Porth's Essentials of Pathophysiology, 4e

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Disorders of Cardiac Function

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General Manifestations, Diagnosis, and Treatment It is increasingly common for congenital heart defects to be diagnosed prenatally. 69 In this case, the infant can be evaluated shortly after birth to confirm the diagnosis and develop a treatment plan. Reliable transabdomi- nal diagnostic images of the fetal heart can be obtained as early as 16 weeks of gestation, and recently, accu- rate trans-vaginal images have been obtained as early as 11 to 14 weeks of gestation. Among the disorders that can be diagnosed with certainty by fetal echocar- diography are AV septal defects, hypoplastic left heart syndrome, aortic valve stenosis, hypertrophic cardiomy- opathy, pulmonic valve stenosis, and transposition of the great arteries. Disorders that result in an abnormal four-chamber view, an image typically obtained during routine prenatal ultrasonography, are the most likely to be detected. 69 In the postnatal period, congenital heart defects may present with numerous signs and symptoms, most com- monly a murmur audible on auscultation. Some defects, such as patent ductus arteriosus and small ventricular septal defects, close spontaneously. In other less-severe defects, there may be no obvious signs and symptoms and the disorder may be discovered during a routine health examination. Cyanosis, pulmonary congestion, cardiac failure, and decreased peripheral perfusion are the major concerns in children with more severe defects. Such defects often cause problems immediately after birth or early in infancy. The child may exhibit cyano- sis, respiratory difficulty, and fatigability, and is likely to have difficulty with feeding and failure to thrive. Heart failure manifests itself as tachypnea or dyspnea at rest or on exertion. For the infant, this most commonly occurs during feeding. Recurrent respiratory infections and excessive sweating may also be reported. 70 The infant whose peripheral perfusion is markedly decreased may be in a shocklike state. A generalized cyanosis that persists longer than 3 hours after birth suggests congenital heart disease. An oxygen challenge (administration of 100% oxygen for 5 to 10 minutes) can help to determine whether con- genital heart disease is present in a cyanotic newborn. 70 Because infant cyanosis may appear as duskiness, it is important to assess the color of the mucous membranes, fingernails, toenails, tongue, and lips. Several programs have instituted routine pulse oximetry screening for all newborns. 71 Pulmonary congestion in the infant causes an increase in respiratory rate, orthopnea, grunting, wheezing, coughing, and crackles. A chest radiograph can quickly differentiate infants who have reduced pul- monary vascular markings (densities) from those who have normal or increased markings. The treatment plan usually includes supportive therapy (e.g., digoxin, diuretics, and feeding supple- mentation) designed to help the infant compensate for the limitations in cardiac reserve and to prevent com- plications. Surgical intervention often is required for severe defects. It may be done in the early weeks of life or, conditions permitting, delayed until the child is

older. Children with structural congenital heart disease and those who have had corrective surgery may have a higher-than-expected risk for development of infec- tive endocarditis. Prophylactic antibiotic therapy before dental procedures or other periods of increased risk for bacteremia is suggested for children with certain types of heart defects or surgical procedures. 72 Children with congenital heart disease also experi- ence a higher than expected incidence of developmental delays. 73,74 A characteristic pattern of combined disabili- ties in the areas of visual motor integration, language, motor skills, attention, executive function and behavior has been described in multiple research studies. 73–75 In an effort to promote early detection of developmental delays and appropriate intervention, the American Heart Association and the American Academy of Pediatrics issued a joint guideline statement in 2012 suggest- ing systematic surveillance, screening, and evaluation throughout childhood to assess academic, behavioral, psychosocial and adaptive functioning. 76 Early detec- tion of developmental problems will direct interventions which can prevent or reduce long-term issues known to have a profoundly negative impact on quality of life and ability to achieve optimum potential in adulthood. 77 Types of Defects Congenital heart defects can affect almost any of the cardiac structures or central blood vessels (Fig. 19-21). Defects include communication between heart cham- bers, interrupted development of the heart chambers or valve structures, malposition of heart chambers and great vessels, and altered closure of fetal communica- tion channels. The particular defect reflects the embryo’s stage of development at the time it occurred. It is com- mon for multiple defects to be present in one child and for some congenital heart disorders, such as tetralogy of Fallot, to involve several defects. Patent Ductus Arteriosus. Patent ductus arteriosus results from persistence of the fetal ductus beyond the prenatal period. 78 In fetal life, the ductus arteriosus is the vital link by which blood from the right side of the heart bypasses the lungs and enters the systemic circula- tion (Fig. 19-21G). After birth, this passage no longer is needed, and it usually closes during the first 24 to 72 hours of life. The physiologic stimulus and mechanisms associated with permanent closure of the ductus are not entirely known, but the fact that infant hypoxia predis- poses to a delayed closure suggests that the increase in arterial oxygen levels that occurs immediately after birth plays a role. Additional factors that contribute to clo- sure are a fall in endogenous levels of prostaglandins and adenosine and the release of vasoactive substances. After constriction, the lumen of the ductus becomes per- manently sealed with fibrous tissue within 2 to 3 weeks. Ductal closure may be delayed or prevented in very pre- mature infants, probably as a result of a combination of factors, including decreased medial smooth muscle in the ductus wall, decreased vasoconstriction response to oxy- gen, and increased circulating levels of prostaglandins,