A Rare Case of Intramitral Valve Ring in the Setting of Shone Complex Diagnosed by Echocardiography

Dear Editor,

A 23-year-old young male patient, a known case of Shone’s syndrome, was admitted to our hospital with dyspnea on exertion (functional class III). He had a history of aortic valve repair during his childhood due to a stenotic bicuspid valve and also stenting for coarctation of the aorta when he was 11. Comprehensive echocardiography, including transthoracic and transesophageal studies, was performed for precise assessment of structural heart disease. Echocardiography showed a deformed, thickened, and previously repaired aortic valve with severe stenosis and moderate-to-severe regurgitation. The stent of the previous coarctoplasty was also visible in the proximal portion of the descending thoracic aorta with no significant residual stenosis. The mitral valve was thickened with eccentric leaflets opening due to a “parachute-like” mitral valve with asymmetric papillary muscles as well as a membranous “intramitral” ring together resulting in moderate mitral stenosis (with an overall 7 mmHg mean gradient across the mitral valve during diastole in sinus rhythm with a heart rate about 70 bpm). The stenosis was more severe at the level of the tip of the mitral valve rather than the intramitral ring [Figures 1-4]. Mitral and aortic valve replacement (St. Jude Medical mechanical valves) was later performed for him after a comprehensive preoperative evaluation. The mitral valve annulus was not hypoplastic; hence, it could be easily replaced with a “St. Jude Regent 27” mechanical valve by the surgeon, which seemed to be appropriate for his relatively small body size (body surface area = 1.68 m²). Postoperative echocardiography showed acceptable gradients across both prosthetic valves, and the patient was finally discharged from the hospital after an uneventful postoperative period.

Figure 1.

Transthoracic echocardiography, apical four-chamber view showing membranous intramitral ring within the funnel of the mitral valve

Figure 4.

Transesophageal echocardiography, mid-esophageal window at four-chamber view, (a) and 165° long-axis view, (b) showing the intramitral ring within the funnel of the mitral valve. Multiplanar reconstruction three-dimensional study with planimetry showing mitral stenosis less severe at the level of intramitral ring, (c) than the tip of the mitral valve (d)

Figure 2.

Transthoracic echocardiography, apical three-chamber view showing membranous intramitral ring within the funnel of the mitral valve

Figure 3.

Transesophageal echocardiography, mid-esophageal window, 118° view showing diastolic turbulent flow in the left ventricular inflow and outflow tracts due to mitral stenosis and aortic regurgitation

Shone complex is a rare congenital entity, first described by Dr. John Shone in 1963, and its prevalence is about 0.6% in adults with congenital heart disease. It consists of a constellation of left-sided, usually obstructive cardiac lesions, mostly including mitral ring, parachute mitral valve, subaortic stenosis, and aortic coarctation. Incomplete variants of Shone complex consist of a mitral valve anomaly associated with other lesions involving the subaortic region, aortic valve, or thoracic aorta and are much more prevalent than the complete forms.[1,2]

The pathogenesis of Shone complex is hypothesized to be initially caused by a disruption to the left ventricular (LV) inflow tract from a congenital mitral valve anomaly during embryogenesis, resulting in the underdevelopment of the LV cavity and leading to various degrees of LV outflow tract obstruction and aortic coarctation.[1,3,4] A previous study found that 11% of Shone complex cases were associated with de novo mutations in the MYH6 gene encoding cardiac alpha-myosin heavy chain.[5]

The congenital mitral ring is a rare subtype of congenital mitral stenosis. Two types of congenital mitral ring are described: supramitral ring and intramitral ring. The supramitral ring is a fibrous shelf-like membrane just above the mitral annulus, not adhering to the valve leaflets and associated with a normal subvalvular apparatus. It differs from cor triatriatum sinister for its attachment between the opening of the atrial appendage and the mitral annulus. The intramitral ring is a thin membrane within the mitral funnel closely adherent to the valve leaflets. It consistently impairs valve leaflets motion and is combined with Shone complex and abnormal subvalvular apparatus.[6]

The mitral abnormalities associated with the intramitral ring include hypomobility of the posterior leaflet, reduced chordal length, reduced interpapillary muscles distance, hypoplastic mitral annulus, and asymmetrical dominance of the papillary muscle (mostly anterolateral one).[6]

Most patients with mitral ring initially present with aortic coarctation. The associated intracardiac lesions and the diagnosis of the Shone complex are usually apparent after the neonatal period. The supramitral ring is easier to identify than the intramitral ring because it is clearly discernible from the mitral valve leaflets.[6]

Patients with Shone complex typically present in childhood with a spectrum of symptoms, including poor feeding, failure to thrive, and signs of reduced cardiac output.[7] The severity of mitral valve obstruction is the main predictor of prognosis.[8] Management involves cardiac surgery during childhood, and the most common interventions include surgical coarctation repair, subaortic resection, and mitral valve repair.[9] Mortality is low in patients who reach adulthood; however, morbidities are substantial, including arrhythmias, heart failure, and the need for re-interventions.[1]

In the approach to the mitral ring, surgery of the intramitral ring is more challenging. Ring resection is rarely sufficient because the anatomy of the subvalvular apparatus also contributes significantly to inflow obstruction. The predictors of poor repair outcome include mitral annulus hypoplasia at birth, anomalous subvalvular apparatus, and age <1 year.[6]

We introduced this case of intramitral ring in the setting of an incomplete variant of Shone complex (with subaortic stenosis replaced by aortic valve disease) due to rarity and potential difficulties in its diagnosis. Echocardiography must be performed comprehensively and carefully in any patient with congenital heart diseases where lesions often coexist; particularly – for this case – in approaching a patient with LV outflow tract obstruction, we should search for any kind of obstruction in the upstream pathway, with great concern to rare supra and especially intramitral ring due to difficult visualization of a thin structure, especially in early childhood.

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Conflicts of interest

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