Overriding aorta

Overriding aorta is a congenital heart defect characterized by the displacement of the aortic valve over the ventricular septal defect (VSD), straddling the left and right ventricles. This condition is a critical component of several congenital heart diseases, most notably Tetralogy of Fallot and to a lesser extent, Double Outlet Right Ventricle (DORV) and Transposition of the Great Arteries (TGA). The presence of an overriding aorta is significant because it impacts the hemodynamics of the heart, leading to a mixture of oxygenated and deoxygenated blood, and affecting the systemic circulation.

Etiology

The exact cause of an overriding aorta is not fully understood, but it is believed to be related to abnormal development of the conotruncal septum during the first 8 weeks of fetal development. Genetic factors, maternal diabetes, and certain medications during pregnancy have been associated with an increased risk of congenital heart defects, including the overriding aorta.

Pathophysiology

In a normal heart, the aorta arises from the left ventricle, and the pulmonary artery arises from the right ventricle without any overlap. In the case of an overriding aorta, the aortic valve is positioned above a ventricular septal defect, allowing blood from both the left and right ventricles to enter the aorta. Depending on the size of the VSD and the degree of the override, this can lead to varying levels of mixed blood being pumped into the systemic circulation. The physiological consequences include hypoxemia and cyanosis due to the reduced oxygen content of the systemic blood, and over time, this can lead to complications such as Eisenmenger's syndrome.

Clinical Manifestations

Symptoms of an overriding aorta can vary widely depending on the severity of the condition and the presence of associated congenital heart defects. Common signs include cyanosis, difficulty breathing, poor growth, and heart murmurs. Severe cases may present with episodes of acute cyanosis, also known as "Tet spells," particularly in children with Tetralogy of Fallot.

Diagnosis

Diagnosis of an overriding aorta typically involves imaging studies to visualize the heart's structure. Echocardiography is the primary diagnostic tool, allowing detailed observation of the aortic valve's position, the size of the VSD, and the blood flow through the heart. Cardiac MRI and CT scans can also provide valuable information, especially in complex cases or when planning surgical intervention.

Treatment

The treatment for an overriding aorta usually involves surgical correction to repair the VSD and reposition the aorta. The specific surgical approach depends on the associated congenital heart defects and the patient's overall condition. In cases of Tetralogy of Fallot, complete repair involves patch closure of the VSD and relief of right ventricular outflow tract obstruction. Postoperative care is crucial for monitoring and managing complications, and long-term follow-up is necessary to assess heart function and the need for additional interventions.

Prognosis

The prognosis for individuals with an overriding aorta has improved significantly with advances in surgical techniques and postoperative care. Early diagnosis and timely surgical intervention are key factors that influence outcomes. While many patients lead relatively normal lives post-surgery, they may require lifelong cardiac care and monitoring for potential complications, such as arrhythmias, heart valve dysfunction, and heart failure.