Congenital Heart Disease part 9

UNIVENTRICULAR HEART

The term univentricular heart summarizes a variety of malformations where either the right ventricle or left ventricle is missing or, if present, is hypoplastic, and thus not amenable for biventricular repair, such as :

• Tricuspid atresia
• Hypoplastic heart syndrome variants (pulmonary atresia with intact ventricular septum variants)
• Hypoplastic left heart syndrome variants, including mitral atresia
• Double inlet left ventricle
• Double inlet right ventricle
• Extreme forms of unbalanced complete atrioventricular septal defects
• Single ventricle with undefined morphology

These malformation are always associated with additional intra and/or extracardiac lesions such as:

• Atrial septal defect, ventricle septal defect, atrioventricular septal defect, patent ductus arteriosus
• Aortic stenosis (valvular, subvalvular)
• Aortic arch anomalies: hypoplasia, interruption, coarctation
• Pulmonary stenosis (valvular, subvalvular), pulmonary atresia
• Pulmonary artery anomalies: peripheral stenosis, hypoplasia, one-sided absence
• Discordant connection, malposition of the great arteries
• Atrioventricular valve stenosis, regurgitation, overriding, straddling
• Left or right atrial isomerism, abnormal systemic or pulmonary venous connections
• Left superior vena cava, absent infra hepatic inferior vena cava with azygos or hemyazygos continuity
• Aortic to pulmonary collateral arteries
• Polysplenia or asplenia

Basically, two different haemodynamic situations can be identified:

• No anatomic restriction to pulmonary blood flow. If pulmonary circulation remain unmodified (no surgery), many patients will die in childhood due to intractable heart failure. Those who survive this period will have develop developed severe pulmonary vascular disease. This will be  a main determinant of long term outcome. Many will have had  pulmonary banding to restrict pulmonary blood flow in early childhood. An effective banding will protect against pulmonary vascular disease, while allowing enough pulmonary blood flow to limit the degree of cyanosis. A banding that is too loose will result in pulmonary overflow and pulmonary vascular disease despite the banding. If the banding is to tight, pulmonary blood flow will be extremely limited, resulting in severe cyanosis.

• Obstruction to pulmonary blood flow (frequently valvular and/or subvalvular pulmonary stenosis or atresia): sometimes the obstruction is such that the pulmonary circulation is adequate (not excessive, thus avoiding development of pulmonary hypertension, and not too restricted, thus without extreme cyanosis) This balanced situations are the exeption but allow survival  into adulthood without having surgery. Most patients have a very restricted pulmonary blood flow, necessitating  a systemic to pulmonary artery shunt operation in childhood. If a systemic to pulmonary artery shunt is too large, pulmonary overflow will result in pulmonary vascular disease at adult age. If the shunt to small, patient will be extremely cyanotic. Beyond infancy, an anastomosis between the superior vena cava and pulmonary artery is a possibility: the classical Glenn anastomosis to the right pulmonary artery or end-to-end anastomosis with pulmonary artery, creating bidirectional cavopulmonary anastomosis. An adequate shunt will lead to a balanced situation.