Anatomy And Pathophysiology
“The heart is purest theater…throbbing in its cage palpably as any nightingale.”—Richard Selzer, in “Mortal Lessons,” 1976
The fetal circulation differs from that of the child in several important ways. Most importantly, structures that allowed blood to bypass the pulmonary circulation must close; namely, the ductus arteriosus and foramen ovale.
In utero, the ductus arteriosus connects the pulmonary artery to the aorta, but a fall in pulmonary vascular resistance after birth causes the ductus to close. However, in the presence of hypoxia, acidosis, and with ductal-dependent lesions, the ductus remains open. In these ductal-dependent lesions (hypoplastic left heart syndrome, pulmonic/aortic stenosis, transposition of the great arteries, coarctation of the aorta, and interrupted aortic arch), survival may depend on a persistently open ductus. The foramen ovale (a hole between the left and right atria) also begins to close after birth, a process that normally completes by 3 months of age.
Congenital heart disease occurs in 8/1000 live births and may cause symptoms in the neonatal period.10 Infants may present to the ED with tachypnea, sudden onset of cyanosis or pallor that may worsen with crying, sweating with feeds, lethargy, or failure to thrive.11 Congenital heart disease lesions that present in the first 2-3 weeks of life are typically ductal-dependent cardiac lesions. The open ductus arteriosus, which sustains blood flow in utero, closes after birth, and these infants suddenly become ill. (See Figure 1.) In these newborns, closure of the ductus arteriosus either interrupts blood supply to the lungs (e.g., etralogy of Fallot or tricuspid atresia), producing cyanosis, or disrupts blood supply to the systemic circulation (e.g., coarctation of the aorta or hypoplastic left heart syndrome), leading to shock. Depending on the underlying structural abnormality, these neonates will present with either sudden cyanosis or signs of cardiovascular collapse.
The most common causes of structural cyanotic congenital heart disease are tetralogy of Fallot, tricuspid atresia, transposition of the great arteries, truncus arteriosus, total anomalous pulmonary venous return, and pulmonary atresia or stenosis.
Ductal-dependent cardiac lesions that involve cardiovascular collapse include a coarctation of the aorta, aortic stenosis, or hypoplastic left heart syndrome. When the ductus closes to a critical degree, these infants will develop sudden onset of decreased perfusion with mottling, altered mental status, and oliguria.
The other class of congenital cardiac lesions that present in the first month of life is the left-to-right intracardiac shunt, such as ventricular septal or atrioventricular canal defects. As the normal pulmonary vascular resistance falls over the first month of life, any preexisting left-to-right shunt will see a gradual increase in flow, resulting in rightsided overload and heart failure. Such infants will have a history of sweating with feeds and hepatomegaly. The differential diagnosis of congenital heart diseases that cause congestive heart failure includes not only the left-to-right intracardiac shunts, but also hypoplastic left ventricle syndrome, coarctation of the aorta, truncus arteriosus, endocardial cushion defect, patent ductus arteriosus, aortic stenosis, interrupted aortic arch, aortic atresia, and mitral valve atresia.12,13
Patients with arrhythmias such as complete heart block and paroxysmal supraventricular tachycardia may also present with congestive heart failure. In newborns, the heart rate is greater than 220 BPM (even as high as 280-300 BPM), with the electrocardiogram (ECG) demonstrating a narrow complex tachycardia without discernible P waves or beat-tobeat variability.9 In children less than 12 years of age, the most common cause of supraventricular tachycardia is an accessory atrioventricular pathway.14
During the fifth to eighth embryonic week, the intestine projects out of the abdominal cavity and then rotates 270º before returning into the abdomen. If the rotation does not occur correctly, the intestine will not be anchored at the mesentery and is considered malrotated and at risk for volvulus. The incidence of malrotation is 1/500 live births, with a 2:1 male-to-female ratio in the newborn period.15 Volvulus is the twisting of a loop of bowel about the mesenteric attachment. The incidence of volvulus is, however, much less frequent, with up to 75% of cases occurring within the first month of life.15
Hirschsprung’s disease is the absence of intramural ganglion cells in the rectum, which may extend to the sigmoid colon in many patients and can involve the entire colon in a few.16 The incidence is 1/5000 live births, with a male-to-female ratio of 4:1. The diagnosis should be suspected if the patient presents with lack of meconium stool within the first 24-48 hours of life. Vomiting and abdominal distension may also be present.
Hemoglobin in the normal-term infant ranges from 13.7 to 20.1 g/dL; anemia in the immediate newborn period is considered a hemoglobin of less than 13 g/dL. A physiologic hemoglobin nadir of 11.4 ± 0.9 g/dL is reached between 8 and 12 weeks of life. Causes of anemia in the newborn include premature cord clamping with resultant blood accumulation in the placenta, ABO incompatibility, and congenital viral infections such as those seen with the TORCH syndromes (toxoplasmosis, rubella, cytomegalovirus, and herpes simplex.
Inborn errors of metabolism are biochemical disorders that result in alteration of a protein structure or amount of protein synthesis. They are usually the result of a deficiency of an enzyme needed to convert one metabolite to another. This results in the accumulation of a metabolic intermediate, which at high levels can cause serious effects, particularly to the central nervous system. These toxic metabolic intermediates include ammonia, lactic acid, organic acids, and ketones. Consanguinity and family history of similar disorders are important contributors. A history of unexplained male deaths implies an X-linked process such as ornithine carbamoyl transferase deficiency. Reye’s syndrome deaths—in the past attributed to the use of aspirin during viral syndromes— may actually have been inborn errors of metabolism, such as amino acid, urea cycle, organic acid, and fatty acid oxidation deficiencies. Congenital adrenal hyperplasia is due to a deficiency in one of five enzymes involved in the production of cortisol. This results in decreased conversion of 17-OH progesterone to 11-desoxycortisol and a subsequent drop in cortisol levels that can lead to cardiovascular collapse. The most common form of congenital adrenal hyperplasia is due to 21-hydroxylase deficiency, which accounts for 90%-95% of cases.17 Most of the enzyme deficiencies lead to decreased aldosterone production and subsequent hyperkalemia and hyponatremia.
All states screen newborns for phenylketonuria and hypothyroidism, but not necessarily for inborn errors of metabolism or congenital adrenal hyperplasia.18