PHYSIOLOGIC CONSEQUENCES OF CONGENITAL HEART DISEASE 



475 



blood at right ventricular level. This is principally due 

 to the reduction in size of the effective right ventricle 

 resulting from malposition of the septal and posterior 

 cusps of the tricuspid \alve. As a result there is a de- 

 crease in the amount of blood the right ventricle can 

 accept during diastole. In addition, tricuspid regurgi- 

 tation may be present, further interfering with for- 

 ward flow of blood through the right ventricle (151). 



In three-fourths of the cases either the foramen ovale 

 is patent or the fossa of the valve is fenestrated. Since 

 the defective right ventricle cannot handle the return- 

 ing blood, a large proportion is shunted through the 

 foramen o\'ale into the left atrium and thence into the 

 systemic circulation. 



Keith and co-workers (147) found that in 17 

 cases reported in the literature the systemic arterial 

 oxygen saturation varied from 64 to 97 per cent. 

 Three-fourths of these patients had evidence of cyanosis 

 at some time. Four who were exercised showed a de- 

 crease in arterial oxygen saturation. These findings are 

 similar to those reported previously by Kilby and asso- 

 ciates (151). 



Right ventricular- and pulmonary-artery pressures 

 are normal; the right atrial mean pressure may or 

 may not be elevated. Usually there is a prominent A 

 wave in the right atrial pressure-pulse tracing which is 

 considered to result from impedance to normal 

 emptying of the right atrium due to the "obstruction" 

 to flow into the right \'entricle (147). Right atrial 

 pressure-pulse tracings with prominent V waves, 

 presumably due to tricuspid regurgitation, have been 

 shown by G0tzsche & Falholt (121) and by Kjellberg 

 and collaborators (153). 



Continuous pressure readings obtained in a 26-year- 

 old man diu'ing withdrawal of a catheter from the 

 pulmonary-artery wedge position to the right atrium 

 is shown in figure 43 (282). The right atrial pressure 

 was elevated and showed an increased pulsation. The 

 pulmonary-artery wedge pressure, however, was nor- 

 mal and lower than the right atrial pressure. There 

 was no significant change in pressure or contour when 

 the catheter passed the region of the tricuspid valve 

 from the right ventricle to the right atrium as judged 

 roentgenoscopically. The oxygen saturation of sys- 

 temic arterial blood varied from 88 to gi per cent in 

 this patient and there was no e\idence of arterializa- 

 tion from blood samples withdrawn from the right side 

 of the heart. 



VALVULAR ATRESIAS. Atresia of one of tiie \alves of the 

 heart is associated with serious hemodynamic disturb- 

 ances that frequently permit survival only into early 



infancy. Such a defect is nearly always part of a com- 

 plex anomaly, since communications between the 

 right and left sides of the heart are necessary for sur- 

 vival. Since blood from the right and left sides of the 

 heart becomes mixed, oxygen desaturation of systemic 

 arterial blood must always be present. 



Aortic atresia. In this condition the normal outlet 

 from the left side of the heart is closed and the blood 

 entering this side is shunted to the right, usually 

 through a patent 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 an aortic- 

 pulmonary communication, usually a patent ductus 

 arteriosus. As would be expected, survival beyond 

 early infancy is rare. 



Mitral atresia. The hemodynamic alterations pro- 

 duced by mitral atresia are similar to those of aortic 

 atresia. Blood entering the left atrium via the pulmo- 

 nary veins is shunted to the right atrium. In this in- 

 stance the systemic circulation is supplied by either a 

 ventricular .septal defect or an aortic-pulmonary com- 

 munication such as a patent ductus. The prognosis as 

 to survival is similar to that for aortic atresia. 



Pulmonary atresia. Atresia of the pulmonary valve 

 may be associated with a ventricular septal defect or 

 rarely an interatrial communication. Survival beyond 

 early infancy is uncommon. Usually, there is an asso- 

 ciated patent ductus arteriosus. Systemic venous blood 

 enters the left atrium or left ventricle via an interatrial 

 or interventricular communication and the total pul- 

 monary and systemic blood flow enters the systemic 

 circulation. An aortic-pulmonary communication and 

 a bronchial-artery collateral circulation are the only 

 means of blood flow to the pulmonary circuit. Oxygen 

 saturation of the systemic arterial blood is decreased 

 and, if the ductus arteriosus is closed, may be ex- 

 tremely low. 



Tricuspid atresia. Although there are numerous 

 anatomic \ariations associated with tricuspid atresia, 

 the intracardiac circulation is similar in all. Blood 

 entering the right atrium from systemic veins passes 

 into the left atrium. The left ventricle then becomes 

 the propelling chamber maintaining, directly or in- 

 directly, both pulmonary and systemic circulations. 

 The right ventricle is usually diminutive, there fre- 

 quently being only a small channel to the pulmonary 

 artery. The degree of arterial hypoxemia is inversely 

 related to the pulmonary blood flow. When a severe 

 obstruction to pulmonary flow is present the degree 

 of cyanosis is usually severe. 



