Precise knowledge of the normal anatomy of the mitral valve and the interpretation of echocardiographic studies is essential to understanding the mechanism of mitral valve regurgitation or stenosis (functional classification), elucidate the location of leaflet dysfunction (segmental valve analysis), and plan and achieve successful surgical repair. The anatomy of the normal mitral valve in the child does not differ from that in the adult.1
The embryology of the mitral valve is complex. Our understanding of the formation of the leaflets and suspension apparatus has evolved, so that the current approach is mainly based on immunohistochemistry, in vivo labeling of cushion tissue, and scanning electron micrography of human and avian embryos.2,3 In humans, the mitral valve develops between the 5th and 15th weeks of embryonic life. During the fifth week, the atrioventricular canal is defined and lined with two cushions mostly toward the left side of the canal. The anterior leaflet of the mitral valve derives from the junction of the superior and inferior cushions, whereas the posterior leaflet derives from an infolding of the atrioventricular–muscular wall and the development of a lateral cushion. The wedging of the aortic root into the superior bridging leaflet (mostly originating from the superior cushion) will separate the developing mitral valve from its septal attachments and create the aortomitral continuity.4 The process required for the transformation of the endocardial cushion into valvar tissue is poorly understood. The presence of calcineurin and periostin is required. As the cushion tissue elongates and grows toward the ventricular cavity, it is gradually delaminated from the underlying myocardium and the leaflet becomes progressively shaped as a funnel-like structure totally attached to the myocardium. Perforations then appear into the valve leaflet and grow to form the chordae tendineae. The atrial aspect of the cushion will generate the spongy atrial layer and the ventricular layer will generate the fibrous part of the mitral valve and chordal apparatus. The separation between atrial and ventricular myocardium is dependent on the sulcus tissue located on the epicardial side of the junction. The development of the papillary muscles takes place simultaneously, originating from the myocardium. A horseshoe-shaped ridge lies within the left ventricle. The anterior and posterior parts of this ridge lose contact with the ventricular wall, forming the papillary muscles and increasing in size, while maintaining structural continuity with the cushion tissue at the tip of the papillary muscle. The midportion of the muscular ridge will be incorporated into the apical trabeculations of the left ventricle.5
Congenital stenosis and insufficiency of the mitral valve are presented together, as their pathology and associated lesions are similar. Moreover, they frequently coexist in the same patient.
A common cause of congenital mitral valve stenosis, the supravalvar mitral ring is an acquired fibrous structure attached to the posterior annulus of the mitral valve, running from both commissures to the mid-height of the anterior leaflet. The lesion is stenotic and often more significant than the extent of the ring would suggest. This is mostly due to the consequent limitation in the opening mechanism of the anterior leaflet rather than to the actual diaphragm-like effect of the ring. Strictly attached to the mitral valve annulus, it is to be differentiated from cor triatriatum (Chapter 80). The supravalvar mitral ring is thought to develop as a consequence of turbulent flow through the mitral orifice. The primary lesion of the mitral valve responsible for this turbulent flow can be stenotic or regurgitant or can be very discrete and difficult to identify (Fig. 81-1). It can be related to a prominent coronary sinus, as found in hearts with persistence of the left superior vena cava.6 The stenosis may be initially functional and created by a very large left-to-right shunt. For these reasons, the supravalvar mitral ring is probably prone to recur after surgical resection unless (or even when) the underlying anatomic anomaly has been identified and corrected. The supravalvar ring can be encountered very early in life, in the neonate or young infant. It should be suspected when a transvalvar gradient appears to increase at follow-up or when the Doppler gradient is greater than what the anatomy depicted with echocardiography would suggest; sometimes, it is only found at operation.
Very often isolated, a cleft mitral valve can be easily differentiated from a left atrioventricular valve in a partial atrioventricular septal defect.7,8 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 midportion bears the attachment of the strut chordae. Both papillary muscles are normal. Rarely, a cleft mitral valve is associated with a leaflet tissue shortening and thickening of the cleft edges. These are acquired lesions secondary to chronic regurgitation through the cleft. The defect is never stenotic and may generate only little regurgitation for a long time.
In this specific anomaly, the interchordal spaces are filled with a dense network of immature valve tissue. When there is continuity between the anterior and posterior leaflets, the accessory valvar tissue may be generating a gradient inversely correlated with the size of the perforations in the accessory tissue (Fig. 81-2). When the accessory valve tissue is entrapped in the left ventricular outflow tract, the mitral valve may become regurgitant due to the traction exerted by the accessory valvar tissue on the anterior leaflet, making the valve incompetent in midsystole.9 Left ventricular outflow tract obstruction is nevertheless the predominant hemodynamic lesion observed with this pathology.10 Very often, patients are asymptomatic and show no hemodynamic disturbances on echocardiographic studies.
Three major anatomic types of lesions are associated with lack of valvar tissue. The functional endpoint of the lesion can be either normal, predominantly regurgitant or stenotic, or both.
A parachute mitral valve (PMV) can be found in isolation and is also observed in association with Shone complex.11,12 The most common finding is that of a predominant single papillary muscle with the orifice of the mitral valve overriding its tip. With this particular pathology, there is a spectrum of abnormality of the suspension apparatus, ranging from complete fusion of the tip of the papillary muscle to the free edge of the valve to relatively normal-looking chordae with good mobility of the leaflet. Accessory papillary muscles are usually very small and connected to only a short segment of the free edge or even to the undersurface of the leaflet tissue (as would be the case in a larger-than-normal secondary chorda). The functional anatomy of the PMV depends on the interaction between the amount of tissue and the mobility of the leaflet, the presence and size of the fenestrations, and the presence, length, and quality of the chordae.11 The PMV almost always has a stenotic component. Double-orifice mitral valve is an exceedingly rare variant of PMV, with the lesser papillary muscle supporting a complete orifice. This lesion should be differentiated from the left atrioventricular valve, in which an accessory orifice is often found in the case of diminutive or absent left lateral leaflet (mural leaflet). The second orifice is almost always competent and should not be closed at the time of the repair.
This anomaly, which can be limited to only one papillary muscle, ranges from cases with short chordae to those in which the tip of the papillary muscle is actually directly attached or fused to the commissural area of the free edge. The valve is generally more regurgitant than restrictive; this is due to the lack of valvar tissue and the consequent restriction of leaflet motion (Fig. 81-3). When the papillary muscles are hypertrophied, the bulk of their mass is generally responsible for a predominantly restrictive physiology. Some Anglo-Saxon authors refer to this anatomy as arcade mitral valve.4
Here the suspension apparatus may have lost all resemblance to the normal anatomy. No papillary muscle may be identifiable or there may be multiple very small ones behind the posterior leaflet. The leaflets are suspended by a network of chordae directly attached to the posterior wall of the ventricle. This attachment is generally displaced toward the base of the heart, with an excess of tension on the anterior leaflet and extreme limitation in the motion of the posterior leaflet. The valve is most often predominantly regurgitant.
It is difficult to ascertain the congenital origin of these lesions, since the anatomy of the mitral valve is otherwise normal. Although most publications on congenital anomalies of the mitral valve include them,12 there is no evidence of their congenital origin. Unlike the previously mentioned anomalies, they are in fact not found at birth. They are usually associated with conditions characterized by significant volume loading of the left ventricle [i.e., large ventricular septal defect (VSD) or large patent ductus arteriosus]. The pathophysiology is that of initial dilation of the posterior annulus due to the effect of the increase in volume overload. Secondarily, the marginal chordae elongate and create prolapse of the free edge of the anterior leaflet. These lesions are not rare, as they account for 15 to 40 percent of the patients reported in the literaturewith congenital mitral valve regurgitation. Functional mitral regurgitation secondary to cardiomyopathy is not included in this chapter.
Mitral valve regurgitation found in an anomalous left coronary artery from the left pulmonary artery (ALCAPA) is of ischemic origin and is described in detail in Chapter 83. In this particular anomaly, mitral regurgitation is a constant finding and is quantitatively almost always greater than moderate. The typical patient is between 2 and 4 months of age at diagnosis. Correction of the ALCAPA reduces the grade of regurgitation but rarely suppresses it entirely. Structural modification of the suspension apparatus with infarction of the anterolateral papillary muscle and elongation of the chordae originating from the latter usually prevent complete regression of the regurgitation without concomitant mitral valve repair at some point.13
Mitral Valve Disease with Excess Leaflet Tissue: Mitral Valve Prolapse and Connective Tissue Disorder.
Whether to include the mitral valve prolapse syndrome (limited in its more common form to the middle scallop of the posterior leaflet) in the congenital group is debatable. The histologic anomalies are limited in adults to the middle scallop of the posterior leaflet, with predominant alteration of the elastic fibers and proliferation of myxomatous tissue; these anomalies, in all likelihood, have a genetic etiology.14,15 In the more extensive form of mitral valve prolapse (Barlow’s disease, with excess of tissue distributed to both the anterior and posterior leaflets), histology demonstrates extensive infiltration of the spongiosa with myxomatous tissue. This more extensive form can also be seen in neonates and infants. It is encountered in sporadic cases or in familial forms and has been associated with at least one locus mutation on chromosome 16. The histologic anomalies are identical to those found in Marfan,16 Loeys–Dietz, and Elher–Danlos syndromes. Similar valvar alterations are found in Hurler syndrome (mucopolysaccharidosis type I).
Acute rheumatic fever (ARF) is an autoimmune disorder in which the immune response to group A streptococcal (GAS) M protein generates T cells and antibodies that cross-react with cardiac antigens.17,18 ARF does not generate long-term sequelae to brain, joints, or skin. Only the heart (specifically the mitral and/or aortic valves) may be permanently affected. The acute damage to the valves may cause chronic and evolving lesions secondary to the scarring process and/or to modifications in hemodynamics. This chronic picture is known as rheumatic heart disease (RHD), which is the most common pediatric heart disease in developing countries. Not all individuals are equally susceptible to ARF. Only 3 to 5 percent have an inherited susceptibility, although the basis of this is unknown. Also, only a limited number of GAS strains can initiate ARF in the susceptible host.
Acute lesions are exclusively regurgitant. On inspection, the valvar tissue and chordae are swollen but supple. Prolapse of either leaflet can be seen, but the anterior leaflet is predominantly affected.19 This prolapse is usually related to elongation of limited groups of chordae, while chordal rupture is rare. Multiple small nodules (2–3 mm in diameter) can be seen on the free edge of either of the mitral leaflets. Mitral regurgitation is a combination of annular dilation (secondary to rheumatic pancarditis) and various degrees of prolapse.
The scarring process generates retraction of the valvar tissue and, to a lesser degree, the chordae. This process is sometimes sufficient to correct the prolapse of the acute phase. The healing of the spongiosa induces fusion of chordae, as demonstrated by the dramatic reduction in the number of chordae together with the large increase in their size. The physiology of the regurgitation is a combination of prolapse of the anterior leaflet, retraction of the posterior leaflet, and annular dilation (Fig. 81-4). In the pediatric age group, the mitral valve is exclusively or predominantly regurgitant, while stenosis typically appears later in the chronic phase of the disease with continuation of the retraction process. The degree of stenosis and the age at which stenoses can be found varies from population to population. The younger the age during the primary attack of rheumatic fever, the younger the patient when stenosis appears. Other factors may play a role. Calcifications are rare in the pediatric population with RHD.
Figure 81-4
A. Chronic evolved rheumatic mitral insufficiency. The anterior and posterior leaflets are severely retracted. There is limitation of the posterior leaflet motion, prolapse of the anterior leaflet, commissural fusion, and paucity of chordae, which are thickened and fused. B. Repair with posterior leaflet extension, correction of anterior type II and remodeling annuloplasty.
Bacterial endocarditis (BE) of the mitral valve is rare and, excluding patients with RHD, represents less than 2 percent of all BE in children. At the Royal Children’s Hospital (RCH), Melbourne, a history of mitral valve anomaly before the diagnosis of BE was uncommon. The resulting physiology is always that of a regurgitant lesion. Intraoperatively, a vegetation is the most common finding and typically grows on the atrial side of the mitral valve; however, vegetations are not always present at the time of surgery. Rarely the vegetation will have embolized and, more commonly, it will either regress with medical therapy or have never been there. Other findings are perforation of the leaflet (Fig. 81-5), abscess formation within the mitral annulus, or extension toward the aortic valve. Histologic examination of vegetations discloses microorganism-infiltrated fibrin thrombi. Findings in the affected valvar tissue at the vegetation implantation site suggest a strong inflammatory reaction with neovascularization and infiltration of lymphocytes, giant cells, and fibroblasts. At the time of surgical repair, it is very important to differentiate intact valvar tissue (supple, thin, and resistant) from infected tissue (thickened, edematous, and friable).
Figure 81-5
Acute endocarditis of the mitral valve. Perforation of the anterior leaflet (A). Result following the repair with autologous pericardium treated with glutaraldehyde (B). ASD, atrial septal defect. (Image courtesy of Luca Vricella, Division of Cardiac Surgery, The Johns Hopkins University.)
For both stenosis and regurgitation, the clinical presentation in this age group includes cardiac failure, with dyspnea on exertion (feeding) and tachypnea at rest. Severe failure to thrive is usually present. Clinical examination shows hepatomegaly and cool extremities. Cyanosis may be present. Auscultation is often unyelding, but a strong apical systolic murmur should indicate significant mitral regurgitation, whereas a diastolic murmur in the case of mitral stenosis can be difficult to auscultate or may even be absent in the context of low cardiac output or associated atrial-level left-to-right shunting.
Beyond the neonatal period, failure to thrive, dyspnea on exertion, and a history of repeated chest infections are predominant in mitral stenosis. Pallor and cold extremities, tachycardia, and dyspnea suggest low cardiac output. Signs of pulmonary hypertension, with an exacerbated second heart sound, prominent right ventricular impulse, and hepatomegaly are frequent. A diminished first sound with a low-intensity mid-diastolic murmur suggests thickened leaflets with limited excursion and can be absent in a low-output state. Older infants and toddlers with mitral regurgitation present with various degrees of failure to thrive and dyspnea with feeds or on exertion. An enlarged left ventricular impulse (with a high-frequency, high-intensity holosystolic murmur heard at the apex and extending into the axillae) is easily auscultated, with signs of right heart failure rarely being seen.
There is left atrial enlargement in both mitral stenosis and regurgitation and left ventricular enlargement in mitral regurgitation; right atrial and right ventricular enlargement is seen when pulmonary hypertension is present. In the pediatric population, the rhythm is almost always sinus.
Chest x-ray will typically demonstrate the “double density” seen in left atrial enlargement; this is more often the case in regurgitation than in stenosis; other findings are those of variable pulmonary plethora and enlarged contour of the main pulmonary artery. In the presence of mitral valve regurgitation, left ventricular enlargement is responsible for most of the prominence of the cardiac silhouette.
Echocardiographic assessment is obligatory and essential. Systematically conducted, it provides all the information necessary to diagnose the mitral anomaly, determine its severity,20,29 and assist the surgeon with the repair.21,30
The transthoracic four-chamber view is best for obtaining an accurate transvalvar gradient and, together with the parasternal long axis view, defining the precise amplitude of any prolapse or restriction; in general, it is much more accurate than other views in grading the degree of regurgitation. The short-axis view of the mitral valve and the left ventricle provides direct imaging of the area of the mitral orifice as well as the location of origin of the regurgitation jet (in the en face view). It allows a precise analysis of the papillary muscles (presence, size, location, and symmetry) and of anterior leaflet integrity. Transesophageal echocardiography (TEE) is superior in defining the anatomic details of the suspension apparatus and evaluating the functional classification. By moving the probe within the esophagus, the operator can obtain 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 anatomic landmarks.
For mitral stenosis, the peak instantaneous and mean gradients across the valve must be interpreted according to the quality of diastolic function and of associated lesions. The overall impact of the gradient on the surgical indication must be weighed against pulmonary artery pressure and clinical context.
Transthoracic echocardiography (TTE) and TEE make it possible to classify mitral valve pathology, according to the motion of the leaflets, into one of the three following types (Carpentier’s functional classification). This classification is irrespective of anatomy and etiology but is essential for carrying out accurately the repair.22,31
Mitral regurgitation results from a lack of coaptation between the leaflets.
The free edge of one or both leaflets overrides the plane of the orifice during systole.
The motion of one or both leaflets is limited. This can be secondary to short or stiff leaflet tissue or suspension apparatus (type IIIa or diastolic) or because the leaflet is pulled away from the coaptation area by a paradoxical motion of the ventricular wall (type IIIb or systolic).
Currently, the major benefit of three-dimensional (3-D) echocardiography is to provide a surgical view of the mitral valve to the surgeon (from the atrium, with the anterior commissure to the left and the posterior commissure to the right) and to precisely localize on this view the prolapse and restriction of the leaflets. 3-D echocardiography has made very important progress in the past few years. Pediatric probes are now available and can be inserted in patients smaller than 5 kg. Even if spatial definition, speed of acquisition and slice thickness have improved, thin and fast-moving structures like leaflet tissue and chordae are less well seen in infants and young children than in adults. In larger patients (weighing more than 12 kg), information on the origin of the regurgitant jet, the volume of the jet, and ventricular ejection volume can be obtained as in adults.23
Computed tomography (CT) allows precise calculation of the mitral valve regurgitant fraction with flow measurement, so does magnetic resonance imaging (MRI) when correction for the modification of the plane of the valve with three-directional velocity-encoded MRI is used. The mitral valve area is calculated with MRI, and correlations with echocardiographic findings are very strong.24 Whatever the imaging technique employed, there are limitations in small patients, in whom resolution is critical. Neither MRI nor CT has enough spatial resolution to visualize valvar tissue or suspension apparatus in small children.
In the current era, there is very limited indication for an invasive diagnostic and hemodynamic study in the assessment of mitral valve disease. Associated lesion or consideration for balloon valvuloplasty may warrant cardiac catheterization.
There is no laboratory test for the diagnosis of ARF, hence the diagnosis remains clinical. The diagnosis requires the evidence of a preceding GAS infection (elevated or rising antistreptolysin O titers, a positive throat culture, or positive rapid antigen test for group A streptococci); although this is necessary, it is not sufficient. The probability of a diagnosis of ARF varies according to geographic location (according to ARF incidence) and ethnicity. For diagnostic purposes, clinicians follow Jones’s criteria, updated in 1992.25
Medical treatment must be vigorous when the annulus is too small to allow implantation of a mechanical prosthesis in the anatomic position. In the setting of predominant mitral regurgitation, the treatment should include diuretics, and, if necessary, blood transfusion26 and positive pressure ventilatory support. In patients who do not yet require surgery, the benefit of angiotensin-converting enzyme (ACE) inhibitors is not clear.27 In mitral stenosis, any vasodilator or afterload-reducing agent is obviously contraindicated.
Indications for surgical intervention in chidren are different than in adults. Within the pediatric age group, the cut-off point is more related to the size of the mitral valve annulus than to the age of the patient. The rationale for this is in the risk involved with valve replacement in nona-natomical position or with oversized prosthesis.
“Large” implies an annulus greater than 30 mm in female patients and greater than 32 mm in males. Using a wide range of mitral valve repair techniques, the probability of a successful repair of the valve with a large annulus is very high. A mitral annuloplasty or even a remodeling annuloplasty will not be outgrown and will not generate stenosis with the growth of the patient. The repair of virtually all valves is, when a sizeable annulus is present, an accessible goal.
In neonates (<28 days), infants (>28 days and <1 year), and generally in every pediatric patient with a mitral valve annulus less than 19-20 mm in size, repair is technically very challenging, while replacement is possible only with the use of surgical artifacts associated with significantly increased mortality.28 In these patients, surgical intervention should be deferred as long as the patient can be managed with intense medical therapy, including transfusion and continuous positive airway pressure (CPAP). Aggressive medical therapy allows, in some cases, postponement of surgical intervention for several months, often generating significantly more favorable operating conditions.
In these patients, with a mitral valve annulus greater than 20 mm but smaller than adult size, mitral valve replacement (MVR) can be safely performed in the anatomic position.29 Therefore, the timing of the mitral valve repair does not have to be delayed for fear of replacement in an unfavorable position. In this age group, this anatomic situation is found in patients between the ages of 1 to 12 years; it is generally safe to wait for quite a long time (up to several years) in cases of severe regurgitation provided that adequate monitoring of pulmonary artery pressure and ventricular function is achieved.30,31
At our institution, cardiopulmonary bypass is conducted with moderate hypothermia (32°C), hemoglobin of 10 to 12 g/dL, pump flow of 150 to 200 mL/min/kg, or 2.4 L/min/m2. Myocardial protection is achieved with warm blood cardioplegia administered every 20 min. The time for preparation for bypass is used for mandatory intraoperative TEE. Venous cannulation should allow as much access as possible to the atrioventricular groove. Direct cannulation of the superior vena cava at a distance from the cavoatrial junction and of the inferior vena cava immediately at its origin allows for precise application of the retractor blades. Limited dissection of the groove is performed and, after cross-clamping, the left atrium is entered in the interatrial groove. Exposure is enhanced with mattress sutures inserted into the posterior annulus, pulling the valve upward and to the right, toward the operator. The tourniquet on the inferior vena cava is pulled upward and to the left. A self-retaining retractor for mitral surgery adapted to the size of the patient is used in our practice. Approach through the interatrial septum provides a lesser edge for anchoring of the retractor blades and exposes the conduction tissue to more pressure. Approach through the roof of the left atrium does not expose the posterior commissure and the posterior papillary muscle well. We also believe that the ranseptal approach provides lesser exposure.
Once satisfactory exposure of the mitral valve is achieved, the valve is systematically analyzed and findings are compared with the echocardiographic information. The functional classification is confirmed as well as its location (A1, A2 or A3, P1, P2 or P3), but the extent of the mitral valve prolapse or restriction is based on echocardiographic studies of the beating heart. Then analysis of the anatomy follows: a supravalvar ring is confirmed or eliminated; the diameter of the annulus is carefully assessed; texture, aspect, and size of the mitral valve leaflets are noted; the presence and location of any jet lesion is determined as well as the number, aspect, and distribution of the chordae; finally, the presence of commissural tissue and dedicated suspension apparatus as well as the size, location, and morphology of the papillary muscles are assessed. The examination ends with a careful check for accessory mitral valve tissue in the interchordal spaces. The diameter of the annulus and of the opening of the mitral valve is compared to the normal values reported for the patient’s body surface area. We use a modification of the sizes provided by Kirklin.32 The treatment is adapted to the predominant functional class.
With the exception of some isolated type I abnormalities without annular dilation (mostly the cleft mitral valve), an annuloplasty is mandatory in all cases of mitral valve insufficiency. In most other cases, attempts to perform mitral valve repair without annuloplasty have resulted in recurrence.12 In order to accommodate an adult-size device or a larger-size annulus than what would be indicated from the area of the anterior leaflet, leaflet enlargement with glutaraldehyde-treated autologous pericardium of the posterior leaflet (Fig. 81-6), the anterior leaflet (Fig. 81-7), or both are used.12,33 When no remodeling annuloplasty is available for the size of the patient or the device is thought to be too small, an annuloplasty limited to the posterior annulus is indicated. The annuloplasty must incorporate both fibrous trigones and can be interrupted to allow for further growth. In our hands, the best method for posterior annuloplasty, allowing for growth without compromising the inflow, is a row of interrupted compression U stitches tied individually (Fig. 81-8).21 Also, for bigger patients, a single layer of ePTFE (expanded polytetrafluoroethylene/Goretex) band can be used. We try to avoid bulky material in small annuli; this can be later responsible for fibrosis of the posterior leaflet.34
Figure 81-8
Annuloplasty limited to the posterior annulus in patients with less than adult size annulus. Two techniques are represented and used at the Royal Children’s Hospital, Melbourne. Mattress sutures are implanted along the posterior annulus from one commissure to the other. (1) The mattress sutures are tied over themselves and compress the annulus. (2) A band of PTFE is used to calibrate the shortening. Care is taken not to overtighten the knots.
Multiple techniques are available to correct the enhanced leaflet motion seen in this functional class. Whether these techniques are to be used in isolation or in combination depends on the extension in width of the prolapse (localized or extended to the whole width of the free edge). It is the height of the prolapse (based on the findings of TEE) and the quality of the chordae that will dictate the choice of technique.
As long as the anatomic correction is adequate (restoring a large surface of apposition between the anterior and posterior leaflets), all techniques are effective and reliable. Overcorrection will generate stress directly on the repaired area and deprive the valve of the relief of stress provided by the surface of apposition. All overcorrections eventually fail, most often in the first few days postoperatively.
This technique requires thin and flexible chordae.22 This form of correction generates important shortening of the chordae and is only adopted when the prolapse is wide (Fig. 81-9). It is a time-consuming procedure and is to be considered if multiple chordae are to be shortened, requiring also access to the mid-height level of the papillary muscles.
Chordal transfer between secondary chordae and the free edge (more than chordal transfer from the posterior leaflet to the anterior leaflet) allows for correction of localized prolapse. The chorda 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 (Fig. 81-10).
Wedge resection of the papillary muscle (Fig. 81-11) and sliding plasty (Fig. 81-12) generate different degrees of correction of prolapse of multiple chordae. These techniques are very well adapted to prolapse involving a large segment of the anterior leaflet.
This technique can be used in combined anterior and posterior type II deformity. It is useful when the papillary muscle as a whole has to be shortened, as is usually the case in chronic ischemic papillary muscle or in Barlow’s disease (Fig. 81-13).
Artificial chordae should be used only in the absence of available chordae of appropriate strength and quality in the area of prolapse. The insertion requires rigorous technique to avoid overcorrection and large knots at the free edge (Fig. 81-14).
Figure 81-14
Technique for insertion of ePTFE chordae: (1) A template is made from a short plastic tube cut at the required length and slid over the distal part of the stitch. (2) This template can be taken from the facing posterior leaflet edge. (3) The free edge of the leaflet is lowered to the contact of the papillary muscle. The artificial chordae is tied while the template is clamped. (4) The template is removed and the mattress suture is pulled to bring the knot in contact of the papillary muscle.
Successful correction of restricted leaflet motion and insufficient leaflet tissue is the essence of working with congenital mitral anomalies, especially in the first year of life. It falls into three general categories:
Posterior leaflet mobilization and enlargement associated with mobilization of the papillary muscles. Access to the suspension apparatus is the key to adequate mobilization of the latter. It can be done through the mitral valve orifice when it is sufficiently large. Most often, it is very small and does not allow for good access to the suspension apparatus. In these situations, detachment of the posterior leaflet generates a good view of the papillary muscles. Adequate thinning, mobilization from the posterior wall, and splitting and fenestration of the papillary muscles can then be performed safely with good exposure. After full mobilization, the posterior leaflet is reconstructed with enlargement of the valvar tissue (see Fig. 81-6).12,21
Enlargement of valvar tissue using autologous pericardium treated with glutaraldehyde. Augmentation of the valvar leaflet tissue is the only way to treat a lack of valvar tissue. It can be limited to the anterior leaflet (see Figs. 81-6 and 81-7) or the posterior leaflet or be used for both. 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 extends from one commissure to another, the extension should reproduce a shape with three scallops and two subcommissures to allow for a large opening in diastole. 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) in order to avoid mechanical stress at this level. The height of the extension should not be greater than two-fifths of the height of the anterior leaflet, leaving the area close to the free edge intact to allow for a supple and efficient surface of coaptation. Unless required by a specific anatomy, the enlargement should be symmetrical from trigone to trigone.
3. Resection of supravalvar rings and accessory mitral valve tissue. Resection of supravalvar tissue requires excellent exposure of the leaflets. The supravalvar tissue can sometimes be peeled off the valvar tissue. More often, there will be the need for a careful cleavage plane with blunt dissection. Perforation of the anterior leaflet may occur; this should be closed with a figure-of-eight suture (Fig. 81-15). The resection of accessory mitral valve tissue requires a similarly rigorous surgical technique, and very good exposure of the subvalvar apparatus is needed to perfectly differentiate the mitral valve chordae from what can be resected without compromising the integrity of the suspension apparatus. Various approaches to the suspension apparatus may have to be combined: through the mitral valve orifice and the aortic valve or by detachment of the posterior leaflet (Fig. 81-16).
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