Porth's Essentials of Pathophysiology, 4e

476

Circulatory Function

U N I T 5

A Patent ductus arteriosus

B Atrial septal defect

C Ventricular septal defect

D Endocardial cushion defect

E Pulmonary stenosis

F Tetralogy of Fallot

G Transposition of the great vessels

H Postductal coarctation of the aorta

FIGURE 19-21. Congenital heart defects. (A) Patent ductus arteriosus.The high-pressure blood of the aorta is shunted back to the pulmonary artery. (B) Atrial septal defect. Blood is shunted from left to right. (C) Ventricular septal defect. Blood is usually shunted from left to right. (D) Endocardial cushion defect. Blood flows between the chambers of the heart. (E) Pulmonary stenosis, with decreased pulmonary blood flow and right ventricular hypertrophy. (F) Tetralogy of Fallot.This involves a ventricular septal defect, dextroposition of the aorta, right ventricular outflow obstruction, and right ventricular hypertrophy. Blood is shunted from right to left. (G) Transposition of the great vessels.The pulmonary artery is attached to the left side of the heart and the aorta to the right side. (H) Postductal coarctation of the aorta.

which have a vasodilating effect. Ductal closure also may be delayed in infants with congenital heart defects that produce a decrease in oxygen tension. 78 Persistent patency of the ductus arteriosus is defined as a duct that remains open beyond 3 months in the full-term infant. The size of the persistent ductus and the difference between the systemic and pulmonary vascular resistance determine its clinical manifesta- tions. Blood typically shunts across the ductus from the higher-pressure left side (systemic circulation) to the lower-pressure right side (pulmonary circulation). After the infant’s pulmonary vascular resistance falls, the patent ductus arteriosus provides for a continuous runoff of aortic blood into the pulmonary artery. With a large patent ductus, the runoff is continuous, result- ing in increased pulmonary blood flow, pulmonary congestion, and increased resistance against which the right side of the heart must pump. Increased pulmonary venous return and increased work demands may lead to left ventricular failure. 79

Spontaneous closure of the ductus seldom occurs after infancy. In the full-term infant or older child, clo- sure can be achieved with either surgical ligation or device occlusion. In children with a small patent ductus, closure is done to prevent infective endocarditis or other complications. In children with a moderate to large pat- ent ductus, closure is accomplished to treat heart failure, prevent the development of pulmonary vascular disease, or both. 78 Drugs that inhibit prostaglandin synthesis (e.g., indomethacin) may be used to induce closure of a patent ductus in preterm newborns. Indomethacin works best if it is used in infants younger than 13 days of age; it is not effective later than 4 to 6 weeks of age. 78 Although closure of a patent ductus is uniformly rec- ommended when it is present as an isolated lesion, delib- erate maintenance of ductal patency can be a lifesaving therapy for children with complex forms of congenital heart disease who have ductal-dependent pulmonary or systemic blood flow, or those with obligatory mixing of the arterial and venous circulations (i.e., transposition