<s>
Atrioventricular	B-Algorithm
block	I-Algorithm
(	O
AV	B-Algorithm
block	I-Algorithm
)	O
is	O
a	O
type	O
of	O
heart	B-Algorithm
block	I-Algorithm
that	O
occurs	O
when	O
the	O
electrical	O
signal	O
traveling	O
from	O
the	O
atria	O
,	O
or	O
the	O
upper	O
chambers	O
of	O
the	O
heart	O
,	O
to	O
ventricles	O
,	O
or	O
the	O
lower	O
chambers	O
of	O
the	O
heart	O
,	O
is	O
impaired	O
.	O
</s>
<s>
In	O
an	O
AV	B-Algorithm
block	I-Algorithm
,	O
this	O
electrical	O
signal	O
is	O
either	O
delayed	O
or	O
completely	O
blocked	O
.	O
</s>
<s>
Some	O
AV	B-Algorithm
blocks	I-Algorithm
are	O
benign	O
,	O
or	O
normal	O
,	O
in	O
certain	O
people	O
,	O
such	O
as	O
in	O
athletes	O
or	O
children	O
.	O
</s>
<s>
There	O
are	O
three	O
types	O
,	O
or	O
degrees	O
,	O
of	O
AV	B-Algorithm
block	I-Algorithm
:	O
(	O
1	O
)	O
first-degree	O
,	O
(	O
2	O
)	O
second-degree	O
,	O
and	O
(	O
3	O
)	O
third-degree	O
,	O
with	O
third-degree	O
being	O
the	O
most	O
severe	O
.	O
</s>
<s>
An	O
ECG	B-Application
is	O
used	O
to	O
differentiate	O
between	O
the	O
different	O
types	O
of	O
AV	B-Algorithm
blocks	I-Algorithm
.	O
</s>
<s>
However	O
,	O
one	O
important	O
consideration	O
when	O
diagnosing	O
AV	B-Algorithm
blocks	I-Algorithm
from	O
ECGs	B-Application
is	O
the	O
possibility	O
of	O
pseudo	O
-	O
AV	B-Algorithm
blocks	I-Algorithm
which	O
are	O
due	O
to	O
concealed	O
junctional	O
extrasystoles	O
.	O
</s>
<s>
It	O
is	O
important	O
to	O
diagnose	O
AV-blocks	O
precisely	O
because	O
unnecessary	O
pacemaker	B-Device
placement	O
in	O
patients	O
with	O
pseudo-AV	O
blocks	O
can	O
worsen	O
symptoms	O
and	O
create	O
complications	O
.	O
</s>
<s>
First-degree	B-Algorithm
AV	I-Algorithm
block	I-Algorithm
occurs	O
when	O
there	O
is	O
a	O
delay	O
,	O
but	O
not	O
disruption	O
,	O
as	O
the	O
electrical	O
signal	O
moves	O
between	O
the	O
atrium	O
and	O
the	O
ventricles	O
through	O
the	O
AV	O
node	O
.	O
</s>
<s>
On	O
ECG	B-Application
,	O
this	O
is	O
defined	O
by	O
a	O
PR	B-Algorithm
interval	I-Algorithm
greater	O
than	O
200	O
msec	O
.	O
</s>
<s>
Second-degree	B-Algorithm
AV	I-Algorithm
block	I-Algorithm
occurs	O
when	O
the	O
electrical	O
signal	O
between	O
the	O
atria	O
and	O
ventricles	O
is	O
even	O
more	O
impaired	O
than	O
in	O
a	O
first-degree	B-Algorithm
AV	I-Algorithm
block	I-Algorithm
.	O
</s>
<s>
In	O
a	O
second-degree	B-Algorithm
AV	I-Algorithm
block	I-Algorithm
,	O
the	O
impairment	O
results	O
in	O
a	O
failure	O
to	O
conduct	O
an	O
impulse	O
,	O
which	O
causes	O
a	O
skipped	O
beat	O
.	O
</s>
<s>
Mobitz	B-Algorithm
I	I-Algorithm
is	O
characterized	O
by	O
a	O
progressive	O
yet	O
reversible	O
block	O
of	O
the	O
AV	O
node	O
.	O
</s>
<s>
On	O
ECG	B-Application
,	O
this	O
is	O
defined	O
by	O
progressive	O
prolongation	O
of	O
the	O
PR	B-Algorithm
interval	I-Algorithm
,	O
with	O
a	O
resulting	O
dropped	O
beat	O
(	O
the	O
PR	B-Algorithm
interval	I-Algorithm
gets	O
longer	O
and	O
longer	O
until	O
a	O
beat	O
is	O
finally	O
dropped	O
,	O
or	O
skipped	O
)	O
.	O
</s>
<s>
There	O
is	O
a	O
low	O
risk	O
of	O
a	O
Mobitz	B-Algorithm
I	I-Algorithm
AV	B-Algorithm
block	I-Algorithm
leading	O
to	O
heart	O
attack	O
and	O
complete	B-Architecture
heart	I-Architecture
block	I-Architecture
.	O
</s>
<s>
Mobitz	B-Algorithm
II	I-Algorithm
is	O
caused	O
by	O
a	O
sudden	O
,	O
unexpected	O
failure	O
of	O
the	O
His-Purkinje	O
cells	O
to	O
conduct	O
the	O
electrical	O
impulse	O
.	O
</s>
<s>
On	O
ECG	B-Application
,	O
the	O
PR	B-Algorithm
interval	I-Algorithm
is	O
unchanged	O
from	O
beat	O
to	O
beat	O
,	O
but	O
there	O
is	O
a	O
sudden	O
failure	O
to	O
conduct	O
the	O
signal	O
to	O
the	O
ventricles	O
,	O
and	O
resulting	O
in	O
random	O
skipped	O
beat	O
.	O
</s>
<s>
The	O
risks	O
and	O
possible	O
effects	O
of	O
Mobitz	B-Algorithm
II	I-Algorithm
are	O
much	O
more	O
severe	O
than	O
Mobitz	B-Algorithm
I	I-Algorithm
in	O
that	O
it	O
can	O
lead	O
to	O
severe	O
heart	O
attack	O
.	O
</s>
<s>
Third-degree	B-Architecture
AV	I-Architecture
block	I-Architecture
occurs	O
when	O
the	O
signal	O
between	O
the	O
atria	O
and	O
ventricles	O
is	O
completely	O
blocked	O
,	O
and	O
there	O
is	O
no	O
communication	O
between	O
the	O
two	O
.	O
</s>
<s>
On	O
ECG	B-Application
,	O
there	O
is	O
no	O
relationship	O
between	O
P	B-Algorithm
waves	I-Algorithm
and	O
QRS	B-Algorithm
complexes	I-Algorithm
,	O
meaning	O
the	O
P	B-Algorithm
waves	I-Algorithm
and	O
QRS	B-Algorithm
complexes	I-Algorithm
are	O
not	O
in	O
a	O
1:1	O
ratio	O
.	O
</s>
<s>
Third-degree	B-Architecture
AV	I-Architecture
block	I-Architecture
is	O
the	O
most	O
severe	O
of	O
the	O
AV	B-Algorithm
blocks	I-Algorithm
.	O
</s>
<s>
Persons	O
with	O
third-degree	B-Architecture
AV	I-Architecture
block	I-Architecture
need	O
emergency	O
treatment	O
including	O
but	O
not	O
limited	O
to	O
a	O
pacemaker	B-Device
.	O
</s>
<s>
There	O
are	O
many	O
causes	O
of	O
AV	B-Algorithm
block	I-Algorithm
,	O
ranging	O
from	O
a	O
normal	O
variant	O
among	O
people	O
to	O
the	O
result	O
of	O
a	O
heart	O
attack	O
.	O
</s>
<s>
First-degree	B-Algorithm
AV	I-Algorithm
block	I-Algorithm
and	O
Mobitz	B-Algorithm
I	I-Algorithm
second-degree	O
block	O
are	O
often	O
thought	O
to	O
be	O
just	O
normal	O
,	O
benign	O
,	O
conditions	O
in	O
people	O
,	O
and	O
do	O
not	O
often	O
result	O
from	O
a	O
severe	O
underlying	O
condition	O
.	O
</s>
<s>
Mobitz	B-Algorithm
II	I-Algorithm
second-degree	O
block	O
and	O
third-degree	B-Architecture
AV	I-Architecture
block	I-Architecture
are	O
not	O
normal	O
variants	O
and	O
are	O
associated	O
with	O
an	O
underlying	O
condition	O
.	O
</s>
<s>
It	O
is	O
also	O
possible	O
that	O
a	O
high	O
degree	O
block	O
can	O
result	O
after	O
cardiac	O
surgery	O
during	O
which	O
the	O
surgeon	O
was	O
in	O
close	O
proximity	O
to	O
the	O
electrical	O
conduction	B-Algorithm
system	I-Algorithm
and	O
accidentally	O
injured	O
it	O
.	O
</s>
<s>
Reversible	O
causes	O
of	O
Mobitz	B-Algorithm
II	I-Algorithm
and	O
third-degree	B-Architecture
heart	I-Architecture
block	I-Architecture
include	O
untreated	O
Lyme	O
disease	O
,	O
hypothyroidism	O
,	O
hyperkalemia	O
(	O
high	O
levels	O
of	O
potassium	O
)	O
,	O
and	O
drug	O
toxicity	O
.	O
</s>
<s>
Drugs	O
that	O
slow	O
the	O
conduction	B-Algorithm
of	O
the	O
electrical	O
signal	O
through	O
AV	O
node	O
,	O
such	O
as	O
beta-blockers	O
,	O
digoxin	O
,	O
calcium	O
channel	O
blockers	O
,	O
and	O
amiodarone	O
,	O
can	O
cause	O
heart	B-Algorithm
block	I-Algorithm
if	O
they	O
are	O
taken	O
in	O
excessive	O
amounts	O
,	O
or	O
the	O
levels	O
in	O
the	O
blood	O
get	O
too	O
high	O
.	O
</s>
<s>
The	O
synchronized	O
contraction	O
of	O
the	O
heart	O
occurs	O
through	O
a	O
well-coordinated	O
electrical	B-Algorithm
signal	I-Algorithm
pathway	I-Algorithm
.	O
</s>
<s>
This	O
simultaneous	O
contraction	O
results	O
in	O
the	O
P	B-Algorithm
wave	I-Algorithm
seen	O
in	O
an	O
ECG	B-Application
tracing	O
.	O
</s>
<s>
This	O
delay	O
accounts	O
for	O
the	O
ECG	B-Application
period	O
between	O
the	O
P	B-Algorithm
wave	I-Algorithm
and	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
,	O
and	O
creates	O
the	O
PR	B-Algorithm
interval	I-Algorithm
.	O
</s>
<s>
From	O
the	O
AV	O
nodes	O
,	O
the	O
electrical	O
signal	O
travels	O
through	O
Bundle	B-Algorithm
of	I-Algorithm
His	I-Algorithm
and	O
divides	O
into	O
the	O
right	O
bundle	O
and	O
left	O
bundle	O
,	O
which	O
are	O
located	O
within	O
the	O
interventricular	O
septum	O
.	O
</s>
<s>
Finally	O
,	O
the	O
electrical	O
signal	O
travels	O
into	O
the	O
Purkinje	B-Algorithm
fibers	I-Algorithm
.	O
</s>
<s>
The	O
division	O
of	O
the	O
signal	O
into	O
a	O
right	O
and	O
left	O
bundle	O
and	O
then	O
into	O
the	O
Purkinje	B-Algorithm
fibers	I-Algorithm
allows	O
for	O
a	O
simultaneous	O
depolarization	O
and	O
contraction	O
of	O
the	O
right	O
and	O
left	O
ventricles	O
.	O
</s>
<s>
The	O
contraction	O
of	O
the	O
ventricles	O
results	O
in	O
the	O
QRS	B-Algorithm
complex	I-Algorithm
seen	O
on	O
an	O
ECG	B-Application
tracing	O
.	O
</s>
<s>
The	O
repolarization	O
creates	O
the	O
T	B-Algorithm
wave	I-Algorithm
in	O
the	O
ECG	B-Application
tracing	O
.	O
</s>
<s>
An	O
electrocardiogram	B-Application
,	O
or	O
ECG	B-Application
,	O
is	O
used	O
to	O
differentiate	O
between	O
the	O
different	O
types	O
of	O
AV	B-Algorithm
block	I-Algorithm
.	O
</s>
<s>
In	O
AV	B-Algorithm
block	I-Algorithm
,	O
there	O
is	O
a	O
disruption	O
between	O
the	O
signal	O
traveling	O
from	O
the	O
atria	O
to	O
the	O
ventricles	O
.	O
</s>
<s>
This	O
results	O
in	O
abnormalities	O
in	O
the	O
PR	B-Algorithm
interval	I-Algorithm
,	O
as	O
well	O
as	O
the	O
relationship	O
between	O
P	B-Algorithm
waves	I-Algorithm
and	O
QRS	B-Algorithm
complexes	I-Algorithm
on	O
the	O
ECG	B-Application
tracing	O
.	O
</s>
<s>
If	O
the	O
patient	O
is	O
symptomatic	O
from	O
their	O
suspected	O
AV	B-Algorithm
block	I-Algorithm
,	O
it	O
is	O
important	O
that	O
an	O
ECG	B-Application
is	O
also	O
obtained	O
while	O
having	O
symptoms	O
.	O
</s>
<s>
Physicians	O
may	O
also	O
order	O
a	O
continuous	O
ECG	B-Application
(	O
i.e.	O
</s>
<s>
Holter	O
monitor	O
or	O
implanted	O
cardiac	O
monitor	O
)	O
to	O
monitor	O
the	O
patient	O
for	O
symptoms	O
and	O
conduction	B-Algorithm
abnormalities	O
over	O
a	O
longer	O
period	O
of	O
time	O
,	O
as	O
AV	B-Algorithm
blocks	I-Algorithm
can	O
be	O
intermittent	O
.	O
</s>
<s>
Because	O
some	O
types	O
of	O
AV	B-Algorithm
block	I-Algorithm
can	O
be	O
associated	O
with	O
underlying	O
structural	O
heart	O
disease	O
,	O
patients	O
may	O
also	O
undergo	O
echocardiogram	B-Application
to	O
look	O
at	O
the	O
heart	O
and	O
assess	O
the	O
function	O
.	O
</s>
<s>
Laboratory	O
diagnosis	O
for	O
AV	B-Algorithm
blocks	I-Algorithm
include	O
electrolyte	O
,	O
drug	O
level	O
and	O
cardiac	O
enzyme	O
level	O
tests	O
.	O
</s>
<s>
Based	O
upon	O
clinical	O
suspicion	O
,	O
the	O
physician	O
may	O
do	O
lab	O
tests	O
to	O
assess	O
for	O
reversible	O
causes	O
of	O
AV	B-Algorithm
block	I-Algorithm
,	O
such	O
as	O
hypothyroidism	O
,	O
rheumatologic	O
disorders	O
,	O
and	O
infections	O
(	O
such	O
as	O
Lyme	O
disease	O
)	O
.	O
</s>
<s>
Management	O
is	O
dependent	O
upon	O
the	O
severity	O
,	O
or	O
degree	O
,	O
of	O
the	O
blockage	O
,	O
the	O
consistency	O
of	O
symptoms	O
,	O
as	O
well	O
as	O
the	O
cause	O
of	O
the	O
AV	B-Algorithm
block	I-Algorithm
.	O
</s>
<s>
Patients	O
with	O
first-degree	B-Algorithm
AV	I-Algorithm
block	I-Algorithm
do	O
not	O
have	O
any	O
resulting	O
severe	O
or	O
life-threatening	O
symptoms	O
,	O
such	O
as	O
symptomatic	O
bradycardia	B-Algorithm
or	O
hypotension	O
,	O
and	O
,	O
thus	O
,	O
do	O
not	O
require	O
treatment	O
.	O
</s>
<s>
Similarly	O
,	O
patients	O
with	O
second-degree	B-Algorithm
Mobitz	I-Algorithm
I	I-Algorithm
AV	I-Algorithm
block	I-Algorithm
rarely	O
develop	O
life-threatening	O
symptoms	O
,	O
and	O
patients	O
who	O
are	O
asymptomatic	O
do	O
not	O
require	O
treatment	O
.	O
</s>
<s>
However	O
,	O
in	O
some	O
cases	O
,	O
patients	O
with	O
Mobitz	B-Algorithm
I	I-Algorithm
block	O
can	O
develop	O
life-threatening	O
symptoms	O
that	O
require	O
intervention	O
.	O
</s>
<s>
These	O
patients	O
often	O
respond	O
well	O
to	O
atropine	O
,	O
but	O
may	O
require	O
temporary	O
transcutaneous	B-Algorithm
pacing	I-Algorithm
or	O
transvenous	B-Algorithm
pacing	I-Algorithm
until	O
they	O
are	O
no	O
longer	O
symptomatic	O
.	O
</s>
<s>
Patients	O
with	O
second-degree	B-Algorithm
Mobitz	I-Algorithm
II	I-Algorithm
and	O
third-degree	B-Architecture
heart	I-Architecture
block	I-Architecture
are	O
much	O
more	O
likely	O
to	O
have	O
symptomatic	O
bradycardia	B-Algorithm
and	O
hemodynamic	O
instability	O
,	O
such	O
as	O
hypotension	O
.	O
</s>
<s>
Additionally	O
,	O
there	O
is	O
an	O
increased	O
risk	O
of	O
patients	O
with	O
Mobitz	B-Algorithm
II	I-Algorithm
heart	B-Algorithm
block	I-Algorithm
developing	O
third-degree	B-Architecture
heart	I-Architecture
block	I-Architecture
.	O
</s>
<s>
Therefore	O
,	O
these	O
patients	O
often	O
require	O
temporary	B-Algorithm
pacing	I-Algorithm
with	O
transcutaneous	B-Algorithm
or	O
transvenous	B-Algorithm
pacing	I-Algorithm
wires	O
,	O
and	O
many	O
will	O
ultimately	O
require	O
a	O
permanent	O
implanted	B-Device
pacemaker	I-Device
.	O
</s>
<s>
If	O
the	O
heart	B-Algorithm
block	I-Algorithm
is	O
found	O
to	O
be	O
caused	O
by	O
a	O
reversible	O
condition	O
,	O
such	O
as	O
Lyme	O
disease	O
,	O
the	O
underlying	O
condition	O
should	O
first	O
be	O
treated	O
.	O
</s>
<s>
Often	O
,	O
this	O
will	O
lead	O
to	O
resolution	O
of	O
the	O
heart	B-Algorithm
block	I-Algorithm
and	O
the	O
associated	O
symptoms	O
.	O
</s>
