Transposition of the great arteries (TGA), a cause of congenital cyanosis, is due to failure of septation. The fetal aorticopulmonary septum normally spirals during septation of the truncus arteriosus, and errors in this process lead to the aorta emerging from the right ventricle and the pulmonary artery emerging from the left ventricle.
Without an alternate route for circulation of oxygenated blood into the aorta and systemic circulation, infants with this condition will die at birth. Infants who survive postnatally thus depend on either intracardiac (ventricular septal defects and/or patent foramen ovales) or extracardiac (patent ductus arteriosus or bronchopulmonary collaterals) shunts in order to supply the systemic circulation with oxygenated blood. At present, fetal diagnosis of TGA is challenging, and most cases are diagnosed after birth by echocardiography. Surgical correction is required.
Fuloria and Kreiter discuss common emergencies and abnormal findings in the newborn exam. They note particularly that the causes of cyanosis in infants are diverse and, beyond congenital heart defects such as TGA and truncus arteriosus, infants may be cyanotic due to metabolic and endocrine disorders, hypothermia, or pulmonary disorders such as pneumothorax or diaphragmatic hernia.
Freidberg et al. prospectively studied a series of infants with major congenital heart disease (CHD) at 3 referral centers in Northern California. They found that 98/309 (36%) infants with major CHD were diagnosed prenatally (leading to 27 pregnancy terminations). The cardiac defects with the lowest rates of prenatal ultrasound diagnosis were total anomalous pulmonary venous return (0%) and TGA (19% of TGA cases), compared to the highest, hypoplastic left heart syndrome, 61%.
Video V shows circulation in uncorrected TGA.
Answer 1: Ventricular septal defects result most commonly from defects in fusion of the membranous ventricular septum.
Answer 3: One theory about the pathogenesis of aortic coarctation says that extension of ductal tissue into the aorta creates a thickened segment that is pulled tight when the ductus arteriosus closes.
Answer 4: Omphalocoele is a midline abdominal wall defect wherein abdominal viscera fail to reenter the abdomen, with organs located in a sac outside the body.
Answer 5: Patent foramen ovale results from failure of fusion of the atrial septum primum and secondum. This typically results in left-to-right shunting, and would not result in early cyanosis.
Fuloria M, Kreiter S. The newborn examination: part I. Emergencies and common abnormalities involving the skin, head, neck, chest, and respiratory and cardiovascular systems. Am Fam Physician. 2002 Jan 1;65(1):61-8. PubMed PMID: 11804443
PMID:11804443 (Link to Abstract)
Friedberg MK, Silverman NH, Moon-Grady AJ, Tong E, Nourse J, Sorenson B, Lee J, Hornberger LK. Prenatal detection of congenital heart disease. J Pediatr. 2009 Jul;155(1):26-31, 31.e1. doi: 10.1016/j.jpeds.2009.01.050. Epub 2009 Apr 24. PubMed PMID: 19394031
PMID:19394031 (Link to Abstract)
USMLE World Step 1 QBank Question #35. Copyright © USMLEWorld, LLC 2012