PHYSIOLOGIC CONSEqUENCES OF CONGENITAL HEART DISEASE 



421 



STENOSIS OR ATRESIA OF INTRACARDIAC VALVES. Any 



of the four intracardiac v^alves may be stenotic; how- 

 ever, the most commonly affected is the pulmonary 

 valve, stenosis of which occurs as a single defect in 

 more than 2 per cent of congenital cardiovascular 

 anomalies. It can also occur in complexes such as 

 tetralogy of Fallot, and is frequently associated with 

 an atrial septal defect or with the usual type of ven- 

 tricular septal defect. 



In addition to stenosis of the pulmonary or aortic 

 valves there may be a localized fibrous collarlike 

 narrowing in the outflow tract of the right or the 

 left ventricle. Rarely, stenosis of the infundibular 

 ostium of the right ventricle is the only abnormality. 

 In the usual case there is an associated ventricular 

 septal defect. Subaortic stenosis, on the other hand, 

 is more likely to occur as a single abnormality, and 

 the resulting functional disturbances are similar to 

 those of acquired aortic stenosis. 



''Valvular atresias" account for approximately 4 

 per cent of all congenital cardiovascular defects, 

 atresia of the aortic valve apparently being the most 

 common and atresia of the tricuspid valve the least 

 common. 



Atresia of the tricuspid orifice, as the name implies, 

 is characterized by absence of the usual inflow orifice 

 to the right ventricle. The great veins communicate 

 properly with the atria. The only outlet for blood 

 from the right atrium is through an atrial septal 

 defect, which usually takes the form of a patent fora- 

 men ovale. The left atrium represents a common 

 mixing chamber for venous and oxygenated blood, 

 and from this chamber blood enters a large left- 

 sided ventricular chamber through a wide mitral 

 orifice. A ventricular septal defect is present in most 

 cases. The arterial connection with the ventricles 

 varies from normal to transposition, or a truncus 

 arteriosus may be present. There may be pulmonary 

 or subpulmonary stenosis in some cases, whereas in 

 others there is no barrier to the flow of blood to the 

 lungs. 



In atresia of the mitral orifice the route of the cir- 

 culation is opposite in direction to that in tricuspid 

 atresia. Oxygenated blood from the left atrium flows 

 usually through an opening in the atrial septum into 

 the right atrium. The pathway of exit for left atrial 

 blood is usually inadequate, and thus there exists a 

 barrier to pulmonary venous blood drainage. The 

 mixture of pulmonary and systemic \enous blood in 

 the right atrium flows through a large tricuspid orifice 

 into the ventricular portion of the heart. In some 

 cases there are two ventricles and a ventricular septal 



defect, and in other instances there is a common 

 ventricle. Transposition of the great vessels is fre- 

 quently associated. Survival beyond infancy is un- 

 common. 



Pulmonary atresia was mentioned previously in 

 connection with tetralogy of Fallot. In pulmonary 

 atresia with intact ventricular septum the atresia 

 is at valve level, the leaflets of the pulmonary valves 

 being fused to form a fibrous diaphragmlike mem- 

 brane. The right ventricular chamber is usually 

 small and the right ventricular wall is thick, out of all 

 proportion to the size of the chamber. An opening 

 in the atrial septum is the route by which venous 

 blood that enters the right atrium escapes into the 

 left atrium. The blood supply to the lungs is usually 

 via a patent ductus arteriosus. This malformation 

 rarely if ever allows the patient to live beyond early 

 infancy. 



Atresia of the aortic orifice is characterized by 

 fusion of the aortic leaflets to form an imperforate 

 diaphragm at the level of the aortic valve. The ven- 

 tricular septum is usually intact. In some cases aortic 

 and mitral atresia may coexist. In most cases, how- 

 ever, there is a small, but normally developed mitral 

 valve. Whether or not mitral atresia coexists, the 

 normal outlet for the left side of the heart is closed 

 and the blood is shunted from the left atrium to the 

 right, usually through a valve-incompetent foramen 

 ovale. The right atrium and right ventricle thus 

 become, in essence, a common atrium and a common 

 ventricle, respectively. The systemic circulation is 

 supplied through the pulmonary artery by way of a 

 patent ductus arteriosus. Survival beyond early 

 infancy is rare. 



INCOMPETENCE OF iNTRACARDL\c VALVES. Incompetent 

 intracardiac valves are usually associated with other 

 intracardiac anomalies or are part of a developmental 

 complex. Examples of these are insufficiency of the 

 aortic valve in the presence of \entricular septal 

 defect and the developmental complex, common 

 atrioventricular canal, which is a defect in develop- 

 ment of the atrioventricular valves from the embryo- 

 logic endocardial cushion. Insufficiency of the pul- 

 monary valve rarely if ever occurs as a congenital 

 defect. 



PERSISTENT COMMON ATRIOVENTRICULAR CANAL. Per- 

 sistent common atrioventricular canal, which occurs 

 in nearly 2 per cent of all congenital cardiovascular 

 defects, may be considered to appear in the complete 

 form and the partial form (253). In the complete 



