Cardiovascular System
Core concepts
Understand fetal circulation and the transition at birth: closure of the ductus arteriosus, foramen ovale, and ductus venosus, and how failure of these transitions produces persistent pulmonary hypertension of the newborn (PPHN). Know congenital heart lesions and their presentation: cyanotic (tetralogy of Fallot, transposition, tricuspid atresia) versus acyanotic (VSD, ASD, PDA, coarctation). Recognize ductal-dependent lesions and the role of prostaglandin E1 to maintain ductal patency. Understand shock states, blood pressure norms by gestational age, and the significance of a murmur, cyanosis unresponsive to oxygen, and differential cyanosis. Grasp maternal cardiac disease in pregnancy: increased plasma volume, cardiac output, and the risk of heart failure in the third trimester and postpartum.
Traps
Questions test hyperoxia testing - cyanotic heart disease often does not improve with supplemental oxygen, unlike pulmonary disease. Another trap: assuming a murmur is always pathologic; timing and associated findings matter. Also beware confusing ductal-dependent systemic lesions (coarctation) with ductal-dependent pulmonary lesions (pulmonary atresia).
Worked example
A newborn has cyanosis and saturations that remain low despite 100% oxygen, with a normal chest radiograph. Rule of thumb: cyanosis unresponsive to oxygen suggests a cardiac cause - obtain echocardiography and consider prostaglandin E1 if ductal-dependent.
Study focus
Map each congenital lesion to its dependency on the ductus and its clinical presentation.