Parachute mitral valve and supramitral ring

 

Parachute mitral valve and supramitral ring are both rare congenital anomalies of the mitral valve apparatus, often associated with left-sided obstructive lesions and sometimes coexisting as part of Shone’s complex. They share the common feature of producing left atrioventricular inflow obstruction, but their anatomical basis and clinical implications differ.

Parachute mitral valve is characterized by the insertion of all, or most, of the chordae tendineae into a single papillary muscle instead of the normal two. In some cases, there may be two papillary muscles present but one is underdeveloped and functionally all chordae converge to the dominant one. This abnormal arrangement causes restricted opening of the mitral valve leaflets, leading to varying degrees of mitral inflow obstruction. The severity of obstruction depends on the degree of chordal crowding and leaflet tethering. Clinically, parachute mitral valve can manifest in childhood with symptoms of pulmonary congestion, dyspnea, and sometimes failure to thrive, but in mild cases it may remain asymptomatic until adulthood. It is frequently associated with other left-sided obstructive lesions such as coarctation of the aorta and supravalvular mitral ring, forming part of the Shone’s complex.

Supramitral ring, sometimes referred to as supravalvular mitral ring, is a ridge or shelf of fibrous or fibromuscular tissue located in the left atrium just above the mitral valve annulus. This ring can partially or completely encircle the mitral orifice and may adhere to the mitral leaflets. Depending on its extent and thickness, it can significantly obstruct blood flow from the left atrium to the left ventricle. Unlike the parachute mitral valve, the pathology lies above the annulus and not in the subvalvular apparatus. Clinically, patients present with features similar to mitral stenosis, including exertional dyspnea, pulmonary venous hypertension, and recurrent respiratory infections in childhood. In severe cases, the supramitral ring can mimic rheumatic mitral stenosis, but the congenital origin and younger age at presentation help distinguish it.

Both conditions are diagnosed by echocardiography, which clearly delineates the site of obstruction and the associated anomalies. Management depends on the severity of obstruction and clinical symptoms. In symptomatic patients with significant obstruction, surgical intervention may be required. In parachute mitral valve, surgery involves mobilization of chordae or splitting of the papillary muscle, whereas in supramitral ring, excision of the obstructive ridge is performed. Prognosis depends on the severity of the obstruction and the presence of associated cardiac anomalies.