Ann Thorac Surg 2003;75:1752-1762
© 2003 The Society of Thoracic Surgeons
Original article: cardiovascular
Cleft mitral valve without ostium primum defect: anatomic data and surgical considerations based on 41 cases
Stella Van Praagh, MDa,b*,
Diego Porras, MDb,
Guido Oppido, MDb,
Tal Geva, MDa,
Richard Van Praagh, MDa,b
a Departments of Cardiology and Pathology, Children’s Hospital Boston, Boston, Massachusetts, USA
b Department of Pediatrics and Pathology, Harvard Medical School, Boston, Massachusetts, USA
Accepted for publication January 17, 2003.
* Address reprint requests to Dr Stella Van Praagh, Cardiac Registry, Children’s Hospital Boston, 300 Longwood Ave, Boston, MA 02115, USA.
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Abstract
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BACKGROUND: Cleft mitral valve without an ostium primum defect, referred to as isolated cleft mitral valve, has been the subject of many reports; yet its morphology and operability remain incompletely understood.
METHODS: The anatomic findings in 36 postmortem cases, five explanted hearts, and relevant clinical data constitute the material basis of this report. Cardiac catheterization data were available in 29 cases and two-dimensional echocardiograms in 13 cases.
RESULTS: Twenty cases had normally related great arteries with subpulmonary conus. Of these cases 4 (20%) had tetralogy of Fallot and 1 had tricuspid atresia. Twenty-one cases had abnormal ventriculoarterial relationships with subaortic or bilateral conus resulting in transposition in 16 (76%) and double-outlet right ventricle in 5 (24%). In the cases with normally related great arteries, the morphology of the ventricular septal defect and the mitral cleft were similar to those of the more complete forms of atrioventricular canal defects. The mitral cleft usually resulted in progressive mitral regurgitation, which can be treated by surgical closure of the cleft. In the cases with abnormal conus, the morphology of the ventricular septal defect and the mitral cleft did not resemble atrioventricular canal defects. The attachment of the cleft usually produced obstruction of the left ventricular pulmonary outflow tract. Surgical repair of the cleft cannot eliminate this obstruction.
CONCLUSIONS: There are two different anatomic types of isolated cleft mitral valve: the canal type, and abnormal conus type. Diagnosis of the associated ventriculoarterial relationships helps to guide their surgical treatment.
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Introduction
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A cleft anterior leaflet of the mitral valve without an ostium primum defect is a relatively rare malformation that may or may not be associated with a variety of other congenital heart defects. These additional defects may include ventricular septal defect (VSD), tetralogy of Fallot, transposition of the great arteries (TGA), double-outlet right ventricle (DORV), tricuspid atresia, and double-inlet left ventricle.
Unresolved questions that have been discussed in the literature [1–5] are the following: Is isolated mitral valve cleft related morphogenetically to the more complete forms of common atrioventricular canal? Is there more than one type of isolated mitral valve cleft? Can surgical closure of the cleft eliminate the hemodynamic disturbances resulting from this cleft?
The principal purpose of this article is to address these questions with special emphasis on their diagnostic and surgical relevance.
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Material and methods
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Among the 3,369 heart specimens with congenital structural heart defects preserved in the Cardiac Registry of the Children’s Hospital Boston from 1957 to 2002, we identified 41 cases (1.2%) with cleft mitral valve without an ostium primum defect. To date, this is the largest series documented with findings from pathology.
The medical records of these 41 cases were reviewed to obtain the frequency of the premortem or pretransplantation diagnosis of the mitral valve abnormality. The 13 available two-dimensional (2D) echocardiograms obtained after 1982 were reviewed with specific attention to the point of attachment of the cleft of the anterior leaflet of the mitral valve.
Terminology
Cleft, derived from the verb to cleave, is defined as a space or opening made by splitting. A cleft mitral valve has a split anterior leaflet with each part of the anterior leaflet typically attaching to a different papillary muscle group.
Commissure, from com (cum) and mittere, literally means a sending or thrusting together (Latin). A mitral valve commissure is an area in which the anterior and posterior leaflets are thrust together by chordal attachments to the same papillary muscle group.
Membranous VSD with posterior extension is the situation in which the deficiency of the membranous septum extends posteriorly under part of the septal leaflet of the tricuspid valve.
Membranous VSD with anterior extension is the situation in which the deficiency of the membranous septum extends anterosuperiorly under the rightward part of the conal septum.
A VSD of the atrioventricular (AV) canal type is the situation in which the deficiency of the membranous septum extends posteriorly under the entire length of the septal tricuspid leaflet.
Tetralogy of Fallot VSD with inlet extension is the situation in which the usual conoventricular VSD of tetralogy of Fallot extends under the septal leaflet of the tricuspid valve.
Conoventricular VSD with conal septal hypoplasia or malalignment is the situation in which the VSD lies between the conal septum superiorly and the septal band and ventricular septum inferiorly. The malalignment of the conal (infundibular) septum may be toward the right ventricular cavity, ie, rightward malalignment in D-ventricular loops or posterior conal septal malalignment, ie, toward the posterior left ventricle in D- or L-ventricular loops.
A cleft mitral valve without an ostium primum defect has been often referred to as an isolated cleft mitral valve (ICMV) [2, 6]. Because of its brevity, we will use this term in this report with the meaning that the cleft mitral valve is not associated with an ostium primum defect, but that it may coexist with several other heart malformations.
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Results
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Anatomic findings
Of the 41 cases, 20 (49%) had normally related great arteries and are presented in Table 1.
Twenty-one cases (51%) had an abnormal conus resulting in TGA or DORV and are presented in Tables 2 through 4.
The morphology of the mitral
valve cleft (ie, whether it was complete, incomplete, narrow, wide, with or without thickening and rolling of its free margins)
and the kind of VSD present are described in Tables 1 through 4. The attachments of the mitral valve cleft, ie, to the membranous septum when intact or to the various parts of the VSD crest, or to the free wall of the left ventricle (LV), are also described in Tables 1 through 4 and documented in Figures 1 through 9.
Tables 1 through 4 also include the LV septal inlet/outlet length ratio and
the associated cardiac defects in each of the 41 cases.
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Fig 1. Left ventricle of girl, aged 6 years 10 months, with normally related great arteries (case 1, Table 1). Ventricular septum is intact. Mitral valve (MV) cleft attaches to membranous septum, which is under commissure between right coronary cusp (RCC) and noncoronary cusp (NCC) of aortic valve. Absence of ventricular septal defect results in semivertical direction of MV cleft toward left ventricular outflow. Margins of MV cleft are thickened and rolled. Anterolateral papillary muscle (ALPM) and posteromedial papillary muscle (PMPM) of MV are hypertrophied and close together. Left ventricular inlet/outlet ratio = 0.8.
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Fig 2. Left atrial and left ventricular view of heart of girl, aged 12 years 8 months, with normally related great arteries (case 2, Table 1). Mitral valve (MV) cleft is very wide with rolled, thickened margins. Cleft attaches to the intact membranous septum. Left atrium is enlarged and receives right pulmonary veins (RtPVs) and left pulmonary veins (LtPVs). Atrial septum is intact. Left ventricle (LV) is markedly hypertrophied. Left ventricular inlet/outlet ratio = 0.8. (MPA = main pulmonary artery; Septum 1° = septum primum.)
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Fig 3. Heart of 23-year-old woman (case 10, Table 1) with tetralogy of Fallot and ventricular septal defect (VSD) extending into area of membranous septum. (A) Right atrial and right ventricular view. (B) Opened left ventricle. Left ventricle inlet septal length is shorter than that of outlet (0.675). Mitral valve (MV) cleft attaches to inferoposterior crest of the VSD. Plane of cleft is perpendicular to plane of ventricular septum. Posteromedial papillary muscle (PMPM) is larger than anterolateral papillary muscle (ALPM), corresponding to larger size of posterior segment of anterior mitral valve leaflet. Distance between the two papillary muscle groups is shorter than normal. The margins of cleft are thickened and rolled, indicative of mitral regurgitation. (AoV = aortic valve; CoS = coronary sinus; EV = Eustachian valve; FO = fossa ovalis; TV = tricuspid valve.)
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All
cases had visceroatrial situs solitus. The 20 cases with
normally related great arteries are summarized in Table 1. D-TGA with ventricular D-loop was present in the 10 cases summarized in Table 2, and
DORV with ventricular D-loop was present in the 5 cases in Table 3. Table 4 summarizes
the 6 cases with L-TGA and ventricular L-loop. Two cases with normally related great arteries and 4 cases with D-TGA had
an intact ventricular septum (Figs 1, 2, 5). All 41 cases had two separate atrioventricular valves, and the tricuspid valve did not have a cleft.
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Fig 4. Heart and part of lungs of 2-month-old girl with tetralogy of Fallot (case 7, Table 1). Mitral valve (MV) cleft attaches to ventricular septum. Ventricular septal defect has been surgically closed. The two segments of the anterior MV leaflet connect with a very hypoplastic posteromedial papillary muscle (PMPM). A much larger anterolateral papillary muscle (ALPM) is fused with leaflet tissue of MV. Interchordal spaces are obliterated. Left atrial appendage (LAA) was enlarged and hypertrophied. Left ventricular inlet/outlet ratio = 0.71. Cleft functions as orifice of MV and is very stenotic. The resulting pulmonary venous hypertension caused pulmonary artery hypertension despite stenosis of RV outflow. (Ao = aorta; LAD = left anterior descending coronary artery; LPA = left pulmonary artery; RV = right ventricle; VS = ventricular septum.)
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Fig 5. Left ventricle of explanted heart of 11-year-old boy with transposition {S, D, D} after Senning atrial switch in early infancy (case 9, Table 2). Mitral valve (MV) cleft attaches to free wall of left ventricle (LV) superiorly to transposed pulmonary valve, which has been replaced with a prosthetic pulmonary valve (PV). Free margins of mitral valve cleft are thickened and rolled, although the patient had minimal mitral regurgitation. Thickened free margins of cleft and fibrous ridge (impact lesion) on the septal surface of LV caused severe left ventricular outflow obstruction. Anterolateral papillary muscle (ALPM) and posteromedial papillary muscle (PMPM) are hypertrophied and close together. Left ventricular inlet/outlet ratio = 1.
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Fig 6. Open left ventricle of 11-month-old girl with double-outlet right ventricle {S,D,D} and conoventricular ventricular septal defect (VSD) (case 4, Table 3). Mitral valve (MV) cleft is incomplete and its raphé attaches on anterosuperior crest of VSD. Posteromedial papillary muscle is twice the size of the anterolateral papillary muscle, corresponding to larger posterior part of the anterior mitral leaflet. Left ventricle is markedly hypertrophied. Conal septum (CS; not seen in this figure) is malpositioned to right of ventricular septum. Left ventricular inlet/outlet ratio = 1.
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Fig 7. Left ventricular outflow of 6-year-old boy with transposition {S, D, D} and conoventricular ventricular septal defect (VSD) with posterior conal septal malalignment (case 7, Table 2). Mitral valve (MV) cleft attaches to free wall of LV above and to left of PV and, in combination with posteriorly malaligned conal septum, produces significant subpulmonary stenosis. The MV cleft is incomplete and narrow, dividing equally the anterior MV leaflet. Anterolateral papillary muscle (ALPM) and posteromedial papillary muscle (PMPM) are of equal size and close to each other. Left ventricular inlet/outlet ratio = 1. It is obvious that surgical closure of the MV cleft will not affect LV outflow obstruction. (PV = pulmonary valve.)
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Fig 8. (A) Right ventricle of 17-year-old boy with double-outlet right ventricle {S, D, D} and conoventricular ventricular septal defect (VSD) with rightward malalignment of conal septum (case 5, Table 3). (B) Left ventricle (LV) of the same heart. Mitral valve (MV) attaches to left ventricular free wall to the left and slightly inferior to the PV. Free margins of complete, wide MV cleft are thin and not rolled, indicative of absence of mitral regurgitation. Both parts of MV cleft attach to a single posteromedial papillary muscle (PMPM). Left ventricular inlet/outlet ratio = 1. (Ao = aorta; Inf S = infundibular septum [conal septum]; PV = pulmonary valve; To Ao = stenotic outflow tract to aorta; TV = tricuspid valve.)
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Fig 9. Left ventricle (LV) of 3-day-old girl with transposition {S, L, L} and small restrictive ventricular septal defect (VSD) (case 2, Table 4). Complete, narrow mitral valve (MV) cleft attaches to LV free wall next to right upper border of transposed PV. Posteromedial papillary muscle (PMPM) group is much larger than anterolateral papillary muscle (ALPM), corresponding to larger size of posterior segment of cleft anterior leaflet of MV. Left ventricular inlet/outlet ratio = 1. (CS = conal septum; PV = pulmonary valve; Transposition {S,L,L} = TGA with solitus atria, L-loop ventricles, and L-TGA.)
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In 15 of the 20 cases (75%) with normally related great arteries, the VSD was either a small membranous defect or a large membranous defect extending under the septal leaflet of the tricuspid valve. In the 4 cases of tetralogy of Fallot, the typical anterosuperior conal septal malalignment defect extended into the area of the membranous septum and under the septal leaflet of the tricuspid valve (Figs 3A, 3B). In 1 case with tetralogy of Fallot, the mitral valve cleft was also its orifice, resulting in severe congenital mitral stenosis (Fig 4). The single case with tricuspid atresia had a conoventricular VSD without conal septal malalignment.
Of the 21 cases with abnormal conus, a VSD was present in 17. In 12 of 17 (71%), the VSD was conoventricular with rightward or posterior conal septal malalignment (Figs 6, 7). Two cases, 1 with double-inlet left ventricle and 1 with tricuspid atresia, had a conoventricular VSD in the form of a restrictive bulboventricular foramen (cases 3 and 6, Table 2). Two other cases with straddling tricuspid valve (cases 1 and 3, Table 4) had a VSD of the AV canal type, which almost always is present in cases of straddling tricuspid valve. There was only one true exception to the expected type of VSD in ICMV with abnormal conus, which occurred in case 6 (Table 4). This patient had a large membranous VSD with the mitral cleft attachment in its inferoposterior crest.
The LV septal inlet length/outlet length ratio was significantly different in ICMV with normally related great arteries compared with ICMV with abnormally related great arteries, ie, TGA or DORV (Tables 1–4). In ICMV with normally related great arteries (n = 20), the LV inlet/outlet ratio had a mean of 0.76 ± 0.10, ranging from 0.59 to 1.0, and a median of 0.75; whereas in ICMV with abnormally related great arteries (n = 21), this ratio had a mean of 0.96 ± 0.13, ranging from 0.53 to 1.1, and a median of 1.0 (p < 0.0001). The LV inlet/outlet ratio was less than 1 in the 2 cases with straddling tricuspid valve that had, as expected, a VSD of the AV canal type (cases 1 and 3, Table 4). Nevertheless, even with the inclusion of those 2 cases and case 6 (Table 4) with the large membranous VSD, the p value remains very significant.
Clinical data
The sex was known in all 41 cases. In the 20 cases with normally related great arteries the male/female (M/F) ratio was 0.7. In the 10 cases with D-TGA the M/F ratio was 9. In the 5 cases with DORV the M/F ratio was 1.5, and in the L-TGA cases the M/F ratio was 0.2. The range of the age at death or cardiac transplantation in the cases with normally related great arteries (Table 1) was from a fetus of 27 weeks gestation to an adult of 23 years, the median age being 32/12 years. The range of the age at death or cardiac transplantation in the cases with abnormal conus (Tables 2–4) was 30 hours to 17 years, with a median age of 2 years. Cases 1, 2, and 6 (Table 1), having no additional significant heart defects, had clinical signs of severe mitral regurgitation. In all other cases the clinical symptoms depended on the additional cardiac malformations.
The premortem or pretransplantation diagnosis of mitral valve cleft or mitral regurgitation by cardiac catheterization or by 2D echocardiography is indicated in the clinical data in Tables 1 through 4. In several patients the cardiac catheterization either did not include angiocardiography or was limited to the right cardiac chambers only. For these reasons the mitral cleft was diagnosed in only 1 of the 29 patients who underwent cardiac catheterization. By contrast, the presence of a mitral cleft and mitral regurgitation was diagnosed in 8 of 13 (62%) of the patients who underwent 2D echocardiography. Premortem diagnosis of LV outflow obstruction did not occur in any of the cases with normally related great arteries. Postmortem findings were indicative of LV outflow obstruction in 2 cases (cases 16 and 20; Table 1). Premortem diagnosis of LV outflow obstruction by 2D and Doppler echocardiography or cardiac catheterization occurred in 11 of 21 (52%) cases with TGA or DORV.
Review of the available echocardiograms demonstrated that the cleft in the anterior mitral leaflet was best visualized from a subcostal or a parasternal short-axis view. From the parasternal long-axis view, the presence of a cleft could be suspected based on an abnormal orientation of the anterior mitral leaflet toward the outflow septum. The attachments of the cleft to the ventricular septal crest could best be determined from a parasternal short-axis view. When available, color flow Doppler mapping clearly demonstrated the location and extent of mitral regurgitation. Color and spectral Doppler identified left ventricular outflow obstruction caused by the mitral cleft attachments.
The year of death or cardiac transplantation of each patient is included in all Tables 1 through 4 so that the reader can understand why some patients did not have diagnostic echocardiography performed and why surgical treatment of the associated complex heart defects was not successful.
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Comment
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The presence of a cleft in the anterior leaflet of the mitral valve without the coexistence of an ostium primum defect raises the following question: Do the cases of ICMV constitute a less complete form of an AV canal defect?
The present series of 41 postmortem or transplanted cases helps to answer this question. The examination of these 41 heart specimens made it obvious to us that there were two different groups of ICMV depending on the presence of normal or abnormal conus.
Isolated cleft mitral valve with normal conus and normally related great arteries occurred in 20 of the 41 cases. In this group of patients we observed the following characteristics: (1) The inlet dimension of the left ventricular septal surface was shorter than its outlet dimension in 19 of 20 (95%) cases (cases 1–18, 20; Table 1). This finding is characteristic of AV canal malformation [7]. (2) The ventricular septal deficiency involved the membranous septum, which is part of the AV canal septum, in 17 of the 18 cases (94%) with a VSD. The only conoventricular VSD was present in the patient designated as case 11 (Table 1), who had tricuspid atresia with absent right ventricular sinus. (3) The attachment of the mitral cleft was to the membranous septum when the ventricular septum was intact (Figs 1A, 2). When a large membranous VSD with posterior extension was present, the mitral cleft attached to the inferoposterior border of the defect (Figs 3A, 3B). Hence, when the membranous VSD was large, the direction of the cleft was horizontal—very similar to the orientation of the mitral cleft in ostium primum defect with cleft mitral valve (Fig 3B). (4) Isolated cleft mitral valve with normally related great arteries was associated with trisomies in 50% of the cases (Table 1). Trisomies are often known to have AV canal defects [4]. (5) Isolated cleft mitral valve with normally related great arteries was found to occur in families who also had members with other forms of AV canal defects [4].
On the basis of the above-mentioned findings we think that phenotypic and, probably, morphogenetic similarities exist between ICMV with normal conus and other, more complete forms of AV canal defects. This view has also been expressed by other investigators [1, 4], although the difference between the cases of ICMV with normally related great arteries and the cases with abnormal conus was not mentioned. One of the reasons that some authors disagree with the view that there are similarities between the ICMV with normally related great arteries and cleft mitral valve with ostium primum defect is the observation that the direction of the mitral valve cleft in ICMV is toward the left ventricular outflow and not toward the ventricular septum [2, 3].
In our 20 cases with normal conus, the direction of the mitral valve cleft was influenced by the presence or absence of a membranous VSD. When the ventricular septum was intact or when a very small membranous VSD was present, the direction of the mitral valve cleft was towards the left ventricular outflow, as the membranous septum is immediately below the right coronary–noncoronary commissure of the aortic valve (Fig 1). However, when a large membranous VSD with posterior extension was present, the direction of the mitral valve cleft was horizontal, directed toward the ventricular septum, just like in cases of ostium primum defects with cleft mitral valve (Fig 3B).
Many recent studies have demonstrated that 2D echocardiography is the method of choice for diagnosing a cleft mitral valve and the various degrees of mitral regurgitation [6, 8, 9]. Many of the patients included in this study died either before the availability of 2D echocardiography or before 1986 when color Doppler interrogation did not exist.
The width of the cleft in some cases with normally related great arteries appears to increase with age [10]. In our series, a wide cleft was observed only in children (cases 2 and 5, Table 1, Fig 2) and not in young infants. The same is true for the presence and degree of mitral regurgitation, which, in our patients, started in childhood and was progressive. Successful surgical treatment of wide MV clefts with the use of autologous glutaraldehyde-treated pericardium has been achieved in recent years [11].
Because the mitral regurgitation in ICMV appears to be progressive, early surgical treatment is indicated even when mitral regurgitation is mild [12]. Case 6 (Table 1) in our study had incomplete closure of the mitral valve cleft at the age of 7 years. The surgeon feared the development of mitral stenosis if the cleft were closed completely. Six and one-half years later the continuing mitral regurgitation became severe and was accompanied by marked left ventricular hypertrophy and dysfunction, which necessitated cardiac transplantation.
In 8 of 10 (80%) patients with trisomies (Table 1) and in 1 nontrisomic patient, the mitral valve cleft attached on the ventricular septum with several short chordae. These chordal attachments may interfere with the normal movement of the anterior mitral leaflet and should be cut when the mitral valve cleft is surgically closed [13].
Isolated cleft of the mitral valve with abnormal conus and TGA or DORV occurred in 21 of the 41 cases. It constitutes a different kind of heart defect, both anatomically and developmentally, for the following reasons: (1) The inlet and outlet lengths of the LV septal surface were almost always equal (Tables 2–4). (2) In our series, the attachment of the cleft of the mitral valve was on the free wall of the LV to the left of the transposed pulmonary valve in 14 of 21 (67%) cases of ICMV and abnormal conus (Figs 5, 7, 9). Hence in these cases the plane of the cleft of the anterior leaflet of the mitral valve was parallel with, rather than perpendicular to, the plane of the ventricular septum. (3) When the cleft attached on the septum there was usually a VSD present, and the attachment of the cleft was to its anterosuperior rim (Fig 6). There were two exceptions: case 2 (Table 2) had no VSD, and yet the mitral valve cleft attached to the intact septum below the transposed pulmonary valve; and case 6 (Table 4) had a large membranous defect, and the mitral cleft attached to the inferoposterior instead of to the anterosuperior crest of the VSD. (4) The VSD as a rule was conoventricular with either rightward or posterior conal septal malalignment (Figs 6, 7). Only the 2 cases (cases 1 and 3, Table 4) with straddling tricuspid valve had a VSD of the AV canal type, along with case 6 (Table 4) mentioned in item (3) above.
The cleft of the mitral valve, when associated with TGA or DORV, is usually narrow and seldom results in significant mitral regurgitation. Much more often the cleft of the mitral valve and its attachment to left ventricular wall next to the transposed pulmonary valve creates an unusual (and frequently unsuspected) obstruction of the left ventricular outflow tract. In one of our patients (case 9, Table 2; Fig 5), the systolic pressure gradient between the left ventricle and the transposed pulmonary artery was 100 mm Hg. Yet, almost to the time of his cardiac transplantation, the presence of the cleft mitral valve and its role in the left ventricular outflow obstruction were undiagnosed. Instead, for many years this obstruction was thought to be dynamic due to a bulging of the septum toward the left ventricular cavity. Although not very common, a cleft mitral valve should be included in the differential diagnosis of left ventricular outflow obstruction in cases of TGA or DORV.
An unusual case of ICMV and DORV was observed in case 5 (Table 3; Fig 8). The mitral valve cleft in this case was also the orifice of the mitral valve. This mitral valve attached to a single papillary muscle resulting in mild mitral stenosis (gradient, 5 mm Hg). The free margins of the cleft did not show thickening and rolling, suggesting absence of regurgitation. This case is a rare example of a cleft and parachute mitral valve with only mild stenosis and no regurgitation.
Five cases with D-transposition or DORV and a VSD with rightward conal septal malalignment had coarctation of the aorta and hypoplasia of the aortic isthmus. We suspect that the rightward displacement of the conal septum may have been responsible for diminished flow toward the aorta during fetal life, resulting in hypoplasia of the aortic isthmus. For similar hemodynamic reasons, coarctation of the aorta also occurred in cases with TGA and restrictive VSD (case 2, Table 4; Fig 9). By contrast, posterior conal septal malalignment in cases of D- or L-transposition resulted in subpulmonary obstruction (case 7, Table 2; Fig 7) or pulmonary atresia (cases 4 and 5, Table 4).
Cases of DORV with straddling mitral valve have been reported as ICMV [14, 15]. Strictly speaking, from the anatomic point of view, we think this is not correct. The straddling mitral valve cases have a third papillary muscle in the outflow tract of the right ventricle. The mitral valve attachment to this papillary muscle is not a cleft but, rather, a third commissure (see Terminology). The chordae tendineae from two different leaflets in such trileaflet mitral valve converge and insert into this third papillary muscle in the right ventricular outflow tract.
In summary, the anatomic and clinical data of the 41 cases of this report strongly suggest the following: (1) Cases of ICMV may occur in patients with a variety of additional congenital heart defects. (2) Morphologically, and most likely morphogenetically, there are two distinctly different groups of ICMV: ICMV with normally related great arteries, and ICMV with abnormal conus associated with transposition in D- or L-ventricular loops or DORV. (3) The group with normally related great arteries shares several characteristics with the more complete forms of common AV canal and could be considered as a milder variation of the abnormal development of the AV canal. In this group, the mitral valve cleft results in progressive mitral regurgitation, which can be surgically treated by suturing the cleft (as long as parachute mitral valve does not coexist). (4) The group with abnormal conus resulting in TGA or DORV is characterized by the presence of a conoventricular VSD and lack of similarities with the AV canal malformations. The mitral valve cleft is seldom associated with significant mitral regurgitation but often produces obstruction of the left ventricular outflow by its attachment close to the transposed pulmonary valve. Suturing of such a cleft will not eliminate the left ventricular outflow obstruction. (5) In the two different anatomic types of ICMV, the cleft "points" at the associated abnormal structure. In the canal type of ICMV (Fig 3B), the cleft is oriented approximately horizontally and points at the abnormally formed AV canal with its abnormally small LV septal inlet/outlet ratio (median, 0.75). In the abnormal conus type of ICMV, the cleft is oriented approximately vertically and points at the abnormal conus associated with TGA or DORV (Figs 5–9) and the LV septal inlet/outlet ratio typically is normal (median 1.0, p < 0.0001). (6) Realization of the anatomic differences between ICMV with subpulmonary conus and normally related great arteries versus ICMV with subaortic or bilateral conus and TGA or DORV is essential in planning the surgical management of such patients. (7) The fundamental differences between these two groups of ICMV are appreciated and documented in this report.
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Acknowledgments
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We thank Wendy Newman for photography and Debi Wilkinson for typing.
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References
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Abstract
Introduction
