The supravalvular mitral ring is a rare congenital malformation characterized by the presence of a thin fibrous, membranous, or fibromuscular flap located in the atrial portion of the mitral valve, immediately above the valvular plane.
This structure, also referred to as the "supramitral valve" or "supravalvular membrane," can interfere with the normal diastolic blood flow from the left atrium to the left ventricle, leading to a picture of functional mitral obstruction.
The anomaly can occur in isolation but is more frequently associated with other left heart abnormalities, particularly Shone’s syndrome.
The clinical severity depends on the thickness, distensibility, and location of the membrane relative to the mitral orifices. In mild cases, it may remain silent for years; in severe cases, it may cause symptoms as early as the neonatal period, mimicking congenital mitral stenosis. Early recognition of the lesion is crucial, as mechanical obstruction leads to progressive left atrial overload and increased pulmonary pressures.
The supravalvular mitral ring develops due to a defect in the resorption of the atrial endocardial cushion during embryogenesis, resulting in the formation of abnormal tissue interposed between the left atrium and the mitral valve. The lesion may have variable morphologic appearances, ranging from a thin translucent membrane to a thick, rigid fibrous ring, and it may adhere partially or completely to the mitral valve leaflets.
Based on the extent and degree of adhesion to the valve, two main anatomical variants are distinguished:
In more severe cases, the membrane causes significant diastolic flow obstruction, with increased left atrial pressure, reduced ventricular filling, and the development of pulmonary venous hypertension. Over time, a condition of left ventricular dysfunction may arise due to reduced preload and retrograde pressure overload.
The supravalvular mitral ring is often associated with other structural abnormalities of the left heart, particularly:
Among the known risk factors are certain chromosomal anomalies (particularly deletions of chromosome 7p) and genetic conditions that impair normal development of the left ventricular inflow tract. However, in most cases, the malformation is sporadic and isolated.
The severity of the obstruction determines the timing of symptom onset and the extent of hemodynamic repercussions: in critical cases, signs of pulmonary congestion are observed within the first days of life, whereas in mild or incomplete forms, the diagnosis may be made only during school age or adolescence, often following an abnormal auscultatory finding or symptoms of reduced exercise tolerance.
The clinical presentation of the supravalvular mitral ring is extremely variable and primarily depends on the degree of mitral obstruction and the potential presence of associated cardiac anomalies.
Mild forms may be asymptomatic for years and diagnosed only during an abnormal physical examination.
In contrast, severe cases have early onset, with symptoms compatible with a left heart failure picture.
In neonates and infants, the presentation may occur in the first days or weeks of life with signs of pulmonary congestion, due to increased pressure in the left atrium and pulmonary veins.
The most frequent symptoms include:
On physical examination, a diastolic murmur at the apex may be present, often associated with an accentuated second heart sound. In cases of significant pulmonary hypertension, an increased pulmonary component of the second sound may also be noted. In infants with advanced heart failure, hepatomegaly and signs of respiratory distress may be present.
In older children, the supravalvular mitral ring typically presents with fatigability, exertional dyspnea, and in more advanced cases, palpitations or supraventricular arrhythmias. Disease progression may lead to adverse ventricular remodeling, increased left atrial pressure, and a risk of atrial fibrillation at a later age.
In the presence of associated anomalies – particularly aortic coarctation or subvalvular stenosis – symptoms may be dominated by left ventricular pressure overload and difficulty in maintaining normal systemic output. Clinical evaluation should therefore always consider the spectrum of lesions potentially present in the left heart.
The differential diagnosis includes congenital forms of mitral stenosis, such as double orifice or dysplastic mitral valve, and partial atrioventricular septal defects, where a supravalvular membrane may be part of the anatomical defect. Distinguishing between these entities is crucial, as surgical strategies can vary significantly.
The diagnosis of a supravalvular mitral ring is based on the integration of clinical suspicion, targeted auscultation, and high-resolution echocardiographic imaging.
In mild or incomplete forms, diagnosis may be delayed and established following the detection of a diastolic heart murmur or the onset of symptoms related to reduced ventricular filling.
Conversely, in neonates with severe forms, the clinical picture may mimic congenital mitral stenosis and present with early signs of heart failure.
Physical examination may reveal a diastolic murmur at the apex, sometimes associated with an accentuated second heart sound, though the finding is often subtle and nonspecific. In older children, left atrial hypertrophy may lead to auscultable arrhythmias or a widened apical impulse.
Transthoracic echocardiography is the gold standard diagnostic modality:
the supravalvular membrane appears as an echodense line crossing the left atrial cavity, just above the mitral orifice.
Other important diagnostic features include:
The pressure gradient across the mitral orifice can range from mild to severe. A mean gradient ≥ 5 mmHg indicates significant obstruction. However, the evaluation should always take into account the overall hemodynamic status and the patient’s age.
When the anatomy cannot be clearly defined with transthoracic echocardiography, transesophageal echocardiography is employed, offering a more detailed view of the membrane, particularly in older patients or those with limited acoustic windows. Cardiac magnetic resonance imaging (MRI) may be useful as a complementary tool in complex cases or in postoperative follow-up.
Cardiac catheterization is not routinely required for diagnosis alone but may be indicated to clarify the hemodynamic profile in preparation for surgery or in patients with multiple concomitant left heart lesions. Measurement of atrial and ventricular pressures, along with the trans-mitral gradient, provides a complete diagnostic picture in patients with severe symptoms or surgical indication.
Treatment of the supravalvular mitral ring is surgical in symptomatic cases or when there is a significant gradient across the mitral valve. The goal is to completely remove the obstructive membrane to restore unobstructed diastolic flow into the left ventricle and reduce left atrial and pulmonary circulatory pressures.
Indications for surgery are based on a combination of clinical presentation, transvalvular gradient, and the presence of pulmonary hypertension. In general, a mean gradient ≥ 5 mmHg, combined with symptoms or significant hemodynamic changes, justifies surgical correction.
The procedure consists of complete resection of the supravalvular membrane via a left atrial approach, taking care not to damage the underlying valve leaflets. In cases of significant adhesions or concomitant mitral valve dysplasia, valvuloplasty or, rarely, valve replacement may be required.
When the ring is part of a more complex malformative picture, as in Shone’s syndrome, treatment must address the associated anomalies (coarctation, subvalvular aortic stenosis, etc.) with a coordinated and individualized surgical strategy.
The prognosis is favorable in most patients undergoing isolated membrane resection, especially if the surgery is performed before irreversible damage to ventricular function or the valvular apparatus occurs. The risk of recurrence is low if excision is complete, but it nonetheless requires regular echocardiographic follow-up.
In patients who undergo surgery later or have associated mitral valve dysplasia, residual mitral dysfunction or pulmonary hypertension may persist, potentially requiring additional treatments or reoperations in later life. Early diagnosis and accurate preoperative assessment are crucial for long-term outcomes.
Complications of the supravalvular mitral ring may arise either in the absence of treatment or following surgical correction. In untreated forms, the main consequence is progressive pulmonary venous hypertension secondary to mitral inflow obstruction. In severe cases, this may lead to left heart failure, impaired ventricular filling, and the risk of acute pulmonary edema, particularly in the neonatal period.
Another possible late complication is the development of atrial fibrillation, promoted by progressive dilation of the left atrium. In patients not diagnosed early, a gradual deterioration in left ventricular diastolic function may occur, resulting in reduced functional reserve and decreased exercise tolerance.
Following surgical intervention, the most feared complication is recurrence of the ring, which may occur in cases of incomplete resection or residual fibrous tissue. In such patients, reoperation may be necessary, especially if the transvalvular gradient rises again beyond acceptable limits.
When concomitant mitral valve dysplasia is present, excision of the ring may not be sufficient to restore normal valve function. In these cases, postoperative mitral regurgitation may develop, or early valve replacement may become necessary.
Other complications, though rare in specialized centers, include leaflet injury during resection, transient ventricular dysfunction, and postoperative arrhythmias. For this reason, a structured cardiological follow-up is essential, including regular echocardiographic assessments and clinical monitoring, particularly in the first years following surgery.