Double Orifice Mitral Valve

Etiology

Congenital double-orifice mitral valve is often associated with other congenital cardiac anomalies, such as coarctation of the aorta, patent ductus arteriosus, and bicuspid aortic valve, suggesting the underlying etiology may be an endocardial cushion defect.[2] In an autopsy case series, the most common congenital cardiac defect associated with a double-orifice mitral valve was an atrioventricular septal defect.[3] Few case studies have reported isolated cases of double-orifice mitral valve, incidentally discovered in adult patients.[4][5] Although most cases are congenital, acquired double-orifice mitral valve repair has been documented due to calcification or after edge-to-edge mitral valve repair, whether surgical or percutaneous, including transcatheter mitral valve repair.[6][7][8]

Based on echocardiographic features, there are 3 morphological types of congenital double-orifice mitral valve—eccentric, central, and duplicate mitral valve.[9] The eccentric type, also called the hole type, accounts for approximately 85% of cases and is characterized by a larger main orifice and a smaller accessory orifice at either the posteromedial or anterolateral commissure.[9][10] The central or bridge type is observed in 15% of patients with a double-orifice mitral valve and is characterized by a central bridge of fibrous tissue connecting the 2 leaflets.[9] The 2 orifices may be equal in size or unequal. The duplicate mitral valve type, albeit extremely rare, consists of 2 mitral valve annuli and valves, each possessing leaflets, commissures, papillary muscles, and chordae.[9]

Epidemiology

Due to its rarity, epidemiological data on double-orifice mitral valves are limited. A postmortem study of 2733 autopsied cases from the Cardiac Registry of Boston Children's Hospital identified 28 double-orifice mitral valves (1% of autopsied patients).[10] A retrospective study of echocardiographic data in the adult population estimated an incidence of 0.06%.[11] As in the United States, international data are limited; however, in a Polish retrospective study of echocardiograms from 79,919 patients between 1993 and 2006, the incidence was 0.01%.[12] Currently, no reports suggest a gender preference.

Pathophysiology

Several classifications have been proposed based on the etiology or morphological appearance of double-orifice mitral valves. The majority of cases are attributed to congenital anomalies of the native valve. However, an acquired form of the double-orifice mitral valve can arise when mitral annular calcifications affect the second scallop of the anterior leaflet and the second scallop of the posterior leaflet, causing the mitral valve orifice to split into 2.[13][8][13] Iatrogenic interventions, both surgical (Alfieri stitch) and percutaneous (MitraClip®) edge-to-edge mitral repair, have been documented as underlying causes of double-orifice mitral valves.[6][7] In congenital anomalies of the underlying native valve, double-orifice mitral valves occur due to the abnormal fusion of the dorsal endocardial and the left lateral endocardial cushions with the persistence of the left part of the common atrioventricular canal.[1]

History and Physical

Double-orifice mitral valves are typically asymptomatic unless accompanied by mitral stenosis, mitral regurgitation, or a concurrent congenital cardiac anomaly. In patients with congenital heart defects, clinical manifestations are often related to that specific disorder, as there are no distinctive signs of a double-orifice mitral valve. In an isolated double-orifice mitral valve, symptom severity is influenced by the degree of blood flow turbulence and left atrial pressure, which can lead to pulmonary congestion.

Symptoms in the pediatric population are primarily due to reduced cardiac output. These symptoms range from tachypnea, dyspnea, and wheezing to poor feeding and failure to thrive. Asymptomatic patients may have an unremarkable physical examination, as an isolated double-orifice mitral valve is typically benign and not detectable on cardiac auscultation.

If complicated by mitral stenosis, a low-pitched mid-diastolic murmur may be detected at the apex. Similarly, a double-orifice mitral valve with mitral regurgitation may exhibit a blowing pansystolic murmur at the apical region. As symptoms progress, clinical signs of heart failure, such as increased work of breathing, peripheral cyanosis, elevated jugular venous pressure, palpation of a parasternal heave, pulmonary crackles on auscultation, and peripheral edema, may become apparent.[14]

Evaluation

Transthoracic echocardiography (TTE), using 2-dimensional (2D) or 3-dimensional (3D) imaging, is the primary method for assessing a double-orifice mitral valve.[15] The double orifices of double-orifice mitral valves are best evaluated in the parasternal short-axis view. In contrast, the apical and subcostal 4-chamber views are ideal for visualization of the subvalvular apparatus. The addition of 3D TTE, complementing 2D TTE, enhances the assessment of mitral valve anatomy and function. 3D TTE accurately assesses the size and spatial relationships of the mitral valve and intracardiac structures, enabling detailed inspection of chordal attachments and abnormalities of the subvalvular apparatus.[1][16]

If the lesion is hidden by anatomic distortion or an adequate echocardiographic window cannot be obtained, transoesophageal echocardiography becomes a valuable adjunct.[17]

The addition of color Doppler provides essential information on mitral valve flow, aiding the assessment of valve regurgitation or stenosis. Preoperative transesophageal echocardiography is generally unnecessary, but an intraoperative approach is routinely used to confirm preoperative electrocardiogram (ECG) findings.[17] Cardiac magnetic resonance imaging is of limited utility and is generally not pursued.[18] Additional nonspecific data can be obtained from a chest x-ray and ECG. For instance, a chest x-ray may reveal left atrial enlargement and evidence of pulmonary congestion, such as upper lobe diversion, increased interstitial markings, and Kerley B lines. An ECG is standard in an isolated double-orifice mitral valve. However, possible findings include P mitrale (if left atrial enlargement is present) and voltage criteria for left ventricular hypertrophy (if mitral incompetence is severe enough).

Treatment / Management

Management of double-orifice mitral valves depends primarily on whether patients are symptomatic, which directly correlates to the degree of mitral valve dysfunction. Asymptomatic patients are advised to undergo interval TTE, although current guidelines do not specify the frequency. Management of symptomatic double-orifice mitral valve includes medical therapy, noninvasive interventions, or a surgical approach.

Medical therapy aims to alleviate symptoms of heart failure and pulmonary congestion until more definitive treatment is sought for mitral valve dysfunction. This approach is particularly crucial in the pediatric population, where managing symptoms of congestive heart failure is essential until the infant reaches an age suitable for specific valve interventions. In cases of double-orifice mitral valve with mitral stenosis, percutaneous transcatheter balloon dilatation is a viable option for relieving the obstruction. Surgical mitral valvuloplasty or valve replacement may be considered if balloon dilatation is impractical or unsuccessful.[6]

Symptomatic patients with a regurgitant valve should be evaluated for surgical repair, including leaflet plication and, if indicated, division of the bridging tissue.[19][20] In double-orifice mitral valves, surgical closure of 1 orifice may result in an acute reduction of the mitral valve area, leading to stenotic flow.[21](B3)

During surgery on a double-orifice mitral valve, it is imperative to exercise caution to prevent the accidental severing of the isthmus between the orifices. Such an action can lead to substantial mitral regurgitation, posing a considerable challenge for repair due to the insufficient supporting chordae tendineae in the central part of the valve. In cases of double-orifice valve stenosis, addressing any underlying secondary causes, such as obstructive lesions of the papillary muscle, may contribute to the stenosis.

Occasionally, a division may occur in the leading panel of the larger aperture. Utilizing practical expertise to evaluate whether corrective measures are necessary is recommended. Thoughtful consideration is essential to assess the potential impact on stenosis resulting from repairing the division versus the extent of regurgitation if the issue is left untreated.

Differential Diagnosis

A double-orifice mitral valve is a distinctive disorder with nonspecific symptomatology. The development of symptoms correlates with the severity of mitral valve dysfunction, left atrial pressure, and pulmonary venous congestion. In adults, it is essential to consider other causes of mitral valve disease, including rheumatic heart disease, functional mitral regurgitation, myocardial ischemia, annular calcification in older adults, connective tissue disorders, myxomatous degeneration, and infective endocarditis.[22] Double-orifice mitral valves should be considered in the pediatric population when another congenital heart disease is present, such as coarctation of the aorta, patent ductus arteriosus, bicuspid aortic valve, and atrioventricular septal defect.

Prognosis

In asymptomatic patients without mitral valve dysfunction, the prognosis of a double-orifice mitral valve is reassuring. However, no prospective studies currently establish a timeline for progression from a double-orifice mitral valve to mitral valve dysfunction. Some patients develop early dysfunction in infancy, whereas others may develop it in adulthood.[20][23] With surgical valve repair and noninvasive techniques, the survival rate following intervention for mitral valve dysfunction is significantly higher than that of surgical valve replacement.[24][25][24]

Complications

Complications of double-orifice mitral valves primarily involve mitral valve dysfunction, including stenosis and regurgitation, which can lead to pulmonary edema and congestive heart failure. Atrial arrhythmias, such as atrial fibrillation and atrial flutter, may arise directly from a double-orifice mitral valve, increasing the risk of embolic strokes in affected patients.[26]