Mitral valvular malformations are rare, diverse, and complex. They are often associated with other cardiac or great vessel anomalies that may hide or be hidden by the valvular malformation. They may also be encountered as a persisting anomaly when other, more dominant malformations have been corrected. “Formes frustes” *
* See Glossary .
are frequent and usually not diagnosed during childhood; instead, they are discovered after a long-lasting progression, perplexing the surgeon unfamiliar with these malformations. Proper identification and distinction from other more common etiologies, such as rheumatic valvular disease, then become difficult. In all these circumstances, exemplary knowledge of the anatomy and clinical presentation of these malformations is mandatory for the clinician to recognize them and for the surgeon to perform an efficient reconstructive valve operation.This chapter is based on personal experience with several hundreds children requiring surgery for congenital mitral valve malformations. It describes the various malformations and their clinical picture but does not include the valvular malformations resulting from more dominant cardiac anomalies such as hypoplastic ventricle, single ventricle, and atrioventricular defects.
CLINICAL PRESENTATION
The spectrum of clinical presentations resulting from congenital mitral valve stenosis or regurgitation ranges from lethal manifestations early in infancy to minimal disability in adulthood. In our original series of 155 children **
** This large series benefited from cooperation with Gerard Brom in Leiden, The Netherlands, and Lucio Parenzan in Bergamo, Italy.
with congenital mitral valve malformations, one third (n = 50) displayed stenosis and two thirds (n = 105) regurgitation.Mitral Valve Stenosis
Congenital mitral valve stenosis belongs to the category of anomalies that causes pulmonary venous hypertension. For this reason, the malformation is generally diagnosed and treated early in childhood, within the first 3 to 4 years of life. Clinical manifestations are cardiac failure, dyspnea on exertion, and tachypnea. The diagnosis of mitral valve stenosis is suggested by a diastolic murmur associated with right ventricular and left atrial hypertrophy. The diagnosis may be difficult in the presence of a systolic murmur, which may or may not be related to associated lesions. Atrial fibrillation is extremely rare in children even after a long disease progression. Echocardiography is essential to establish the diagnosis and the type of mitral valve stenosis. Cardiac catheterization is usually performed to assess ventricular functional volumes and to determine associated anomalies. The optimal age for operation depends on physical disability, growth retardation, and severity of pulmonary hypertension. The expected difficulty of the operation, attributable to the fragility of the leaflet tissue and the small size of the mitral valve annulus in children, makes it preferable to delay the surgery as long as possible. However, surgery may be necessary within the first months or years of life because of threatening symptoms of heart failure.
Mitral Valve Regurgitation
Congenital mitral valve regurgitation may result in repeated pulmonary infections, cardiac failure, and growth retardation. With adequate medical therapy, mitral valve regurgitation is slightly better tolerated than mitral valve stenosis, and children usually undergo surgery at a later age, approximately 6 years. The surgery should be performed as late as possible to allow the implantation of an annuloplasty ring near normal size ( Table 23-1 ). In practice, repeated episodes of cardiac failure, progressive enlargement of the left ventricular diameter, and severe pulmonary hypertension should indicate an earlier operation.
| Body Surface Area (Square Meters) | Annular Diameter (Millimeters) |
|---|---|
| 0.25 | 11.2 |
| 0.30 | 12.6 |
| 0.35 | 13.6 |
| 0.40 | 14.4 |
| 0.45 | 15.2 |
| 0.50 | 15.8 |
| 0.60 | 16.9 |
| 0.70 | 17.9 |
| 0.80 | 18.8 |
| 0.90 | 19.7 |
| 1.00 | 20.2 |
| 1.20 | 21.4 |
| 1.40 | 22.3 |
| 1.60 | 23.1 |
| 1.80 | 23.8 |
| 2.00 | 24.2 |
PATHOPHYSIOLOGY: CARPENTIER’S FUNCTIONAL CLASSIFICATION
The diagnosis of the type of malformation is difficult because of the numerous existing forms. Similar to acquired mitral valve disease, echocardiography and magnetic resonance imaging allow classification of the malformations into four functional groups ( Fig. 23-1 ). These diagnostic tests facilitate identification of the malformation ( Table 23-2 ) and determination of a functional approach to valve reconstruction.
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Echocardiography is also essential to assess the degree of valvular stenosis or regurgitation; to measure the size of the annulus, comparing it to normal sizes; and to determine the volumes and contractility of the ventricles. Associated lesions are also systematically identified, often requiring complementary catheterization.
Type I: Mitral Valve Malformations with Normal Leaflet Motion
The following three anomalies are included in this type of malformation: isolated annular dilatation, cleft leaflet, or leaflet defect. They all cause regurgitation.
Isolated Annular Dilatation
Isolated annular dilatation ( Fig. 23-2 ) is a rare but documented cause of congenital mitral valve regurgitation authenticated by a mitral murmur detected before the age of 2 years. It is usually predominant at the posterior annulus involving the P3 segment. An ostium secundum atrial septal defect is often associated. The heart is enlarged with often a greater than normal amount of valvular tissue for the age of the child, which makes it possible to use prosthetic rings larger than the normal size.
Cleft Anterior Leaflet and “Atrioventricular Canal Type” Mitral Valve
These two different malformations ( Fig. 23-3 ) are often described under the sole term “cleft leaflet” because they both display a vertical separation of the anterior leaflet into two hemivalves. They are actually two different malformations; the true cleft anterior leaflet displays a cleft with an otherwise normal valve morphology while the “atrioventricular canal type” mitral valve is a malformation involving the entire mitral valve apparatus.
In “cleft anterior leaflet” (a) , a cleft vertically separates the anterior leaflet into two hemileaflets of similar surface area. The cleft is directed towards the subcommissural triangle separating the right coronary and non–coronary aortic leaflets; it may involve the entire height or only a part of the anterior leaflet. Abnormal chordae tendineae arising from the septum or the edge of a small ventricular septal defect may be attached to the free edge of the cleft. As opposed to the atrioventricular type mitral valve, the two papillary muscles are normal and normally positioned, the commissures are correctly situated, and the posterior leaflet attachment represents two thirds of the circumference of the mitral orifice, as in a normal valve. The segmental anatomy of the posterior leaflet is normal with characteristic P1, P2, and P3 segments.
The “atrioventricular canal type mitral valve” (b) may exist in the absence of any septal defect. It presents all the characteristic anatomical features of the mitral valve in the atrioventricular canal, particularly a trileaflet configuration with three components (anterior, posteromedial, and lateral) of unequal surface areas. The anterior component is larger than the posteromedial component, which itself is larger than the lateral component. The lateral component presents a sharp triangular shape partially filling the gap between the anterior and the posterior components. A careful analysis of these components shows that the lateral component represents P2, whereas P1 and P3 are incorporated into the anterior and posteromedial components, respectively. The three leaflets are delineated by three separations: the anterolateral commissure, the posterolateral commissure, and the septal cleft, which can be complete or partial. The atrioventricular canal may function as a commissure that may be competent in 20% of the cases. The implantation of the papillary muscles is also abnormal with both papillary muscles displaced laterally under the anterolateral and posteromedial commissures.
Leaflet Agenesis
Various defects, such as holes or localized agenesis of the leaflet tissue, may be encountered, particularly in the posterior leaflet ( Fig. 23-4 ). The free edge of the defect is usually free of chordae or may attach thin, nonfunctional, abnormal chordae that aid differentiation of these defects from normal indentations. The combination of the young age of the child and the absence of any history of bacterial endocarditis is evidence of the congenital nature of these malformations.
Type II: Leaflet Prolapse
In type II leaflet prolapse the free edge of one or two leaflets overrides the plane of the orifice during systole ( Fig. 23-5 ). This functional definition excludes nonregurgitant Barlow’s valve, which can be seen in children. The lesions responsible for leaflet prolapse are chordae elongation, papillary muscle elongation, and chordae agenesis. All these anomalies cause regurgitation.
Chordae elongation . Chordae elongation involves several or all of the chordae tendineae arising from a papillary muscle. The corresponding portion of the leaflet tissue prolapses within the atrium during systole.
Papillary muscle elongation . Elongation of a papillary muscle that leads to leaflet prolapse is usually associated with other cardiac anomalies, such as anomalous origin of the left coronary artery from the pulmonary artery or aortic stenosis ( Fig. 23-6 ). It is likely that this lesion results from papillary muscle ischemia. The papillary muscle is fibrotic, thin, and elongated to such an extent that its tip prolapses through the mitral orifice. Histology usually shows scar tissue similar to that seen in a healed infarction. Infarcted areas may also be evident in the adjacent subendocardium of the left ventricle, demonstrating abnormal vascularization.
Chordae agenesis . Chordae agenesis usually involves a limited segment of the mitral valve, thus producing a localized prolapse ( Fig. 23-7 ).
Type III: Restricted Leaflet Motion with Normal Papillary Muscles
In this group of malformations, the motion of one or two leaflets is limited. Two papillary muscles can be clearly identified by echocardiography. They are called “normal” although they may present variations in length, morphology, and relationship with the leaflet tissue. Three malformations belong to this group: papillary muscle-commissure fusion, short chordae, and excess valvular tissue. They may cause valvular stenosis or associated stenosis and regurgitation.
Papillary muscle-commissure fusion . In this condition, the head of one or two papillary muscles is directly implanted on a commissure without any intermediate chordae tendineae ( Fig. 23-8 ). The commissure is obstructed by a cuff of white fibrous tissue (sometimes multiperforated) that covers the head of the underlying papillary muscle. The motion of the leaflets is severely restricted. The central orifice of the valve between the two papillary muscles is severely narrowed to the point that it may have a funnel-shaped appearance. An associated regurgitation results either from hypoplasia of the anterior leaflet or from annular dilatation, or both.
Short chordae . In contrast to rheumatic valve disease, these very short chordae are well delineated, only slightly thickened, and not fused ( Fig. 23-9 ). The interchordal spaces are reduced, which in conjunction with papillary muscle hypertrophy may create an associated subvalvular stenosis. The annulus is often enlarged secondary to the mitral valve regurgitation. A frequently encountered association is short chordae arising from one papillary muscle and papillary-commissure fusion involving the other papillary muscle.
Excess valvular tissue . This group of anomalies includes interchordal space obliteration, double mitral valve orifice, and supravalvular ring ( Fig. 23-10 ). All these malformations cause various degrees of valve stenosis or regurgitation.
Interchordal space obliteration (a) is a malformation either isolated or associated with other mitral valve malformations. Abnormal endocardial tissue is obstructing the interchordal spaces delineated by well-visible chordae.
Double mitral valve orifice (b) is usually described as a bridge of leaflet tissue between the anterior leaflet and the posterior leaflet. It is actually a malformation of the commissure, usually the posterior commissure, with the underlying papillary muscle attaching all the chordae of the corresponding area with a parachute configuration. The remainder of the valvular orifice is wide open and usually has a normal configuration, explaining why this malformation is typically not stenotic. Whenever stenosis is present, its cause should be identified at the subvalvular level of the larger orifice.
The supravalvular ring ( Fig. 23-10 ) is a frequent malformation displaying a circumferential ridge of fibrous tissue (c) . It is truly supravalvular at its attachment 2 to 3 mm above the annulus of the posterior leaflet; however, its attachment is intravalvular at the anterior leaflet, 3 to 5 mm below the annulus (inset). Although the diagnosis may be made preoperatively, the ring is generally identified intraoperatively. In most instances, this anomaly is a discrete secondary lesion attributable to turbulence generated by a primary mitral valve malformation. It may, however, become more stenotic over time.
Type IV: Restricted Leaflet Motion with Abnormal Papillary Muscles
This group consists of three malformations: “parachute” *
* See Glossary .
mitral valve with a single papillary muscle, hammock valve with multiple displaced papillary muscles, and papillary muscle agenesis.Parachute mitral valve . The parachute mitral valve is one of the most common malformations causing mitral valve stenosis ( Fig. 23-11 ). In this condition, all chordae are attached to a single papillary muscle. The single papillary muscle is formed either by the fusion of the two papillary muscles (a) or by a single papillary muscle, usually the posterior one, whereas the other one is usually hypoplastic (b) . The parachute valve is usually stenotic because of the obliteration of the interchordal spaces by excess valvular tissue. It can also be regurgitant as a result of the large functional orifice located near the anterior commissure in the region of the hypoplastic papillary muscle (b) . A parachute valve is often associated with other malformations such as ventricular outflow tract obstruction, aortic coarctation, supravalvular ring, or various combinations of these malformations, as described by Shone. Some parachute mitral valves are functionally adequate; the transvalvular gradient remains stable during follow-up and does not require surgical correction. If the gradient increases, one should suspect a supravalvular mitral ring.
