Ann Thorac Surg 2002;73:274-277
© 2002 The Society of Thoracic Surgeons
Case report
Congenital mitral-aortic discontinuity
Domingo Liotta, MD*a,
Armando Diluch, MDa,
Adriano Malusardi, MDa,
Miguel del Rio, MDa
a Dupuytren-Quilmes Private Hospital, Cardiac Surgery, Faculty of Medicine, University of Morón, Buenos Aires, Argentina
Accepted for publication March 28, 2001.
* Address reprint requests to Dr Liotta, Dupuytren-Quilmes Private Hospital, Faculty of Medicine, University of Morón, 914 Machado St, Morón, (1714) Buenos Aires, Argentina
e-mail: medicina{at}unimoron.edu.ar
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Abstract
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Mitral-aortic (M-A) discontinuity is an uncommonly observed congenital malformation. From the embryologic point of view, it is a failure of the superior endocardial cushion of the A-V canal reach and insert into the aortic root (the mitral-aortic fibrous trigone). It should be differentiated from aorto-left ventricular discontinuity, a complication of endocarditis with excavating abscesses without boundaries. In congenital mitral-aortic discontinuity, the anterior leaflet of the mitral valve fails to insert into the aortic root. We report our experience with 2 patients. In patient 1, the severe left ventricular outflow obstruction was mainly caused by the mobile anterior leaflet of the mitral valve.
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Introduction
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Mitral-aortic (M-A) discontinuity is an uncommonly observed congenital malformation. The anomaly may be discovered during surgery without being diagnosed preoperatively. Congenital M-A discontinuity must be differentiated from aorto-left ventricular discontinuity, a complication of severe endocarditis with formation of subannular abscesses. In M-A discontinuity, only the anterior leaflet of the mitral valve is separated from the aortic root (intervalvular fibrous trigone). Instead, in endocarditis with penetrating abscesses, the pathology is variable, without the usual anatomic boundaries. In patient 1, the severe M-A discontinuity was the main cause for subaortic obstruction.
With the normal M-A continuity, the anterior leaflet of the mitral valve (ALMV) is directly joined to the aortic root. The ALMV has one small portion that inserts into the interventricular septa (adjacent to the membranous septum), and another free portion that forms the M-A continuity (from the nadir point of the left coronary cusp to the nadir point of the noncoronary cusp). M-A discontinuity is a congenital malformation with an existing wide recess over the free portion of the ALMV. The subaortic outflow tract formation is greatly enlarged (fibrous wall of the left ventricular outflow tract).
We report our recent experience with 2 severely ill patients. The diagnosis of M-A discontinuity was made during surgery.
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Case reports
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Patient 1
A 29-year-old man with a childhood history of precordial murmur, with symptoms of worsening dyspnea on exertion, was admitted with a 39°C fever and chills. The patient had no previous episodes of endocarditis. Workup included transthoracic and transesophageal echocardiography, which showed a small, high ventricular septal defect (VSD) with a shunt from the left ventricle to right aorta, and a severe subaortic stenosis with an area of 0.5 cm2, peak gradient of 115 mm Hg, ejection fraction of 50%, aortic valve vegetations, and severe aortic regurgitation. Primary diagnosis was infected subaortic membrane extending to the aortic valve and small VSD. His workup included three sets of positive blood cultures for Staphylococcus aureus. He was placed on Vancomycin (1 g IV every 12 hours), and Gentomycin (160 mg IV daily) for 21 days before undergoing surgery.
The aortic valve was set abnormally high. The left aortic cusp had a perforation and two vegetations. There was a wide M-A discontinuity with a deep fibrous subaortic recess. The base of the ALMV was completely mobile, "floating" within the central part of the aortic area. A small VSD at the base of the right anterior fibrous trigone was present (Fig 1).
There was no subaortic membrane. Secondary to stasis and stress, scattered depositions of fibrous tissue were produced by the mobile obstruction of the anterior leaflet of the mitral valve in the left ventricular outflow tract (LVOT). The mitral valve was examined through a left atriotomy. It showed disseminated spots of acute endocarditis, mainly in the posterior leaflet. The small VSD was visualized through a right atriotomy.
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Fig 1. Patient 1: surgical findings. (1) M-A discontinuity (separation). (2) Deposition of fibrous tissue in left ventricular outflow tract. The aortic leaflet of the mitral valve is "floating" in the left ventricular outflow tract. (3) Perforation of the left coronary cusp. (4) Vegetations in left coronary cusp. (5) Small ventricular septal defect. (6) Left ventricular outflow tract.
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The M-A continuity was restored, employing a continuous 4-0 polypropylene suture. The suture runs from the nadir of the left coronary sinus (left fibrous body) to the nadir of the noncoronary sinus (central fibrous body). The base of the ALMV remained firmly attached to the aortic root.
The patient underwent a mitral valve replacement with a size 27 St. Jude mechanical mitral prosthesis (St. Jude Medical St. Paul, MN), and an aortic valve replacement (AVR) with a size 19 St. Jude Mechanical aortic prosthesis. The aortic prosthesis was implanted, employing interrupted 2-0 pledgeted Dacron sutures to strengthen mitral-aortic continuity. The small VSD was closed via LVOT, using the fixation sutures of the aortic prosthesis. A prophylactic dual-chamber pacemaker (for alternating left bundle branch block and prolonged PR intervals), was implanted early in the postoperative course. The patient was doing well at his 16-month follow-up.
Patient 2
A 26-year-old woman, with a 5-month history of class II to class III dyspnea, presented with cardiac decompensation and severe aortic regurgitation. Workup included transthoracic and transesophageal echocardiography, and left heart catheterization. The studies revealed severe eccentric, aortic regurgitation, and a large aortic root aneurysm (Fig 2).
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Fig 2. Patient 2. (A) aortogram (left anterior oblique view) reveals severe aortic regurgitation and a saccular aortic root aneurysm. An important displacement of the mitral valve toward the left is observed in relation to the aortic valve. It was not recognized before surgery. (B) (1 = mitral valve; 2 = aortic root aneurysm.)
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In surgery, the ALMV was 25 to 30 mm separated from the nadir points of the left and the noncoronary aortic annuli. The superior wall of the left atrium was seen through the thin, fibrous tissue of the subaortic recess (M-A discontinuity). The right aortic cusp with fenestrations was entirely prolapsing into the LVOT. A 3 to 4-cm-diameter saccular aneurysm, emerging from the right coronary sinus of Valsalva, involved the right coronary artery. The aneurysm was lying directly over the superior wall of the right atrium. The M-A continuity was restored. The free base of ALMV was firmly attached to the aortic root, employing the 4-0 continuous suture technique. The patient underwent AVR with a size 21 St. Jude mechanical aortic prosthesis (St. Jude Medical). The aortic prosthesis was implanted employing interrupted 2-0 pledgeted Dacron sutures to strengthen the M-A continuity procedure. The aortic root aneurysm was radically excised, and a saphenous aorto-coronary graft to the proximal right coronary artery segment was performed. The histopathology demonstrated an unusual increase of the wall thickness of the saccular aneurysm. The patient was doing well at her 19-month follow-up.
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Comment
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Aorto-left ventricular discontinuity in severe acute endocarditis with extensive tissue destruction from congenital M-A discontinuity must be discussed. Advanced excavating sepsis of the aortic root, with softening and desintegration of the aortic annulus with subannular abscesses, may lead to aorto-left ventricular discontinuity [1–3]. In surgery, direct visual inspection revealed deep, undermining endocarditis, with pseudoaneurysm formation and penetrating abscesses. The pathology revealed a subannular tissue destruction without boundaries, from the specific point of view of anatomic structures.
On the contrary, in congenital M-A discontinuity, the ALMV fails to insert in the aortic root. The frequent observation of subannular aortic aneurysm due to M-A discontinuity is seen as a genetic disturbance in the Bantu people.
In true congenital M-A discontinuity only, the ALMV does not insert in the aortic root (intervalvular fibrous trigone) [4–6]. This was the case in patient 1. The free base of the ALMV and the deep recess under the aortic root were absolutely free from infective sequelae. Also, the aortic valve was malpositioned and a small atrioventricular septal defect was found. These support the diagnosis of congenital anomalies.
A subannular recess as a sequelae of a chronic abscess should also be considered. The ALMV inserts at the nadir point of the left coronary cusp (left fibrous body and anterior commissure of the mitral valve). When the M-A discontinuity is advancing to the left of this nadir point invading the muscular septum (Fig 3),
there is evidence for the diagnosis of a sequelae of an old chronic abscess.
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Fig 3. The left coronary sinus. (A) The right half of the sinus inserts into the anterior leaflet of the mitral valve. (B) The left half of the sinus inserts into the muscular septum. (L.C.A. = left coronary artery; R.C.A. = right coronary artery.) (Reprinted, with permission, from Liotta D, Cooley DA, Cabrol C. Cirugia Cardiaca y Cardiologia, Buenos Aires: Inter-Medica, 1985:158.)
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Normally, heterogeneity in the origin of cells dominates regional specificity in LVOT morphogenesis. The inferior (dorsal) endocardial cushion of the atrioventricular canal contributes to the cardiogenesis of the membranous septa and the portion of the ALMV that inserts into the interventricular septum [7–9]. The superior (ventral) endocardial cushion contributes to the origin of the fibrous insertion of the ALMV in the aortic root (M-A continuity) [7–9].
The definite atrioventricular valves have a double origin [7, 8]. They are derived partially from young endocardial tissue lining the AV canal (superior and inferior cushions), and partially from ventricular muscle tissue. In principle, a skirt of ventricular muscle tissue covered by endocardial tissue from the AV canal on its atrial side is formed on each atrioventricular orifice. The muscular tissue remains connected to the ventricular wall by the future chordae tendineae. The portion of the endocardial cushions at the left of the septum primum becomes the aortic leaflet of the mitral valve.
The migration of cranial neural crest cells through the pharyngeal region into the aortic arches and then into the outflow tracts of the heart occurs early in cardiogenesis, when they participate in the formation of the two spiral truncoconal ridges. Cranial neural crest cells that evolve from typical neuroepithelium to mesenchyme are essential for normal conotruncal septation. There is an impairment of truncoconal elastogenesis when the cranial neural crest is surgically ablated in birds. The malformations by induced alterations of the truncoconal septation process ranged from a simple M-A discontinuity to severe forms of double-outlet right ventricle and ventricular septal defect [10–12]. In summary, congenital M-A discontinuity appears to be: (A) the failure of the superior endocardial cushion of the AV canal to fuse with the aortic root [7–9]; (B) the inferior endocardial cushion of the AV canal contributes to the origin of the membranous septum [7–9]; and (C) a minor malformation form of a wide-spectrum deviation of the truncoconal septation process into aortic and pulmonary cardiac outlets [10–12].
The anomalies observed in patient 1 were more advanced than the one observed in patient 2. Malposition of the aortic valve, severe M-A discontinuity, and ventricular septal defect were found in patient 1. The acute endocarditis was set on the cardiac anomalies. The LVOT obstruction was mainly ocasioned by the mobile anterior leaflet of the mitral valve.
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Acknowledgments
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We acknowledge with deep appreciation George Lindesmith, MD. We are grateful to Dr Lindesmith for his valuable advice in correcting the English grammar and syntax of the original manuscript.
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References
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Abstract
Introduction
