PHYSIOLOGIC CONSEQUENCES OF CONGENITAL HEART DISEASE 



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CASE NUMBER 



FIG. 41. Magnitude of pulmonary and systemic blood flows in 17 cases of persistent common 

 atrioventricular canal. Note that cardiac index is within range of normal in spite of large left-to- 

 right shunts and that the left-to-right shunt usually occurs at both atrial and ventricular levels. 



pressed in terms of body surface area. The pulmonary 

 flow, also expressed in terms of body surface area, ex- 

 ceeded the systemic flow in all but two cases (fig. 41). 

 The increased pulmonary blood flows were due to 

 large left-to-right shunts occurring at both atrial and 

 ventricular levels, but in most cases chiefly at atrial 

 level. Only in one case was there a predominant shunt 

 at ventricular level. 



The relationship between the ratio of pulmonary to 

 systemic vascular resistance and the net intracardiac 

 shunt in these 17 cases is shown in figure 42. In the 

 presence of a normal total pulmonary resistance and 

 total systemic resistance, large left-to-right shunts pre- 

 dominate. As the total pulmonary resistance exceeds 

 the total systemic resistance, net right-to-left shunts 

 occur with consequent desaturation of the systemic 

 arterial blood. 



The presence of large clefts in the common atrioven- 

 tricular valves could preclude complete closure of the 

 valve leaflets during ventricular systole and produce 

 mitral and tricuspid regurgitation. The atrial and pul- 

 monary arterial pressure pulses in this series of cases, 

 however, showed no evidence of regurgitation. 



In patients with persistent common atrioventricular 

 canal there is less evidence of the preferential shunting 

 of blood from the right lung than is usually seen in 



patients with atrial septal defect in the region of the 

 fossa ovalis. 



In persistent common atrioventricular canal, not 

 only are the right pulmonary veins located at a 

 greater distance from the site of the interatrial defect 

 than in the usual type of atrial septal defect, but a 

 proportion of the left-to-right shunt occurs at ven- 

 tricular level. These factors combine to permit mixing 

 of the streams of blood from each lung to be more 

 nearly complete before shunting occurs than in the 

 usual case of atrial septal defect. 



Septal Defects Willi \'alvular Stenosis 



The hemodynamic alterations occurring with isolated 

 septal defects and isolated abnormalities of the heart 

 valves have been discussed. Two or even more of these 

 abnormalities may occur in the same patient, and some 

 are combined so frequently that they are considered a 

 single entity, such as tetralogy of Fallot. This is the 

 name used to designate the combination of defects 

 most commonly responsible for cyanotic congenital 

 heart disease, namely pulmonary stenosis and ven- 

 tricular septal defect plus an overriding aorta which is 

 frequently associated with a right-sided aortic arch. 



Hemodynamic alterations may be more severe or 



