Ann Thorac Surg 2008;86:1328-1333. doi:10.1016/j.athoracsur.2008.06.041
© 2008 The Society of Thoracic Surgeons
Original Articles: Pediatric Cardiac
Is the Morphologic Mitral Valve in Discordant Atrioventricular Connections Always Normal?
Hideki Uemura, MDa,*,
Iki Adachi, MDb,
Karen P. McCarthy, BSb,
Masahiro Koh, MDa,
Siew Yen Ho, PhDb
a Department of Cardiothoracic Surgery, Royal Brompton Hospital, London, United Kingdom
b Cardiac Morphology Unit, National Heart and Lung Institute, Imperial College London, London, United Kingdom
Accepted for publication June 11, 2008.
* Address correspondence to Dr Uemura, Department of Cardiothoracic Surgery, Royal Brompton Hospital, Sydney Street, London, SW3 6NP, United Kingdom (Email: h.uemura{at}rbht.nhs.uk).
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Abstract
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Background: The purpose of this study was to determine structural features and variations in the mitral valve guarding inflow of the morphologic left ventricle in hearts with discordant atrioventricular connections.
Methods: Morphologic investigation was carried out on the inlet valve to the morphologic left ventricle in 48 autopsied specimens with this particular entity of malformation.
Results: The tension apparatus was straddling to the morphologic right ventricle in 2. Another 34 hearts had a bifoliate valve and the papillary muscles abnormally oriented; a solitary papillary muscle in 3, two papillary muscles but deviated in 5, one of two papillary muscles being dysmorphic in 9, and three or more papillary muscles in 17. The origin of these papillary muscles was frequently deviated. In 5 hearts with a trifoliate or quadrifoliate valve, multiple papillary muscles were also the case. One of these had thick leaflets, a part of which was adherent to a membranous flap around the ventricular septal defect as well as to subpulmonary fibrous tissue tags. Eventually, the valve was comparable with the mitral valve seen in the normally structured heart in only 7 hearts (15%). There was no obvious correlation noted between the presence of abnormality in the mitral valve and that in the tricuspid valve.
Conclusions: Architectural abnormalities are not rare in the morphologic mitral valve in this setting. The valvar structure needs precise recognition.
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Introduction
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Although anatomic biventricular repair has been employed increasingly in patients with discordant atrioventricular connections [1–5], it remains unclear whether the morphologic mitral valve can function well over the longer term after such a definitive procedure. Not only postoperatively, but also prior to the definitive surgical procedure, the presence of mitral regurgitation is deemed an unfavorable factor for anatomic biventricular repair in which the morphologic left ventricle is connected to the aortic pathway because the inlet valve must cope with the systemic circulation subsequent to such a radical approach. Furthermore, some structural abnormalities, straddling of the tension apparatus of the mitral valve for example, can pose fundamental problems in achieving biventricular repair [6], either anatomic or functional. The present study, therefore, was carried out to determine structural features and variations in the mitral valve guarding inflow of the morphologic left ventricle in hearts with discordant atrioventricular connections.
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Material and Methods
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This retrospective and anonymous study was approved by the Institutional Ethics Committee. Any need for individual patient consent or next of kin consent was waived.
Forty-eight hearts with discordant atrioventricular connections were examined. These specimens represent all the cases with this peculiar segmental combination in which it was possible to identify reliably the structure of the morphologic mitral valve. Those hearts with a common atrioventricular junction were excluded.
A usual atrial arrangement was seen in 44 hearts, including one with criss-crossing of atria to ventricular flow pathways, and mirror image arrangement in 4. Ventriculo-arterial connection was discordant in 25, double outlet from the morphologic right ventricle in 11, and pulmonary atresia with the aorta originating from the right ventricle in 11. The remaining one heart had the aortic root connected the right ventricular mass, and the orifice was atretic because of muscular obstruction. The pulmonary trunk originated from the morphologic left ventricle in this heart. A perimembranous ventricular septal defect (VSD) was present in 22; the defect was considered small in 4 of these. In another 12 patients, the VSD was muscular, being surrounded by ventricular musculature all around its margin. In the remaining 14 the ventricular septum was entirely intact. As for the morphologic tricuspid valve, Ebstein malformation was seen in 13, unequivocal dysplasia of its leaflets in 4, orificial stenosis in 3, and straddling or other obvious malformations of the tension apparatus in 2. In another 6, minor abnormalities were present in its tension apparatus. In the remaining 20 hearts, no particular abnormality was identified for the morphologic tricuspid valve.
Morphologic investigation of the inlet valve guarding the morphologic left ventricle was carried out by determining patterns of closure of the valvar leaflets, as well as by clarifying arrangements of the papillary muscles, which tethered the marginal tendinous cords of the leaflets. To evaluate relationship between the abnormalities in the mitral valve and other morphologic features, a standard 
2 test was employed.
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Results
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Of all the 48 specimens, 7 hearts (15%) had a bifoliate valve with paired and balanced papillary muscles (Table 1). In 6 of these, being located in a right-sided morphologic left ventricle, the pattern of closure of the leaflets along a single line of apposition, as well as the tension apparatus, were comparable with mirror imagery of the mitral valve seen in the normally structured heart (Fig 1). One heart with mirror image atrial arrangement had virtually a similar appearance to the mitral valve seen in the normally structured heart.
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Fig 1. Diagrams of the inlet valve guarding the morphologic left ventricle in hearts with discordant atrioventricular connection. The anticipated standard pattern is a mirror image of the mitral valve in the normally structured heart, and was seen in 6 hearts. In another heart with mirror image atrial arrangement, orientation of the mitral valve was similar to the normal mitral valve. Abnormalities in tension apparatus with solitary or dual papillary muscles were present in 17 hearts having a usual apposition between the anterior and the posterior (mural) leaflets. (PM = papillary muscles.)
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In another 2 hearts, straddling of the mitral valve was unequivocal. The anterior structure of the paired papillary muscles attached to musculature of the morphologic right ventricle through a VSD. These 2 hearts had double outlet right ventricle with pulmonary stenosis together with a perimembranous VSD. The pattern of closure of the leaflets was along a single line of apposition as seen in the mitral valve of the structurally normal heart.
The remaining 39 hearts had abnormal formation or orientation of the papillary muscles. The papillary muscle was a solitary structure in 3 hearts, the valve possessing almost parachute-like formation (Fig 1). The valve appeared to be stenotic. In another 14 hearts with usual pattern of closure of the leaflets and a pair of papillary muscles (Fig 2), the architecture of the tension apparatus was bizarre. Attachment of the anterior (superior) or posterior (inferior) papillary muscle to ventricular musculature was deviated in 5, either toward the middle portion of the mural leaflet or toward the commissural edge and, at the same time, toward the atrioventricular groove. One or both of the papillary muscles were also hypoplastic or dysmorphic in 9 (Fig 1). The presence of three or more papillary muscles was not rare, seen in 17 hearts. The variations are illustrated in Figure 3.
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Fig 2. A picture of the mitral valve in a heart with criss-crossing atria to ventricular inflows. The display is orientated to show the mitral structures as if in a normally structured heart. The anterior leaflet and the mural leaflet of the mitral valve appeared to be fairly normal. The leaflets were tethered well as seen in the mitral valve of the normally structured heart. The anterior papillary muscle had an ordinary shape and arose from the apical free wall of the morphologic left ventricle as normal. The posterior papillary muscle was more conjugating and had broader attachment to the ventricular wall. A thin muscle bar (arrow) reached to the annular attachment of the leaflets, and behind the bar there was little space between the annular attachment of the leaflets and the origin of the broad-based papillary muscle. (MV = mitral valve; PM = papillary muscles.)
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Fig 3. Diagrams of the mitral valve with a usual pattern of closure of the leaflets and multiple papillary muscles. (PM = papillary muscles.)
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Multiple papillary muscles were also common in 5 hearts with abnormal pattern of closure of the leaflets (Fig 4). The valve was trifoliate in 2 and quadrifoliate in 3. The supernumerary leaflets were not due to so-called "cleft" within the anterior leaflet, but deep indentations within the mural leaflet had produced additional and obvious apposition zones or commissures, more than the usual scalloped appearance. In one heart with a trifoliate valve, the pair of papillary muscles was fused at the origins and located postero-inferiorly. The valve was grossly abnormal having thick leaflets, a part of which was adherent to a membranous flap around the ventricular septal defect as well as to subpulmonary fibrous tissue tags (Fig 5). Consequently, the ventricular septal defect was partially occluded. Another unusual finding in this particular heart was the presence of a muscular infundibulum at the left ventricular outflow tract leading to the pulmonary trunk.
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Fig 4. Diagrams of the trifoliate or quadrifoliate mitral valve in 5 hearts. The papillary muscles were also abnormal. (PM = papillary muscles.)
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Fig 5. (A) Viewed from the right atrium, this mitral valve was trifoliate (blue arcs) and supported by a pair of fused papillary muscles located postero-inferiorly. The asterisks indicate artifactual incisions. (B) The papillary muscles are separated and the valve displayed to show adhesion of the medial part of the mural leaflet to the ventricular septum (triangle). (C) The left ventricular outflow tract is opened to show the presence of a muscular infundibulum (double-headed arrow). A membranous aneurysm (small arrow) and adhesion of the mitral leaflet occludes a ventricular septal defect leaving a slit-like interventricular communication.
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There was no obvious correlation between the presence of abnormality in the mitral valve and that in the tricuspid valve (Table 2). The morphologic feature of ventricular septal defect did not affect presence or absence of abnormality in the mitral valve, either. As for the pattern of ventriculo-arterial connection, finding of an unusual mitral valve was less common in hearts with pulmonary atresia with the aorta arising from the right ventricle, compared with those with a double outlet or discordant ventriculo-arterial connection, although no particular morphologic reason was found.
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Comment
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Structural abnormalities in the morphologic tricuspid valve have been well-documented in hearts with discordant atrioventricular connections [7–9]. In contrast, little attention has been paid to the morphology of the mitral valve in this setting [10]. This is not surprising because tricuspid regurgitation is one of the most serious clinical impediments before definitive repair and also after functional biventricular repair, whereby the morphologic right ventricle supports the systemic circulation [11–15]. The mitral valve seldom becomes significantly regurgitant subsequent to functional biventricular repair because it functions as an inlet of the morphologic left ventricle supporting the pulmonary circulation. The situation could be slightly different when systolic pressure of the pulmonary ventricle is intentionally maintained higher than the normal setting [16].
Unusual attachments of the papillary muscles of the mitral valve, moreover, sometimes limit placement of a ventricular incision to the morphologic left ventricle [9] at the time of reconstruction of the pulmonary channel for functional biventricular repair. In this respect, precise recognition of the morphologic variation of the mitral valve is requisitely of surgical importance not only when determining indication of anatomic biventricular repair but also when achieving reasonable functional biventricular repair. In hearts with grossly abnormal atrioventricular valvar structures, biventricular repair is less than ideal.
Our present investigation demonstrated a surprisingly high incidence of abnormalities in the mitral valve even though this may be representative of a postmortem series. Gerlis and colleagues [10] previously reported abnormalities of the mitral valve in 55% of their materials. They categorized abnormalities of the mitral into the following three: valves with more than two cusps (seen in 21%); abnormal tension apparatus (in 21%); and dysplasia of the valve (10%). Major abnormalities would very likely have a significant and deleterious impact on cardiac function should anatomic repair be carried out to leave the morphologic left ventricle supporting the systemic load. Minor abnormalities should not necessarily correspond to the clinical finding of regurgitation. Unfortunately, however, there is no direct echocardiographic data with which to make correlations concerning known regurgitation of the atrioventricular valves prior to the deaths of the patients in our present series.
In this respect, the first author was able to review his personal experience, retrospectively, of a clinical series of patients undergoing definitive repair. Since 1988, 46 patients with discordant atrioventricular connections and an obstructed pulmonary pathway have undergone biventricular repair, either anatomic (in 31) or functional (in 15). Of these, 4 patients (9%) had moderate or severe mitral regurgitation preoperatively. When the mitral valve was inspected during the surgical procedure, a cleft was present within the anterior leaflet in 2, the anterior and the mural leaflets were prolapsing (probably related to torn tendinous cords) in 1, and a quadrifoliate valve had marked straddling in 1. The cleft was sutured in 1 patient and anatomic repair was achieved, while plasty or replacement was carried out concomitantly with functional biventricular repair in the other 3. In another patient, mild straddling of the mitral valve was noted in the absence of mitral regurgitation. This patient successfully underwent anatomic repair. Of the 28 patients surviving anatomic repair, mitral regurgitation became moderate within the first postoperative year in one patient who eventually developed atrial fibrillation and died suddenly 26 months after the procedure. In the other 27 patients, no significant mitral regurgitation has progressed thus far; just mild regurgitation has been noted in 5. On the other hand, during the same period, 7 patients with discordant atrioventricular connection and an obstructed pulmonary pathway underwent a Fontan type procedure. Biventricular repair was not employed because of straddling of the mitral valve in 2, marked tricuspid valve straddling in 2, severe Ebstein malformation together with very small right ventricle in 1, small left ventricle in 1, and criss-cross inlet with supero-inferior orientation of the ventricular chambers in 1. Overall, accordingly, 8 out of 53 patients (15%) had malformations of the mitral valve.
Apart from the discrepancy in the proportion of either abnormalities or impediments between the clinical and postmortem series, the current observations confirm that the mitral valve in discordant atrioventricular connection needs morphologic attention. Enthusiasm for anatomic biventricular repair would better be reconsidered, and the surgeon should carefully choose the optimal candidates for such an extensive procedure. Systemic right ventricular dysfunction [17] and tricuspid valve regurgitation can progress after functional biventricular repair, whereas channel obstructions and abnormal mitral valve can pose potential problems, together with late atrial arrhythmia related to the surgical procedure for intraatrial redirection of blood, after the anatomic repair. The associated structural abnormalities in the coronary arterial circulation [18] are another factor to be taken into account. Based on our previous experiences [19], we are convinced that anatomic repair is the optimal solution in some patients. In other patients, however, we need to exclude meticulously major impediments against successful achievement of anatomic repair, or even biventricular repair.
In conclusion, the mitral valve was not always morphologic normal in hearts with discordant atrioventricular connection. Aside from other associated intracardiac malformations, precise and detailed recognition of mitral valve structure is recommended when determining the optimal surgical strategy for a definitive procedure in discordant atrioventricular connection.
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References
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Abstract
Introduction
