Congenital Heart Disease: Cyanotic Lesions with Increased Pulmonary Blood Flow

Abstract

over four times systemic (assuming normal systemic cardiac output) to raise the oxygen saturation greater than 90% when there is complete mixing of the venous returns. Clinically, the degree of cyanosis depends in large part on the pulmonary vascular resistance, which in the fi rst hours of life is high, resulting in less pulmonary blood fl ow and more pronounced cyanosis. As pulmonary vascular resistance falls in the fi rst days of life, infants with complete mixing lesions will have milder cyanosis, yet may ultimately develop signs and symptoms of congestive heart failure if pulmonary blood fl ow increases to excessive degrees. The prime examples of complete mixing lesions are truncus arteriosus, total anomalous pulmonary venous connection (TAPVC), and any single-ventricle anomaly that is associated with limited or no restriction to pulmonary blood fl ow. In transposition physiology, the anatomic arrangement of the major cardiac segments is such that, instead of the systemic and pulmonary circuits being connected in series, they are in parallel. Thus, systemic venous return is primarily ejected back to the aorta, and pulmonary venous return is primarily ejected back to the lungs. Completely separated parallel circuits would be incompatible with life, resulting in progressively severe cyanosis and tissue hypoxia. All cases of survivable transposition physiology must be associated with one or multiple levels of communication between the pulmonary and systemic circuits, typically atrial, ventricular septal, and/or ductal level shunts. Because of the lower resistance in the pulmonary circuit, there will be more fl ow in the pulmonary circuit, but, because of ineffi cient mixing between the parallel circuits, cyanosis results. D-transposition of the great arteries is the most commonly seen anomaly demonstrating this physiologic picture, but it may also be seen in other anomalies, including some forms of double-outlet right ventricle (DORV). Clinically apparent cyanosis typically requires systemic oxygen saturation as low as 80%–85%, depending on the hemoglobin level [1]. In cyanotic cardiac defects associated with increased pulmonary blood fl ow, the degree of cyanosis is most profound in cases of transposition physiology and may be quite mild with complete mixing lesions. Respiratory distress is rarely associated with the cyanosis in the newborn, helping to distinguish cardiac from pulmonary causes of cyanosis. A variety of other signs and symptoms may be seen depending on the specifi c anomaly and the age of the child. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 Transposition of the Great Arteries . . . . . . . . . . . . . . . . . . . . . . . . 116 Truncus Arteriosus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 Total Anomalous Pulmonary Venous Connection . . . . . . . . . . . 118 Single-Ventricle Anomalies with Unobstructed Pulmonary Blood Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119