Aortic stenosis that occurs during fetal development results in added stress on the left ventricle in utero. This can eventually lead to decreased perfusion through the left ventricle which is believed to inhibit ventricular growth. Pathophysiology
At birth, the ductus arteriosus is still open, and there is higher than normal resistance to blood flow in the lungs. This allows for adequate oxygenation via mixing between the atria and a normal appearance at birth. When the ductus begins to close and pulmonary vascular resistance decreases, blood flow through the ductus is restricted and flow to the lungs is increased.In typical anatomy, the left side of the heart receives oxygen-rich blood from the lungs and pumps it to the rest of the body. Patients with HLHS can have a number of cardiac malformations that ultimately lead to a diminutive left ventricle that is unable to supply sufficient blood flow to the rest of the body. There are three main anatomic variants of the disease differentiated by either stenosis or atresia of the aortic and mitral valve.Mitral atresia and aortic atresia (MA-AA) subtype is the most severe form of HLHS resulting in no blood flow entering the left ventricle at all resulting in no possibility of left ventricular output. In the mitral stenosis and aortic atresia (MS-AA) subtype blood is able to fill the left ventricle, however it is unable to be supplied to the systemic circulation via the hypoplastic ascending aorta. Lastly, the mildest form is the mitral stenosis and aortic stenosis (MS-AS) subtype.
In these patients although the left ventricle is able to supply some blood flow to the rest of the body the overall left ventricular systemic output remains inadequate.In all of these cases blood is unable to be pumped to the rest of the body by the left ventricle. The neonate is reliant on blood flowing through an atrial septal defect to mix oxygenated and deoxygenated blood, and on a patent ductus arteriosus to allow blood to reach the aorta and the systemic circulation via the right ventricle. This is what defines HLHS as a "single ventricle" defect.Due to the underdevelopment of the left side of the heart in utero, the increased afterload causes hypertension of the left atrium, pulmonary edema, and therefore lung damage to the fetus before birth. Diagnosis
Hypoplastic left heart syndrome can be diagnosed prenatally or after birth via echocardiography. Typical findings include a small left ventricle and aorta, abnormalities of the mitral and aortic valves, retrograde flow in the transverse arch of the aorta, and left-to-right flow between the atria. It is often recognized during the second trimester of pregnancy, between 18 and 24 weeks gestation. Management
Medical
Without life-prolonging interventions, HLHS is fatal, but with intervention, an infant may survive. A cardiothoracic surgeon may perform a series of operations or a full heart transplant.