Accessory Mitral Orifice

Definition

The accessory mitral orifice is a rare congenital anomaly of the mitral valve, characterized by the presence of an abnormal opening that alters normal blood flow between the left atrium and left ventricle. This malformation can occur in isolation or be associated with other congenital heart diseases, such as atrioventricular septal defect (AVSD), mitral valve duplication, or mitral valve prolapse. The clinical significance of the accessory orifice depends on its location and size. In some patients, the condition is hemodynamically insignificant and discovered incidentally. However, in more severe cases, the orifice can affect valvular function, leading to blood turbulence and progressive mitral regurgitation.

Embryology and Pathogenesis

Mitral valve formation occurs between the fourth and eighth weeks of gestation, involving the fusion of the endocardial cushions and the remodeling of valvular structures. Abnormalities in this process can result in an accessory opening, creating an anomalous passage through the mitral valve. The most accepted pathogenic mechanisms include:

Defects in endocardial cushion fusion: prevent the normal formation of the mitral valve.
Persistence of accessory embryonic tissues: primitive structures that fail to regress completely may form an additional opening.
Genetic alterations: mutations in genes involved in valvular development, often associated with other congenital heart diseases.

In some cases, the accessory mitral orifice is part of a broader clinical condition, such as Shone's syndrome, which includes multiple obstructive anomalies of the left ventricular outflow tract.

Pathophysiology

The hemodynamic impact of this anomaly depends on the size and position of the orifice. A small defect may have no clinical consequences. However, if larger, it can cause:

Mitral regurgitation: blood flows back from the left atrium into the ventricle, disrupting valve coaptation.
Blood turbulence: disorganized flow may predispose the patient to infective endocarditis.
Left atrial dilation: due to increased atrial pressure, potentially leading to atrial fibrillation.
Pulmonary congestion: in severe cases, it may cause progressive dyspnea and heart failure.

Clinical Manifestations

Symptoms vary depending on the extent of the hemodynamic alteration. In mild cases, the patient may remain asymptomatic for years, with an incidental diagnosis during echocardiography. In moderate or severe cases, symptoms may include:

Exertional dyspnea: due to increased left atrial pressure.
Early fatigue: caused by reduced cardiac output.
Palpitations: often related to left atrial dilation and the onset of atrial fibrillation.
Systolic or diastolic murmur: detected on auscultation, caused by blood turbulence.

In newborns and young children with severe forms, the accessory mitral orifice may cause tachypnea, feeding difficulties, and poor weight gain, which are indicative of early heart failure.

Diagnosis

The diagnosis relies on advanced imaging techniques. Transthoracic echocardiography with Doppler is the first-line examination, as it allows visualization of the anomaly and its hemodynamic impact. In more complex cases, additional imaging may be required:

Transesophageal echocardiography: provides a detailed view of the valvular structures.
Cardiac magnetic resonance imaging (CMR): offers an accurate three-dimensional characterization of mitral anatomy.
Cardiac catheterization: reserved for patients with pulmonary hypertension or for a more detailed hemodynamic assessment.

Treatment

The therapeutic approach depends on the severity of the condition. In mild cases, where the defect does not significantly alter mitral function, clinical monitoring with regular check-ups is sufficient to evaluate potential progression of the malformation. For patients with significant hemodynamic alterations, more invasive interventions may be considered:

Surgical closure of the orifice: indicated for symptomatic cases with moderate-to-severe mitral regurgitation.
Mitral valve repair: performed to restore valve coaptation and improve function.
Valve replacement: in severe cases where the mitral valve is not amenable to repair.

Prognosis

The prognosis depends on the severity of the defect and the timeliness of treatment. In patients with small defects, quality of life is excellent, with no significant complications. In more severe cases, timely intervention can prevent heart failure progression and preserve cardiac function.

Conclusion

The accessory mitral orifice is a rare congenital heart defect that, if large enough, can alter mitral valve function and lead to heart failure. Early diagnosis is crucial in determining the need for treatment. In symptomatic patients, surgical correction offers excellent outcomes, ensuring a favorable prognosis and good quality of life.

Bibliografia

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