11.6: Univentricular Heart

Case report

Introduction

Around 10 percent of all congenital heart defect patients have just one functioning ventricle. The other ventricle is present, however it is rudimentary or underdeveloped so it can not function normally. In utero this causes rarely any problems, due to the parallel circulation the other ventricle takes over both functions. It is after birth, if the ductus arteriosus closes, when problems arise.

Pathophysiology

The hypoplastic left heart syndrome (HLHS) is the most common type of univentricular heart. (Figure 11.6.1) Not only the left ventricle, but often the aortic valve, ascending aorta and aortic arch are hypoplastic as well. This will redirect blood from the left atrium into the right atrium, where is will be mixed with venous blood and pumped into the right ventricle and pulmonary artery. The whole systemic circulation depends on the shunt from pulmonary artery through the ductus arteriosus into the aorta. When the ductus starts closing the consequences are dramatic, with severe cyanosis and acidosis.

Figure 11.6.1: Schematic drawing representing the hypoplastic left heart syndrome.

When a hypoplastic right ventricle is present with associated atresia of the pulmonary artery, the pulmonary circulation after birth will solely depend on the left-to-right shunt through the ductus arteriosus.When the ductus starts closing, progressive cyanosis is the main presenting symptom.

Other cardiac defects associated with only one functional ventricle are: tricuspid valve atresia, mitral valve atresia, severe form of Ebstein anomaly, double inlet left ventricle and unbalanced AVSD.

All patients with one functioning ventricle have complete mixing of saturated and desaturated blood leading to chronic hypoxemia (Figure 11.6.2). Furthermore there is a chronic volume overload to the ventricle, serving as both pulmonary and systemic ventricle, leading to an early development of heart failure.

Figure 11.6.2: Echocardiographic image of a male patient with a univentricular heart.

Due to the obligatory intracardiac shunting the pulmonary ‘filter’ is bypassed, which will increase the chance of cardiovascular accidents and brain abscesses.

Treatment

In case of a ductus-dependent defect initial treatment immediately after birth consists of prevention of ductus closure. At first this can be achieved pharmacologically with prostaglandin, however due to the many side effects this is no long-term solution. When there is a dependent pulmonary circulation an aortopulmonary shunt will be constructed during the first weeks of life to ensure accurate blood flow to the lungs after discontinuation of the prostaglandin.

If there is a dependent systemic circulation the surgical treatment usually consists of three different steps. Since the anatomy is by no means normalized, one can not speak of a surgical correction, it is referred to as a definitive palliation. At first a Norwood or Sano procedure is performed in neonates where a neo-aorta is constructed by dividing the pulmonary artery. Second stage is the construction of a cavopulmonary shunt, also known as bidirectional Glenn shunt, which is performed at 4 -6 months of age. The third and final stage is known as Fontan procedure and performed at 18 – 30 months of age, where a total cavopulmonary connection is created. (Figure 11.6.3) All surgical procedures are described in more detail separately.

Figure 11.6.3: Schematic drawing showing the Fontan procedure.

Outcome

With an expanding cohort of survivors of surgical palliation through Fontan completion, increasing information is being accumulated on the long-term morbidity of these patients. Active areas of interest include exercise tolerance, neurodevelopmental outcome, and quality of life.

When assessed prospectively by formal exercise testing, children with HLHS after surgical repair showed considerable age-related decline in exercise performance. Among patients participating in treadmill or bicycle ergometry, those aged 8 to 12 performed at 70 percent of predicted peak oxygen consumption, whereas older children reached only 60 percent of predicted performance.

Several reports have demonstrated significant neurodevelopmental impairment in survivors of HLHS following staged repairs or cardiac transplantation. There is a paucity of data on the quality of life for patients with HLHS. In one report of survivors and their families, parents reported poorer functional health status than patients assessed at 18 years of age.

Risk factors that lower survival include noncardiac congenital anomalies and/or genetic disorder, particularly chromosomal defects, prematurity, low birth weight for gestational age, and living in a high poverty neighborhood.

With an expanding cohort of survivors of surgical palliation through Fontan completion, increasing information is being accumulated on the long-term morbidity of these patients. Active areas of interest include exercise tolerance, neurodevelopmental outcome, and quality of life. When assessed prospectively by formal exercise testing, children with HLHS after surgical repair showed considerable age-related decline in exercise performance. Among patients participating in treadmill or bicycle ergometry, those aged 8 to 12 performed at 70 percent of predicted peak oxygen consumption, whereas older children reached only 60 percent of predicted performance. Several reports have demonstrated significant neurodevelopmental impairment in survivors of HLHS following staged repairs or cardiac transplantation. There is a paucity of data on the quality of life for patients with HLHS. In one report of survivors and their families, parents reported poorer functional health status than patients assessed at 18 years of age. Risk factors that lower survival include noncardiac congenital anomalies and/or genetic disorder, particularly chromosomal defects, prematurity, low birth weight for gestational age, and living in a high poverty neighborhood.