<s>
Bradycardia	B-Algorithm
(	O
also	O
sinus	B-Algorithm
bradycardia	I-Algorithm
)	O
is	O
a	O
slow	O
resting	O
heart	O
rate	O
,	O
commonly	O
under	O
60	O
beats	O
per	O
minute	O
(	O
BPM	O
)	O
as	O
determined	O
by	O
an	O
electrocardiogram	B-Application
.	O
</s>
<s>
In	O
some	O
people	O
,	O
bradycardia	B-Algorithm
below	O
60	O
BPM	O
may	O
be	O
associated	O
with	O
fatigue	O
,	O
weakness	O
,	O
dizziness	O
,	O
sweating	O
,	O
and	O
fainting	O
.	O
</s>
<s>
The	O
term	O
"	O
relative	O
bradycardia	B-Algorithm
"	O
is	O
used	O
to	O
refer	O
to	O
a	O
heart	O
rate	O
slower	O
than	O
an	O
individual	O
's	O
typical	O
resting	O
heart	O
rate	O
.	O
</s>
<s>
Athletes	O
may	O
have	O
athletic	O
heart	O
syndrome	O
,	O
which	O
includes	O
bradycardia	B-Algorithm
as	O
part	O
of	O
the	O
cardiovascular	O
adaptations	O
to	O
training	O
and	O
participation	O
.	O
</s>
<s>
The	O
word	O
"	O
bradycardia	B-Algorithm
"	O
is	O
from	O
the	O
Greek	O
βραδύς	O
bradys	O
"	O
slow	O
"	O
,	O
and	O
καρδία	O
kardia	O
"	O
heart	O
"	O
.	O
</s>
<s>
Atrial	O
bradycardias	B-Algorithm
are	O
divided	O
into	O
three	O
types	O
.	O
</s>
<s>
The	O
first	O
,	O
respiratory	O
sinus	O
arrhythmia	B-Application
,	O
is	O
usually	O
found	O
in	O
young	O
and	O
healthy	O
adults	O
.	O
</s>
<s>
Sinus	B-Algorithm
bradycardia	I-Algorithm
is	O
a	O
sinus	O
rhythm	O
of	O
less	O
than	O
60BPM	O
.	O
</s>
<s>
Studies	O
have	O
found	O
that	O
50	O
–	O
85%	O
of	O
conditioned	O
athletes	O
have	O
benign	O
sinus	B-Algorithm
bradycardia	I-Algorithm
,	O
as	O
compared	O
to	O
23%	O
of	O
the	O
general	O
population	O
studied	O
.	O
</s>
<s>
The	O
third	O
,	O
sick	B-Algorithm
sinus	I-Algorithm
syndrome	I-Algorithm
,	O
covers	O
conditions	O
that	O
include	O
severe	O
sinus	B-Algorithm
bradycardia	I-Algorithm
,	O
sinoatrial	B-Algorithm
block	I-Algorithm
,	O
sinus	B-Algorithm
arrest	I-Algorithm
,	O
and	O
bradycardia-tachycardia	B-Algorithm
syndrome	I-Algorithm
(	O
atrial	B-Application
fibrillation	I-Application
,	O
atrial	O
flutter	O
,	O
and	O
paroxysmal	B-Algorithm
supraventricular	I-Algorithm
tachycardia	I-Algorithm
)	O
.	O
</s>
<s>
An	O
AV-junctional	B-Algorithm
rhythm	I-Algorithm
,	O
or	O
atrioventricular	B-Algorithm
nodal	I-Algorithm
bradycardia	I-Algorithm
,	O
is	O
usually	O
caused	O
by	O
the	O
absence	O
of	O
the	O
electrical	O
impulse	O
from	O
the	O
sinus	O
node	O
.	O
</s>
<s>
This	O
usually	O
appears	O
on	O
an	O
electrocardiogram	B-Application
(	O
ECG	B-Application
)	O
with	O
a	O
normal	O
QRS	B-Algorithm
complex	I-Algorithm
accompanied	O
with	O
an	O
inverted	O
P	B-Algorithm
wave	I-Algorithm
either	O
before	O
,	O
during	O
,	O
or	O
after	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
.	O
</s>
<s>
An	O
AV-junctional	O
escape	O
beat	O
is	O
a	O
delayed	O
heartbeat	O
originating	O
from	O
an	O
ectopic	B-Algorithm
focus	O
somewhere	O
in	O
the	O
AV	O
junction	O
.	O
</s>
<s>
This	O
dysrhythmia	B-Application
also	O
may	O
occur	O
when	O
the	O
electrical	O
impulses	O
from	O
the	O
SA	O
node	O
fail	O
to	O
reach	O
the	O
AV	O
node	O
because	O
of	O
SA	O
or	O
AV	B-Algorithm
block	I-Algorithm
.	O
</s>
<s>
This	O
is	O
a	O
protective	O
mechanism	O
for	O
the	O
heart	O
,	O
to	O
compensate	O
for	O
an	O
SA	O
node	O
that	O
is	O
no	O
longer	O
handling	O
the	O
pacemaking	O
activity	O
and	O
is	O
one	O
of	O
a	O
series	O
of	O
backup	O
sites	O
that	O
can	O
take	O
over	O
pacemaker	B-Device
function	O
when	O
the	O
SA	O
node	O
fails	O
to	O
do	O
so	O
.	O
</s>
<s>
This	O
would	O
present	O
with	O
a	O
longer	O
PR	B-Algorithm
interval	I-Algorithm
.	O
</s>
<s>
Pathological	O
causes	O
include	O
sinus	B-Algorithm
bradycardia	I-Algorithm
,	O
sinus	B-Algorithm
arrest	I-Algorithm
,	O
sinus	O
exit	O
block	O
,	O
or	O
AV	B-Algorithm
block	I-Algorithm
.	O
</s>
<s>
Idioventricular	B-Algorithm
rhythm	I-Algorithm
,	O
also	O
known	O
as	O
atrioventricular	B-Algorithm
bradycardia	I-Algorithm
or	O
ventricular	B-Algorithm
escape	I-Algorithm
rhythm	I-Algorithm
,	O
is	O
a	O
heart	O
rate	O
of	O
less	O
than	O
50	O
BPM	O
.	O
</s>
<s>
Impulses	O
originating	O
within	O
or	O
below	O
the	O
bundle	B-Algorithm
of	I-Algorithm
His	I-Algorithm
in	O
the	O
AV	O
node	O
will	O
produce	O
a	O
wide	O
QRS	B-Algorithm
complex	I-Algorithm
with	O
heart	O
rates	O
between	O
20	O
and	O
40	O
BPM	O
.	O
</s>
<s>
Those	O
above	O
the	O
bundle	B-Algorithm
of	I-Algorithm
His	I-Algorithm
,	O
also	O
known	O
as	O
junctional	O
,	O
will	O
typically	O
range	O
between	O
40	O
and	O
60	O
BPM	O
with	O
a	O
narrow	O
QRS	B-Algorithm
complex	I-Algorithm
.	O
</s>
<s>
In	O
a	O
third-degree	B-Architecture
heart	I-Architecture
block	I-Architecture
,	O
about	O
61%	O
take	O
place	O
at	O
the	O
bundle	O
branch-Purkinje	O
system	O
,	O
21%	O
at	O
the	O
AV	O
node	O
,	O
and	O
15%	O
at	O
the	O
bundle	B-Algorithm
of	I-Algorithm
His	I-Algorithm
.	O
</s>
<s>
AV	B-Algorithm
block	I-Algorithm
may	O
be	O
ruled	O
out	O
with	O
an	O
ECG	B-Application
indicating	O
"	O
a	O
1:1	O
relationship	O
between	O
P	B-Algorithm
waves	I-Algorithm
and	O
QRS	O
complexes.	O
"	O
</s>
<s>
Ventricular	O
bradycardias	B-Algorithm
occurs	O
with	O
sinus	B-Algorithm
bradycardia	I-Algorithm
,	O
sinus	B-Algorithm
arrest	I-Algorithm
,	O
and	O
AV	B-Algorithm
block	I-Algorithm
.	O
</s>
<s>
Treatment	O
often	O
consists	O
of	O
the	O
administration	O
of	O
atropine	O
and	O
cardiac	B-Device
pacing	I-Device
.	O
</s>
<s>
For	O
infants	O
,	O
bradycardia	B-Algorithm
is	O
defined	O
as	O
a	O
heart	O
rate	O
less	O
than	O
100BPM	O
(	O
normal	O
is	O
around	O
120	O
–	O
160	O
BPM	O
)	O
.	O
</s>
<s>
Premature	O
babies	O
are	O
more	O
likely	O
than	O
full-term	O
babies	O
to	O
have	O
apnea	O
and	O
bradycardia	B-Algorithm
spells	O
;	O
their	O
cause	O
is	O
not	O
clearly	O
understood	O
.	O
</s>
<s>
Medications	O
(	O
theophylline	O
or	O
caffeine	B-Application
)	O
can	O
be	O
used	O
to	O
treat	O
these	O
spells	O
in	O
babies	O
if	O
necessary	O
.	O
</s>
<s>
Bradycardia	B-Algorithm
arrhythmia	B-Application
may	O
have	O
many	O
causes	O
,	O
both	O
cardiac	O
and	O
non-cardiac	O
.	O
</s>
<s>
Ultimately	O
,	O
the	O
causes	O
act	O
by	O
three	O
mechanisms	O
:	O
depressed	O
automaticity	O
of	O
the	O
heart	O
,	O
conduction	O
block	O
,	O
or	O
escape	O
pacemakers	B-Device
and	O
rhythms	O
.	O
</s>
<s>
In	O
general	O
,	O
two	O
types	O
of	O
problems	O
result	O
in	O
bradycardias	B-Algorithm
:	O
disorders	O
of	O
the	O
SA	O
node	O
,	O
and	O
disorders	O
of	O
the	O
AV	O
node	O
.	O
</s>
<s>
With	O
SA	O
node	O
dysfunction	O
(	O
sometimes	O
called	O
sick	B-Algorithm
sinus	I-Algorithm
syndrome	I-Algorithm
)	O
,	O
there	O
may	O
be	O
disordered	O
automaticity	O
or	O
impaired	O
conduction	O
of	O
the	O
impulse	O
from	O
the	O
SA	O
node	O
into	O
the	O
surrounding	O
atrial	O
tissue	O
(	O
an	O
"	O
exit	O
block	O
"	O
)	O
.	O
</s>
<s>
Second-degree	O
sinoatrial	B-Algorithm
blocks	I-Algorithm
can	O
be	O
detected	O
only	O
by	O
use	O
of	O
a	O
12-lead	B-Application
ECG	I-Application
.	O
</s>
<s>
It	O
is	O
difficult	O
and	O
sometimes	O
impossible	O
to	O
assign	O
a	O
mechanism	O
to	O
any	O
particular	O
bradycardia	B-Algorithm
,	O
but	O
the	O
underlying	O
mechanism	O
is	O
not	O
clinically	O
relevant	O
to	O
treatment	O
,	O
which	O
is	O
the	O
same	O
in	O
both	O
cases	O
of	O
sick	B-Algorithm
sinus	I-Algorithm
syndrome	I-Algorithm
:	O
a	O
permanent	B-Device
pacemaker	I-Device
.	O
</s>
<s>
AV	O
conduction	O
disturbances	O
(	O
AV	B-Algorithm
block	I-Algorithm
;	O
primary	B-Algorithm
AV	I-Algorithm
block	I-Algorithm
,	O
secondary	B-Algorithm
type	I-Algorithm
I	I-Algorithm
AV	I-Algorithm
block	I-Algorithm
,	O
secondary	B-Algorithm
type	I-Algorithm
II	I-Algorithm
AV	I-Algorithm
block	I-Algorithm
,	O
tertiary	B-Architecture
AV	I-Architecture
block	I-Architecture
)	O
may	O
result	O
from	O
impaired	O
conduction	O
in	O
the	O
AV	O
node	O
,	O
or	O
anywhere	O
below	O
it	O
,	O
such	O
as	O
in	O
the	O
bundle	B-Algorithm
of	I-Algorithm
His	I-Algorithm
.	O
</s>
<s>
The	O
clinical	O
relevance	O
pertaining	O
to	O
AV	B-Algorithm
blocks	I-Algorithm
is	O
greater	O
than	O
that	O
of	O
SA	B-Algorithm
blocks	I-Algorithm
.	O
</s>
<s>
Bradycardia	B-Algorithm
is	O
also	O
part	O
of	O
the	O
mammalian	O
diving	O
reflex	O
.	O
</s>
<s>
A	O
diagnosis	O
of	O
bradycardia	B-Algorithm
in	O
adults	O
is	O
based	O
on	O
a	O
heart	O
rate	O
less	O
than	O
60	O
BPM	O
,	O
although	O
some	O
studies	O
use	O
a	O
heart	O
rate	O
of	O
less	O
than	O
50	O
BPM	O
.	O
</s>
<s>
This	O
is	O
determined	O
usually	O
either	O
by	O
palpation	O
or	O
ECG	B-Application
.	O
</s>
<s>
The	O
treatment	O
of	O
bradycardia	B-Algorithm
is	O
dependent	O
on	O
whether	O
or	O
not	O
the	O
person	O
is	O
stable	O
or	O
unstable	O
.	O
</s>
<s>
If	O
this	O
is	O
not	O
effective	O
,	O
intravenous	O
inotrope	O
infusion	O
(	O
dopamine	O
,	O
epinephrine	O
)	O
or	O
transcutaneous	B-Algorithm
pacing	I-Algorithm
should	O
be	O
used	O
.	O
</s>
<s>
Transvenous	B-Algorithm
pacing	I-Algorithm
may	O
be	O
required	O
if	O
the	O
cause	O
of	O
the	O
bradycardia	B-Algorithm
is	O
not	O
rapidly	O
reversible	O
.	O
</s>
<s>
In	O
clinical	O
practice	O
,	O
elderly	O
people	O
over	O
age	O
65	O
and	O
young	O
athletes	O
of	O
both	O
sexes	O
may	O
have	O
sinus	B-Algorithm
bradycardia	I-Algorithm
.	O
</s>
<s>
The	O
US	O
Centers	O
for	O
Disease	O
Control	O
and	O
Prevention	O
reported	O
in	O
2011	O
that	O
15.2	O
%	O
of	O
adult	O
males	O
and	O
6.9	O
%	O
of	O
adult	O
females	O
had	O
clinically-defined	O
bradycardia	B-Algorithm
(	O
a	O
resting	O
pulse	O
rate	O
below	O
60	O
BPM	O
)	O
.	O
</s>
