I
HEART DISEASE, CONGENITAL
HEART CYCLE
There are three main phases in each heartbeat. The beat is generated by electrical
waves that emanate from the heart’s own pacemaker, the sinoatrial node. The
images in this box show blood flow, an electrocardiogram tracing, and the
direction of electrical impulses at each stage of the cycle.
Diastole
In this resting phase, the heart
fills with blood. Deoxygenated
blood flows into the right side
of the heart; at the same time,
oxygenated blood flows into
the left side.
H e a r t f il ls
w it h b l o o d
Atrial systole
In this second phase, the two
atria (upper chambers of the
heart) contract, squeezing
more blood into the ventricles
(lower chambers) and filling
them completely.
L e ft a t r iu m
c o n t r a c t s
Ventricular systole
The two ventricles contract to
pump deoxygenated blood
into the pulmonary artery and
oxygenated blood into the
aorta. Once the heart is
empty, diastole begins again.
L e ft
v e n t r i c le
c o n t r a c t s
V e n t r ic u l a r
s y s t o l e
In diastole, the heart muscle is
at rest. Towardsthe end ofthis
phase, the sinoatrial node
emits an electrical impulse,
which starts to spread through
the heart muscle.
As the electrical impulse
spreads through the two atria,
it causes them to contract. By
the end of atrial systole, the
impulse reaches another node,
the atrioventricular node.
After a momentary pause,
waves of electrical activity
from the atrioventricular node
pass along special fibres to
all parts of the ventricles,
producing ventricular systole.
t h e
h e a r t ’s
c o n d u c t i n g
s y s t e m .
H e a r t
b l o c k m a y b e c o n g e n i t a l o r m a y b e d u e
t o h e a r t d i s e a s e , s u c h a s
c o r o n a r y a r t e r y
d i s e a s e
.
O t h e r c a u s e s i n c l u d e o v e r d o s e
o f a
d i g i t a l i s d r u g
( u s e d i n t h e t r e a t m e n t
o f h e a r t d i s e a s e ) a n d
r h e u m a t i c f e v e r
.
TYPES
T h e r e
a r e
t w o
m a i n
t y p e s
o f
h e a r t
b l o c k :
a t r i o v e n t r i c u l a r b l o c k
,
a b l o c k a g e i n
t h e h e a r t ’s c o n d u c t i n g s y s t e m b e t w e e n
a n
a t r i u m
( u p p e r c h a m b e r o f t h e h e a r t )
a n d a
v e n t r i c l e
( l o w e r
c h a m b e r
o f t h e
h e a r t ) ;
a n d
b u n d l e
b r a n c h
b l o c k
,
i n
w h i c h t h e b l o c k i s c o n f i n e d t o c o n d u c -
t i o n w i t h i n t h e v e n t r i c l e s .
Atrioventricular block
T h e r e
a r e
t h r e e
d e g r e e s o f a t r i o v e n t r i c u l a r h e a r t b l o c k .
I n
f i r s t
d e g r e e
b l o c k ,
t h e r e
i s
a n
i n c r e a s e d d e l a y b e t w e e n c o n t r a c t i o n o f
t h e a t r i a a n d t h a t o f t h e v e n t r i c l e s .
I n
s e c o n d d e g r e e h e a r t b l o c k , s o m e a t r i a l
b e a t s
f a i l
t o
r e a c h
t h e
v e n t r i c l e s .
I n
c o m p l e t e
h e a r t
b l o c k ,
t h e r e
i s a
t o t a l
b l o c k a g e i n t h e h e a r t ’s c o n d u c t i n g s y s -
t e m
t h a t
p r e v e n t s
a t r i a l
b e a t s
f r o m
b e i n g c o n d u c t e d t o t h e v e n t r i c l e s . T h e
t w o
c h a m b e r s
t h e r e f o r e
b e a t
a t
t h e i r
o w n i n t r i n s i c r a t e , w i t h t h e v e n t r i c l e s
b e a t i n g v e r y s l o w l y a n d c o m p l e t e l y i n -
d e p e n d e n t l y o f t h e a t r i a .
Bundle branch block
E a c h v e n t r i c l e h a s i t s
o w n c o n d u c t i o n s y s t e m , k n o w n a s t h e
r i g h t
a n d
l e f t
b u n d l e
b r a n c h e s . T h e s e
w o r k t o g e t h e r . B l o c k a g e i n o n e o r o t h e r
o f t h e b u n d l e b r a n c h e s
( o r ,
l e s s c o m
-
m o n l y , b o t h ) l e a d s t o a n a b n o r m a l p a t t e r n
o f c o n d u c t i o n t h r o u g h t h e v e n t r i c l e s .
R i g h t b u n d l e b r a n c h b l o c k c a n s o m
e -
t i m e s b e s e e n i n a h e a l t h y h e a r t . I t m a y
a l s o b e d u e t o c e r t a i n c o n d i t i o n s , s u c h
a s c o n g e n i t a l h e a r t d i s e a s e ( 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
).
L e f t b u n d l e b r a n c h b l o c k
i s m o r e s e r i o u s a n d i s a l w a y s a s i g n o f a n
u n d e r l y i n g c a r d i a c d i s o r d e r . I t i s u s u a l l y
c a u s e d b y
c o r o n a r y a r t e r y d i s e a s e
b u t m a y
a l s o
o c c u r
a s
a
r e s u l t
o f
h y p e r t e n s i o n
( h i g h b l o o d p r e s s u r e ) o r
a o r t i c s t e n o s i s
.
SYMPTOMS
F i r s t d e g r e e h e a r t b l o c k a n d l e f t o r r i g h t
b u n d l e
b r a n c h
b l o c k
a l o n e
u s u a l l y
c a u s e n o s y m p t o m s . H o w e v e r , i n m o r e
s e v e r e a t r i o v e n t r i c u l a r
h e a r t b l o c k , t h e
r a t e o f v e n t r i c u l a r c o n t r a c t i o n d o e s n o t
i n c r e a s e
i n
r e s p o n s e
t o
e x e r c i s e . T h i s
m a y c a u s e b r e a t h l e s s n e s s a s a r e s u l t o f
h e a r t f a i l u r e
( r e d u c e d p u m p i n g e f f i c i e n -
c y ) o r c h e s t p a i n s d u e t o
a n g i n a p e c t o r i s
( c a u s e d b y r e d u c e d b l o o d s u p p l y t o t h e
h e a r t
m
u s c l e ) .
I f t h e
v e n t r i c u l a r
b e a t
b e c o m e s v e r y s l o w , o r i f i t s t o p s a l t o g e -
t h e r f o r a f e w s e c o n d s , e p i s o d e s o f l o s s
o f c o n s c i o u s n e s s m a y o c c u r .
DIAGNOSIS AND TREATMENT
B o t h t y p e s a r e u s u a l l y d i a g n o s e d o n a n
E C G
( e l e c t r o c a r d i o g r a m
)
t r a c e .
H e a r t
b l o c k
w
i t h
n o
s y m
p t o m
s
m a y
n o t
r e q u i r e
a n y
t r e a t m
e n t .
H e a r t
b l o c k
c a u s i n g s y m p t o m s i s u s u a l l y t r e a t e d b y
f i t t i n g a p e r m a n e n t a r t i f i c i a l
p a c e m a k e r
.
D r u g s t o i n c r e a s e t h e h e a r t r a t e a n d t h e
s t r e n g t h o f t h e h e a r t ’s c o n t r a c t i o n s m a y
b e
g i v e n
t e m p o r a r i l y .
A n y
u n d e r l y i n g
h e a r t d i s e a s e i s t r e a t e d a s n e c e s s a r y .
heartburn
A
b u r n i n g
p a i n
i n
t h e
c e n t r e
o f t h e
c h e s t , w h i c h m a y t r a v e l f r o m t h e t i p o f
t h e b r e a s t b o n e t o t h e t h r o a t . H e a r t b u r n
i s o f t e n b r o u g h t o n b y l y i n g d o w n o r
b e n d i n g f o r w a r d s . I t m a y b e c a u s e d b y
e a t i n g r i c h o r s p i c y f o o d , o r b y d r i n k -
i n g
a l c o h o l .
R e c u r r e n t
h e a r t b u r n
i s
a
s y m p t o m o f
o e s o p h a g i t i s
( i n f l a m m a t i o n
o f t h e
o e s o p h a g u s ) ,
w h i c h
i s
u s u a l l y
c a u s e d b y
a c i d r e f l u x
.
heart disease, congenital
A
t e r m
t h a t
i s
u s e d
t o
d e s c r i b e
a n y
a b n o r m a l i t y o f t h e
h e a r t
t h a t i s p r e s e n t
f r o m
b i r t h .
C o n g e n i t a l
d e f e c t s
( s e e
T y p e s o f c o n g e n i t a l
h e a r t d i s e a s e
b o x ,
o v e r l e a f )
m a y
a f f e c t
d i f f e r e n t
p a r t s ,
i n c l u d i n g t h e c h a m b e r s ,
v a l v e s
,
o r m a i n
b l o o d v e s s e l s o f t h e h e a r t .
H
367
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