Congenital heart defects are the most common birth defects and together account for the highest resource utilization among all hospitalized children. These defects encompass numerous structural heart lesions, both isolated and in combination, and their resulting unique physiologies and treatments. This chapter will focus on the lesions that most commonly require surgery or critical care during infancy. A brief discussion of other lesions that may be incidentally found on neonatal echocardiograms concludes the chapter. Patent ductus arteriosus and pulmonary hypertension are discussed in Chapters 9 and 30, respectively.
Ventricular Septal Defect
A ventricular septal defect (VSD) is a defect in the ventricular septum between the left and right ventricles. VSDs may be solitary, multiple, or occur as a part of many additional forms of congenital heart disease. VSDs are classified by size and location within the septum.
VSDs occur in 1.5-3.5/1000 live births, and isolated VSDs make up approximately 20% of all congenital heart disease. In premature or low-birthweight infants, VSD may occur in as many as 7/1000 births.
The pathophysiology of VSD depends on the magnitude of left-to-right shunt across the defect. This is primarily influenced by the defect's size.
Blood will flow from an area of high pressure (or resistance) to an area of lower pressure (or resistance), so typically blood flows from the left ventricle (LV) through the VSD to the right ventricle (RV) and out to the pulmonary arteries during systole. Relatively little flow across the defect occurs during diastole as both ventricles are at relatively low pressures.
Small defects restrict significant left-to-right shunting, and no significant pathophysiology occurs. Large or multiple defects allow significant left-to-right shunt, causing the pulmonary circuit to have supranormal blood flow.
At 6 to 8 weeks of age, symptoms of congestive heart failure (CHF) may begin to be evident as pulmonary vascular resistance has fallen since birth and hemoglobin has reached its physiologic nadir; both of these events may result in increased left-to-right shunt. Pulmonary venous return to the left atrium is increased. Initially, the neonatal heart compensates for this volume overload by increasing the resting heart rate. Over time, the volume overload causes the left atrium and LV to become dilated. When the heart can no longer compensate for the increased venous return, pulmonary venous congestion occurs. Following these changes, CHF will eventually result in systemic venous congestion and hepatomegaly.
If a VSD is left uncorrected, pulmonary vascular obstructive disease has been shown to develop as early as 6 to 12 months of age; however, Eisenmenger physiology with right-to-left shunt at the VSD typically does not occur until adolescence.
Multiple genes have been implicated. The risk of VSD is increased with a parent who has a VSD. Patients with chromosomal abnormalities, particularly trisomy 13, 18, and 21, are at increased risk of VSD.
Signs and symptoms...