HEART ATTACK
H
STRUCTURE OF THE HEART
The heart is positioned centrally in
the chest, with its right margin directly
underneath the right side of the
sternum (breastbone). The rest of the
heart points to the left, with its lowest
point (the apex) located underneath
the left nipple.
The heart acts as a dual pump.
Deoxygenated blood from the body
arrives, via the two venae cavae, in the
right atrium (upper heart chamber), is
transferred to the right ventricle (lower
chamber), and is then pumped via the
pulmonary artery to the lungs. There it
is reoxygenated and returns, via the
pulmonary veins, to the left side of
the heart. It enters the left atrium, is
transferred to the left ventricle, and is
then pumped, via a large vessel (the
aorta), to all parts of the body.
Blood supply
Although the heart muscle is continually
pumping blood, it cannot obtain much oxygen
from this flow, so it needs its own blood supply.
This is provided by the two coronary arteries,
which arise from the aorta. These arteries, with
their branches, supply the entire heart muscle.
A network of veins, called coronary veins (not
shown), drains blood back into the right atrium.
A o r t ic v a lv e
P u l m o n a r y
v a lv e
M itr a l v a lv e
L e ft
v e n t r i c le
S e p t u m
A o r t a
R ig h t
c o r o n a r y
a r t e r y
C ir c u m fle x a r t e r y
L e ft a n t e r i o r d e s c e n d i n g a r t e r y
Angiogram of coronary arteries
This image (left) gives a view of the heart from
the rear and clearly shows the coronary arteries.
The image was achieved by angiography: an X-
ray of the heart was taken after the coronary
arteries had been injected with a contrast
medium (a fluid that shows up on X-rays).
A n i n t r a - a o r t i c b a l l o o n p u m p , c o m p r i s -
i n g a b a l l o o n i n t h e
a o r t a
t h a t i n f l a t e s
w i t h e a c h
h e a r t b e a t
,
i n c r e a s e s t h e v o l -
u m e o f b l o o d e n t e r i n g t h e c i r c u l a t i o n .
T h i s
i s
a
c o m m o n l y
u s e d
m e a n s
o f
m e c h a n i c a l c i r c u l a t o r y s u p p o r t a n d m a y
b e
u s e d f o r t h e
f i r s t f e w
d a y s a f t e r a
m y o c a r d i a l i n f a r c t i o n
( h e a r t a t t a c k )
u n t i l
t h e
h e a r t
i s
a b l e
t o
m a i n t a i n
b l o o d
p r e s s u r e
u n a s s i s t e d .
A
l e f t
v e n t r i c u l a r
a s s i s t d e v i c e t a k e s b l o o d f r o m t h e l e f t
v e n t r i c l e
a n d p u m p s i t e l e c t r i c a l l y i n t o
t h e
a b d o m i n a l
a o r t a .
T r u e
a r t i f i c i a l
h e a r t s
a r e
m e c h a n i c a l
h e a r t s ,
w h i c h
a r e p o w e r e d f r o m o u t s i d e t h e b o d y b y
b a t t e r y p a c k s .
P r o b l e m s w i t h
a r t i f i c i a l
h e a r t s
i n c l u d e
t h e f o r m a t i o n o f b l o o d c l o t s w i t h i n t h e
d e v i c e a n d i n f e c t i o n . T h e y a r e t h e r e f o r e
u s e d
a s
a
t e m p o r a r y
m e a s u r e
u n t i l
a
h e a r t t r a n s p l a n t
c a n b e p e r f o r m e d .
heart attack
S e e
m y o c a r d i a l i n f a r c t i o n
.
heartbeat
A
c o n t r a c t i o n o f t h e
h e a r t
t h a t p u m p s
b l o o d t o t h e l u n g s a n d t h e r e s t o f t h e
b o d y . T h e
d i f f e r e n t
p a r t s
o f t h e
h e a r t
c o n t r a c t i n
a
p r e c i s e
s e q u e n c e
t h a t
i s
r e g u l a t e d b y e l e c t r i c a l i m p u l s e s e m a n -
a t i n g f r o m t h e
s i n o a t r i a l n o d e
,
a t t h e t o p
o f t h e r i g h t
a t r i u m
.
E a c h h e a r t b e a t c o n -
s i s t s o f t h r e e p h a s e s , w h i c h o c c u r i n a
c y c l e : t h e d i a s t o l e
( r e s t i n g p h a s e ) , t h e
a t r i a l s y s t o l e ( c o n t r a c t i o n o f t h e h e a r t ’s
u p p e r
c h a m
b e r s ) ,
a n d
t h e
v e n t r i c u l a r
s y s t o l e ( c o n t r a c t i o n o f t h e l o w e r c h a m
-
b e r s ) . T h e
r a t e
a t
w h i c h
c o n t r a c t i o n s
o c c u r i s c a l l e d t h e
h e a r t r a t e
.
T h e t e r m
p u l s e
r e f e r s t o t h e c h a r a c t e r
a n d r a t e o f t h e h e a r t b e a t w h e n f e l t a t a
p o i n t o n t h e b o d y , s u c h a s t h e w r i s t .
heart block
A
c o m
m
o n
d i s o r d e r
o f t h e
h e a r t b e a t
t h a t i s c a u s e d b y a n i n t e r r u p t i o n t o t h e
p a s s a g e
o f e l e c t r i c a l i m p u l s e s t h r o u g h
366
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