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HANDBOOK OF PHYSIOLOGY •^^ CIRCULATION I 



sembling a total or a partial anomalous pulmonary 

 venous connection. 



Anomalous systemic venous connections. Occasionally, 

 in addition to a normal ris;lit superior vena cava, 

 there may be a persistent left superior vena cava. 

 The latter vein joins the left extremity of the coronary- 

 sinus, which is dilated, and the blood is carried into 

 the right atrium. This condition by itself is of no 

 functional significance; however, rarely one or more 

 pulmonary veins may connect to the persistent left 

 superior vena cava. The coronary sinus may occa- 

 sionally open into the left atrium alone or may com- 

 municate with both atria. 



Venous obstruction. Congenital obstruction of the 

 major systemic veins rarely occurs; however, one or 

 more pulmonary veins may be atretic. In these in- 

 stances it is usually possible to trace fibrous strands 

 to the left atrium but there is no lumen. 



Intracardiac Anomalies 



VENTRICULAR SEPTAL DEFECT. Ventricular septal 

 defects are probably the most common congenital 

 cardiovascular anomaly, occurring in approximately 

 15 per cent of all types of congenital cardiovascular 

 defects. They may occur in either the membranous 

 or the muscular portion of the ventricular septum. 

 Occasionally a ventricular septal defect is associated 

 with a deformity of the adjacent aortic valve, pro- 

 ducing aortic insufficiency. Mitral insufficiency also 

 has been described in association with a ventricular 

 septal defect (57). In rare instances the ventricular 

 septal defect is located so as to establish a communi- 

 cation between the left ventricle and the right atrium 

 instead of the right ventricle as is usually the case. 



The size of the ventricular septal defect is extremely 

 variable. It may be so small that it has no functional 

 significance, or the ventricular septum may fail to 

 form so that the ventricular part of the heart is com- 

 mon to both circulations. The latter condition is 

 called cor triloculare biatriatum or common ventricle 

 and occurs in approximately 2 per cent of all cases of 

 congenital cardiovascular defects. Usually two vessels 

 leave the heart and, except in rare cases, there is 

 transposition of the great vessels. This condition is 

 functionallv similar to that in the normal turtle 

 heart. 



INTERATRIAL COMMUNICATIONS. A patent, valve-com- 

 pctent foramen ovale is said to be present in 25 per 

 cent of the population and hence it is not usually 

 considered a true congenital defect. A true atrial 



septal defect allows passage of blood across the atrial 

 septum in both directions. 



Atrial septal defects are one of the six most common 

 congenital cardiovascular anomalies, occurring in 

 approximately 7 per cent of all cases, and are among 

 the commoner types of congenital cardiac anomalies 

 seen in adult life. The usual form of atrial septal defect 

 is a valvular incompetence of the foramen ovale for 

 one or more of three reasons : the valve of the foramen 

 may be short, the foramen may be unusually large, 

 or the valve of the foramen may be perforated. Oc- 

 casionally an atrial septal defect is associated with 

 acquired rheumatic mitral stenosis, constituting the 

 so-called Lutembacher syndrome (167). 



In addition to valve-incompetent foramen ovale, 

 defects in other areas of the atrial septum may occur 

 as a result of incomplete development of the septum 

 primum or the septum secundum. A condition occa- 

 sionally encountered in cases of atrial septal defect 

 is the so-called superior vena caval syndrome (239). 

 This syndrome consists of a defect high in the atrial 

 septum near the superior vena cava and a partial 

 anomalous connection of the pulmonary veins directly 

 to the superior vena cava or to a point near tlie junc- 

 tion of the superior cava and the right atrium. Rarely, 

 as is true of the ventricular septum, the interatrial 

 septum may fail to develop, thus resulting in a com- 

 mon atrium. 



TETRALOGY OF FALLOT. Although this anomaly is a 

 combination of intracardiac defects, it is usually 

 considered a single entity (99). It is the most common 

 malforination causing cyanosis that allows the patient 

 to survive beyond 2 years of age. It is also one of the 

 most common malformations, occurring in nearly 9 

 per cent of patients with congenital cardiovascular 

 disease. The anatomic complex is characterized by 

 biventricular origin of the aorta above a ventricular 

 septal defect, a thick right ventricle and an anatomic 

 barrier to the fiow of blood to the lungs. The anatomic 

 barrier may be caused by one or more of three con- 

 ditions: /) stenosis or atresia of the pulmonary artery, 

 2) stenosis or atresia of the pulmonary valve, and 3) 

 stenosis or atresia of the subpulmonary tract in the 

 right ventricle. A right aortic arch and a right de- 

 scending aorta occur in about 25 per cent of patients 

 with tetralogy of Fallot. The association of right aortic 

 arch with tetralogy of Fallot is sometimes called 

 "Corvisart's disease" (67). An atrial septal defect is 

 not infrequently associated with this complex, in 

 which case it has been termed "pentalogy of Fallot." 



