified from Perrino and Reeves’ The Practice of Perioperative Transesophageal Echocardiography. Philadelphia: Lippincott Williams & Wilkins; 2003; Chapter 8, Fig. 8.7. With permission.



Evaluation of Mitral Regurgitation



Step 1: Determine the Mechanism and Localization of Lesions and Etiology


The TEE evaluation of MR requires a comprehensive structural examination of the MV, to determine the mechanism of MR and localization of lesions. This involves a detailed 2D examination described previously. In each cross section, the appearance and integrity of the leaflets is noted: Are the leaflets thickened or calcified? Are they redundant (too much tissue)? Are they intact? One also looks at leaflet motion: Is it normal, excessive, or restricted? The coaptation point is then examined; is it below, at, or above the annular plane? Is there lack of coaptation?


One then proceeds to color Doppler evaluation of the regurgitant jet(s) and spectral Doppler measurements. When available, 3D echocardiography is useful to supplement a comprehensive 2D examination, but in the vast majority of cases, it is not essential to making a diagnosis.



Key Points



• Pitfall: The echocardiographic appearance of MR is highly dependent on the loading conditions (preload and afterload), which can change during the course of an intraoperative examination. Moreover, general anesthesia is well known to decrease the apparent severity of MR by as much as one full grade (e.g., 4+ → 3+ or 3+ → 2+) owing to its effects on loading conditions.

• Pitfall: The appearance of MR by color Doppler is highly dependent on the gain and Nyquist limit of the transducer. Setting the gain too high or the Nyquist limit too low can make the MR appear more severe.

• Very eccentric jets are usually structural in nature. Functional MR with posterior leaflet tethering often results in a slightly eccentric, posteriorly directed jet. The rest of the overall mitral evaluation allows differentiation between the two. Jet direction is only one of a number of factors used in the evaluation of MR.

• It is very important to establish whether MR is structural or functional: In the context of coronary artery bypass surgery, MR due to a structural leaflet problem is highly unlikely to improve after revascularization alone. Such mitral lesions should be addressed separately.


Examination of the Mitral Annulus



• As stated previously, the mitral annulus is a saddle-shaped, dynamic structure, intimately involved in MV competence. The systematic 2D evaluation of the valve includes a careful look at the annulus. Its diameter should be measured in both major axes, bicommissural (∼60 degrees) and anteroposterior (ME long axis view at ∼150 degrees). The normal MV measures 28 to 32 mm in diameter.

• The anterior leaflet and the commissural areas are well supported by the fibrous trigones. Conversely, the posterolateral mitral annulus is relatively poorly supported. For that reason, the MV annulus tends to dilate predominantly in the anteroposterior axis, in a posterior direction.

Flow chart of MR severity (Figure 2-8).


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Figure 2-8 Flow chart of MR severity.



Severity of Mitral Regurgitation



• Except in cases of severe valve prolapse, no single view or sign is enough by itself to make a diagnosis of severe MR. However, taken as a group, the following signs have a high diagnostic accuracy.


Step 2: Qualitative Assessment



Color Flow Doppler


Color flow Doppler remains the best screening method to diagnose MR. It also allows a semiquantitative assessment of the severity of regurgitation and can provide clues to the mechanism of MR. Pitfall: The appearance of MR by color Doppler is highly dependent on the gain and Nyquist limit of the transducer. Setting the gain too high or the Nyquist limit too low can make the MR appear more severe.


• Total jet area:
• All else being equal, small jets tend to be mild and large jets tend to be more severe (see Pitfall, earlier).

• A surface area of the aliasing jet of 10 cm2 has been associated with severe MR.

• (As stated previously, the size of the MR jet is dependent on gain and Nyquist limit.)

• Jet area/LA area ratio
• When taken as a percentage of the LA area, the specificity of the jet surface area as an index of severity of MR increases.

• Jet surface area/LA surface area greater than 40% is associated with severe MR on cardiac catheterization.

• Eccentricity of the jet
• The term eccentric jet refers to a jet that has a greater than 45-degree angle of incidence from the mitral annular plane.

• Central jets can be structural or functional.

• Eccentric jets tend to be more structural than functional.

• Wall hugging jets
• The term wall hugging jet refers to an eccentric MR jet that hits the LA wall, then follows it for some distance thereafter (Figure 2-9)

• Wall hugging jets should be considered hemodynamically significant until proven otherwise and they always warrant careful examination:
• It takes a high energy jet to follow the LA wall for some distance.

• Owing to a physical phenomenon called the coanda effect, these jets appear smaller on color flow Doppler than they actually are.

• They are almost always due to a structural leaflet problem.

• Direction of the MR jet (see Figure 2-7)
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Figure 2-9 Central (left) vs. wall hugging (right) jet. Note how the latter hits the LA wall, then follows it all the way up to the top of the atrium.


The direction of the jet can provide useful clues about the mechanism of MR and the location of regurgitant lesions.


• In type 1 lesions (normal leaflet motion), the origin and the direction of the jet are usually central.

• In type 2 lesions

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  3. Aortic Valve and Aortic Root
  4. Congenital Heart Disease

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Jun 11, 2016 | Posted by in CARDIOLOGY | Comments Off on Mitral Valve Diseases

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