Section I: Congenital mitral valve disease in children
Definition
Congenital mitral valve disease is a developmental malformation of one or more of the components of the mitral valve apparatus. 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 (AVSD; see Chapter 32 ), aortic atresia and other phenotypes of hypoplastic left heart syndrome (see Chapter 51 ), various forms of AV discordant connection (see Chapter 47 ), or transposition of the great arteries (see Chapter 44 ) are special situations discussed in the chapters describing these conditions. Mitral valve anomalies associated with straddling or univentricular AV connections are described in Chapters 47 and 52 , respectively. Regurgitation from mitral valve prolapse as part of the syndrome of myxomatous degeneration is described in Chapter 11 , but the repair of these in the pediatric age groups will be treated in this chapter. Because the treatment of rheumatic mitral valve and bacterial mitral valve endocarditis in the pediatric age group have unique details, they are also included in this chapter, as is regurgitation of the left AV valve after surgical repair of AVSD.
Congenital mitral valve stenosis and insufficiency generate different pathophysiology and mechanisms of adaptation from the cardiovascular system, but they do have similar pathologies and associated lesions, they are often combined, and they require similar surgical techniques for treatment.
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.
Before the 1960 decade, description of congenital anomalies of the mitral valve was rare and from isolated cases or very limited series, until publications by Jesse E Edwards in the 1960s and Alain Carpentier in the 1970s.
Embryology
The embryology of the mitral valve is complex. The understanding of the formation of the leaflets and suspension apparatus has evolved, and the current approach is based on immunohistochemistry to define cell lineage. Earlier, in vivo labeling of cushion tissue and scanning electron micrograph of human and chick embryos helped define the origin and the evolution of the developing mitral valve. In humans, the mitral valve develops between the 5th and the 15th week of embryonic life. The leaflet and chordal tissue derive from the endocardial cushion tissue formed on the inner surface of the AV junction after the process of endothelial to mesenchymal transfer (EMT). The separation between atrial and ventricular myocardium is dependent on the sulcus tissue located on the epicardial side of the junction. As the cushion tissue elongates and grows toward the ventricular cavity, it forms the leaflet tissue. The tissue transitions into a funnel-like structure first attached then separating itself from the underlying myocardium. Then, perforations into the valve leaflet appear. The perforations grow and form the chordae tendineae. The atrial aspect of the cushion generates the spongy atrial layer, and the ventricular layer generates the fibrous part of the mitral valve and the chords. The development of the papillary muscle takes place at the same time and originates from compacted primitive trabeculations of the myocardium. A horseshoe-shaped ridge with an apical open end lies in the left ventricle. Progressively, the anterior and posterior parts of the ridge lose contact with the ventricular wall. They will form the papillary muscles, and as they increase in size, they stay in contact with the cushion tissue at their tip. The midportion of the muscular ridge will be incorporated into the trabeculations of the LV. The extracellular matrix secretes the collagen structure with a circumferential pattern during the early stage of the formation in the fibrosa while the radial elastic fibers mostly appear in the postnatal period in the ventricularis.
Several AV cushions participate to form the final mitral valve. The most important are the superior and inferior cushions. However, the contribution of these two cushions is asymmetrical. The superior cushion tissue generates most of the anterior leaflet of the mitral valve, whereas the inferior cushion generates most of the septal leaflet of the tricuspid valve. Smaller cushions are involved in the formation of the mural leaflet of the mitral valve. The wedging of the aortic root into the left ventricle separates the developing mitral valve from its septal attachments ( Fig. 49.1 ).
Normal mitral valve leaflet morphology, with the larger anterior leaflet contributing two-thirds of the valve surface area with well-defined scallops A1, A2, and A3. The posterior leaflet contributes the remaining one-third with scallops P1, P2, and P3. Anterior (Ac) and posterior (Pc) commissural leaflets interpose the A1/P1 and A3/P3 zones of apposition.¸
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.
Supravalvar ring
Often considered a congenital anomaly of the mitral valve, the supravalvar mitral ring is a fibrous construction attached to the posterior anulus of the mitral valve; it runs from both commissures to the mid-height of the anterior leaflet. The lesion is stenotic, often to a greater extent than might be suggested by the extension of the ring. This is more a result of the limitation of the opening of the anterior leaflet than of the actual diaphragm effect of the ring. Strictly attached to the mitral valve anulus, it is to be differentiated from cor triatriatum. Like the subaortic membrane in the left ventricular (LV) outflow tract, the supravalvar mitral ring is an acquired lesion resulting from turbulent flow through the mitral orifice. The primary lesion of the mitral valve responsible for the turbulent flow can be obvious stenosis, with or without associated regurgitation, or it can be discrete or mild and difficult to identify. It can be related to a prominent coronary sinus, as found in the left superior vena cava draining into the coronary sinus. , It is perhaps for these reasons that the supravalvar mitral ring is prone to reoccur after surgical resection, unless the underlying anatomic anomaly has been identified and corrected. ( Fig. 49.2 ).
An intraoperative photograph demonstrating a supravalvar mitral ring that has recurred following previous surgical resection. Note that the ring is at the mitral valve anulus level posteriorly and at mid-level of the anterior leaflet.
Mitral anulus anomalies
The mitral anulus may be uncommonly small and obstructive in the absence of 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 while the basic valvar anomaly leading to regurgitation may be subtle and difficult to identify.
If the anatomy of the mitral valve is otherwise normal, it is difficult to ascertain the congenital origin of dilation of the mitral valve anulus and elongation of the suspension apparatus, but these patients are included in most studies of congenital anomalies of the mitral valve and account for 15% to 40% of the patients in published studies of congenital mitral valve regurgitation. However, there is no evidence of their congenital origin. Elongation of papillary muscles can be found at birth in the mitral or the tricuspid apparatus, but the muscles usually have an ischemic, beige aspect on inspection. Sometimes, the ischemic origin is demonstrated by acute rupture at or shortly after birth.
Both dilation of the anulus and elongation of the suspension apparatus are usually found associated with significant volume loading of the left ventricle (e.g., with a large ventricular septal defect [VSD] or large patent ductus arteriosus). The pathophysiology is of initial dilation of the posterior anulus under the effect of the volume loading, followed by elongation of the marginal chords and prolapse of the free edge of the anterior leaflet. In rare cases, minor anomalies of the valvar tissue or the papillary muscles may suggest a congenital origin. For prognostic purposes, mitral valves with isolated anular dilation should be separated from the smaller group with anterior leaflet prolapse and anular dilation.
When a patient older than 4 years has an isolated mitral regurgitation combining anterior leaflet prolapse and various degrees of posterior leaflet retraction, especially if the latter is thickened, a rheumatic origin should be ruled out when the patient originates from a geographical area of high prevalence.
Functional mitral regurgitations secondary to cardiomyopathies are not discussed here.
Mitral leaflet anomalies
Cleft mitral valve.
The cleft mitral valve is often isolated and can be easily differentiated from a left AV valve in a partial AVSD. It is an actual cleft with no suspension apparatus on the edges of the defect. The cleft is centered on the aortic commissure between the noncoronary and left coronary cusps. Each half of the anterior leaflet at the midportion bears the attachment of the strut chordae. With time, the cleft mitral valve regurgitation will generate secondary lesions at the edges of the cleft, such as thickening, rolling up, and retraction. The defect is never stenotic and may generate only little regurgitation for a long time.
Lesions associated with lack of valvar tissue.
Three major anatomic types of lesions are almost always associated with a lack of valvar tissue to various degrees and are worth characterizing: parachute mitral valve, papillary muscle to commissure fusion, and hammock or arcade valve. There is, however, a continuum between these three types and the normal anatomy. The functional lesion can be either predominantly regurgitant or predominantly stenotic, or it can be both stenotic and regurgitant. In rare cases, the valve may function normally. Although they had been described well before the current refined understanding of the mitral valve embryology, they overlap the various stages of the mitral valve formation.
Parachute mitral valve.
The parachute mitral valve is rarely found in isolation and almost always associated with another cardiac anomaly, such as atrial septal defect (ASD), VSD, or coarctation. It was integrated in the description of the Shone syndrome. It can also be seen in various degrees of hypoplasia of the left ventricle, resulting in the need for univentricular palliation. The anatomic essence is a predominant or single papillary muscle, with the orifice of the mitral valve centered at its tip ( Fig. 49.3 ). The spectrum of lesions for the suspension apparatus starts with complete fusion of the tip of the papillary muscle to the free edge of the valve. At the other end of the spectrum, there are relatively normal looking chords, with good mobility of the leaflet. The accessory papillary muscle is usually small and devoted to a short segment of the free edge, or even to the under surface of the leaflet tissue, as would be seen if it were a larger-than-normal secondary chord. The leaflet tissue can be intact or perforated.
Anatomic specimen demonstrating a parachute mitral valve, with a dominant papillary muscle centered on the orifice of the valve and a small lateral one.
The functional class depends on the interaction between the amount of tissue and the mobility of the leaflet; presence and size of the fenestrations; and presence, length, and quality of the chords. The parachute mitral valve almost always has a stenotic component. As the valve grows the gradient does not evolve and some of these patients may not require a valve operation.
Double-orifice mitral valve, in which the lesser papillary muscle supports a complete orifice, is an exceedingly rare variation of the parachute mitral valve. It should be differentiated from the left AV valve of the AVSD, where an accessory orifice is often found in the inferior bridging leaflet when there is a diminutive or absent left lateral leaflet (LLL; mural leaflet).
Papillary muscle to commissure fusion.
Fusion of papillary muscle to the commissure, also called short chordae syndrome, is defined by the presence of short chords and a papillary muscle tip that is attached or fused to the commissural area of the free edge. In the most extreme form, the chords are completely absent. The papillary muscles can be of normal size and volume. The valve is then generally more regurgitant than restrictive, because of the lack of valvar tissue and the restriction of the leaflet motion. When the papillary muscles are hypertrophied, the bulk of their mass is responsible for a predominantly restrictive valve. Some authors assimilate this lesion with the arcade mitral valve (when the continuity between the papillary muscles and the short free edge of the anterior leaflet resembles an arcade) ( Fig. 49.4 ).
Anatomic specimen demonstrating papillary muscle to commissure fusion, referred to as an arcade mitral valve by some authors.
Hammock valve.
In this lesion, the suspension apparatus may have lost all resemblance to the normal anatomy. The papillary muscles are not identifiable, instead an array of multiple small papillary muscles close to the base of the heart carries the chords for the leaflets and resembles a hammock. This attachment, displaced toward the base of the heart, generates excess tension on the anterior leaflet and limitation of posterior leaflet motion. The valve is most often predominantly regurgitant.
Isolated mitral leaflet hypoplasia.
This rare condition is almost completely restricted to the middle scallop of the posterior leaflet.
Accessory mitral valve tissue.
The interchordal spaces are filled with a dense network of valve tissue. When there is continuity between the anterior and the posterior leaflet, the accessory valvar tissue may generate a gradient directly related to the size of the perforations in the accessory tissue. When the accessory valve tissue is entrapped in the LV outflow tract, the mitral valve may become regurgitant because the traction exerted by the accessory valvar tissue on the anterior leaflet results in the valve opening at mid-systole ; however, in that case, the LV outflow tract obstruction is the predominant hemodynamic lesion and is usually responsible for the diagnosis. Often, the accessory mitral valve tissue does not generate significant gradient or insufficiency ( Figs. 49.5 and 49.6 ).
Specimen of accessory mitral valve tissue, demonstrating a dense network of valve tissue in the interchordal spaces.
A parasternal long-axis echocardiographic view demonstrating accessory mitral valve tissue causing left ventricular outflow tract obstruction.
Mitral valve disease with excess leaflet tissue and mitral valve prolapse.
It is debatable whether the mitral valve prolapse syndrome—in its most common form, limited to the middle scallop of the posterior defect—is congenital. In a large population of neonates, using strict criteria, the incidence of mild bulging of the anterior leaflet was negligible and no prolapses were detected. This tends to prove that mitral valve prolapse is a disease evolving over several decades probably with a genetic substrate. , In its common form, it is rarely encountered in neonates or infants. In adults, the histologic anomalies are limited to the middle scallop of the posterior leaflet, with predominant elastic fiber alteration and myxomatous tissue proliferation.
On the other hand, the more extensive form of mitral valve prolapse is seen in neonates and infants. In this form, an excess of tissue is distributed to both the anterior and posterior leaflets, and histologic examination reveals extensive infiltration of the spongiosa with myxomatous tissue. The histologic anomalies are identical to those found in patients with Marfan syndrome, Ehlers-Danlos syndrome, and osteogenesis imperfecta. Marfan syndrome is an autosomal dominant disorder with varying penetrance. The mutation is found on the fibrillin1 gene in chromosome 15q21.1 or the TGFβ receptors in chromosome 3. Ehlers-Danlos syndrome is represented by a constellation of mutations linked to different subtypes. The extensive form of the mitral valve prolapse syndrome is encountered in sporadic cases or in familial forms demonstrating autosomal dominant and X-linked inheritance. Three different loci, on chromosomes 16, 11, and 13, have been linked to mitral valve prolapse, but no specific gene has been described.
Coexisting cardiac anomalies
Congenital mitral stenosis is rarely isolated. In about 30% of cases, it coexists with VSD. In more than 50%, it coexists with one or another form of LV outflow obstruction, a situation classically called Shone syndrome. The mitral valve may be dysplastic or with an isolated supravalvar mitral ring. The LV outflow tract obstruction may be valvar, discrete subvalvar, or combined valvar and subvalvar aortic stenosis, with or without coarctation.
Hypoplastic left ventricle.
Neonates and young infants with borderline LV size and LV outflow tract obstruction also often have a hypoplastic mitral valve (multiple obstructive left-sided lesions rather than Shone syndrome in this age group). Anatomically, the mitral valve may be small in absolute terms but in proportion with the size of the ventricle. The valve may not appear stenotic hemodynamically on color Doppler flow assessment when the left ventricle is unloaded by atrial left-right shunting and the systemic output is supported by the right ventricle and a patent ductus.
In patients of this age, the anatomy of hypoplastic mitral valves is very hard to investigate precisely with ultrasound, as accurate anatomic diagnosis would require high spatial and temporal resolution. While a significant proportion of such patients have a hypoplastic mitral valve but of normal anatomy, the diagnosis of an associated congenital mitral valve anomaly may only be suspected or even overlooked entirely on noninvasive assessment. The prevalence of persistent left superior vena cava draining to the coronary sinus is high in these neonates. It is possibly responsible for mitral valve inflow obstruction during fetal life and consequently ventricular growth imbalance. All of this supports to consider congenital mitral valve disease as an important component in the entity known as hypoplastic left heart syndrome (see Chapter 51 ).
Recurrent left atrioventricular valve regurgitation
After repair of complete or partial AVSD, there are two main mechanisms for regurgitation in valves with a normally developed LLL. The cleft may be open because the cleft closure performed in the initial surgery has ruptured or because it was never done. In this case, the regurgitation occurs through the cleft directly. On color Doppler examination, the regurgitation jet is oriented vertically through the cleft.
Alternatively, when the cleft was completely closed and has remained so, the predominant mechanism for the regurgitation is the absence of a coaptation surface in front of the tip of the LLL. In the unrepaired AVSD, the small size of the zone of apposition is an inherent feature of these parts of the superior and inferior bridging leaflets. Direct closure of the cleft does not create a larger coaptation surface; in fact, the little coaptation surface that exists can be reduced and distorted by the cleft closure. This is even more so when the cleft closure has ruptured or is stretching the free edge of the valve. On color Doppler examination, a regurgitation jet oriented posteriorly hugging the posterior wall of the left atrium is characteristic of this mechanism.
If the regurgitation is a long-standing condition, secondary lesions or dysplastic lesions on the edges of the cleft are severe, with thickening and retraction of the leaflet tissue, and sometimes even calcification. On the other hand, the LLL is usually thin and pliable, with no secondary or dysplastic lesion. There is no restriction of the LLL motion and no prolapse.
In the presence of hypoplastic or absent LLL, the cleft cannot be closed at the time of the primary repair without generating inflow restriction. The residual or recurrent regurgitation occurs through the cleft. On an echocardiographic study, the anatomy is suspected when a strong asymmetry of the papillary muscles can be seen on the short-axis view of the left ventricle. The predominant papillary muscle, usually the anterior one, is connected to both superior and inferior bridging leaflets. The presence of a double orifice is also a strong indicator. It is usually directly suspended to a diminutive posterior papillary muscle and within the body of the inferior bridging leaflet. On Doppler examination, the regurgitation jet is oriented vertically through the cleft.
Clinical features and diagnostic criteria
The diagnosis of a congenital mitral valve anomaly relies on the clinical findings, the chest radiograph, the electrocardiogram, and, most importantly, the echocardiographic study. A clinical diagnosis of an isolated mitral valve anomaly can often be made before the echocardiographic examination. However, in neonates, when there are associated cardiac anomalies, the clinical investigation may only raise the index of suspicion of a mitral valve disease, or it may be missed completely. Echocardiography is part of the initial evaluation of all pediatric patients with cardiac signs, but when there are associated lesions, it is essential to the diagnosis of a congenital mitral valve anomaly. In most patients, echocardiography shows the congenital nature of the anomaly by demonstrating the deviation from the normal anatomy. The functional evaluation of the mitral valve and assessment of the impact of the lesion on the cardiovascular system are also best made with echocardiographic study. Neither a catheter study nor a ventriculogram has any value in the diagnosis of or preoperative assessment for mitral valve disease. Beyond the echocardiographic study, the associated cardiac anomalies in neonates and young infants and more in particular with the mitral valve hypoplasia may warrant further investigation with cardiac computed tomography (CT), less so with cardiac magnetic resonance imaging (MRI). Precise dimensions of the aortic arch and the aortic anulus together with the evaluation of the LV height and size are necessary.
Symptoms and signs
Patients rarely present with mitral stenosis during the neonatal period, but when they do, the associated lesions may predominate. Beyond the neonatal period, symptoms may include failure to thrive, dyspnea on exertion, pallor, hypotrophy, and a history of repeated chest infections. Signs of low cardiac output can be found, such as pallor and cold extremities, tachycardia, and dyspnea. Signs of pulmonary hypertension are present, with exacerbated second heart sound and palpation of the right ventricular (RV) impulse. A diminished first heart sound suggests thick leaflets of limited excursion. A low-intensity mid-diastolic murmur is the only direct auscultation sign, and it can be absent in a low-output situation.
Patients presenting with mitral regurgitation in the neonatal period are rare. At all ages, patients with greater than moderate mitral regurgitation present with various degrees of dyspnea at rest or with exertion, but this may be absent. Infants have degrees of failure to thrive and dyspnea while feeding. An enlarged LV impulse is present, and a high-frequency, high-intensity holosystolic murmur is heard at the apex extending into the axillae.
Electrocardiography
The electrocardiogram shows left atrial and LV enlargement in patients with mitral regurgitation. Right atrial and RV enlargements are seen when pulmonary hypertension is present. In the pediatric population, there is almost always sinus rhythm.
Chest radiography
Chest radiography demonstrates double density of the left atrial enlargement and various degrees of pulmonary plethora with an enlarged main pulmonary artery. LV enlargement in the presence of mitral valve regurgitation is evident.
Echocardiography
The echocardiographic study is essential. Systematically conducted, it provides all the information necessary for the diagnosis of the mitral anomaly, its severity, and its impact on the physiology. The anatomic lesion can usually be strongly suspected. Echocardiography together with the clinical tolerance will dictate the indication for surgery. It gives assistance to the surgeon in planning the repair.
The four-chamber view obtained with the transthoracic echocardiographic study is best to provide an accurate transvalvar gradient and define the precise amplitude of any prolapse or restriction. The short-axis view of the mitral valve (en face view) gives a direct vision of the area of the mitral orifice and allows good localization of the origin of the regurgitant jet. It allows a precise analysis of the papillary muscles (presence, size, location, and symmetry). Transesophageal echocardiography is superior for anatomic details of the suspension apparatus and evaluation of the functional classification. The probe can be moved up and down in the esophagus, providing precise localization of the area of prolapse along the free edge of the anterior leaflet, using the anterior commissure (probe up) and the posterior commissure (probe down) as benchmarks.
For mitral stenosis, the peak instantaneous and mean gradients across the valve must be interpreted according to the evaluation of the diastolic function of the heart and the associated lesions (essentially the presence of ASD or patent foramen ovale with the left to right gradient across it, or a large VSD). The overall impact of the transmitral gradient on the indication for surgery must be weighed with the pulmonary artery pressure, and more so with the clinical tolerance. Neonates with borderline small ventricles need precise measurements of the mitral valve anulus size as well as the LV height compared to the right ventricle.
Three-dimensional echocardiography is progressing rapidly with the exponential increase of computer power and miniaturization of the probes. However, the information generated is of less value in very small patients because the spatial and temporal resolutions remain insufficient. Stitch artifacts then often make the images uninterpretable. Generally, in older patients, the most obvious benefit of 3-dimensional echocardiography is the ability to locate precisely on the 3-dimensional en-face view the site of a corresponding 2-dimensional cut. It is then only on the 2-dimensional cut that the degree of prolapse or restriction can be quantified precisely. Three-dimensional transesophageal probes are currently being introduced for neonates.
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
CT plays a limited role in evaluating the congenitally abnormal mitral valve, but MRI can provide important morphologic information that may supplement that provided by echocardiography. In addition, MRI can provide functional information such as quantification of mitral regurgitant fraction and valve orifice area in diastole.
Whatever imaging technique is used, there are limitations in small or very small patients, in whom spatial and temporal resolutions are critical. Cardiac CT has spatial resolution for the valvar tissue or the suspension apparatus in adults but much less so in small children. Cardiac MRI does not help for valves.
MRI allows calculation of the ventricular volumes with the caveat of the septal geometry; this may aid in the decision making for treatment of patients with small LV and mitral valve stenosis. The regurgitation fraction is measured accurately. Gradients and flows are accurately demonstrated with MRI in patients of school age or older. In younger patients, MRI does not help with the analysis of the valve anatomy nor with the gradient. On the other hand, cardiac MRI can provide useful functional information while cardiac CT with contrast is superior for morphology analysis of the heart and the great vessels preoperatively.
Functional classification of mitral valve anomalies
Carpentier’s functional classification of mitral valve physiology describes leaflet motion, regardless of the anatomy and the cause. It is an essential tool for mitral valve repair and should be studied on echocardiography preoperatively. It can also give significant clues to the lesions that will eventually be found during surgery.
Type I. Normal leaflet motion. The anomaly can be either a perforation or a defect of one or two leaflets, or an anular dilation. Anular dilation is most often associated with a type II function of the anterior leaflet and/or type III function of the posterior leaflet.
Type II. Increased leaflet motion. Most pediatric mitral valve regurgitations with a predominant type II function start from anular dilation, the ensuing loss of coaptation generating stress on the suspension apparatus of the anterior leaflet and resulting in its progressive elongation.
Type III. Restricted leaflet motion. The valve may be stenotic or regurgitant, or both. Most patients with congenital anomalies of the mitral valve belong to this type. ,
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, ASD, VSD, coarctation, and hypoplastic left ventricle; 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; 3 were asymptomatic without important hemodynamic abnormalities, 3 presented with stenosis, and 3 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 or less in early life, and about half the patients with it do not show important symptoms. Symptoms and need for intervention usually come earlier when it coexists with other important cardiac anomalies.
Medical therapy
Maximal medical therapy should be employed when the anulus is too small to receive a mechanical prosthesis in the anatomic position. When mitral regurgitation is predominant, the treatment should include diuretics and, if necessary, red-blood cell transfusion in infants. Noninvasive airway positive pressure or assisted ventilation may be necessary. Angiotensin-converting enzyme inhibitors are often prescribed, but their efficiency has not been demonstrated. In patients with mitral stenosis, afterload reduction is contraindicated. Ventilation requirement and most importantly dependance in neonates and infants indicate the need for surgical treatment.
Operative technique
Mitral valve repair
The techniques for mitral valve repair were described by Carpentier for adult surgery, with modifications for pediatric patients and hypoplastic congenital mitral valves. , The conduct of cardiopulmonary bypass is described in Chapter 2 . Moderate hypothermia (28°C-32°C) is routine. Venous cannulation should allow as much access to the AV groove as possible. The superior vena cava is cannulated directly, at a distance from the cavoatrial junction and the inferior vena cava immediately at the origin. Limited dissection of the groove is performed. After cross-clamping, the left atrium is entered via the AV groove. The exposure is enhanced with traction on the mattress sutures, inserted into the posterior anulus, that pull the valve upward and toward the operator. The snugger on the inferior vena cava pulls upward and to the left. A self-retaining retractor for mitral surgery must be adapted to the size of the patient. No traction on the left pericardial edges should be exerted and opening the left side pleura may help in allowing the rotation of the mitral valve anulus toward the operator. Alternative approaches are less satisfactory. The transatrial septal approach does not provide an edge for the retractor blades to anchor and it exposes the conduction tissue to more pressure. It also takes time to reconstruct.
During preparation for bypass, the preoperative transesophageal echocardiographic study is performed when possible. Once the mitral valve is satisfactorily exposed, it is systematically analyzed, integrating preoperative information. The functional class is confirmed, whereas the extent of mitral valve prolapse or restriction is based on echocardiographic studies only. The location (A1 to 3, P1 to 3) (see Chapter 11 ) is eventually confirmed intraoperatively. In small patients an epicardial echo as well with a 12-MHz probe may be useful, on bypass before cross clamping, with various degrees of volume loading. After surgical exposure, the morphologic and anatomic examination is performed, which includes the following elements: a supravalvar ring is confirmed or eliminated, and determinations are made of (1) the anular diameter; (2) the texture, aspect, and size of the mitral valve leaflets; (3) the number and distribution of the chords; (4) the presence of commissural tissue and dedicated suspension apparatus; and (5) the presence, size, location, and morphology of the papillary muscles. The examination finishes with a careful check for accessory mitral valve tissue in the interchordal spaces and for signs and extent of endocardial fibroelastosis. The measured diameters of the anulus and of the mitral valve opening are compared with that calculated for the patient’s body surface area.
The treatment is adapted to the predominant functional class. The correlation between functional class, anatomic pathology, and surgical treatment is similar to that for adults (see also Chapter 11 ). ,
Correction of type I: Anuloplasty.
The anuloplasty is mandatory in all operations for mitral valve insufficiency, except in some patients with an isolated type I mitral valve anomaly without anular dilation, mostly cleft mitral valves. The purpose of the anuloplasty is to adapt the area of the mitral valve orifice in systole to the leaflet tissue available. Attempts to perform mitral valve repair without anuloplasty have resulted in recurrence. A remodeling anuloplasty involves inserting a rigid adult-size ring (or a size larger than would be indicated by the area of the anterior leaflet). To achieve an adult-size ring in children or teenagers, the leaflet tissue may need to be enlarged—usually the posterior leaflet, less often the anterior leaflet, or both. , In patients with a type III mitral valve anomaly, the detachment of the posterior leaflet to gain access to the suspension apparatus is used for the leaflet enlargement. When no device is available for the size of the patient, or when the device is thought to be too small, the anuloplasty is limited to the posterior anulus. The anuloplasty must incorporate both trigones. Experience suggests that greater stability of the anuloplasty is achieved with a continuous strip of polytetrafluoroethylene (PTFE) for larger patients. , A sheet of expanded 0.4- or 0.6-mm PTFE folded two or three times is useful to avoid corrugating. For neonates, infants, and young children, a row of compression mattress sutures tied over themselves allows for adequate growth. With the latter technique, some postoperative relaxation of the compression should be accounted for when sizing the anuloplasty intraoperatively. Mattress sutures should not be tied too tightly ( Fig. 49.7 ).
Techniques of mitral valve anuloplasty in children to correct type I mitral valve regurgitation in patients with a dilated mitral valve anulus. A series of compression mattress sutures in neonates and young infants may be adequate (1 and 2), while in older children the use of a continuous strip of PTFE confers more stability to the repair (3).
(From Oppido G, Davies B, McMullan DM, et al. Surgical treatment of congenital mitral valve disease: midterm results of a repair-oriented policy. J Thorac Cardiovasc Surg . 2008;135(6):1313-1320; discussion 1320-1321.)
Correction of type II.
Correction of type II mitral valve anomalies is rarely necessary in patients with congenital mitral regurgitation. Type II is mostly a secondary lesion, or it is seen with associated lesions (mostly large volume loading of the left ventricle), but correction is always required in patients with a connective tissue disorder and mitral valve prolapse. Multiple techniques are available to correct the enhanced leaflet motion. Whether techniques should be used in isolation or in combination depends on the extension in width of the prolapsus (i.e., localized or extended to the whole width of the free edge). It is the height of the prolapse (based on the preoperative echocardiographic study) that will dictate the choice of the technique.
All techniques are efficient and reliable, providing that the correction restores a large surface of apposition between anterior and posterior leaflets. Overcorrection, however, generates stress directly on the repaired area and negates the stress relief provided by the apposition surface. All overcorrections eventually fail.
Artificial chords are used when chords of appropriate strength and quality are not available in the prolapsed area. The insertion requires rigorous technique to avoid overcorrection and large knots at the free edge. Artificial chords are safe for pediatric patients. Adequate growth of the repair will come from the papillary muscle and the leaflet tissue ( Fig. 49.8 ).
Technique of implantation and length calibration of artificial PTFE chordae for correction of type II mitral regurgitation, avoiding overcorrection and free-edge knots.
(From Oppido G, Davies B, McMullan DM, et al. Surgical treatment of congenital mitral valve disease: midterm results of a repair-oriented policy. J Thorac Cardiovasc Surg . 2008;135(6):1313-1320; discussion 1320-1321.)
Chordal shortening requires thin and flexible chords. The correction generates significant shortening of the chords and is performed only when high and localized prolapse is considered ( Fig. 49.9 ).
(A and B) Techniques to treat localized leaflet prolapse resulting in type II mitral regurgitation with chordal shortening (A) or papillary muscle sliding technique (B) when chords are thickened and rigid.
(From Oppido G, Davies B, McMullan DM, et al. Surgical treatment of congenital mitral valve disease: midterm results of a repair-oriented policy. J Thorac Cardiovasc Surg . 2008;135(6):1313-1320; discussion 1320-1321.)
Chordal transfer between secondary chords and the free edge is preferred to chordal transfer from posterior leaflet to anterior leaflet because the length is naturally adapted for the correction of localized prolapse. The chord should be detached from the body of the anterior leaflet with a minimal amount of valvar tissue. It is then attached to the free edge directly at the required length with a small running suture.
Wedge resection of the papillary muscle ( Fig. 49.10 ) and sliding plasty generate different degrees of correction of prolapse to multiple chords. They are well adapted to prolapse that includes a large segment of the anterior leaflet free edge.
Technique of papillary muscle wedge resection used to correct type II mitral regurgitation involving a large segment of anterior leaflet prolapse involving multiple chords.
(From Oppido G, Davies B, McMullan DM, et al. Surgical treatment of congenital mitral valve disease: midterm results of a repair-oriented policy. J Thorac Cardiovasc Surg . 2008;135(6):1313-1320; discussion 1320-1321.)
Papillary muscle shortening is used in Marfan and mitral valve prolapse for the correction of combined anterior and posterior type II; it requires strong and dense quality of the papillary muscle. The shortening should be conservative to avoid overcorrection and rupture.
Some teams have proposed an Alfieri edge-to-edge technique without any attempt at conventional surgery to alleviate the complexity of bileaflet prolapse repair. When difficult aortic surgery is associated, that approach may be justified when risk benefit-evaluation, experience, and institutional strategy are considered.
Correction of type III.
Type III congenital mitral anomalies consist primarily of restricted leaflet motion and insufficient leaflet tissue, and their combined successful correction is essential, especially in the first year of life.
Mobilization of papillary muscles.
Access to the suspension apparatus is necessary to adequately mobilize the papillary muscles. Access can be through the mitral valve orifice when it is sufficient, but often the mitral orifice is small and does not allow sufficient access to the suspension apparatus. In these situations, detachment of the posterior leaflet can provide good exposure to the suspension apparatus. The detachment needs to be done exactly at the anular level to allow for strong tissue for the reconstruction. Adequate thinning, mobilization from the posterior wall, and splitting and fenestration of the papillary muscles can then be performed safely. The posterior leaflet is later reconstructed with enlargement of the leaflet tissue when necessary ( Fig. 49.11 ).
Technique of mobilization of the posterior suspension apparatus by detachment of the posterior mitral leaflet and subsequent leaflet patch augmentation to correct type III mitral regurgitation.
(From Oppido G, Davies B, McMullan DM, et al. Surgical treatment of congenital mitral valve disease: midterm results of a repair-oriented policy. J Thorac Cardiovasc Surg . 2008;135(6):1313-1320; discussion 1320-1321.)
Enlargement of valvar leaflet with pericardial patch.
Augmentation of the leaflet tissue is the only way to treat a lack of valvar tissue. The anterior leaflet, the posterior leaflet, or both can be extended. Extension of the posterior leaflet should be limited to less than half of the height of the leaflet; it can be limited to the area of the middle scallop. Alternatively, when the detachment is extended from one commissure to another, the extension should reproduce a shape with three scallops and two commissures to allow a large opening in diastole. Crescent-shaped patches with a short inner edge are stenotic and the stenosis worsens with time. The extension of the anterior leaflet should be done in the body of the leaflet, leaving a strip of valvar tissue close to the hinge point to avoid mechanical stress at this level. The height of the extension should not be greater than two fifths of the height of the leaflet, leaving the area close to the free edge intact to allow a supple and effective surface of coaptation. If possible, it should be symmetrical from trigone to trigone. Since the early 1980s, the best default material has been autologous pericardium cross-linked intraoperatively with glutaraldehyde. Other materials can be used. Long-term results have been somewhat satisfactory, but the large experience is almost exclusively in rheumatic patients. In choosing the patch material, great care must be applied in matching the pliability of the patch with the one of the host valve.
Resection of supravalvar rings and accessory mitral valve tissue.
Resection of supravalvar tissue requires excellent exposure of the leaflet tissue. The supravalvar tissue can sometimes be peeled off the valvar tissue. More often, careful blunt dissection is needed. If perforation of the anterior leaflet occurs, it should be closed with simple figure-of-eight sutures.
Resection of accessory mitral valve tissue requires similarly rigorous surgical technique. Good exposure of the subvalvar apparatus is needed to perfectly delineate the mitral valve chords from what can be resected without compromising the integrity of the suspension apparatus. Various approaches to the suspension apparatus may have to be combined, such as through the mitral valve orifice and the aortic valve, and via detachment of the posterior leaflet ( Fig. 49.12 ).
Technique of resection of accessory mitral valve tissue from the interchordal spaces combined with papillary muscle splitting to enhance leaflet mobility.
(From Oppido G, Davies B, McMullan DM, et al. Surgical treatment of congenital mitral valve disease: midterm results of a repair-oriented policy. J Thorac Cardiovasc Surg . 2008;135(6): 1313-1320; discussion 1320-1321.)
Repair of cleft mitral leaflet.
When sufficient anterior or posterior mitral leaflet tissue is present on both sides of a cleft leaflet, the cleft is sutured closed with interrupted simple sutures to achieve competence. If there is insufficient leaflet tissue, the cleft closure can be augmented with a patch. Commonly, when the cleft was not leaking significantly, no anuloplasty is needed. If the regurgitation was severe, with anular dilation, an anuloplasty adapted to the size of the patient needs to be added.
Repair of recurrent left atrioventricular valve regurgitation.
In the setting of recurrent left AV valve regurgitation following repair of AVSD, two separate anatomies leading to different surgical techniques must be identified according to the size of the LLL. The most common one is a normally developed LLL. The least common is an absent or diminutive LLL.
In the presence of a normal LLL, in some cases the AV valve can be repaired by suturing or re-suturing the cleft. To achieve a stable long-term result with simple suturing, the cleft edges should be thin and pliable, and there should be redundant leaflet tissue to avoid putting the sutures under stress and to allow for a large zone of apposition facing the tip of the LLL. When the cleft has not ruptured or when there is significant retraction of the edges of the cleft, the valve should be repaired with the addition of valvar tissue, and a pericardial patch should be used. The area of the combined superior and inferior bridging leaflet can be augmented at the septal end of the leaflets. It is preferrable to create a coaptation surface in front of the LLL using the cleft patch augmentation technique. The area of the cleft closure is debrided of all secondary lesions around the regurgitation zone. Sufficient resection is performed to reach pliable leaflet tissue. The area of the cleft is then closed with a long and narrow patch. The patch extends into the ventricular cavity to create a coaptation surface in front of the tip of the LLL.
In the case of absent or hypoplastic LLL, the cleft is reopened where it had been partially closed, and a surface of coaptation is constructed on both edges of the cleft. In this anatomy, three different techniques are used, according to the difficulty and the anatomy; most commonly, the edges of the cleft can be directly suspended using expanded PTFE chords. A patch may be necessary to increase the surface area of the superior bridging leaflet and favor the creation of a large coaptation surface between native valvar tissue ( Fig. 49.13 ). Alternatively, a partial mitral valve homograft of adapted size can be used to reproduce the zone of apposition. This technique has demonstrated good early and intermediate results and should allow sufficient palliation time until an adult-size prosthesis can be used.
