Mitral valve atresia is an infrequent congenital heart malformation, part of the hypoplastic left heart syndrome. The syndrome is complete when the aortic valve is also atretic. By itself, mitral valve atresia is always accompanied by a small left ventricle and is caused by septal malalignement, excessive growth of the endocardial cushions or atrioventricular canal defect. The small left ventricle is incapable to offer appropriate systemic output, resulting in early heart failure.
Presentation depends on heart anatomy and associated abnormalities: anomalies of other valves, coarctation of the aorta, transposition of the great arteries, patent ductus arteriosus or other systemic-pulmonary circulation shunts. The pulmonary artery may be hypoplastic and the abnormalities are sometimes diagnosed in utero .
During childhood, the physician will notice dyspnea, central cyanosis, weak peripheral pulses and heart failure signs. Symptoms may set in early and may be severe, therefore the baby needs to be delivered in a center that can immediately address the condition, if the diagnosis is known before birth . The child grows normally in utero, but failure to thrive is noticed after delivery. Cyanosis sets in soon if the foramen ovale is small or closed, but may be absent in the newborn period. The closure of the ductus arteriosus marks a turning point in the child's presentation. He or she may become pale, may exhibit tachypnea, respiratory distress, lethargy and oliguria at this time. Additional findings include those of cardiogenic shock, like hypothermia, tachycardia, anuria and hepatosplenomegaly. A diastolic rumble over the entire precordial area or a high-pitched holosystolic murmur over the inferior portion of the left sternal border may be auscultated, but their presence is not mandatory . The precordium may be hyperactive.
After the malformation has been surgically addressed, the clinical examination should focus on the cardiovascular and neurologic symptoms, because patients often exhibit seizures . Stroke and intracranial hemorrhage are also possibilities , as are phrenic and recurrent laryngeal nerve injury .
Blood workup should include a complete cell blood count with differential, in order to exclude sepsis, that can cause similar symptoms. Hemoglobin levels should be investigated, because anemia can also cause high-output congestive heart failure. A constant characteristic of mitral valve atresia is severe metabolic acidosis, that often becomes worse after oxygen administration. Acid-base status, lactic acid and electrolyte levels measurement are mandatory. Renal failure secondary to heart failure is assessed by blood urea nitrogen and creatinine levels. Transient hepatic cytolysis is sometimes observed. Arterial oxygen and carbon dioxide determination help set mechanical ventilation parameters.
A hypoplastic left ventricle causes right axis deviation on the electrocardiogram. Right ventricular hypertrophy and right atrial enlargement patterns, as well as ST-T wave modifications can sometimes be recognized.
Thoracic radiography shows cardiomegaly and increased pulmonary vascular markings, but echocardiography helps to achieve the final diagnosis. This method accurately delineates the morphology of the mitral valve and the presence of an anterograde or retrograde flow, the function of the aortic valve, the size of both ventricles and the presence of interatrial and interventricular communications and their restrictive or non-restrictive character. The examiner is able to describe the position, the dimensions and the origin of the great arteries. Tricuspid regurgitation is considered to be a preoperative risk factor.
Cardiac catheterization is necessary in cases where echocardiography cannot answer all the questions. It can also be used in order to measure saturation in all four cardiac chambers, chamber pressures and pulmonary vascular resistance. The presence of aortopulmonary collateral vessels should also be investigated on that occasion .
Cytogenetic abnormalities and heterozygous mutations have been described by several authors  . If suspicion is raised, a karyotype analysis may be performed.