The development of morphologically right-sided structures on one side of the body, and morphologically left-sided structures on the other side, is termed lateralization or situs. The normal arrangement, in which right-sided structures are on the right side of the body and vice versa, is known as situs solitus. The term visceroatrial situs is often used to refer to the situs of the viscera, or noncardiac organs, and atria when their situs is in agreement. In normal atrial arrangement or atrial situs solitus, the left atrium is on the left side and right atrium is on the right side. In atrial situs inversus, the left atrium is on the right side and right atrium is on the left side. The morphology of the lungs and the relation between the bronchial tree and the pulmonary arteries are useful in determining situs. A morphologically right lung typically has three lobes, and a morphologically left lung typically has two lobes. Furthermore, the right lung tends to have an eparterial bronchus, or one that branches superior to the first lobar division of the pulmonary artery, in contrast to the left-sided lung, which has a hyparterial bronchus, or one that branches inferior to the first lobar division of the respective pulmonary artery (Figure 85-1). Tracheobronchial anatomy can generally be assessed from examination of the chest radiograph.21 Dextrocardia is present when the base to apex axis of the heart is directed to the right side of the chest (Figure 85-2). Another possible location for the heart is mesocardia, where the apex is in the midline. Situs solitus is the normal location of the atria and abdominal organs as described previously, whereas situs inversus is present when the right atrium is on the left, the left atrium is on the right, and the liver and stomach are similarly reversed. Situs ambiguous, with the liver and stomach in the midline, is seen in neonates with either bilateral right-sidedness or left-sidedness also commonly referred to as heterotaxy syndrome. Babies with bilateral right-sidedness tend to have asplenia, and their atrial and pulmonary morphologic features are characteristic of bilateral right atria and lungs. Babies with bilateral left-sidedness tend to have polysplenia and bilateral morphologic left atria and lungs. These conditions are invariably associated with a multitude of other intracardiac abnormalities. Dextrocardia with situs inversus is referred to as the mirror image dextrocardia and is generally associated with normal cardiac anatomy. It could, however, be a part of Kartagener syndrome or immotile cilia syndrome. Most often these are detected clinically with the heart sounds being auscultated on the right chest and incidental chest radiograph demonstrating dextrocardia (see Figure 85-2). In contrast, babies born with dextrocardia and situs solitus frequently have associated congenital heart defects, ranging from simple uncomplicated septal defects to complex lesions such as l-transposition of the great arteries.8 The same is true for those neonates with situs inversus of their abdominal organs with levocardia (normal cardiac position with base to apex axis to the left) who almost always have associated cardiac defects. Asplenia syndrome or bilateral right-sidedness should be suspected whenever complex cardiac defects are identified in association with total anomalous pulmonary venous connection.35 Because there is no morphologic left atrium, pulmonary venous drainage is rarely directly to the patient’s left-sided atrium. Similarly, in this condition, the coronary sinus, which lies posterior to the normal left atrium, is usually absent. In addition to this abnormal pulmonary venous return, systemic venous return is also abnormal, with the presence of bilateral superior vena cava. The left superior vena cava may enter directly into the roof of the left-sided morphologic right atrium or the coronary sinus, whereas the right superior vena cava generally enters the right atrium in a normal fashion. The right inferior vena cava is present, and there might be an additional left inferior vena cava. Another relatively common variety encountered in cardiac position is dextrocardia with an associated common atrium and a single atrioventricular valve, resulting in either a common ventricle or a large ventricular septal defect. Severe pulmonary stenosis or atresia is common in this particular defect.10 In addition to their complex congenital heart disease, these babies are often immunologically compromised because of their lack of spleen.36 Daily, lifelong administration of a prophylactic antibiotic to reduce the risk for bacterial sepsis is both necessary and important. Absent hepatic segment of the inferior vena cava, so-called interrupted inferior vena cava, is an excellent clue to the presence of polysplenia or bilateral left-sidedness in a neonate with ambiguous abdominal situs.45 Because the baby has no true right atrium, the course of the inferior vena cava is abnormal. Drainage of the inferior vena cava is through the azygos or hemiazygos veins and into the superior vena cava. With bilateral left atria, the pulmonary veins usually return to the heart in a bilateral fashion to their closest atrium (right-sided pulmonary veins return to the right-sided atrium). The presence of polysplenia is often associated with levocardia, normally related great arteries, a common atrium, and two ventricles with a ventricular septal defect. The pulmonary valve in these cases is usually normal. Although the patient has multiple small spleens, splenic function can be either normal or abnormal regardless of the presence of Howell-Jolly bodies on blood smear, which as previously stated may indicate hyposplenism.34 Arteriovenous malformations (AVMs) are an abnormal, direct connection between arteries and veins via a network of vessels called the nidus that lack an intervening capillary bed. Cerebral AVMs usually manifest in the neonatal period with signs of congestive heart failure, including a hyperdynamic precordium and hepatomegaly. Most of these are vein of Galen malformations, although neonates with large pial malformations and congestive heart failure have been described. Vein of Galen malformations can be classified as choroid and mural type, of which the choroidal type usually presents in the neonatal period.20 Arteriovenous malformations in the neonatal period usually present as congestive heart failure, and initial medical management consists of diuretics and inotropes. Because these lesions present with right heart volume overload, systemic afterload-reducing agents such as angiotensin converting enzyme (ACE) inhibitors would not provide any benefit. The use of digoxin is controversial in this group of neonates because of concern about poor renal perfusion and toxicity.16 Surgical management of cerebral arteriovenous malformations is difficult because of their size and location and because of the multiple feeder vessels. Embolization, with catheter-delivered metal coils or cyanoacrylate, of the arterial and venous channels before surgery has improved the results; however, complete cure of the defect is still unusual. Mortality and morbidity rates have improved dramatically in the past decade, but neurologic function after a combined interventional and surgical approach can be abnormal in up to 50% of survivors.24 Cardiomyopathy refers to a diverse group of myocardial diseases with multiple causes. These are rare disorders that account for only approximately 1% of childhood cardiac disease. In 1995, the World Health Organization classified cardiomyopathies into hypertrophic, dilated, restrictive, and mixed type.37 This classification is based on the pathophysiology of the disease. However, with rapid evolution of molecular genetics in cardiology, the American Heart Association in 2006 has classified cardiomyopathies into two major groups based on predominant organ involvement and etiology.28 Primary cardiomyopathies (genetic, nongenetic, acquired) are those solely or predominantly confined to heart muscle and are relatively few in number (Figure 85-3). Secondary cardiomyopathies show pathologic myocardial involvement as part of a large number and variety of generalized systemic (multiorgan) disorders (Box 85-1).28 Myocarditis, an inflammatory, usually infectious, process affecting the myocardium, may also result in either a dilated (common) or restrictive (rare) cardiomyopathy.
Cardiovascular Problems of the Neonate
Cardiac Malposition and Abnormalities of Abdominal Situs
Bodily Arrangement and Situs
Associated Lesions
Arteriovenous Malformations
Treatment
Myocardial Diseases: Cardiomyopathy and Myocarditis
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