Chapter 56 Cardiology
VENTRICULAR SEPTAL DEFECT
ETIOLOGY
What Is a Ventricular Septal Defect?
Ventricular septal defect (VSD) is the most common congenital heart defect. Most VSDs are small, do not cause any cardiac symptoms, and eventually close spontaneously. Large VSDs are clinically more problematic, however, because the high-volume left-to-right shunt causes increased pulmonary blood flow, increased pulmonary venous return, and left ventricular volume overload. The volume overload causes congestive heart failure (CHF), which presents in infants with increased respiratory rate and effort, diaphoresis, difficulty feeding, and poor weight gain (failure to thrive). If a large VSD is untreated, the chronically increased pulmonary artery pressures eventually cause increased pulmonary vascular resistance and progressive cyanosis (Eisenmenger’s syndrome).
EVALUATION
What Do I Need to Look for in an Infant with a Ventricular Septal Defect?
Always look for signs of CHF. Ask about the specifics of feeding: how much the infant takes, how long each feeding takes, if respiratory distress occurs during feeding, or if other feeding difficulties occur. An infant with a VSD should not be cyanotic, but this is still a good issue to ask about. The growth chart should be carefully plotted, with particular attention to the weight curve, because poor feeding may manifest as a falloff in weight gain. On physical examination, it is most important to observe the infant’s work of breathing: respiratory rate, chest wall excursion, use of accessory muscles, and retractions. Hepatomegaly is common in infants with CHF, with the liver edge usually more than 2 cm below the right costal margin. Crackles (rales) are not commonly heard on auscultation of the lungs in infants with CHF. Jugular venous distention and peripheral edema, common signs of CHF in adults, are rarely seen in infants with CHF. A large VSD will typically cause a loud, harsh, holosystolic murmur, but the intensity of the murmur does not correlate well with the size of the VSD or the presence of CHF.
What Studies Are Needed to Diagnose Ventricular Septal Defect?
The most important problems to assess are growth and signs of CHF—no diagnostic studies are needed to make this assessment. CHF is a clinical diagnosis; it cannot be diagnosed by electrocardiogram (ECG), chest radiograph, or echocardiogram. The chest radiograph may be helpful to assess heart size, pulmonary blood flow, or the presence of pneumonia in a child with respiratory symptoms that are not clearly CHF. The ECG may demonstrate left or right ventricular hypertrophy, and this may help in the overall assessment of the infant’s hemodynamic state. Echocardiography is essential for the initial diagnosis of the VSD but does not really aid day-to-day management.
TREATMENT
What Treatment Is Needed for an Infant with Ventricular Septal Defect?
Small VSDs almost all close spontaneously and thus require no specific therapy. Larger VSDs that cause CHF can be managed medically, and many of these defects will become smaller with time as well. Medical management consists primarily of digoxin and diuretics (furosemide). If CHF and failure to thrive do not improve with medical management, open-heart surgery to close the VSD will be required. Large VSDs resulting in pulmonary hypertension also require surgical closure. Overall, the prognosis of infants with a VSD is excellent, even if surgical closure is needed. Antibiotic prophylaxis to prevent subacute bacterial endocarditis (SEB) is no longer recommended for a VSD.
ATRIAL SEPTAL DEFECT
ETIOLOGY
What Is an Atrial Septal Defect?
Atrial septal defect (ASD) is common, with isolated ASDs accounting for approximately 5% of all congenital heart defects. An ASD can also be present in association with more complex heart defects. Most ASDs are located in the region of the foramen ovale (secundum ASD). Less commonly, ASDs can be close to the atrioventricular valves (primum ASD) or the superior vena cava (sinus venosus ASD). All types of ASD cause left-to-right shunting from left atrium to right atrium, increased pulmonary blood flow, and right ventricular volume overload. Isolated ASDs rarely cause symptoms in children but will often result in symptomatic right heart failure in adults if not corrected.
EVALUATION
What Do I Need to Look for in a Child with an Atrial Septal Defect?
A child with an ASD typically presents at a few years of age with an asymptomatic heart murmur that may not have been noticed previously. Symptoms, if present, are caused by the increased pulmonary blood flow and will most likely manifest as shortness of breath with exertion or as respiratory infections that are more frequent or more severe than expected. Symptomatic infants typically have failure to thrive.
What Findings Should Make Me Suspect an Atrial Septal Defect?
The murmur in a child with an ASD is caused by the increased pulmonary blood flow. This pulmonary flow murmur can be very subtle and unimpressive, or it may be obvious. Wide, fixed splitting of the second heart sound is the pathognomonic finding of an ASD but may be difficult to appreciate. Wide, fixed splitting occurs because increased pulmonary blood flow causes delayed pulmonic valve closure.
What ECG Findings Are Characteristic of Atrial Septal Defect?
The ECG is almost always abnormal in children with a significant ASD, making this a valuable tool for assessing any asymptomatic heart murmur. ECG findings of an ASD include right axis deviation, right atrial enlargement, and right ventricular hypertrophy with a right ventricular volume overload pattern (rsR′ in V1).
TREATMENT
What Treatment Is Required for an Atrial Septal Defect?
A clinically apparent ASD is likely large enough to cause significant right ventricular volume overload and thus to require closure. Surgery is typically delayed until 3 to 5 years of age because some ASDs will spontaneously diminish in size and thus may not require closure. Although most ASDs often require open-heart surgery, some can be closed by a device delivered via catheterization. In either case the long-term prognosis is excellent. Antibiotic prophylaxis to prevent SEB is not recommended for ASDs.
TETRALOGY OF FALLOT
ETIOLOGY
What Is Tetralogy of Fallot?
Tetralogy of Fallot (TOF) is the most common cyanotic congenital heart defect. The four components of the tetralogy are VSD, aortic override, pulmonic stenosis, and right ventricular hypertrophy. Cyanosis is the most important clinical finding and develops when the VSD and right ventricular outflow obstruction combine to cause right-to-left shunting through the VSD.
EVALUATION
What Do I Need to Look for in an Infant with Tetralogy of Fallot?
Infants with TOF may have cyanosis at birth but may also be acyanotic and develop cyanosis weeks to months later. Look for presence and/or degree of cyanosis on physical examination. Pulse oximetry will detect oxygen desaturation, which, when mild, can be subtle or even impossible to detect by physical examination alone. An infant with oxygen saturation above 85% may appear acyanotic, particularly to an untrained observer. Essentially all infants with TOF have a heart murmur caused by the right ventricular outflow tract obstruction, but the murmur is not a reliable indicator of the severity of the obstruction.
What Complications Occur in an Infant with Tetralogy of Fallot?
Hypercyanotic spells, also called “tet spells,” can occur in infants with TOF before surgical correction. Classically, the infant’s crying triggers these spells because crying causes increased systemic venous return to the right ventricle, which has a fixed outflow obstruction. This increased volume cannot get past the right ventricular obstruction, so the deoxygenated blood shunts from right to left through the VSD and into the systemic arterial circulation, causing increased cyanosis. Tet spells can be life threatening and thus require emergency treatment. Other complications of TOF, rarely seen now with early surgical correction, include polycythemia, stroke, and brain abscess.
What Diagnostic Studies Are Needed?
Oxygen saturation obtained by pulse oximetry is the most important information for an infant with TOF. An ECG will show evidence of right ventricular hypertrophy, but this is not particularly helpful in management. A chest radiograph may show the characteristic boot-shaped heart but does not really aid in managing the infant. Echocardiography is essential in the diagnosis of TOF but is not part of the routine management performed by the pediatrician.
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