PHYSIOLOGIC CONSEQUENCES OF CONGENITAL HE.ART DISEASE 



47> 



nificantly higher than tliat in the systemic arteries, 

 especially if there is a large ventricular septal defect 

 with equalization of pressures between the ventricles. 

 Blood that is shunted into the right ventricle via the 

 ventricular septal defect will return to the left ven- 

 tricle via the pulmonary veins in addition to that 

 blood returning from the systemic veins and must 

 either be ejected into the aorta or be shunted again 

 into the right ventricle. The magnitude of the left-to- 

 right shunt will depend on the relative resistance 

 offered to the outflow of blood from the right and left 

 ventricles. The presence of the ventricular septal defect 

 may prevent "pressure overloading" of the left ven- 

 tricle but in this situation only at the expense of an in- 

 creased volume load on the pulmonary circulation as 

 well as on the left ventricle, since the blood "escaping" 

 from the left ventricle via the septal defect must return 

 again to the left ventricle via the pulmonary circula- 

 tion. In any event a high enough systolic pressure 

 must be generated in the left ventricle to maintain 

 systemic blood flow through the stenotic aortic valve. 

 These two defects are sometimes associated with a 

 patent ductus arteriosus plus a coarctation of the aorta 

 upstream to tlte aortic end of the ductus. In this situa- 

 tion there is usually a very high pulmonary flow and 

 the major blood supply to the lower part of the body 

 is via the ductus, whereas that to the upper part is via 

 the stenotic aortic valve. On occasion, patients with 

 these four defects maintain a surprising degree of 

 cardiovascular compensation into early adult life. 



Ventricular septal defect with mitral stenosis. Mitral 

 stenosis associated with a ventricular septal defect 

 will, as in the case of mitral stenosis with an aortic- 

 pulmonary communication, lead to a higher inci- 

 dence of pulmonary hypertension and increased pul- 

 monary vascular resistance. The predisposing factors 

 leading to this are elevated left atrial and pulmonary 

 venous pressures owing to the mitral stenosis, and an 

 increased pulmonary blood flow or pressure or both 

 owing to the ventricular septal defect. The resulting in- 

 creased pulmonary vascular resistance and pulmonary 

 hypertension will lead to an earlier development of 

 right-heart failure than if either condition occurred 

 alone. 



J'entricular septal defect with pulmonary stenosis. The con- 

 genital anomalies, ventricular septal defect with pul- 

 monary stenosis and the well-known complex, tetral- 

 ogy of Fallot, will be discussed together, since from 

 the hemodynamic viewpoint this latter complex is in 

 essence a ventricular septal defect plus pulmonary 

 stenosis. In general, the term "ventricular septal de- 

 fect with pulmonary stenosis" has been used in those 



T.ABLE 8. Average and Range of Hemodynamic Data in 

 /J Patients With I'entricular Septal Defect 

 and Pulmonary Stenosis 



patients without readily apparent cyanosis, whereas 

 tetralogy of Fallot includes those patients who are 

 cyanotic at rest. As in patients with ventricular septal 

 defect, the relative volumes of blood flowing into the 

 systemic or pulmonary circulation depend on the size 

 of the ventricular septal defect and the relative resist- 

 ance to the outflow of blood from the right and left 

 ventricles. 



In ventricular septal defect with pulmonary stenosis 

 the resistance to the flow of blood into the pulmonary 

 circulation is due in large part to the resistance to 

 blood flow through the region of stibvalvular or 

 valvular stenosis upstream to the pulmonary circula- 

 tion. The "overriding" aorta that is classically found 

 in tetralogy of Fallot plays no readily demonstrable 

 role in the direction and magnitude of the shunts. 

 From the hemodynamic standpoint, ventricular septal 

 defect with pulmonary stenosis and tetralogy of Fallot 

 merely represent two stages or degrees of the same 

 anatomic abnormalities. 



Hemodynamic findings. The average and range of 

 hemodynamic values are shown in table 8 for 15 pa- 

 tients with "ventricular septal defect with pulmonary 

 stenosis" studied by Brotmacher & Campbell (44), 

 and in table g for 36 patients with tetralogy of Fallot 

 studied by Bing and co-workers (29). As would be 

 expected, there is a wide range of values for pulmonary 

 blood flows and pressures in the right side of the heart, 

 as well as for the oxygen saturation of systemic arterial 

 blood. In the series of cases studied by Brotmacher 

 and Campbell, the average value for pulmonarv blood 

 flow was nearly double the average value for systemic 

 blood flow, whereas the average value of 95 per cent 

 for arterial oxygen saturation was within the range of 

 normal. In the series studied by Bing et al., however, 

 the average pulmonary blood flow was markedly de- 

 creased, being only 1.3 liters per min per m- of body 

 surface area, and the value for systemic arterial oxygen 

 saturation averaged 72 per cent. Bing and associates 

 have shown that in some of their cases the pulmonary 

 capillary blood flow exceeded the pulmonary-artery 



