Cardiac Disease

Congenital heart disease produces cyanosis when obstruction to right ventricular outflow causes intracardiac right-to-left shunting or when complex anatomic defects, many unassociated with pulmonary stenosis, cause an admixture of pulmonary and systemic venous return in the heart. Cyanosis from pulmonary edema may also develop in patients with heart failure caused by left-to-right shunts, although the degree is usually less severe. Cyanosis may be caused by persistence of fetal pathways, for example, right-to-left shunting across the foramen ovale and ductus arteriosus in the presence of pulmonary outflow tract obstruction or persistent pulmonary hypertension of the newborn (PPHN) (Chapter 95.8).

Differential Diagnosis

The hyperoxia test is one method of distinguishing cyanotic congenital heart disease from pulmonary disease. Neonates with cyanotic congenital heart disease are usually not able to significantly raise their arterial PaO₂ during administration of 100% oxygen. If the PaO₂ rises above 150 mm Hg during 100% oxygen administration, an intracardiac right-to-left shunt can usually be excluded, although this is not 100% confirmative, as some patients with cyanotic congenital heart lesions may be able to increase their PaO₂ to >150 mm Hg because of favorable intracardiac streaming patterns. In patients with pulmonary disease, PaO₂ generally increases significantly with 100% oxygen as ventilation-perfusion inequalities are overcome. In infants with cyanosis due to a CNS disorder, the PaO₂ usually normalizes completely during artificial ventilation. Hypoxia in many heart lesions is profound and constant, whereas in respiratory disorders and in persistent pulmonary hypertension of the neonate (PPHN), arterial oxygen tension often varies with time or changes in ventilator management. Hyperventilation may improve the hypoxia in neonates with PPHN and only occasionally in those with cyanotic congenital heart disease.

Although a significant heart murmur usually suggests a cardiac basis for the cyanosis, several of the more severe cardiac defects (transposition of the great vessels) may not initially be associated with a murmur. The chest roentgenogram may be helpful in the differentiation of pulmonary and cardiac disease; in the latter, it indicates whether pulmonary blood flow is increased, normal, or decreased.

Two-dimensional echocardiography is the definitive noninvasive test to determine the presence of congenital heart disease. Cardiac catheterization is less often used for diagnostic purposes, and is usually performed to examine structures that are sometime less well visualized by echocardiography, such as distal branch pulmonary arteries or aortopulmonary collateral arteries in patients with tetralogy of Fallot with pulmonary atresia (Chapter 424.2), coronary arteries and right ventricular sinusoids in patients with pulmonary atresia and intact ventricular septum (Chapter 424.3). If echocardiography is not immediately available, the clinician caring for a newborn with possible cyanotic heart disease should not hesitate to start a prostaglandin infusion (for a possible ductal-dependent lesion). Because of the risk of hypoventilation associated with prostaglandins, a practitioner skilled in neonatal endotracheal intubation must be available.