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Ann Thorac Surg 2006;81:997-1001
© 2006 The Society of Thoracic Surgeons
Escorts Heart Institute and Research Centre, New Delhi, India
Accepted for publication June 24, 2005.
* Address correspondence to Dr K. S. Iyer, Department of Pediatric and Congenital Heart Surgery, Escorts Heart Institute and Research Centre, New Delhi 110025, India (Email: iyerks_ehirc{at}yahoo.com).
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Abstract |
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METHODS: Between 1996 and 2004, 15 patients with supramitral ring were managed in this institution. The demographic and clinical features, diagnostic modalities, morphology of the rings, and the surgical management were studied retrospectively.
RESULTS: Accurate preoperative diagnosis was possible by transthoracic echocardiography in 11 patients (73%). The associated anomalies were ventricular septal defects in 8 patients (53%) and abnormalities of the left ventricular outflow tract in 7 patients (47%). A circumferential supramitral ring, separate from the mitral valve, was present in 8 patients (53%). In the remaining, the ring was attached circumferentially to the anterior and the posterior mitral leaflets and was most densely adherent at the posteroinferior commissure in 4 of these 7 patients (57%). Complete excision of ring was possible in all cases, without damage to the mitral valve. There was 1 in-hospital death (6%). At a mean follow-up of 30 months, 14 survivors continue to do well, with no significant recurrence of mitral stenosis.
CONCLUSIONS: Patients with supramitral ring constitute a subset of patients with congenital mitral stenosis who have a relatively good prognosis. In many cases, the supramitral ring is entirely separate from the mitral valve, and when attached, it is usually most prominent at the posteroinferior commissure. In both cases, complete resection is surgically feasible and usually provides lasting relief.
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Introduction |
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In Carpentier's classification of congenital mitral stenosis [2], supramitral ring is categorized under congenital mitral stenosis associated with normal papillary muscles. It is a rare malformation—fewer than 100 cases having been reported in literature according to a recent review [10]. Another recent study indicates that supramitral ring may be present in upto 8% of all children with congenital mitral valve disease [11]. Increasing awareness of this condition as well as refinements in diagnostic techniques will probably allow more frequent diagnosis of this condition [21]. The identification of this subset of patients is important, however, because of the relatively better prognosis with appropriate management. There is paucity of information in the literature about the pathology, diagnosis, and surgical management of this entity, and this retrospective analysis of a series of 15 patients managed in our institution attempts to address some of these issues.
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Material and Methods |
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Clinical Presentation
Two children (13%) were asymptomatic, and were diagnosed on incidental postnatal echocardiography. Twelve patients (81%) presented with failure to thrive or frequent respiratory tract infections. One child (6%) presented with pulmonary edema requiring preoperative ventilatory and inotropic support.
Cardiac morphology was delineated by transthoracic echocardiography in all cases. Cardiac catheterization and angiocardiography was performed when associated anomalies were not clearly defined on echocardiography (n = 4), or when assessment of pulmonary vascular disease was required.
Preoperative Diagnosis
Preoperative diagnosis was possible by transthoracic echocardiography (Fig 1), at the first examination, in 11 patients (73%). In 1 patient (7%), the diagnosis was made at a follow-up examination (see below) whereas in 3 patients (20%), the diagnosis was made at the time of surgery during examination of the mitral valve for suspected mitral valve abnormalities. Among these, 1 patient had had a repair of coarctation of aorta and pulmonary artery banding for multiple muscular ventricular septal defects (VSDs) at the age of 4 months. When she presented for definitive closure of VSDs, the transthoracic echocardiogram revealed turbulence across the mitral valve prompting inspection of the valve at surgery, when a supramitral ring was discovered.
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The third patient was found to have a supramitral ring at the time of mitral valve repair for mitral regurgitation due to elongated anterior chordae. The fourth patient had a VSD along with a gradient and turbulence across the mitral valve. On exposure of the mitral valve, the supramitral ring was detected and excised. Two patients (13%) had the constellation of findings associated with Shone's complex. The additional cardiac anomalies are described in Table 1. Only 1 patient had an isolated supramitral ring.
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The morphology of the supramitral rings in our patients is detailed in Figure 3. In all patients, the supramitral ring was circumferential. In 7 patients (47%), the supramitral ring was attached to the left atrium away from the mitral annulus (supra-annular supramitral ring). In this subgroup, the mitral valve was found to be normal in 5 patients (63%). In the remaining 2 patients, the mitral valvular anomalies found were elongated anterior chordae causing regurgitation in 1 patient and hypoplastic annulus with all chordae being attached to a single papillary muscle in the other: both were amenable to adequate repair.
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Altogether, in 11 of the 15 patients (73%) the mitral valve was found to be normal after the excision of the supramitral ring, and did not require any surgical intervention.
Surgery
All the intracardiac anomalies were corrected in a single-stage procedure. After institution of standard cardiopulmonary bypass, topical cooling, antegrade cold blood cardioplegia, and systemic hypothermia to 30°C, the mitral valve was approached in all cases through the interatrial septum. Morphologic abnormalities of the mitral valve were systematically assessed. The full extent of the supramitral ring was delineated. After discerning the anatomy clearly, radial incisions were made in the supramitral ring at the level of both the commissures (1 and 2 in Fig 4A and B) up to the mitral annulus. Using pointed scissors, the segment of the ring adjacent to the anterior leaflet was excised (Fig 4C). Next, several radial incisions (multiple arrows in Fig 4D) were made in the posterior part of the ring. These incisions included the full thickness of the ring and extended into the media of the posterior leaflet. The segments of the ring between these incisions were then resected in this plane. In the patients with abnormal mitral valves, appropriate repair was carried out. For the patient with the associated elongated anterior chordae, chordal shortening and commissuroplasty was performed. The child with fused chordae and papillary muscles was managed by splitting of the chordae and papillary muscles. The 2 patients with Shone's complex had severely dysplastic leaflets with fused subvalvular apparatus, and in these patients mitral valve repair was not feasible. In the rest of the patients, the mitral valve leaflets were then thoroughly inspected for any perforations, and competency of the valve was assessed by instillation saline into the left ventricular cavity. The mitral annulus was also sized with appropriately sized dilators. The associated cardiac anomalies were then corrected. All patients had intraoperative epicardial or transesophageal echocardiography to assess the adequacy of surgery.
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Results |
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The remaining 14 patients had relatively uncomplicated postoperative courses. Mean duration of ventilation was 26 hours, and mean intensive care stay was 6.6 days (range 3 to 10 days). The postoperative gradients are detailed in Figure 2.
Long-Term Results
All 14 survivors are on regular follow-up and are being reviewed by our pediatric cardiologist. Mean follow-up has been 30 months (range, 3 months to 5.5 years).
There were no late deaths, and there were no patients who required reoperation. All patients are off cardiac medications. Postoperative transthoracic echocardiogram revealed no significant mitral stenosis in any patient (Fig 5). One patient with Shone's complex has moderate left ventricular outflow obstruction. The transmitral gradients by echocardiography at follow-up is shown in Figure 2.
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Comment |
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Supramitral ring must be differentiated from the more common cor triatriatum [19]. Cor triatriatum develops as a result of failure of embryological development of the left pulmonary vein during the fifth week of gestation. Hence, the left atrium gets divided into distinct proximal and distal chambers. Usually an atrial septal defect is associated. Additionally, in cor triatriatum, the membrane is generally well separated from the mitral valve, is proximal to the left atrial appendage, and consists of fibromuscular tissue. In contrast, supramitral ring is thought to be derived from a failure of the endocardial cushions to divide completely. It is usually located in close proximity to the mitral valve, and the opening of the left atrial appendage is usually above a supramitral ring. The ring is fibrous.
The physiologic consequence of the supramitral ring is similar to that of other obstructive anomalies that can occur in the left atrium, namely, pulmonary vein stenosis, cor triatriatum, and mitral valvular stenosis, and includes elevated pulmonary venous pressure as well as pulmonary arterial hypertension. Hence, children present with congestive heart failure and failure to thrive. Preoperative diagnosis of supramitral ring is difficult. Using transthoracic echocardiography, the diagnosis has generally been made in only approximately 50% of cases. In a study by Sullivan and coworkers [20], postoperative retrospective analysis of echocardiographic tapes utilizing a detailed frame-by-frame examination yielded the diagnosis in 91%; however, the preoperative diagnosis was made in this study only in 45% of the cases. In our series, too, preoperative diagnosis was made in only 73% of cases. That could possibly reflect difficulties in delineating a membrane in the atrium in our patients, most of whom had associated ventricular septal defects with left to right shunts and hence increased blood flow in the left atrium. In our patients in whom diagnosis was made intraoperatively, the preoperative echocardiogram revealed only turbulence across the mitral valve; and upon exposure of the mitral valve, the valve itself was found to be normal, the only anomaly being the supramitral ring, which was excised with good outcome. Although the supramitral ring can occasionally be diagnosed by angiocardiography [17], it is fairly insensitive in the diagnosis of the condition. Transesophageal echocardiography is perhaps the best tool to diagnose supramitral ring [21]. It can differentiate supramitral ring from cor triatriatum, define the attachment of the obstructing membrane, and quantify the gradient.
The cardiac anomalies associated with supramitral ring have not been well described. From this study, we propose that the associated cardiac anomalies can be grouped broadly into two categories: supramitral ring associated with VSD and supramitral ring associated with left-sided obstructive pathologies, especially subaortic membrane, bicuspid aortic valve, and coarctation of the aorta. In the first scenario, this is important in the context of patients with VSD and turbulence across the mitral valve in which a supramitral ring needs to be ruled out. In the second scenario, in patients with multilevel left heart obstructions, a supramitral ring should be excluded to prevent residual defects, as has been reported previously [22, 23].
The levoatriocardinal vein that was associated with the supramitral ring in one of our patients is the first description of the association of these two anomalies. In this patient, the levoatriocardinal vein acted as a "pop-off" valve and allowed decompression of the left atrium, reducing the severity of pulmonary venous hypertension and delaying the onset of debilitating symptoms.
This study also gives a comprehensive description of the spectrum of morphologic variations of the supramitral ring. We have seen that it may be a complete circumferential ring or a partial ring, and that it may adhere to and interfere with the posterior leaflet of the mitral valve, a finding observed by others too [10].
We emphasis that the transseptal approach can be planned in most cases. This allows for adequate surgical exposure for excision of the ring as well as for optimal assessment of mitral valve anatomy. Most of the commonly associated anomalies can be managed through this incision such as VSD closure, subaortic membrane excision through the VSD, and correction of double outlet right ventricle, facilitating a single stage total correction for all patients.
The first surgical correction of supramitral ring was described by Lynch and colleagues [13] in 1962 in a study of 14 patients operated on at the Hospital for Sick Children in London. The study showed that surgical correction of this anomaly can be performed successfully, leading to excellent late clinical results. This finding has been confirmed by our study. Our only death was an infant with Shone's complex, which itself is a complex disease process with a guarded prognosis. All the rest of our patients have done well as demonstrated by follow-up echocardiograms.
In conclusion, supramitral ring is an entity whose morphology and optimal management is still being elucidated. A high index of suspicion is required when performing transthoracic echocardiography in the clinical settings discussed above, and transesophageal echocardiogram is recommended whenever transmitral gradients are obtained. A transseptal approach allows optimal exposure of the ring and the mitral valve, allowing ring excision without compromising mitral valve function, while also facilitating simultaneous correction of associated cardiac anomalies. Appropriate evaluation and management of this rare anomaly results in a gratifying long-term outcome.
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References |
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  A. Toscano, L. Pasquini, R. Iacobelli, R. M. Di Donato, F. Raimondi, A. Carotti, V. Di Ciommo, and S. P. Sanders Congenital supravalvar mitral ring: an underestimated anomaly. J. Thorac. Cardiovasc. Surg., March 1, 2009; 137(3): 538 - 542. [Abstract] [Full Text] [PDF]
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