Mitral Valve Anomalies
Mitral Valve Anomalies
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Mitral valve disease in children encompasses a wide and complex spectrum of congenital and acquired abnormalities. Echocardiography remains the cornerstone of diagnosis and physiological assessment, yet interpretation requires a detailed understanding of valve anatomy, developmental biology, and the interplay between structure and function. This chapter provides a comprehensive overview of mitral valve anatomy, mechanisms of dysfunction, and key congenital anomalies encountered in pediatric practice, with emphasis on echocardiographic evaluation.
The mitral valve is a crucial component of the heart, connecting the left atrium to the left ventricle. It is a somewhat unique valve with specific anatomical features and can be affected by a wide range of anomalies, particularly in children.
I. Anatomy and Normal Function
The mitral valve is a highly specialized and elegantly designed structure that ensures unidirectional flow from the left atrium to the left ventricle. The mitral valve is composed of two main leaflets: the anterior leaflet and the posterior (mural) leaflet. The posterior leaflet occupies the largest part of the mitral annulus's circumference. These leaflets are further divided into segments for precise description, especially useful in adult mitral valve repair:
Anterior Leaflet Segments: A1 (external), A2 (middle), A3 (internal).
Posterior Leaflet Segments: P1 (external), P2 (middle), P3 (internal).
As such, each leaflet is subdivided into three scallops, designated (Anterior) A1 to A3 and (Posterior) P1 to P3 from medial to lateral. While the anterior leaflet occupies only one third of the annular circumference, it contributes to approximately two thirds of the leaflet area, whereas the posterior leaflet spans the majority of the annulus but contributes less leaflet surface.
The valve also features two commissures: the lateral (or anterior) commissure and the medial (or posteromedial) commissure. Supporting the leaflets are two mitral pillars (papillary muscles)—an anterolateral pillar and a posteromedial pillar—which project chordae tendineae. These chordae attach to both the leaflets and the commissures. From a surgical perspective, the mitral annulus is not perfectly circular. When viewed on echocardiography, particularly in a short-axis cut, a normal mitral valve presents a characteristic "smile" appearance or fishmouth appearance. The mitral valve opens in a coordinated, three-dimensional motion resembling a dynamic orifice, and modern three-dimensional echocardiography has significantly enhanced our ability to appreciate this complexity beyond traditional two-dimensional imaging.
II. Analysis and Imaging
Analysis of the mitral valve typically proceeds systematically, starting with the papillary muscles, then the commissures, and finally the leaflets (anterior and posterior). This assessment includes examining the leaflets, pillars, chordae, annulus, and overall function. Imaging, particularly echocardiography, is crucial. For instance, the short-axis view is well-suited for cardiology examinations (in parasternal or subcostal view). Detailed descriptions using segments (A1, P1, etc.) are often useful for surgical repair in adults, though less so in congenital cardiology. In young children, precise echocardiographic descriptions can be challenging. The "smile of the mitral" view is often used to correctly analyze the valve in children with malformations.
Comprehensive echocardiographic assessment checklist of the mitral valve:
The annular size must be evaluated as the primary inlet, followed by inspection for supravalvar mitral rings, which may sit on the leaflets and contribute to obstruction.
Leaflet morphology should be assessed for thickening, redundancy, or abnormal motion.
The chordal apparatus must be carefully examined to determine presence, length, and insertion of chordae, as well as their relationship to the papillary muscles.
An often underappreciated component is the concept of the secondary inlet. Blood flow does not simply pass through the annulus but must traverse the subvalvar apparatus, including chordae and papillary muscles. In some cases, obstruction may occur at this level despite a relatively normal annulus, leading to underestimation of disease severity if only the primary inlet is considered.
Papillary muscle number and position are critical elements of evaluation, and the presence of one versus two papillary muscles often provides essential diagnostic clues. Ultimately, the functional assessment focuses on the presence and severity of mitral stenosis and regurgitation.
LMCA: Left Main Coronary Artery.
Aortic Valve: Right coronary cusp (R); Left coronary cusp (L); Non coronary cusp (NC)
Tricuspid Valve: Anterior, Septal and Posterior leaflets.
2D-grayscal Sweep from aortic valve to LV apex
View of the RV and LV in cross-sectional area at the level of the base of the left ventricle.
Two-dimensional imaging and color Doppler remain essential tools in daily practice, but three-dimensional echocardiography has transformed our understanding of mitral valve anatomy. It allows visualization of the valve as a dynamic, living structure, providing detailed information about leaflet morphology, chordal architecture, and spatial relationships. Three-dimensional imaging enables identification of jet origin within the valve, enhances surgical planning, and supports advanced applications such as transcatheter edge-to-edge repair. New rendering techniques, including transparent or “glass” imaging, further improve visualization of subvalvar structures. Parametric modeling and quantitative analysis are increasingly used, particularly in adult structural heart disease, to guide interventions and personalize treatment strategies.
Multiple jets mitral insufficiency
III. Anomalies of the Mitral Valve
Mitral valve disease in children differs fundamentally from that in adults. Pediatric disease is predominantly congenital, including structural abnormalities such as mitral arcade, parachute mitral valve, clefts, and double orifice valves. Connective tissue disorders such as Marfan syndrome, Ehlers-Danlos syndrome, and osteogenesis imperfecta are associated with mitral valve prolapse. In addition, congenital heart lesions such as atrioventricular septal defects are among the most common causes of left atrioventricular valve dysfunction in this population. Acquired disease in children includes rheumatic heart disease and infective endocarditis, although these are less common in developed settings. Secondary mitral valve disease results from abnormalities outside the valve itself. In dilated cardiomyopathy, ventricular enlargement leads to leaflet tethering and functional regurgitation. In anomalous left coronary artery from the pulmonary artery, ischemia of the papillary muscles results in dysfunction and regurgitation. Volume overload lesions such as ventricular septal defects or patent ductus arteriosus may cause ventricular dilation and secondary mitral regurgitation, while pressure overload conditions such as aortic stenosis can similarly alter valve mechanics. Hypertrophic cardiomyopathy may produce systolic anterior motion of the mitral valve, leading to regurgitation. Mitral valve anomalies can be broadly categorized into anomalies of the leaflets and anomalies of the subvalvular apparatus.
A. Leaflet Anomalies (and Related Atrial Anomalies)
Atresia and Hypoplasia:
Mitral Atresia: The mitral valve is completely closed or nearly closed.
Mitral Hypoplasia: The valve is minuscule. These conditions often lead to a very small left ventricle and are part of severe pathologies like hypoplastic left heart syndrome.
Insufficiency: Quantification of mitral regurgitation in children remains challenging. Unlike adults, where standardized methods exist, pediatric mitral regurgitation is often characterized by multiple eccentric jets and complex mechanisms. There is no universally accepted gold standard for echocardiographic quantification. Methods such as vena contracta measurement, regurgitant fraction, and regurgitant volume can be applied, but their reproducibility and clinical correlation are limited. Even under core laboratory conditions, variability between observers remains significant. Furthermore, children often lack overt symptoms, making clinical correlation difficult, and standard tools such as exercise testing or functional classification are less applicable. Importantly, left ventricular dilation does not always correlate reliably with severity of regurgitation in children, highlighting the need for integrated and cautious interpretation.
Moderate TR and MR.
Significant mitral regurgitation with jet reaching almost the roof of the atrium and a dilatation of the LA
Prolapse: Mitral valve prolapse occurs when a portion of the valve prolapses into the left atrium during ventricular contraction, leading to mitral regurgitation (leakage). Mitral valve prolapse is characterized by systolic displacement of one or both leaflets into the left atrium. It may be congenital or associated with connective tissue disorders and is a common cause of mitral regurgitation. Regurgitation typically begins in mid-systole, corresponding to leaflet prolapse. Three-dimensional imaging is particularly useful in identifying the specific scallops involved, which is critical for surgical planning.
Adult Presentation: It is a well-known anomaly in adults, predominantly affecting women, often before menopause. This is typically termed "dystrophic mitral insufficiency".
Pediatric Presentation: In children, mitral prolapse is much rarer and frequently associated with connective tissue disorders, particularly Marfan syndrome and Marfan-like syndromes. In Marfan syndrome, both leaflets may pass behind the annulus, appearing thickened. Prolapse of the tricuspid valve and dilatation of the aortic root are frequently associated findings in these patients. Measuring the annulus and the depth of prolapse guides potential surgical repair. Mitral valve annular dysjunction (MAD) may also occur in Marfan or Marfan-like syndromes.
Clefts: A cleft is a slit, typically in the anterior leaflet of the mitral valve. A cleft mitral valve represents a true defect in the leaflet, most commonly involving the anterior leaflet. It occurs in the setting of two distinct annuli, with the aortic valve interposed between the mitral and tricuspid valves. The cleft is typically directed toward the left ventricular outflow tract. Embryologically, this lesion represents incomplete fusion of the superior and inferior bridging leaflets during development, making it the mildest form of atrioventricular septal defect. In contrast, atrioventricular septal defects are characterized by a single common annulus. The so-called cleft in this setting is not a true defect but rather the zone of apposition of the bridging leaflets, oriented toward the ventricular septum. Differentiating these entities is essential, as they have distinct anatomical and surgical implications. The direction of the leaflet deficit is a key diagnostic feature used to differentiate these two conditions:
The cleft is typically a deficit in the anterior leaflet that is directed toward the left ventricular outflow tract (LVOT) and the aorta . This occurs because the cleft "swings away" from the ventricular septum during embryonic development.
In an AVSD, the space where the superior and inferior bridging leaflets come together is directed toward the ventricular septum in a perpendicular fashion.
Double Orifice: Double orifice mitral valve is a rare anomaly characterized by a fibrous bridge dividing the valve into two orifices. These orifices may be symmetric or asymmetric and can be associated with other congenital heart defects, particularly atrioventricular septal defects. The diagnosis is most readily made in the parasternal short-axis view, where two distinct openings are visualized. Color Doppler reveals dual inflow jets. In many cases, valve function is preserved, although regurgitation or stenosis may occur.
Straddling Mitral Valve (Overriding): Straddling occurs when a mitral valve leaflet, or part of its subvalvular apparatus (like a papillary muscle), inserts into the "wrong" ventricle by crossing an interventricular communication. This means a portion of the valve effectively straddles the interventricular septum. It is sometimes described as the valve "overriding" the interventricular communication or the septal crest. Straddling and clefts are considered related or very closely associated anomalies. Straddling of the mitral valve occurs in association with conotruncal anomalies and results from malalignment of the conal septum. The valve overrides the ventricular septum and may have chordal attachments within the right ventricle. This lesion can mimic a cleft valve but is distinguished by its association with ventricular septal defects and abnormal papillary muscle distribution. It has significant surgical implications, particularly when constructing left ventricular outflow pathways.
Supra-mitral Membrane: A supra-mitral membrane is a fibrous membrane located just above the mitral valve, within the left atrium. This membrane can obstruct blood flow, causing symptoms similar to mitral stenosis. It is crucial to distinguish it from Cor Triatriatum, which is an anomaly of pulmonary vein incorporation resulting in a membrane dividing the left atrium into a posterior part (receiving pulmonary veins) and an anterior part (connected to the left atrial appendage and mitral valve). A supra-mitral membrane is situated below the left atrial appendage and above the mitral valve.
Intra-mitral Membrane: An intra-mitral membrane is a rare anomaly where a membrane or fibrous cockade is found within the mitral valve leaflets themselves, often attached to them. This can significantly impede leaflet function, causing both stenosis and regurgitation, and may necessitate valve replacement.
B. Subvalvular Apparatus Anomalies
These anomalies are generally more complex to diagnose and repair.
Parachute Mitral Valve: Normally, there are two distinct mitral pillars (papillary muscles). In a parachute mitral valve, these papillary muscles are fused or abnormally close, resulting in a single functional papillary muscle. All the chordae tendineae converge and attach to this single pillar, creating an appearance similar to a parachute canopy, which often leads to a single, often stenotic, mitral orifice. The chordae converging onto a single papillary muscle creates a funnel-like configuration. This results in mitral stenosis and is commonly associated with other left-sided obstructive lesions (possibly secondary to restrictive LV preload in fetal life limiting growth related to flow), forming part of the Shone complex. Echocardiographically, a single papillary muscle is identified, and inflow is eccentric. Three-dimensional imaging provides a striking depiction of the valve’s parachute-like appearance. One must be careful to not miss straddling mitral valve as it can also appear with a signle papillary muscle in the LV, when there is attachment of the valve on the other side of the septum.
Shone complex is a rare congenital syndrome characterized by multiple levels of obstruction of the left heart inflow and outflow tract, originally described by John Shone in 1963. The classic (complete) Shone complex consists of four obstructive lesions occurring together. The four components (the “classic tetrad”):
Supravalvar mitral ring: A fibrous membrane located above the mitral valve, often adherent to the leaflets, causing inflow obstruction.
Parachute mitral valve
Subaortic obstruction (subaortic membrane or ridge): A fibrous or fibromuscular narrowing in the left ventricular outflow tract below the aortic valve.
Coarctation of the aorta
Mitral Arcade or Hammock: This broad category encompasses various malformations characterized by total or partial muscular fusion close to the leaflets and pillars, often with thick, muscular, or short chordae tendineae. In severe forms, there might be a direct attachment of the valvular leaflets to the ventricular wall without distinct chordae, forming a muscular mass or band. These anomalies are notoriously difficult to diagnose and repair and often result in mitral regurgitation, though stenosis can also occur. Such valves are often severely dysfunctional and symptomatic, especially in the neonatal period. In summary, mitral valve arcade is a severe anomaly in which the papillary muscles connect directly to the valve leaflets with absent or markedly shortened chordae. This results in restricted leaflet motion and progressive mitral stenosis, often accompanied by regurgitation. The lesion is frequently associated with other left-sided obstructive conditions such as coarctation of the aorta or aortic stenosis (possibly due to restricted flow in fetal life due to relatively reduced LV preload). Although valve function may be relatively preserved in early life, progressive obstruction is typical, and many patients ultimately require valve replacement. Echocardiography reveals papillary muscles extending directly to the leaflets with limited excursion, and three-dimensional imaging highlights the narrowed inflow at the level of the subvalvar apparatus.
Mitral Arcade to Mitral Hammock (worsening)
Mitral stenosis: The criteria for identifying and grading mitral stenosis in pediatric and newborn patients involve a combination of hemodynamic measurements, anatomic assessments, and secondary physiological indicators. Clinicians primarily utilize mean pressure gradients derived from echocardiography to quantify the severity of the obstruction. A mean gradient above 15 mmHg is generally classified as severe mitral stenosis. In the context of evaluating the success of a surgical intervention, such as after a septal defect repair, a post-operative mean gradient of less than 5 to 6 mmHg is typically considered an acceptable amount of residual stenosis. When assessing the anatomy of the valve, it is essential to look beyond the primary inlet. The primary inlet is defined by the diameter of the annulus where the valve attaches between the left atrium and the left ventricle. However, the secondary inlet—which includes the entire pathway of the chordae tendineae and the papillary muscles—is often the actual site of narrowing in congenital cases. An assessment of the valve is not complete without evaluating this deeper pathway, as a patient may appear to have an adequate primary annulus while still suffering from functional stenosis due to abnormalities in the chordae or papillary muscles. Specific structural malformations serve as definitive criteria for certain types of stenosis. For example, a supervalvar mitral ring is a structure that sits on the leaflets and causes narrowing of the inflow . In a mitral valve arcade, the chordae tendineae are either absent or extremely shortened, leading to a direct connection between the papillary muscles and the leaflets . This results in poor leaflet excursion and the development of significant, often progressive, stenosis. Similarly, a parachute mitral valve is identified by the attachment of all or most chordae to a single, dominant papillary muscle, which gives the valve a characteristic funnel-like appearance on imaging and restricts blood flow into the ventricle. Secondary clinical indicators also provide critical diagnostic criteria. One of the most important pieces of information in a patient with suspected mitral stenosis is the right ventricular (RV) pressure. Elevated RV pressure indicates the presence of post-capillary pulmonary hypertension, which is a common consequence of significant mitral obstruction. Additionally, in children old enough to perform exercise, the mean gradient across the mitral valve will typically increase as cardiac output demands rise, further confirming the physiological impact of the stenosis. Technological advancements in imaging have refined these criteria. While traditional 2D and color Doppler imaging remain the standard for identifying narrow inflow jets and measuring gradients, three-dimensional echocardiography allows for a more comprehensive assessment. 3D imaging provides a view of the valve as a "living pathology specimen," making it easier to visualize the funneling of a parachute valve or the restricted movement in a valve arcade. This detailed modeling helps clinicians and surgeons understand the specific topography of the valve, such as tenting volume and leaflet area, which are increasingly used as criteria for determining the most appropriate intervention strategy.
Mitral annular disjunction (MAD) refers to a structural separation between the left atrial–mitral valve junction and the basal left ventricular myocardium, most often involving the posterior annulus. In adults, it has been described in association with myxomatous mitral valve disease and arrhythmic risk, but its relevance in the neonatal population remains largely undefined. In neonates, the mitral annulus is inherently dynamic and less fibrous, and distinguishing true MAD from physiologic annular motion or imaging artifact can be challenging. When suspected on echocardiography—typically in parasternal long-axis or apical views—it appears as a systolic displacement of the posterior mitral annulus away from the ventricular myocardium, sometimes accompanied by exaggerated annular motion. From a neonatal hemodynamic perspective, the clinical significance of MAD is uncertain. It may occasionally be identified in association with congenital mitral valve abnormalities or connective tissue phenotypes, but in most cases it is an incidental or subtle finding without clear functional consequence. Careful assessment of mitral valve competence, left ventricular function, and atrial dimensions remains essential, as these parameters carry more immediate clinical relevance. At present, MAD in neonates should be interpreted cautiously, with emphasis on longitudinal follow-up rather than immediate intervention, while the field continues to define its true prevalence and potential implications in early life.
IV. Mitral Valve Anomalies in Acquired Heart Conditions:
The mitral valve can also be affected secondary to other congenital heart conditions or acquired diseases.
Ischemic Mitral Insufficiency: This is a distinct anomaly characterized by whitish, ischemic papillary muscles on echocardiography, often in a dilated heart. It is typically associated with Anomalous Left Coronary Artery from the Pulmonary Artery (ALCAPA), a condition leading to myocardial ischemia and severe mitral regurgitation.
Functional Mitral Insufficiency:
Dilated Cardiomyopathy: Mitral regurgitation can arise from the dilatation of the mitral annulus due to an enlarged heart, as seen in dilated cardiomyopathies.
Hypertrophic Cardiomyopathy: In obstructive hypertrophic cardiomyopathy, mitral regurgitation can be caused by the Systolic Anterior Motion (SAM) of the anterior mitral leaflet, where it is brought anteriorly into the left ventricular outflow tract during systole due to a vortex effect intra-cavitary.
Endocarditis: Infective endocarditis can affect the mitral valve, leading to serious damage. This may manifest as large vegetations destroying a leaflet (e.g., the posterior leaflet) or perforations within a leaflet (e.g., the anterior leaflet). The subvalvular apparatus can also appear "glued". Endocarditis can occur on native valves (though rare in children) or prosthetic valves.
Rheumatic Mitral Disease: While less common in some regions, rheumatic fever is a significant cause of mitral valve disease in pediatric populations in endemic areas. It can lead to both mitral insufficiency and stenosis, presenting with classic echocardiographic images.
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