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292 P R I N C I P L E S A N D P R A C T I C E O F C R I T I C A L C A R E

Fused cusps
Cusp Cusp

Orifice Orifice

Normal valve Normal valve Stenosed valve Regurgitant valve
(open) (closed) (open) (closed) B
A

Stenosed
mitral
valve

Mitral
valve does
not close
properly

C D

FIGURE 12.1 Valvular stenosis and regurgitation: (A) normal position of valve leaflets (cusps) when the valve is open and closed; (B) open position of a
stenosed valve (left) and closed position of a regurgitant valve (right); (C) haemodynamic effect of mitral stenosis shows the mitral valve is unable to open
completely during left atrial systole, limiting left ventricular filling; (D) haemodynamic effect of mitral regurgitation shows the mitral valve does not close
completely during left ventricular systole, allowing blood to re-enter the left atrium.
43

trends, the prevalence of rheumatic fever and rheumatic Aortic valve disease
heart disease among Indigenous Australians is one of the Aortic stenosis is a narrowing of the opening of the valve
highest in the world. Also, Pacific Islanders living in New between the left ventricle and aorta (Figure 12.1). This
2
Zealand have much higher rates of rheumatic fever than stenosis often results from degenerative changes that
the general population. As a result, valvular disorders are occur with age or as a result of congenital abnormalities
3
much more common in these groups. Rheumatic fever is such as a bicuspid aortic valve (prevalence of bicuspid
discussed under infective endocarditis in Chapter 10. aortic valve in the general population is 0.5% and may
cause aortic stenosis or regurgitation). Aortic stenosis is
Stenotic valves have a tightened, restricted orifice, so that usually associated with left ventricular hypertrophy in
blood must be forced through at higher pressure response to the high pressure needed to push blood into
(Figure 12.1). In regurgitation, also called valvular incom- the aorta. Increased myocardial oxygen demands from
petence or insufficiency, incomplete closure of the valve the hypertrophied muscle also mean that angina is
leaflets results in backflow of blood. Valvular conditions common. Often the first sign of aortic stenosis is left heart
can result from congenital deformities, but also from the failure, which is a culmination of these two effects and
degenerative changes associated with ageing, from infec- adaptive dilation. On auscultation, additional heart
4
tion and rheumatic diseases. When a valve is stenosed, sounds are heard as a systolic murmur and a loud S4.
higher pressure is required to push blood through the
narrow opening and the heart compensates by hypertro- Aortic regurgitation may occur acutely when the aortic
phy and dilation. When a valve is incompetent the heart valve is damaged by endocarditis, trauma or aortic dis-
does not empty sufficiently, so again the heart compen- section, and presents as a life-threatening emergency.
sates by hypertrophy and dilation. In both these condi- Chronic aortic regurgitation usually results from rheu-
tions heart failure may result; however, in regurgitation, matic heart disease, syphilis, chronic rheumatic condi-
pressure in the ventricles and atrium grows and this pres- tions or congenital conditions. Again the left ventricle
sure is reflected back into the pulmonary or venous compensates by hypertrophy and dilation, which ulti-
system. Although the heart contains four valves, the mately can result in left heart failure. When left heart
majority of disorders affect the mitral and aortic valves in failure occurs, left atrial pressure rises and may cause
the left side of the heart. pulmonary hypertension. In the acute situation, the