Congenital Mitral Valve Disease

Definition

Congenital mitral valve disease is a developmental malformation of one or more of the components of the mitral valve apparatus, including that portion of left atrial wall immediately adjacent to the mitral anulus that produces stenosis or regurgitation or, occasionally, a combined lesion. It often coexists with other cardiac anomalies, particularly those involving the left-sided cardiac chambers and aorta.

Left atrioventricular valve (AV) anomalies associated with AV septal defects (see Chapter 34 ), aortic atresia and other forms of hypoplastic left heart physiology (see Chapter 49 ), various forms of AV discordant connection (see Chapter 55 ), or transposition of the great arteries (see Chapter 52 ) are special situations discussed in the chapters describing these conditions. Mitral valve anomalies associated with straddling or univentricular AV connections are described in Chapter 35, Chapter 56 , respectively. Regurgitation from mitral valve prolapse as part of the syndrome of myxomatous degeneration is described in Chapter 11 .

Historical Note

Heterogeneity of congenital mitral valve disease and frequency of its association with other cardiac anomalies make it difficult to trace the historical evolution of knowledge about this entity. However, as early as 1902, Fisher described two cases of congenital disease of the left side of the heart, one of which was a stenotic supravalvar ring. Parachute mitral valve, another entity in this spectrum, was not described until 1961 and was not fully documented until 1963.

One of the first reports of surgical treatment of congenital mitral valve disease was that by Starkey in 1959. In 1962, Creech and colleagues reported repairing congenital mitral regurgitation resulting from a cleft in the posterior leaflet in a 2-year-old girl. Although the child's condition was improved by suturing the cleft, moderate mitral regurgitation persisted.

Morphology

The congenital anomaly may involve any component of the mitral apparatus and may result in stenosis with or without regurgitation or in pure regurgitation. Although only one component may be involved, more often the entire valve is affected.

Congenital mitral stenosis without or with regurgitation may result from supravalvar, anular, or valvar narrowing and may be accentuated by subvalvar obstruction produced by hypertrophied and misplaced papillary muscles or sheets of fused chordae. Frequently, stenosis is a result of abnormalities at multiple levels. Although embryologic origins of these complex anomalies are poorly understood, recent studies suggest that abnormal development of a transient left ventricular (LV) structure, a horseshoe-shaped ventricular myocardial ridge, results in various obstructive mitral valve lesions, including parachute mitral valve and formation of asymmetric mitral valves.

Congenital mitral regurgitation may result from anular dilatation secondary to anterior or posterior leaflet prolapse or to posterior leaflet hypoplasia with chordal shortening. Chordal elongation and valve prolapse may be so severe that chordal rupture can develop even in young children, producing severe regurgitation. Congenital mitral regurgitation may also be produced by clefts, gaps, or perforations in the anterior mitral leaflet, by accessory commissures, or by leaflet hypoplasia at medial or lateral commissures.

Supravalvar Ring

A tough fibrous ring may be situated just on the left atrial side of the mitral anulus. The pulmonary veins and left atrial appendage enter the left atrium above (proximal to) the ring, in contrast to the situation in cor triatriatum (see Chapter 32 ). The supravalvar ring may be nonobstructive and an incidental finding, or it may protrude into the orifice, producing a variable degree of obstruction. A ring may also occur on the left atrial aspect of the mitral valve leaflets that, when circumferential, prevents their adequate opening, causing obstruction. This lesion may be particularly difficult to identify echocardiographically.

A supravalvar ring is an isolated lesion in about half the cases in which it contributes importantly to death in the first year of life ( Fig. 50-1 ). In the other half, it coexists with other cardiac anomalies, particularly with other mitral valve anomalies and with LV outflow tract obstruction.

Figure 50-1, Supravalvar ring producing severe obstruction above mitral orifice in an infant dying of heart failure at age 9 months. Arrows indicate small (3 mm) orifice produced by stenosing ring. Key: AS, Fossa ovalis atrial septal defect; LA, left atrium.

Mitral Anulus

The mitral anulus uncommonly is small and obstructive in the absence of severe LV hypoplasia or other valvar abnormalities. It may be small but not obviously obstructive, particularly in hearts with coarctation of the aorta. The anulus may be enlarged, usually secondary to mitral regurgitation resulting from some other deformity of the valve. However, the basic valvar anomaly leading to regurgitation may be subtle and difficult to identify. Carpentier and colleagues found essentially isolated anular dilatation in 8 (17%) of 47 cases with congenital mitral valve disease, although some deficiency of commissural tissue is implied by their description.

Leaflet Anomalies

The orifice through the mitral valve is frequently narrowed by congenital absence of one or both commissures, which are replaced by a continuous sheet of leaflet tissue. Small perforations may be present at what is usually a commissure ( Fig. 50-2 ). The leaflets often then take the form of an inverted cone; in this circumstance, chordae are usually short and intermixed and the orifice further obstructed by abnormal and hypertrophied papillary muscles beneath it (the so-called hammock valve). In other cases, there may be congenital leaflet thickening and immobility and consequent orifice narrowing, even though commissures are present ( Fig. 50-3 ).

Figure 50-2, Transthoracic real-time three-dimensional echocardiogram: view from left ventricular aspect. Posterior mitral leaflet is immobile and anterior leaflet restricted. Both leaflets are thickened, and well-formed commissures are absent, resulting in a small, circular mitral valve orifice.

Figure 50-3, Specimen with severe congenital mitral stenosis from an infant dying at age 10 weeks with an associated ventricular septal defect. All components of valve are abnormal and contribute to stenosis. A, Viewed from left ventricle (LV) with mitral valve (MV) essentially intact. Leaflets are diffusely thickened without commissures, papillary muscles are bulky and almost reach the leaflets, and chordae are thick, fused, and short. B, Viewed from LV with mitral anulus divided. C, Viewed from left atrium. It is not possible to distinguish anterior from posterior leaflet except by their attachments to anulus. Key: A, Anterior mitral leaflet; ALP, anterolateral papillary muscle; AoV, aortic valve; LA, left atrium; LAA, left atrial appendage; LV, left ventricle; P, posterior mitral leaflet; PMP, posteromedial papillary muscle; S, muscular interventricular septum.

When congenital mitral regurgitation without important stenosis is the functional lesion, a variety of mitral leaflet anomalies may be responsible. The posterior leaflet may be severely hypoplastic and represented only by tags of fibrous tissue. In other cases, the anterior leaflet may be long and billowing and the chordae thin, elongated, and occasionally ruptured. This has been observed as a cause of severe mitral regurgitation in patients as young as age 2 years. It may represent prolapse or myxomatous degeneration of the mitral valve appearing in the very young (see “Mitral Valve Prolapse” under Morphology in Section I of Chapter 11 ).

Without any stigmata of an AV septal defect, the anterior leaflet or, less commonly, the posterior leaflet may be separated into two leaflets by an accessory commissure or a cleft, with resultant regurgitation through that area. The abnormality is considered an accessory commissure if there are chordae tendineae associated with it, and a cleft if there are none. Chordae tendineae may pass from the edges of an accessory commissure to ventricular septum or rudimentary papillary muscles (as was the case in two of five cases reported by Carpentier and colleagues ), or the cleft may simply represent leaflet deficiency in that area ( Fig. 50-4 ) without chordal support. Rarely, there may be a hole in the anterior leaflet.

Figure 50-4, Specimen from a 9-year-old boy who died with heart failure from severe mitral regurgitation. There is a large cleft, or gap, without chordae in anterior mitral leaflet.

Commissural leaflet tissue may be absent at one or the other commissure, resulting in an accessory orifice and mitral regurgitation.

Chordal Anomalies

Short chordae (often thick and fused) or complete chordal absence bring leaflet tissue down onto the papillary muscles and result in a narrow orifice ( Fig. 50-5 ). Complete absence of chordal development is common in congenital mitral stenosis. Accessory chordae that attach along the entire free edge of the anterior leaflet rather than leaving its central third free are a cause of restricted leaflet motion and, therefore, stenosis.

Figure 50-5, Steady-state free precession cardiac magnetic resonance image. Long-axis view demonstrating severe restriction of mitral valve leaflet opening. It confirms insertion of two papillary muscles into the leaflets via abnormally short chordae, along with markedly dilated left atrium.

Chordal abnormalities can also result in congenital mitral regurgitation. The most common is chordal elongation, sometimes with lengthened papillary muscles, the tips of which prolapse along with the leaflet into the left atrium during ventricular systole.

Papillary Muscle Anomalies

There may be a single large papillary muscle with all chordae attaching to it, the so-called parachute valve described first by Schiebler and colleagues and emphasized by Shone and colleagues ( Figs. 50-6 and 50-7 ). Usually the chordae are short and thick and limit leaflet movement. This restricts the primary orifice through the opened valve as well as secondary orifices between chordae, resulting in mitral stenosis. In other cases, there is a single large papillary muscle, and near it is a hypoplastic one with only a few chordae attached; the valve orifice is narrowed by the same mechanisms. A parachute valve usually produces only severe stenosis, but it may also produce mitral regurgitation.

Figure 50-6, Specimen of a heart with congenital mitral stenosis from parachute mitral valve, viewed from left ventricular aspect. Chordae are thickened, and all attach to a single posteromedial papillary muscle. Anterolateral papillary muscle is absent. Key: AoV, Aortic valve; LV, left ventricle; MV, mitral valve; PMP, posteromedial papillary muscle.

Figure 50-7, Mid-ventricular short-axis view from a magnetic resonance imaging cine sequence of a 4-year-old girl. There is only one papillary muscle, at the posteromedial position, supporting the mitral valve (arrow) . Anterolateral papillary muscle is absent.

Two hypertrophied and abnormally placed contiguous papillary muscles, usually situated posteriorly, are also a cause of subvalvar obstruction. Obstruction is often further aggravated by coexistence of short, thick chordae and anomalous thick muscular bands. In other cases, there are three or more closely placed and hypoplastic or bulky papillary muscles, a situation in which short, thick chordae are often also present and contribute to stenosis. In all these cases, absence of the normal wide interpapillary distance contributes to obstruction in the mitral pathway.

An anomalous papillary muscle arcade (mitral arcade) formed by a bridge of fibrous tissue running through the free aspect of the anterior mitral leaflet, between the anterolateral and posteromedial papillary muscles, may produce mitral regurgitation ( Fig. 50-8 ).

Figure 50-8, Specimen of a heart with mitral arcade producing mitral regurgitation. There is a thick fibrous band stretching between tips of the two papillary muscles along edge of anterior leaflet. Key: A, Anterior mitral leaflet; ALP, anterolateral papillary muscle; FW, left ventricular free wall; LAA, left atrial appendage; P, posterior mitral leaflet; PFO, patent foramen ovale; PMP, portion of posteromedial papillary muscle; S, muscular septum.

Coexisting Cardiac Anomalies

Patients with congenital mitral regurgitation often have coexisting cardiac anomalies, but they tend to be less severe than in congenital mitral stenosis ( Table 50-1 ).

Table 50-1

Coexisting Cardiac Anomalies in Patients Undergoing Operation for Mitral Regurgitation

Data from Chauvaud and colleagues.

Anomaly	No.	% of 51
Atrial septal defect	13	25
Ventricular septal defect	12	24
Coarctation of aorta	6	12
Patent ductus	5	10
Constrictive pericarditis	3	6
Subaortic stenosis	3	6
Tricuspid valve regurgitation	3	6
Aortic arch anomaly	1	2
Aortic valve regurgitation	1	2
Aortic valve stenosis	1	2
Coronary artery fistulas	1	2
Pulmonary artery stenosis	1	2
Transposition of the great arteries	1	2

Congenital mitral stenosis is rarely an isolated malformation. In about 30% of cases, it coexists with ventricular septal defect (VSD). In more than 50%, it coexists with one or another form of LV outflow obstruction, a situation termed Shone syndrome . This may consist only of coarctation or some hypoplasia of the distal aortic arch, with or without patent ductus arteriosus ( Table 50-2 ). LV outflow tract obstruction may be valvar, discrete subvalvar, or combined valvar and subvalvar aortic stenosis, with or without coarctation. Rarely, there is diffuse tunnel subvalvar stenosis, with or without the other forms of LV outflow tract obstruction. The aortic valve may be bicuspid. Frequency of association of LV outflow tract obstruction with congenital mitral valve disease is evidenced by Rosenquist's finding of 31 instances of coexisting important congenital mitral valve anomalies among autopsy specimens from 53 patients whose primary diagnosis in life was coarctation of the aorta. However, when a large surgical series of coarctation repair is considered that includes adults as well as infants and children, only 2% of patients demonstrate congenital mitral valve disease. All of this supports considering congenital mitral valve disease as an important component in the entity known as hypoplastic left heart physiology (see Chapter 49 ).

Table 50-2

Associated Cardiac Anomalies in Infants with Congenital Mitral Valve Stenosis ^a

Data from Moore and colleagues.

Anomaly	No.	% of 85
None	3	4
Subaortic, subvalvar stenosis	47	55
Coarctation	33	39
Ventricular septal defect	28	33
Patent ductus arteriosus	21	25
Atrial septal defect	21	25
DORV	15	18
Small left ventricle	15	18
Tetralogy of Fallot	5	6

Key: DORV, Double outlet right ventricle.

a Age 7.1 ± 6.4 months; weight 5.6 ± 2.3 kg.

Rare coexistence of a stenosing supravalvar ring with tetralogy of Fallot is noteworthy because, if undetected, it may cause death after tetralogy repair. Congenital mitral valve disease and subaortic stenosis may rarely coexist with subpulmonary stenosis and intact ventricular septum, subpulmonary stenosis and VSD, or valvar pulmonary stenosis.

Clinical Features and Diagnostic Criteria

Symptoms and Signs

Isolated Mitral Valve Disease

Symptoms and clinical signs are identical to those of acquired mitral valve disease, the congenital etiology being apparent only when presentation is in infancy or early childhood and there is no rheumatic history (see Clinical Features and Diagnostic Criteria in Section I of Chapter 11 ). Symptoms of pulmonary venous hypertension include dyspnea, orthopnea or paroxysmal nocturnal dyspnea, and recurrent pulmonary infection. Pulmonary hypertension is usually present in severe lesions, terminating in heart failure, often with peripheral and central cyanosis.

Mitral stenosis is associated with a prominent apical mid-diastolic murmur, sometimes with presystolic accentuation, and there may be an opening snap, although the morphologic features commonly resulting in limitation of leaflet movement make this less common than in acquired mitral stenosis. Mitral regurgitation is evidenced by an apical pansystolic murmur radiating to the axilla, frequently with a third heart sound or a short mid-diastolic murmur and LV overactivity. When there is pulmonary hypertension, the second heart sound is accentuated and there is a right ventricular lift.

Mitral Valve Disease and Left Ventricular Outflow Tract Obstruction

Unless a VSD or patent ductus arteriosus is also present, the mitral signs are usually clinically diagnostic, particularly when the only additional important site of obstruction is a coarctation. When there is severe congenital aortic stenosis, the mitral lesion, unless also severe, may not be clinically obvious, although it worsens the clinical presentation.

Electrocardiography

Electrocardiographic (ECG) evidence of left atrial hypertrophy of greater degree than is usually found in the coexisting cardiac anomaly suggests associated congenital mitral valve disease. Right ventricular hypertrophy is evident on the ECG when there is the usual raised pulmonary vascular resistance and right atrial enlargement, whereas LV hypertrophy is evident on the ECG when there is severe mitral regurgitation or associated LV outflow tract obstruction. Atrial fibrillation is rare.

Chest Radiography

Left atrial enlargement out of proportion to that usually present in any coexisting cardiac anomaly is the most important clue in the chest radiograph of the possible presence of congenital mitral valve disease. There is cardiac enlargement regardless of whether the disease is isolated or complex. Signs of pulmonary venous hypertension and occasionally overt pulmonary edema may be present in severe cases, but pulmonary plethora from a coexisting left-to-right shunt may obscure these signs.

Two-Dimensional Echocardiography

Two-dimensional echocardiography combined with Doppler interrogation can provide a complete analysis of the morphology and function of congenitally abnormal mitral valves ( Fig. 50-9, A-F ). However, diagnosis by echocardiography of some forms of congenital mitral valve disease, especially supravalvar ring and double orifice mitral valve, requires considerable care and can easily be missed. Three-dimensional echocardiography can provide important morphologic details that may not be visible with standard imaging (see Fig. 50-2 ).

Figure 50-9, Echocardiographic evaluation of congenital mitral valve disease. A, Four-chamber view showing mitral stenosis secondary to parachute mitral valve (MV) . A single papillary muscle (SPM) is present. Note eccentric opening of MV oriented toward SPM. Left atrium (LA) is markedly enlarged. B, Four-chamber color Doppler view in diastole showing flow disturbance and acceleration at mitral inlet, indicating important mitral stenosis. C, Four-chamber view with color Doppler in systole, showing mitral regurgitation in setting of congenital mitral stenosis. D, Four-chamber echocardiographic image showing supramitral ring (SMR) in congenital mitral stenosis. Ring is echo dense and present circumferentially just downstream from MV anulus. Note enlarged LA. E, Short-axis view of left ventricle at level of MV orifice, showing cleft in mitral anterior leaflet. F, Echocardiographic image with color flow Doppler revealing regurgitant jet through mitral valve cleft (MVC) . Key: LV, Left ventricle.

Cardiac Catheterization and Cineangiographic Studies

Cardiac catheterization and cineangiographic studies are often performed to evaluate possible associated lesions and define the degree of pulmonary vascular disease. Morphology of the congenitally abnormal valve can be further evaluated by its cineangiographic appearance.

Computed Tomography and Magnetic Resonance Imaging

Computed tomography (CT) plays a limited role in evaluating the congenitally abnormal mitral valve, but magnetic resonance imaging (MRI) can provide important morphologic information that may supplement that provided by echocardiography (see Figs. 50-5 and 50-7 ). In addition, MRI can provide functional information such as quantification of mitral regurgitant fraction and valve area in diastole ( Fig. 50-10 ).

$Figure 50-10, Short-axis view at level of mitral valve orifice during diastole: high-velocity mitral inflow is seen as white. During systole, regurgitant jet can be visualized and analyzed, and a regurgitant fraction can be calculated as a percentage of inflow. Mitral orifice area in diastole can be calculated by planimetry and is expressed in square centimeters. Two papillary muscles are demonstrated.$

Natural History

Congenital mitral valve disease is a rare congenital cardiac anomaly, occurring in 0.6% of autopsied patients with congenital heart disease and 0.21% to 0.42% of clinical cases of congenital heart disease.

Natural history is highly variable and depends most importantly on severity of resultant stenosis or regurgitation and on type and severity of coexisting lesions, rather than on the particular morphologic mitral valve lesion itself. For example, in one study, parachute mitral valve was associated with 95% freedom from mitral valve surgery at 6 months and 80% freedom at 10 years. However, associated cardiac defects were present in essentially all cases, particularly LV outflow tract abnormalities, atrial septal defect, VSD, coarctation, and hypoplastic LV; these strongly influence natural history. In another study, only 4% of patients with parachute mitral valve required a procedure on the valve, with intervention dominated by associated cardiac anomalies. Parachute mitral valve presenting in the adult is rare but does occur and is more likely to be an isolated anomaly than when diagnosed in infants and children. Nine patients have been identified in the literature over the past 50 years; three were asymptomatic without important hemodynamic abnormalities, three presented with stenosis, and three with regurgitation.

Isolated congenital mitral stenosis usually is severe and often produces symptoms and death if untreated during the first 4 to 5 years of life. When congenital mitral stenosis coexists with other important cardiac anomalies, symptoms occur even earlier. When it is associated with other components of hypoplastic left heart physiology, severe symptoms often develop during the first year of life.

Isolated congenital mitral regurgitation is often only moderate in severity in early life, and about half the patients with it do not show development of important symptoms. Symptoms and need for intervention usually come earlier when it coexists with other important cardiac anomalies.

Technique of Operation

The overall approach to the neonate, infant, and young child is different from that for older patients. Preservation of the native valve is of paramount importance, even if it means accepting residual valve disease that might otherwise not be considered acceptable in a fully grown patient. The valve must be carefully studied preoperatively and at operation, seeking ways in which it can be repaired rather than replaced. Specific techniques such as rectangular resection, which if unsuccessful will result in obligatory valve replacement as a fallback option, should generally be avoided. Some techniques used for congenital mitral valve disease are the same as those used for older patients with acquired disease, and these are described for both mitral stenosis and regurgitation under Technique of Operation in Section I of Chapter 11 . However, many techniques are specific for congenital abnormalities such as supramitral ring ( Fig. 50-11 ), mitral arcade ( Fig. 50-12 ), and single papillary muscle ( Fig. 50-13 ). In general, repair is possible in 50% to 80% of patients. Additional comments specific to congenital mitral valve disease follow.

Figure 50-11, Repair of supramitral ring. A, Long-axis depiction of left heart showing left atrium, left ventricle, and mitral and aortic valves. A supramitral ring (SMR) is present on mitral valve. B, Close-up cutaway view of mitral valve and anulus showing SMR. Ring can be cut away circumferentially using sharp dissection as shown here, but in some cases, it can be peeled away bluntly once the plane between underlying endocardium and ring tissue is established. Ring may be discrete (as shown here) but may also extend to a variable degree onto mitral leaflets, sometimes extending across length of leaflet onto chordal structures, causing thickening, contraction, and immobility. In this case, using both sharp and blunt dissection, as much of the abnormal tissue as possible is removed from leaflet without damaging underlying leaflet tissue.

Figure 50-12, Repair of mitral arcade. A, En face view of mitral valve with arcade formation of subvalvar mechanism. Note fused, or hammock-like, nature of papillary muscles, and crowded thickened chordal arrangement. B-E, Repair involves splitting the lateral attachments between chords, and the papillary muscle between chordal groups.

Figure 50-13, Repair of parachute mitral valve. A, Note single papillary muscle with all chordal structures attaching to it. B, Repair involves splitting the papillary muscle between the two large chordal groups supporting each commissure. Commissural fusion and lateral attachments of chords may also be present, requiring commissurotomy and splitting of lateral chordal attachments.

Repair of Congenital Mitral Stenosis

When the valve leaflets are fused into one and are stenotic, leaflet incisions may be made in the areas in which commissures would be expected to have developed. Consideration is given to inserting polyester or polytetrafluoroethylene (PTFE) chordae (see “ Repair of Chordae ” later in this chapter). At times, fused papillary muscles or chordae may be split or partly excised in an attempt to enlarge the orifice (see Fig. 11-7 in Chapter 11 ).

Because these maneuvers may result in regurgitation, immediately after discontinuing cardiopulmonary bypass (CPB), a regurgitant mitral jet may first be detected by palpating the posterior left atrial wall and then the superior left atrial wall beneath the aorta. Intraoperative transesophageal echocardiography (TEE) is invaluable at this stage in determining that mitral valve function is sufficiently good to avoid valve replacement. If TEE documents important regurgitation accompanied by high left atrial pressure and a suboptimal hemodynamic state, CPB is reestablished and the valve repaired further or replaced; otherwise, early and late results are unsatisfactory. If hemodynamics are acceptable but regurgitation is moderate to severe, the decision to replace the valve is complex. Importantly, the smaller the patient and mitral anulus, the more likely will be the tendency to accept the result, recognizing that this will be a temporary solution.

Repair of Congenital Mitral Regurgitation

The mitral valve is carefully examined with the possible pathologic bases for congenital mitral regurgitation clearly in mind, because these determine the most appropriate type of operation. Repair based on pathology is performed whenever possible. Specific maneuvers include anuloplasty, repair of cleft leaflet, various forms of chordal repair including shortening, lengthening, and resuspension of ruptured chords, partial leaflet resection, chordal replacement, and partial commissural closure (see Technique of Operation in Section I of Chapter 11 ).

Anuloplasty

Occasionally, anular dilatation is the dominant pathology even in young children, but it is usually associated with some abnormal thickening and prolapse of a billowing anterior leaflet. If a reasonable anterior leaflet without ruptured chordae is present, anuloplasty is indicated. Anuloplasty is also appropriate when there is marked hypoplasia or near absence of the posterior leaflet, which probably initially was responsible for the regurgitation and subsequent anular dilatation. Following anuloplasty, the mitral valve is essentially converted to a monoleaflet valve.

Although use of an anuloplasty ring is optimal in adults, it is not used in infants and children because it precludes growth of the anulus. Thus, a technique such as the Reed asymmetric measured anuloplasty is chosen (see Fig. 11-15 in Chapter 11 ).

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