Ann Thorac Surg 2000;69:1934-1937
© 2000 The Society of Thoracic Surgeons
Case reports
Critical subaortic stenosis in a newborn caused by accessory mitral valve tissue
Klaus Meyer-Hetling, MDa,
Vladimir V. Alexi-Meskishvili, MD, PhDb,
Ingo Dähnert, MDb
a "Left of the Weser" Central Hospital, Bremen, Germany
b German Heart Institute Berlin, Berlin, Germany
Address reprint requests to Dr Meyer-Hetling, Department of Thoracic, Cardiac, and Vascular Surgery, "Left of the Weser" Central Hospital, Senator Wessling Str 1, 28177 Bremen, Germany
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Abstract
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A 2-week-old newborn girl underwent successful surgery in our clinic for critical subaortic stenosis caused by accessory mitral valve tissue, which, because of excessive growth, protruded into the left ventricular outflow tract. The preoperative pressure gradient below the aortic valve was 80 mm Hg. The operation consisted of resection of the accessory tissue through a combined aortotomy and atriotomy approach without residual pressure gradient and mitral valve incompetence. This approach is recommended to ensure that accessory tissue is removed without damaging the mitral valve.
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Introduction
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As opposed to valvular aortic stenosis, congenital membranous or muscular subaortic stenosis is rare in newborns. In some cases, tumors or congenital anomalies of the mitral valve can also cause left ventricular outflow tract obstruction. This also includes accessory mitral valve tissue, which can cause clinically critical aortic stenosis and cardiac decompensation, thus necessitating emergency surgery, as in the case reported below.
A 14-day-old newborn girl was transferred from a local hospital to our clinic because of a cardiac murmur with tachypnea at rest and difficulty drinking. Cardiac catheterization and echocardiography performed in the German Heart Institute Berlin revealed a subaortic stenosis with an inhomogenous contrast medium recess in the vicinity of the left ventricular outflow tract (Fig 1), as well as a patent foramen ovale with left-to-right shunt. The pressure gradient was 80 mm Hg. The body weight was 3,900 g at a body size of 49 cm. Balloon dilatation of the subaortic stenosis during cardiac catheterization was unsuccessful. Therefore, an emergency operation was performed through median sternotomy on normothermic cardiopulmonary bypass and crystalloid cardioplegia. After the aortotomy, an examination of the aortic valve and left ventricular outflow tract revealed that although the valve was normal, accessory mitral tissue was present in the vicinity of the anterior leaflet of the mitral valve. The tissue was connected to the anterior papillary muscle of the left ventricle by small chords. After right atriotomy, the atrial septum was opened and, because of the smallness of the aorta and the potential danger of injuring the mitral valve, the accessory mitral valve tissue was removed by cutting the connective chords to the anterior papillary muscle and separating them from the anterior mitral valve leaflet. After the accessory tissue had been removed, saline solution was injected into the left ventricle to verify the mitral valve’s competence. The remaining intraoperative course proceeded without complication. Aortic cross-clamp time was 29 minutes; bypass time was 49 minutes. Histologic examination revealed mesenchymal tissue that was covered with a monostratified cell layer. The resected accessory tissue was approximately 5 x 4 mm. Postoperative echocardiography revealed first-degree aortic valve insufficiency as well as good biventricular function without insufficiency of the mitral valve. A pressure gradient no longer existed. A third-degree atrioventricular block developed postoperatively, but it receded to a stable sinus rhythm. The patient was extubated on the first postoperative day. By the third postoperative day, the child was able to be returned to the referring hospital in a hemodynamically stable condition. One year after the operation, the child had developed well, corresponding to her age, without clinical or echocardiographic signs of the subaortic stenosis or mitral valve incompetence.
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Fig 1. Preoperative left ventriculography. In a lateral view, subaortic stenosis caused by accessory mitral valve tissue expresses itself as a filling defect in the left ventricular outflow tract (asterisk).
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Comment
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To date, 42 operations have been reported for subaortic stenoses caused by accessory mitral valve tissue (Table 1). Four patients had associated ventricular septal defect. Only 3 patients, including the one reported in our case, were newborns, one of whom died [1]. To our knowledge, the present case represents the youngest child who was successfully operated on. In almost all of the reported cases, the inspection of the aortic valve and removal of the accessory tissue on the mitral valve was carried out through aortotomy. However, as made apparent by the necessity for six repeat operations aortotomy alone did not always yield positive results [2–7]. A combined approach to the mitral valve through the aorta and atriotomy provides greater safety and complete removal of the accessory tissue, without the danger of damaging the mitral valve especially in small infants. In the older children, the anterior leaflet of the mitral valve can be tightened with a retaining suture, so that the accessory mitral valve tissue can be more readily recognized and safely removed via aortotomy [8]. Accessory mitral valve tissue can be removed via right atriotomy on an existing ventricular septal defect, for instance, in the case of a very small ascending aorta, thus making aortotomy and atrioseptotomy unnecessary. As a rule, left ventriculotomy, used by some authors is no longer necessary and is avoided because of its risks [1, 4, 9]. In conclusion, contrary to valvular aortic stenosis, subvalvular stenosis caused by accessory mitral valve tissue is not accessible through interventional catheter dilation. The greatest problem during surgery is recognizing the anatomical relationship between the accessory tissue and the mitral valve. Therefore, aortotomy and atriotomy should be recommended and performed, especially in small infants, to ensure that accessory tissue is removed without damaging the mitral valve structures.
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References
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Accepted for publication October 22, 1999.
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Abstract
Introduction
