Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
Mitral Valve Malformations
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.
TABLE 23-1
Normal Mitral Annular Size
| 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 |
Modified from Rowlatt UF, et al.
Approximate standard deviations: 1.9 mm for body surface area < 0.3 m 2 , and 1.6 mm for body surface area > 0.3 m 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.
TABLE 23-2
Functional Classification: Congenital Malformations
|
|
|
|
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.
You're Reading a Preview
Become a Clinical Tree membership for Full access and enjoy Unlimited articles
If you are a member. Log in here