Ann Thorac Surg 2000;69:130-134
© 2000 The Society of Thoracic Surgeons
Original Articles
Surgical management of the straddling mitral valve in the biventricular heart
Ryo Aeba, MDa,
Toshiyuki Katogi, MDa,
Shigeyuki Takeuchi, MDa,
Shiaki Kawada, MDa
a Division of Cardiovascular Surgery, Keio University, Tokyo, Japan
Address reprint requests to Dr Aeba, Division of Cardiovascular Surgery, Keio University, 35 Shinanomachi, Shinjuku, Tokyo 160-8582, Japan
e-mail: aeba{at}mc.med.keio.ac.jp
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Abstract
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Background. The straddling mitral valve in the biventricular heart is a rare condition that may complicate biventricular repair.
Methods. Treatment and outcomes in 5 consecutive patients who underwent primary repair between 1992 and 1997 were reviewed. Their ages at repair ranged from 2 months to 8 years. Three patients had a double-outlet right ventricle with a subaortic (n = 2) or subpulmonary (n = 1) ventricular septal defect. Two patients had transposition of the great arteries {S,D,D}, a ventricular septal defect, and left ventricular outflow tract obstruction. The attachments of the papillary muscles of the straddling mitral valves were located on the right ventricular aspect of the ventricular septum. Four patients underwent baffle partitioning of the ventricular cavity. The baffle suture line was used to secure the chordae tendineae crossing the ventricular septal defect, or was intentionally omitted at the papillary muscle. The right ventricular outflow tract was reconstructed with patch augmentation, an extracardiac conduit, or an arterial switch operation. One patient with transposition who had a giant papillary muscle to the straddling mitral valve associated with abnormal insertion of the tricuspid valve on the conal septum underwent univentricular repair.
Results. There were no early or late postoperative deaths. There was no mitral valve dysfunction, left ventricular outflow tract obstruction, or heart block in the 4 patients who underwent biventricular repair.
Conclusions. Although there are several exceptional situations in which ventricular partitioning may result in early and late complications, a straddling mitral valve does not preclude biventricular repair.
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Introduction
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The straddling mitral valve (SMV) is a relatively common malformation in patients with congenital cardiac anomalies which exhibit the pathophysiology of a single ventricle. The incidence of SMV in patients with a biventricular heart and a ventricular septal defect (VSD), however, is low [1]. Although biventricular repair is theoretically appealing, the results in earlier reports have been disappointing [2, 3]. The high risk of mitral valve dysfunction, tricuspid valve dysfunction, left ventricular outflow tract obstruction, right ventricular outflow tract obstruction, and heart block has limited the utility of this technique. Its superiority over univentricular repair has consequently been questioned by subsequent authors [4–7]. The purpose of this article was to review our surgical experience in patients with a biventricular heart and an SMV who underwent intracardiac repair.
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Patients and methods
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Between 1992 and 1997, there were 5 consecutive patients with congenital heart disease who underwent surgical repair at the Keio University Hospital and fulfilled the following four inclusion criteria: (1) congenital heart disease associated with a VSD, (2) two ventricles with well-balanced volume (end-diastolic volume ratio between 0.7 and 1.3 measured by echocardiography), (3) concordant atrioventricular alignment, and (4) an SMV.
Independent of the associated SMV, these patients were suitable candidates for biventricular repair. An SMV was defined as a mitral valve with a portion of the support mechanism extending across a VSD and inserting into the right ventricle [5]. An overriding mitral valve was thus distinguished from an SMV.
There were 3 male and 2 female patients, ranging in age at the time of operation from 2 months to 8 years (Table 1). Three had a double-outlet right ventricle with a subaortic (n = 2) or subpulmonary (n = 1) VSD. The other two patients had transposition of the great arteries {S,D,D}, a VSD, and left ventricular outflow tract obstruction. One of the patients with transposition of the great arteries, a VSD, and left ventricular outflow tract obstruction (patient 2) had previously undergone a modified right Blalock-Taussig shunt.
Preoperative echocardiography failed to demonstrate the support mechanism crossing the VSD in any of the patients, although a group of the chordae of the mitral valve was identified as attaching to the crest of the VSD in 1 patient (patient 3). The alignment of the ventricular septum and atrioventricular valves was normal (overriding atrioventricular valves were not identified). Two papillary muscles of the mitral valve were identified in the left ventricle. The left anterior papillary muscle was slightly hypoplastic in 2 patients. In 1 patient (patient 1), the medial papillary muscle of the tricuspid valve was abnormally large. Color Doppler flow mapping revealed nonobstructive mitral inflow into the left ventricle only. The mitral valve was completely or almost completely competent.
All operations were performed with cardiopulmonary bypass, moderate hypothermia, and cardioplegic heart arrest. Intraoperative transesophageal echocardiography was not used. In all cases, the SMV was identified by intraoperative inspection. All of the VSDs were large enough to be nonrestrictive and were located in the middle or anterior portion of the septum. They were all adjacent to the tricuspid and mitral valves, but the degree of commitment to the semilunar valves varied. The VSDs were subaortic in 3 patients, subpulmonary in 1 patient, and not committed in 1 patient. Attachment of the papillary muscle of the SMV was located inferiorly on the right ventricular endocardial surface of the ventricular septum either within 1 cm of (type A) or more distant from (type B) the VSD [5]. None of the patients had type C straddling, where the attachment was on the free wall of the right ventricle.
A total of 4 patients underwent partitioning of the ventricular cavity by the creation of a left ventricular outflow tunnel or closure of the VSD. A baffle or patch of expanded polytetrafluoroethylene patch (cardiovascular patch, W.L. Gore and Associates Co, Flagstaff, AZ) was tailored and secured with interrupted Dacron-pledgetted horizontal mattress sutures. In 3 patients (patients 2, 4, and 5), the baffle partitioning was accomplished through a right ventriculotomy with concomitant reconstruction of the right ventricular outflow tract. In the patient with a double-outlet right ventricle and a subpulmonary VSD (patient 3), an arterial switch operation was performed after baffle placement through a right atriotomy. In 3 patients with a type A SMV (patients 3, 4, and 5), the papillary muscles had a low profile and were considered an extension of the septal band. The chordae of both the tricuspid and mitral valves converged at the right posterior division of the band, which was located on the right side of the ventricular septum, 5 to 10 mm away from the ventricular crest. In these patients, the chordae of the mitral and tricuspid valves were easily divided by the baffle suture line. The baffle suture line was shifted inferior and to the right, so that the abnormal mitral valve attachment was behind the baffle and did not disturb the tricuspid valve. As a result, the chordae and papillary muscle crossing the VSD were left untouched, and were incorporated into the left ventricular outflow tract [8]. In 1 patient with transposition of the great arteries, a VSD, left ventricular outflow tract obstruction, and a type B SMV (patient 2), a distinct papillary muscle with a narrow base and a forked tip was identified on the right side of the ventricular septum, 10 to 15 mm away from the ventricular septal crest (Fig 1). The chordae of the tricuspid valve attached to the papillary muscle were thin and scarce. The baffle suture line was intentionally omitted at the tip of the papillary muscle of the SMV. Right ventricular outflow tract obstruction was relieved using an extracardiac conduit. In 1 patient who had a normal size right ventricle but a hypoplastic tricuspid valve (Z value, -4.8; patient 5), a bidirectional superior cavopulmonary shunt was added. This resulted in a one-and-one-half ventricular repair [9].
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Fig 1. Schematic illustration as seen through the right ventricle in a patient with transposition of the great arteries {S,D,D}, a ventricular septal defect, and left ventricular outflow tract obstruction (patient 2). The ventricular septal defect was immediately below the aortic valve. Note the omitted suture line at the papillary muscle of the straddling mitral valve (left). After the completion of the baffle placement, the support mechanism of the straddling mitral valve was secured between the ventricular septum and the baffle (right). The cranial half of the baffle has been removed, showing the aortic valve.
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In the other patient with transposition of the great arteries, a VSD, left ventricular outflow tract obstruction, and a type A SMV (patient 1), the abnormally attached mitral papillary muscle was large and extended to the center of the VSD. Moreover, there was an abnormal insertion of the tricuspid valve on the conal septum (Fig 2). This patient underwent univentricular repair with total cavopulmonary connection. The right atrial wall flap was used for reconstruction of the systemic venous tract between the inferior vena cava and the right branch pulmonary artery.
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Fig 2. Schematic illustration as seen through the right ventricle in a patient with transposition of the great arteries {S,D,D}, a ventricular septal defect, and left ventricular outflow tract obstruction (patient 1), showing the aortic valve. Note the large papillary muscle on the right ventricular aspect of the ventricular septum near the crest, and the associated abnormal insertion of the tricuspid valve into the conal septum. It was determined that a biventricular repair would lead to left ventricular outflow obstruction as well as atrioventricular valve dysfunction. A univentricular repair was performed.
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Results
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There were no early or late postoperative deaths during the follow-up period (2 to 6 years). The postoperative recovery was uneventful in the 4 patients who underwent biventricular or one-and-one-half ventricular repair. The patient who underwent univentricular repair (patient 1) had a pleural effusion that did not resolve for several months after the operation. None of the patients experienced heart block. After discharge from the hospital, all of the patients were asymptomatic.
Postoperative echocardiography in the patient in whom the baffle suture line was intentionally omitted (patient 2) revealed a residual interventricular communication. This patient experienced late obstruction of the extracardiac conduit between the right ventricle and pulmonary trunk and underwent conduit replacement 65 months after the initial intraventricular repair. At reoperation, the papillary muscle of the SMV, which was inspected through the right ventricle, appeared atrophic. The interventricular communication was identified as a pin hole, which was closed with a Dacron-pledgetted horizontal mattress suture.
Follow-up catheterization and echocardiography with color Doppler flow mapping was performed in all patients. In all 4 patients who underwent biventricular or one-and-one-half ventricular repair, the mitral valve function was normal and the left ventricular outflow tract was not obstructed. The peak systolic pressure gradients between the left ventricle and ascending aorta were 10 mm Hg or less.
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Comment
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The SMV continues to be a challenging malformation for both the cardiologist and surgeon. In our series, none of the 5 patients was properly diagnosed preoperatively by echocardiography or angiocardiography. Because the chordae of the SMV are often difficult to visualize using currently available diagnostic modalities, they often are not identified before cardiotomy. Unlike the superior cavopulmonary shunt for the management of the straddling tricuspid valve, there is no safeguard adjunct in the treatment of the SMV.
Application of the biventricular repair in patients with an SMV carries the potential risk of mitral and tricuspid valve dysfunction because the baffle suture line often secures or mechanically involves the support mechanisms of the atrioventricular valves just inferior to the VSD. In addition, a shift of the baffle suture line to the left and superior or to the right and inferior to avoid the papillary muscle of the SMV may result in left or right ventricular outflow tract obstruction. It has yet to be determined whether these complications can be prevented during biventricular repair. The high risk of complete heart block is another problem. Milo and associates [4] have reported that the conduction tissues do not arise from the regularly situated atrioventricular node. They therefore recommended intraoperative mapping.
Baffle partitioning after division of the chordae tendineae of the SMV with prosthetic mitral valve replacement may be the surgical option of choice. However, valve replacement in the pediatric population is a source of major concern because of the limited size application, the high incidence of life-threatening complications such as thromboembolism, and the need for mandatory reoperation for outgrown prostheses and abnormal perivalvular tissue overproliferation. In these situations, univentricular repair is thought to be superior to biventricular repair [4–7]. Recently, Serraf and colleagues [8] have reported 11 patients with an SMV, the majority of which were treated with a biventricular repair. In their series, one early death occurred in a patient with a double-outlet right ventricle, caused by subaortic tunnel stenosis after biventricular repair. One patient in our series (patient 1) had a comparable anomaly. At operation, it was determined that biventricular repair performed by enlargement of the VSD to the left of the attachment of the papillary muscle of the SMV, creation of a myocardial flap of the abnormal papillary muscle insertion of the tricuspid valve at the conal septum, baffle partitioning, reattachment of the muscle flap to the baffle, and reconstruction of the right ventricular outflow tract using an extracardiac conduit or translocation of the pulmonary artery onto the right ventricle would result in significant stenosis of the left ventricular outflow tract, mitral or tricuspid valve dysfunction, or atrioventricular block. Although anecdotal, these two cases illustrate the limitations of the nonselective application of biventricular repair.
Biventricular repair using a baffle requires special surgical tricks. The Tokyo Women’s Medical College group [10] has reported the successful treatment of 2 patients with a double-outlet right ventricle, subpulmonary VSD, and an SMV. The chordae of the SMV, which supported a small portion of the mitral valve, were divided. No mitral insufficiency developed postoperatively. This is a simple solution for the SMV. However, when the SMV has a larger contribution to the mitral valve, it should be managed differently. Our approach leaves the support mechanism crossing the VSD untouched by shifting the baffle suture line to the right and inferior, unless this would result in tricuspid valve dysfunction or right ventricular outflow tract obstruction. This approach is applicable in the majority of patients with a type A SMV. Although Serraf and coworkers [8] have reported a similar approach to ours when left ventricular outflow tunnel was concomitantly constructed, the management of the SMV during the arterial switch operation and VSD closure was different. They advocated a baffle placement technique in which the chordae of the SMV were pulled through the pulmonary valve toward the left ventricle using a hook. The potential risk of this technique is related to modulation of the length and angle of the chordae of the SMV. We believe that the management of the SMV should not be individualized based on the method of left ventricular outflow tract reconstruction.
Types B and C SMVs are even more challenging lesions for biventricular repair. To avoid right ventricular inflow and outflow obstruction by the baffle, it should be placed between the crest of the VSD and the attachment of the papillary muscle of the SMV, which inevitably secures the chordae crossing the VSD. Keeping the length and angle of the SMV in the original position in systole may minimize the development of mitral dysfunction. One patient (patient 2) in our series underwent biventricular repair using this approach, which resulted in successful preservation of the mitral valve function. Chordae transection and realignment may be applicable in selected patients with an SMV or straddling mitral and tricuspid valves. This technique has been applied by Reddy and associates [11] in patients with a straddling tricuspid valve. The effect of inhibition of papillary muscle function on global mitral valve function with this technique is a matter of concern.
Recent refinements in surgical technique, operative materials, cardiopulmonary bypass, myocardial preservation, and perioperative management have contributed to the successful application of biventricular repair in these difficult situations. One of the most challenging problems in the surgical management of an SMV is determining whether ventricular cavity partitioning is feasible without the risk of major early complications. In addition, the long-term prognosis must be considered and weighed when deciding between univentricular and biventricular repairs. Further complicating the situation, the decision must often be made during the cardiac or circulatory arrest period.
We have demonstrated that an SMV does not preclude biventricular repair. Conversion to univentricular repair should be considered only after all responsible surgical options for a biventricular approach have been attempted and failed. In general, however, patients with a giant papillary muscle and an abnormal tricuspid valve insertion cannot undergo biventricular repair. Future evolution of diagnostic modalities may contribute to proper selection of procedures, thereby improving short- and long-term prognosis.
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Footnotes
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This article has been selected for the open discussion forum on the STS Web site: http://www.sts.org/section/atsdiscussion/
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References
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Accepted for publication June 16, 1999.
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Abstract
Introduction
