I
HEAT DISORDERS
DISORDERS
H e a r t v a l v e s m a y b e a f f e c t e d b y
s t e n o s i s
( n a r r o w i n g ) , i n w h i c h t h e h e a r t m u s t
w o r k h a r d e r t o f o r c e b l o o d t h r o u g h , o r
b y i n c o m
p e t e n c e o r i n s u f f i c i e n c y ( l e a k -
i n e s s ) ,
w h i c h m a k e s
t h e
v a l v e
u n a b l e
t o
p r e v e n t
r e g u r g i t a t i o n
( b a c k w a s h )
o f
b l o o d . T h e s e d e f e c t s c a u s e h e a r t
m u r m u r s
.
D e f e c t s
o f t h e
h e a r t v a l v e s
m a y
b e
p r e s e n t
f r o m
b i r t h
( s e e
h e a r t d i s e a s e ,
c o n g e n i t a l
)
o r a c q u i r e d l a t e r i n l i f e . T h e
m o s t c o m
m
o n c o n g e n i t a l v a l v e d e f e c t s
a r e
a o r t i c s t e n o s i s
a n d
p u l m o n a r y s t e n o s i s
.
A c q u i r e d h e a r t - v a l v e d i s e a s e i s u s u a l l y
t h e
r e s u l t
o f d e g e n e r a t i v e
c h a n g e s
o r
i s c h a e m i a
( r e d u c e d b l o o d s u p p l y ) a f f e c -
t i n g
p a r t
o f t h e
h e a r t a n d l e a d i n g
t o
a o r t i c
s t e n o s i s
o r
m i t r a l i n c o m p e t e n c e
.
R h e u m a t i c f e v e r
c a n c a u s e
m i t r a l s t e n o s i s
,
m i t r a l
i n c o m p e t e n c e ,
d e f e c t s
o f
t h e
a o r t i c v a l v e ,
t r i c u s p i d s t e n o s i s
,
a n d
t r i c u s -
p i d i n c o m p e t e n c e
.
H e a r t v a l v e s m a y a l s o
b e d a m a g e d b y b a c t e r i a l
e n d o c a r d i t i s
.
H e a r t - v a l v e d i s o r d e r s c o m
m o n l y l e a d
t o
h e a r t f a i l u r e
,
a r r h y t h m i a s
,
o r
s y m p -
t o m s
t h a t
a r i s e
f r o m
r e d u c e d
b l o o d
s u p p l y t o t h e t i s s u e s .
H e a r t - v a l v e
d e f e c t s
m a y
b e
d i a g n o s e d
b y
a u s c u l t a t i o n
,
c h e s t X - r a y
,
E C G ,
o r
e c h o -
c a r d i o g r a p h y
a n d m a y
b e
c o r r e c t e d b y
h e a r t - v a l v e s u r g e r y
.
heart-valve surgery
A n
o p e r a t i o n
t o
c o r r e c t
a
h e a r t v a l v e
d e f e c t o r t o r e m o v e a d i s e a s e d o r d a m -
a g e d v a l v e . A h e a r t v a l v e m a y h a v e t o b e
r e p a i r e d , w i d e n e d , o r r e p l a c e d b e c a u s e
i t i s e i t h e r i n c o m p e t e n t ( l e a k y ) , s t e n o t i c
( n a r r o w e d ) ,
o r
b o t h .
W
i d e n i n g
o f a
v a l v e m a y i n v o l v e
v a l v o t o m y
o r
v a l v u l o -
p l a s t y
.
A d a m a g e d v a l v e c a n b e r e p l a c e d
b y a m e c h a n i c a l
o n e ( f a s h i o n e d f r o m
m e t a l a n d p l a s t i c ) , a v a l v e c o n s t r u c t e d
f r o m
h u m a n t i s s u e ,
a p i g v a l v e ,
o r
a
v a l v e t a k e n f r o m a h u m a n d o n o r a f t e r
d e a t h . A
h e a r t - l u n g m a c h i n e
i s u s e d d u r -
i n g v a l v e r e p l a c e m e n t .
A f t e r
h e a r t - v a l v e s u r g e r y ,
t h e r e m a y
b e s y m p t o m s o f b r e a t h l e s s n e s s f o r s e v e -
r a l w e e k s t h a t r e q u i r e c o n t i n u e d m
e d i -
c a t i o n . S o m e p e o p l e r e q u i r e l o n g - t e r m
t r e a t m e n t
w i t h
a n t i c o a g u l a n t d r u g s
t o
p r e v e n t
t h e
f o r m a t i o n
o f b l o o d
c l o t s
a r o u n d t h e n e w v a l v e . C e r t a i n t y p e s o f
r e p l a c e m e n t v a l v e , s u c h a s m e c h a n i c a l
v a l v e s ,
a r e
m
o r e
l i k e l y
t o
c a u s e
c l o t s
t h a n o t h e r t y p e s .
heat cramps
P a i n f u l m u s c l e
c o n t r a c t i o n s
c a u s e d b y
s a l t l o s s t h r o u g h p r o f u s e
s w e a t i n g
.
H e a t
c r a m p s a r e u s u a l l y b r o u g h t o n b y s t r e n -
u o u s a c t i v i t y i n e x t r e m e h e a t . T h e y m a y
d e v e l o p i n d e p e n d e n t l y o r m a y o c c u r a s
a s y m p t o m
o f
h e a t e x h a u s t i o n
o r
h e a t -
s t r o k e
.
P r e v e n t i o n a n d t r e a t m e n t c o n s i s t
o f d r i n k i n g
p l e n t y o f f l u i d s , a l t h o u g h
h e a t c r a m p s o f t e n r e s o l v e t h e m s e l v e s .
heat disorders
T h e b o d y f u n c t i o n s m o s t e f f i c i e n t l y a t a
t e m p e r a t u r e
o f a b o u t
3 7 ° C ,
a n d
a n y
m
a j o r d e v i a t i o n f r o m t h i s t e m p e r a t u r e
d i s r u p t s b o d y p r o c e s s e s . T h e b o d y h a s
s p e c i a l
m e c h a n i s m s
f o r
k e e p i n g
i t s
i n t e r n a l t e m p e r a t u r e c o n s t a n t ; a n y m a l -
f u n c t i o n i n g
o r
o v e r l o a d i n g
o f
t h e s e
m e c h a n i s m s m a y c a u s e a h e a t d i s o r d e r .
T h e m e c h a n i s m s b y w h i c h t h e b o d y
l o s e s e x c e s s h e a t a r e c o n t r o l l e d b y t h e p a r t
o f t h e b r a i n k n o w n a s t h e
h y p o t h a l a m u s
.
H
HEART-VALVE REPLACEMENT TYPES
There are three main types of
replacement heart valve: bioprostheses
(such as the Carpentier-Edwards valve,
right), mechanical valves (such as the
tilting-disc valve, centre right), and
homografts (valves taken from a human
donor, far right). A valve is only
replaced if it cannot be repaired. Heart-
valve replacement (see previous page)
is carried out by open surgery, which
requires a
c a r d i o p u l m o n a r y b y p a s s .
The
most frequently replaced valves are
the aortic and mitral valves.
Bioprostheses
These are taken from pigs
(as above) or can be made from
porcine or bovine tissue and used
with or without a stent (a tube to
help the valve to hold its shape).
Mechanical valves
There are two main types: those
with one (as above) or more
tilting-discs, and ball-and-cage.
Mechanical valves are made from
carbon fibre, metal, and plastic.
Homografts
These are healthy valves taken
from a person who has died of a
disease that does not affect the
heart. Homografts are a type of
bioprosthesis.
Examples
Bioprosthesis (xenograft)
Mechanical
Homograft
Made from
Bovine or porcine tissue with
or without a stent (rigid tube)
Metal and plastic
Human valve
Availability
Readily available
Readily available
Limited availability
Suitable age group
Over 60
All ages
All ages
Duration
Up to 15 years
Lifetime
15 to 20 years
Post-operative drug therapy
Three months’ treatment with
anticoagulant drugs
Lifelong treatment with
anticoagulantdrugs
Three months’ treatment
with anticoagulant drugs
Possible complications
Infection; stroke; tendency to
become calcified
Infection; stroke; calcification;
leakage around base ofvalve
Less prone to infection
373
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