Chapter 5

Critical heart disease in the newborn includes all congenital heart lesions that would result in neonatal demise unless immediate intervention is undertaken. It is estimated that congenital heart disease occurs in about 8 per 1000 live births.1 Not all congenital heart disease (CHD) presents in the newborn period. However, there are a handful of conditions that need immediate management in a newborn infant, the failure of which precludes survival. Roughly 3.5 in 1000 live births have critical CHD.1 Neonatal critical heart diseases can be broadly described as those that present as severe cyanosis (right heart obstruction) and those that present as shock (left heart obstruction). Table 5-1 lists common conditions in both categories. The common denominator to all critical heart diseases presenting in the neonatal period is that they need a patent ductus arteriosus for survival until further palliative procedures can be undertaken. To understand the physiology of these lesions, it is important to have knowledge of the circulatory changes that happen right after birth.

Table 5-1. Common Neonatal Critical Congenital Heart Diseases (CHD)

### Fetal Circulation

Blood oxygenated in the placenta is returned by way of the umbilical veins. Most of the umbilical venous blood shunts through the ductus venosus to the inferior vena cava (IVC), which provides a low-resistance bypass.2 The IVC blood is composed of streams of hepatic venous blood, umbilical venous blood, and blood from lower extremities. The stream of umbilical venous blood selectively enters the left atrium, though the foramen ovale guided by the eustachian valve. The left ventricle (LV) pumps out this blood into the ascending aorta for distribution to the coronaries, head, and upper extremities.2 The superior vena caval stream and rest of the IVC blood pass into the right ventricle (RV). The RV pumps out this blood into the pulmonary trunk. A small amount of this blood enters the pulmonary circulation, and the rest passes through the ductus arteriosus into the descending aorta and finally reaches the placenta via the umbilical arteries. Figure 5-1 shows the key elements of fetal circulation. The main differences between fetal circulation and postnatal circulation consist of the following:

• Placental circulation provides gas exchange for the fetus
• Absence of gas exchange in the collapsed lungs; this results in very little flow of blood to the lungs
• Presence of a ductus venosus providing a low-resistance bypass for umbilical venous blood to reach the IVC
• Widely open foramen ovale to provide a route to the oxygenated blood to reach the ...

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