PHYSIOLOGIC CONSEQUENCES OF CONGENITAL HEART DISEASE 



473 



stenosis were severe, inHow ol' blood to the right ven- 

 tricle would be impeded and significant alterations in 

 the systemic circulation would result. The direction 

 and magnitude of the shunt due to the \cntricular 

 septal defect would, however, be relatively independ- 

 ent of these systemic eflfects. 



ATRIAL SEPTAL DEFECT WITH VALVULAR STENOSIS. H'lt/l 



aortic stenosis. This combination of defects occurs inlre- 

 quently. The hemodynamic alterations produced by 

 the atrial septal defect are not changed by the presence 

 of aortic stenosis unless left-heart failure supervenes. 

 When this occurs, the left ventricular diastolic pres- 

 sure increases, resulting in an increase in left atrial 

 pressure. This then results in an increase in the left- 

 to-right shunt through the atrial septal defect. Left 

 ventricular filling sufficient to maintain the systemic 

 cardiac output must, however, be maintained. As a 

 consequence, an increase in both right and left atrial 

 pressure occurs and pulmonary hypertension also fre- 

 quently develops. The mechanism of this sequence of 

 events has not been fully elucidated 



Atrial septal defect with mitral stenosis. Atrial septal de- 

 fecf associated with mitral stenosis has been termed 

 the "Lutembacher syndrome." If the stenosis is con- 

 genital, blood flow into the left ventricle is impeded 

 during fetal life so that the left atrial pressure is in- 

 creased and, as a consequence, an increased propor- 

 tion of blood flows into the right ventricle and the 

 pulmonary artery and thence enters the aorta via the 

 ductus arteriosus. At birth the right side of the heart 

 and the pulmonary artery are large and the pressure 

 in the left atrium usually exceeds that in the right 

 atrium so that the shunt is in the left-to-right direction 

 and tends to be large. Left atrial pressure must be ele- 

 vated in order to maintain systemic blood flow through 

 the stenotic mitral valve. Pulmonary hypertension is a 

 common complication of this combination of defects. 



If stenosis of the mitral valve develops later in life 

 as a result of rheumatic endocarditis, the left-to-right 

 shunt is increased as a result of the increased resistance 

 to flow through the mitral valve and the concomitant 

 elevation of left atrial pressure which must be sustained 

 at a sufficiently high level to maintain systemic flow. 

 The incidence of pulmonary hypertension is much 

 higher than in uncomplicated atrial septal defect. 



Atrial septal defect with pulmonary stenosis. This com- 

 bination of defects is, next to the tetralogy of Fallot, 

 the most common cause of cyanotic congenital heart 

 disease. In patients who have pulmonary stenosis and 

 atrial septal defect, blood may be shunted through the 

 defect in either direction. When, as a result of severe 



pulmonary stenosis, the mean pressure in the right 

 atrium increases to levels in excess of that in the left 

 atrium, the shunt becomes partially or completely 

 right to left. When the shunt is completely or pre- 

 dominantly right to left and is large, the condition 

 clinically may resemble tetralogy of Fallot. When 

 right atrial pressure exceeds that in the left atrium, a 

 right-to-left shunt will occur through a valve-com- 

 petent foramen ovale. L'nder such circumstances, if 

 there is no demonstrable left-to-right shunt, it is im- 

 possible to be certain from hemodynamic evidence 

 whether the pulmonary stenosis is associated with a 

 true defect in the atrial septum or with the valve-com- 

 petent type of patent foramen ovale, which is found 

 in 25 per cent of normal individuals. 



Average and range of hemodynamic variables. As would 

 be expected, the amount of blood flow through the 

 pulmonary circulation is extremely variable, depend- 

 ing on the severity of the pulmonary stenosis and the 

 competence of the right ventricular musculature. The 

 average and range of hemodynamic variables in 15 pa- 

 tients with pulmonary stenosis and atrial septal defects 

 are shown in table 10 (42, 50). Although systolic pres- 

 sures in the right ventricle and systemic artery are 

 usually similar when patients with pulmonary stenosis 

 have a ventricular septal defect, in atrial septal defect 

 with pulmonary stenosis the right ventricular systolic 

 pressure may be less than, equal to, or greater than the 

 systemic arterial pressure (42, 50). These pressure rela- 

 tionships are laetter illustrated in table 1 1 , which shows 

 the differences in systolic pressures for the two groups. 

 In five patients with pulmonary stenosis and ven- 

 tricular .septal defect the differences in systemic systolic 

 and right ventricular systolic pressure are small, 

 averaging 4 mm of mercury, with a range from —4 to 

 I 7 mm. However, in five patients with atrial septal 

 defect, these differences were frequently quite large, 

 averaging 44 mm of mercury, with a range of —25 to 

 75 mm. 



Dynamics of pulmonary-artery obstruction. It is of inter- 

 est that in this condition elevations in riglit ventricular 

 pressure to levels in excess of systemic arterial systolic 

 pressure may be tolerated for many years without evi- 

 dence of failure of the right ventricle. The possibility 

 that the atrial septal defect acts asa "safety valve," per- 

 mitting some of the l^lood entering the right side of the 

 heart to be shunted into tiie left atrium, has been con- 

 sidered. 



Brecher & Opdyke (40) carried out acute studies in 

 open-chest dogs in which the pulmonary artery could 

 be partially occluded. They found that progressive oc- 

 clusion of the pulmonary artery in dogs with intact 



