<s>
Pacemaker	B-Algorithm
syndrome	I-Algorithm
is	O
a	O
condition	O
that	O
represents	O
the	O
clinical	O
consequences	O
of	O
suboptimal	O
atrioventricular	O
(	O
AV	O
)	O
synchrony	O
or	O
AV	B-Algorithm
dyssynchrony	I-Algorithm
,	O
regardless	O
of	O
the	O
pacing	O
mode	O
,	O
after	O
pacemaker	B-Device
implantation	O
.	O
</s>
<s>
Individuals	O
with	O
a	O
low	O
heart	O
rate	O
prior	O
to	O
pacemaker	B-Device
implantation	O
are	O
more	O
at	O
risk	O
of	O
developing	O
pacemaker	B-Algorithm
syndrome	I-Algorithm
.	O
</s>
<s>
Patients	O
who	O
develop	O
pacemaker	B-Algorithm
syndrome	I-Algorithm
may	O
require	O
adjustment	O
of	O
the	O
pacemaker	B-Device
,	O
or	O
fitting	O
of	O
another	O
lead	O
to	O
better	O
coordinate	O
the	O
timing	O
of	O
atrial	O
and	O
ventricular	O
contraction	O
.	O
</s>
<s>
No	O
specific	O
set	O
of	O
criteria	O
has	O
been	O
developed	O
for	O
diagnosis	O
of	O
pacemaker	B-Algorithm
syndrome	I-Algorithm
.	O
</s>
<s>
Most	O
of	O
the	O
signs	O
and	O
symptoms	O
of	O
pacemaker	B-Algorithm
syndrome	I-Algorithm
are	O
nonspecific	O
,	O
and	O
many	O
are	O
prevalent	O
in	O
the	O
elderly	O
population	O
at	O
baseline	O
.	O
</s>
<s>
In	O
the	O
lab	O
,	O
pacemaker	B-Device
interrogation	O
plays	O
a	O
crucial	O
role	O
in	O
determining	O
if	O
the	O
pacemaker	B-Device
mode	O
had	O
any	O
contribution	O
to	O
symptoms	O
.	O
</s>
<s>
Vital	O
signs	O
may	O
reveal	O
hypotension	O
,	O
tachycardia	B-Application
,	O
tachypnea	O
,	O
or	O
low	O
oxygen	O
saturation	O
.	O
</s>
<s>
Studies	O
have	O
shown	O
that	O
patients	O
with	O
Pacemaker	B-Algorithm
syndrome	I-Algorithm
and/or	O
with	O
sick	B-Algorithm
sinus	I-Algorithm
syndrome	I-Algorithm
are	O
at	O
higher	O
risk	O
of	O
developing	O
fatal	O
complications	O
that	O
calls	O
for	O
the	O
patients	O
to	O
be	O
carefully	O
monitored	O
in	O
the	O
ICU	O
.	O
</s>
<s>
Complications	O
include	O
atrial	B-Application
fibrillation	I-Application
,	O
thrombo-embolic	O
events	O
,	O
and	O
heart	O
failure	O
.	O
</s>
<s>
However	O
several	O
risk	O
factors	O
are	O
associated	O
with	O
pacemaker	B-Algorithm
syndrome	I-Algorithm
.	O
</s>
<s>
In	O
postimplantation	O
,	O
an	O
increased	O
percentage	O
of	O
ventricular	O
paced	O
beats	O
is	O
the	O
only	O
variable	O
that	O
significantly	O
predicts	O
development	O
of	O
pacemaker	B-Algorithm
syndrome	I-Algorithm
.	O
</s>
<s>
Patients	O
with	O
intact	O
VA	O
conduction	O
are	O
at	O
greater	O
risk	O
for	O
developing	O
pacemaker	B-Algorithm
syndrome	I-Algorithm
.	O
</s>
<s>
Around	O
90%	O
of	O
patients	O
with	O
preserved	O
AV	O
conduction	O
have	O
intact	O
VA	O
conduction	O
,	O
and	O
about	O
30-40	O
%	O
of	O
patients	O
with	O
complete	O
AV	B-Algorithm
block	I-Algorithm
have	O
preserved	O
VA	O
conduction	O
.	O
</s>
<s>
Intact	O
VA	O
conduction	O
may	O
not	O
be	O
apparent	O
at	O
the	O
time	O
of	O
pacemaker	B-Device
implantation	O
or	O
even	O
may	O
develop	O
at	O
any	O
time	O
after	O
implantation	O
.	O
</s>
<s>
Other	O
factors	O
correlated	O
with	O
development	O
of	O
pacemaker	B-Algorithm
syndrome	I-Algorithm
include	O
decreased	O
stroke	O
volume	O
,	O
decreased	O
cardiac	O
output	O
,	O
and	O
decreased	O
left	O
atrial	O
total	O
emptying	O
fraction	O
associated	O
with	O
ventricular	B-Device
pacing	I-Device
.	O
</s>
<s>
The	O
loss	O
of	O
physiologic	O
timing	O
of	O
atrial	O
and	O
ventricular	O
contractions	O
,	O
or	O
sometimes	O
called	O
AV	B-Algorithm
dyssynchrony	I-Algorithm
,	O
leads	O
to	O
different	O
mechanisms	O
of	O
symptoms	O
production	O
.	O
</s>
<s>
Ventricular	B-Device
pacing	I-Device
is	O
associated	O
with	O
elevated	O
right	O
and	O
left	O
atrial	O
pressures	O
,	O
as	O
well	O
as	O
elevated	O
pulmonary	O
venous	O
and	O
pulmonary	O
arterial	O
pressures	O
,	O
which	O
can	O
lead	O
to	O
symptomatic	O
pulmonary	O
and	O
hepatic	O
congestion	O
.	O
</s>
<s>
Patients	O
with	O
pacemaker	B-Algorithm
syndrome	I-Algorithm
exhibit	O
increased	O
plasma	O
levels	O
of	O
ANP	O
.	O
</s>
<s>
A	O
major	O
cause	O
of	O
AV	B-Algorithm
dyssynchrony	I-Algorithm
is	O
VA	O
conduction	O
.	O
</s>
<s>
Nevertheless	O
,	O
many	O
conditions	O
other	O
than	O
VA	O
conduction	O
promote	O
AV	B-Algorithm
dyssynchrony	I-Algorithm
.	O
</s>
<s>
At	O
the	O
time	O
of	O
pacemaker	B-Device
implantation	O
,	O
AV	O
synchrony	O
should	O
be	O
optimized	O
to	O
prevent	O
the	O
occurrence	O
of	O
pacemaker	B-Algorithm
syndrome	I-Algorithm
.	O
</s>
<s>
Where	O
patients	O
with	O
optimized	O
AV	O
synchrony	O
have	O
shown	O
great	O
results	O
of	O
implantation	O
and	O
very	O
low	O
incidence	O
of	O
pacemaker	B-Algorithm
syndrome	I-Algorithm
than	O
those	O
with	O
suboptimal	O
AV	O
synchronization	O
.	O
</s>
<s>
Diet	O
alone	O
cannot	O
treat	O
pacemaker	B-Algorithm
syndrome	I-Algorithm
,	O
but	O
an	O
appropriate	O
diet	O
to	O
the	O
patient	O
,	O
in	O
addition	O
to	O
the	O
other	O
treatment	O
regimens	O
mentioned	O
,	O
can	O
improve	O
the	O
patient	O
's	O
symptoms	O
.	O
</s>
<s>
No	O
specific	O
drugs	O
are	O
used	O
to	O
treat	O
pacemaker	B-Algorithm
syndrome	I-Algorithm
directly	O
because	O
treatment	O
consists	O
of	O
upgrading	O
or	O
reprogramming	O
the	O
pacemaker	B-Device
.	O
</s>
<s>
In	O
patients	O
with	O
other	O
pacing	O
modes	O
,	O
other	O
than	O
ventricular	B-Device
pacing	I-Device
,	O
symptoms	O
usually	O
resolve	O
after	O
adjusting	O
and	O
reprogramming	O
of	O
pacemaker	B-Device
parameters	O
,	O
such	O
as	O
tuning	O
the	O
AV	O
delay	O
,	O
changing	O
the	O
postventricular	O
atrial	O
refractory	O
period	O
,	O
the	O
sensing	O
level	O
,	O
and	O
pacing	O
threshold	O
voltage	O
.	O
</s>
<s>
Hysteresis	O
reduces	O
the	O
amount	O
of	O
time	O
spent	O
in	O
pacing	O
mode	O
,	O
which	O
can	O
relieve	O
symptoms	O
,	O
particularly	O
when	O
the	O
pacing	O
mode	O
is	O
generating	O
AV	B-Algorithm
dyssynchrony	I-Algorithm
.	O
</s>
<s>
If	O
symptoms	O
persist	O
after	O
all	O
these	O
treatment	O
modalities	O
,	O
replacing	O
the	O
pacemaker	B-Device
itself	O
is	O
sometimes	O
beneficial	O
and	O
can	O
alleviate	O
symptoms	O
.	O
</s>
<s>
Possible	O
complications	O
include	O
heart	O
failure	O
,	O
hypotension	O
,	O
tachycardia	B-Application
,	O
tachypnea	O
,	O
and	O
oxygenation	O
deficit	O
.	O
</s>
<s>
After	O
consulting	O
an	O
electrophysiologist	B-Application
,	O
possibly	O
an	O
additional	O
pacemaker	B-Device
lead	O
placement	O
is	O
needed	O
,	O
which	O
eventually	O
relieve	O
some	O
of	O
the	O
symptoms	O
.	O
</s>
<s>
The	O
reported	O
incidence	O
of	O
pacemaker	B-Algorithm
syndrome	I-Algorithm
has	O
ranged	O
from	O
2%	O
to	O
83%	O
.	O
</s>
<s>
The	O
wide	O
range	O
of	O
reported	O
incidence	O
is	O
likely	O
attributable	O
to	O
two	O
factors	O
which	O
are	O
the	O
criteria	O
used	O
to	O
define	O
pacemaker	B-Algorithm
syndrome	I-Algorithm
and	O
the	O
therapy	O
used	O
to	O
resolve	O
that	O
diagnosis	O
.	O
</s>
<s>
Pacemaker	B-Algorithm
syndrome	I-Algorithm
was	O
first	O
described	O
in	O
1969	O
by	O
Mitsui	O
et	O
al	O
.	O
</s>
<s>
as	O
a	O
collection	O
of	O
symptoms	O
associated	O
with	O
right	O
ventricular	B-Device
pacing	I-Device
.	O
</s>
<s>
The	O
name	O
pacemaker	B-Algorithm
syndrome	I-Algorithm
was	O
first	O
coined	O
by	O
Erbel	O
in	O
1979	O
.	O
</s>
<s>
Since	O
its	O
first	O
discovery	O
,	O
there	O
have	O
been	O
many	O
definitions	O
of	O
pacemaker	B-Algorithm
syndrome	I-Algorithm
,	O
and	O
the	O
understanding	O
of	O
the	O
cause	O
of	O
pacemaker	B-Algorithm
syndrome	I-Algorithm
is	O
still	O
under	O
investigation	O
.	O
</s>
<s>
In	O
a	O
general	O
sense	O
,	O
pacemaker	B-Algorithm
syndrome	I-Algorithm
can	O
be	O
defined	O
as	O
the	O
symptoms	O
associated	O
with	O
right	O
ventricular	B-Device
pacing	I-Device
relieved	O
with	O
the	O
return	O
of	O
A-V	O
and	O
V-V	O
synchrony	O
.	O
</s>
