PHYSIOLOGIC CONSEqUENCES OF CONGENITAL HEART DISEASE 



449 



LEFT RADIAL loo - 

 125 



o. AORTA 



E 



75 



PULMONARY ARTERY 

 Lu 50 



w 



UJ 



Q: 



a. 



LEFT ATRIUM ^° 

 20 



ECG 



LEFT 

 VENTRICLE 

 (Thru Cofheter) 



FIG. 19. Simultaneously recorded 

 pressure pulses from various sessels and 

 cardiac chambers in a 49-year-old man 

 with "pure" mitral stenosis (operative 

 diagnosis). Individual waves contained 

 in usual left atrial pressure pulse are 

 labeled; for explanation of these sym- 

 bols see text. 



used in describing these waxes is that of Mackenzie 

 (169, 170) and VViggers (260) and is similar to that 

 used in tlie description of the periplieral venous pulse. 

 Tlie first positive wave, tlie A wave, be.gins shortly 

 after the onset of the P wave of the electrocardiogram 

 and represents an increase in left atrial pressure due 

 to atrial contraction. It is usually followed by a small 

 dip in pressure, the Z point, just prior to the onset of 

 ventricular systole, which is generally believed to be 

 caused by relaxation of the atrium. The second 

 positive wave, the G vva\e, appears shortly after the 

 onset of ventricular contraction and is believed to 

 result from closure of the mitral valve, with pushing 

 back into the atrium of the small amount of blood 

 contained between the leaflets, as well as from bulging 

 of the leaflets into the left atrium, thus encroaching 

 on its cavity. A second and larger dip in atrial pres- 

 sure, the X wave, follows, and this is generally 

 believed to result from the drawing down of the 

 atrioventricular septum by the contracting ventricle, 

 enlarging the atrial cavity, and thus producing a 

 decrease in left atrial pressure. During the time that 

 the left ventricle is ejecting blood into the aorta, the 

 mitral valve being closed, continued inflow of blood 

 into the left atrium produces the third positive wave, 

 the V wave, the peak of which occurs in proto- 

 diastole. The atrial pressure then decreases rapidly to 

 the Y point. This decrease in pressure at the onset of 

 diastole, the "Y descent," is due to the opening of 

 the mitral valve and flow of atrial blood into the 

 ventricle. 



In mitral stenosis, in addition to the increase in the 



general le\el of left atrial pressure, there is a more 

 gradual descent of the \' wave (Y descent) after the 

 mitral valve opens. This results from resistance to 

 flow across the \al\e. The left ventricular diastolic 

 pressure is normal, resulting in a pressure gradient 

 acro.ss the mitral valve. Normally, there is a minimal 

 gradient of i mm of mercury or less. The gradient in 

 mitral stenosis usually varies between 5 and 30 mm 

 of mercury at rest, depending on the severity of the 

 stenosis and the rate of blood flow across the valve. 



For further discussion of mitral stenosis refer to the 

 work of other investigators (88, 117, 146, 168) and 

 to Chapter 20. 



MITRAL REGURGITATION. Incompetence of the mitral 

 valve occurs congenitally as the manifestation of a 

 rare partial form of persistent common atrio\entricu- 

 lar canal, in which the interior \-alve leaflet shows a 

 cleft. The more usual forms of mitral incompetence 

 are acquired. 



Wiggers & Fell (263) ha\e described in detail the 

 immediate eflects of experimentally created regurgita- 

 tion of the mitral valve. Their work was confirmed by 

 Lanari & Molins (160). Keys & Friedell (150) first 

 demonstrated the magnitude of regurgitation by 

 determining ijoth roentgenokymographic (total) and 

 Fick (stroke) outputs. They found that regurgitation 

 varied from 25 to 100 per cent of the aortic stroke 

 output. 



The left atrial pulse contour in patients with 

 mitral regurgitation shows typical characteristics, 

 whicli are as follows (fig. 20): /) a high peak V wave 



