<s>
Sinus	B-Algorithm
node	I-Algorithm
dysfunction	I-Algorithm
(	O
SND	O
)	O
,	O
also	O
known	O
as	O
sick	B-Algorithm
sinus	I-Algorithm
syndrome	I-Algorithm
(	O
SSS	O
)	O
,	O
is	O
a	O
group	O
of	O
abnormal	B-Application
heart	I-Application
rhythms	I-Application
(	O
arrhythmias	B-Application
)	O
usually	O
caused	O
by	O
a	O
malfunction	O
of	O
the	O
sinus	O
node	O
,	O
the	O
heart	O
's	O
primary	O
pacemaker	B-Device
.	O
</s>
<s>
Tachycardia-bradycardia	O
syndrome	O
is	O
a	O
variant	O
of	O
sick	B-Algorithm
sinus	I-Algorithm
syndrome	I-Algorithm
in	O
which	O
the	O
arrhythmia	B-Application
alternates	O
between	O
fast	O
and	O
slow	B-Algorithm
heart	I-Algorithm
rates	I-Algorithm
.	O
</s>
<s>
Often	O
sinus	B-Algorithm
node	I-Algorithm
dysfunction	I-Algorithm
produces	O
no	O
symptoms	O
,	O
especially	O
early	O
in	O
the	O
disease	O
course	O
.	O
</s>
<s>
Signs	O
and	O
symptoms	O
usually	O
appear	O
in	O
more	O
advanced	O
disease	O
and	O
more	O
than	O
50%	O
of	O
patients	O
will	O
present	O
with	O
syncope	O
or	O
transient	O
near-fainting	O
spells	O
as	O
well	O
as	O
bradycardias	B-Algorithm
that	O
are	O
accompanied	O
by	O
rapid	O
heart	O
rhythms	O
,	O
referred	O
to	O
as	O
tachycardia-bradycardia	O
syndrome	O
Other	O
presenting	O
signs	O
or	O
symptoms	O
can	O
include	O
confusion	O
,	O
fatigue	O
,	O
palpitations	B-Algorithm
,	O
chest	O
pain	O
,	O
shortness	O
of	O
breath	O
,	O
headache	O
,	O
and	O
nausea	O
.	O
</s>
<s>
The	O
most	O
common	O
complication	O
of	O
sinus	B-Algorithm
node	I-Algorithm
dysfunction	I-Algorithm
is	O
the	O
development	O
of	O
tachycardia-bradycardia	O
syndrome	O
with	O
abnormal	O
atrial	O
rhythms	O
such	O
as	O
atrial	B-Algorithm
tachycardia	I-Algorithm
,	O
atrial	B-Application
fibrillation	I-Application
,	O
and	O
flutter	O
.	O
</s>
<s>
Developing	O
sinus	B-Algorithm
arrest	I-Algorithm
,	O
sinus	B-Algorithm
node	I-Algorithm
exit	I-Algorithm
block	I-Algorithm
,	O
sinus	B-Algorithm
bradycardia	I-Algorithm
,	O
atrioventricular	B-Algorithm
block	I-Algorithm
,	O
and	O
other	O
types	O
of	O
abnormal	O
rhythms	O
are	O
also	O
common	O
complications	O
.	O
</s>
<s>
Sinus	B-Algorithm
node	I-Algorithm
dysfunction	I-Algorithm
has	O
a	O
close	O
association	O
with	O
the	O
presence	O
of	O
atrial	B-Application
fibrillation	I-Application
due	O
to	O
their	O
shared	O
etiology	O
of	O
remodeling	O
.	O
</s>
<s>
Sinus	B-Algorithm
node	I-Algorithm
dysfunction	I-Algorithm
can	O
be	O
caused	O
by	O
intrinsic	O
and	O
extrinsic	O
factors	O
that	O
affect	O
the	O
normal	O
functioning	O
of	O
the	O
sinus	O
node	O
.	O
</s>
<s>
Intrinsic	O
causes	O
can	O
include	O
degeneration	O
,	O
dysfunction	O
,	O
or	O
remodeling	O
of	O
the	O
sinus	O
node	O
while	O
extrinsic	O
causes	O
can	O
create	O
or	O
worsen	O
underlying	O
atrial	O
arrhythmias	B-Application
.	O
</s>
<s>
Intrinsic	O
causes	O
tend	O
to	O
be	O
responsible	O
for	O
permanent	O
sinus	B-Algorithm
node	I-Algorithm
dysfunction	I-Algorithm
while	O
extrinsic	O
causes	O
are	O
more	O
commonly	O
temporary	O
.	O
</s>
<s>
Other	O
intrinsic	O
causes	O
include	O
inherited	O
ion	O
channel	O
dysfunctions	O
,	O
remodeling	O
diseases	O
such	O
as	O
heart	O
failure	O
and	O
atrial	B-Application
fibrillation	I-Application
,	O
infiltrative	O
diseases	O
such	O
as	O
sarcoidosis	O
,	O
amyloidosis	O
,	O
hemochromatosis	O
,	O
and	O
connective	O
tissue	O
diseases	O
,	O
inflammatory	O
etiology	O
such	O
as	O
rheumatic	O
fever	O
,	O
Chagas	O
disease	O
,	O
and	O
Lyme	O
disease	O
,	O
as	O
well	O
as	O
atherosclerotic	O
and	O
ischemic	O
changes	O
to	O
the	O
sinus	O
node	O
artery	O
.	O
</s>
<s>
Inherited	O
sinus	B-Algorithm
node	I-Algorithm
dysfunction	I-Algorithm
has	O
been	O
associated	O
with	O
mutations	O
of	O
the	O
gene	O
responsible	O
for	O
the	O
formation	O
of	O
the	O
alpha	O
subunit	O
of	O
the	O
sodium	O
channel	O
(	O
SCN5A	O
)	O
.	O
</s>
<s>
Common	O
cardiac	O
pharmacology	O
such	O
as	O
beta-blockers	O
,	O
calcium	O
channel	O
blockers	O
,	O
digoxin	O
,	O
sympatholytic	O
medication	O
,	O
and	O
other	O
antiarrhythmics	O
can	O
alter	O
sinus	O
node	O
function	O
to	O
create	O
an	O
arrhythmia	B-Application
such	O
as	O
sick	B-Algorithm
sinus	I-Algorithm
syndrome	I-Algorithm
.	O
</s>
<s>
Hypothyroidism	O
,	O
hypoxia	O
,	O
hypothermia	O
,	O
and	O
various	O
toxins	O
have	O
also	O
been	O
associated	O
with	O
sinus	B-Algorithm
node	I-Algorithm
dysfunctions	I-Algorithm
.	O
</s>
<s>
The	O
primary	O
12-lead	O
electrocardiogram	B-Application
(	O
ECG	B-Application
)	O
finding	O
in	O
sinus	B-Algorithm
node	I-Algorithm
dysfunction	I-Algorithm
is	O
inappropriate	O
sinus	B-Algorithm
bradycardia	I-Algorithm
.	O
</s>
<s>
Sinus	B-Algorithm
node	I-Algorithm
dysfunction	I-Algorithm
can	O
also	O
present	O
with	O
sudden	O
sinus	B-Algorithm
arrest	I-Algorithm
with	O
or	O
without	O
junctional	B-Algorithm
escape	I-Algorithm
,	O
sinoatrial	B-Algorithm
block	I-Algorithm
,	O
prolonged	O
asystolic	O
period	O
followed	O
by	O
tachycardias	O
,	O
or	O
tachycardia-bradycardia	O
syndrome	O
presenting	O
as	O
various	O
atrial	O
arrhythmias	B-Application
such	O
as	O
atrial	B-Application
fibrillation	I-Application
,	O
flutter	O
,	O
tachycardia	B-Algorithm
,	O
or	O
paroxysmal	B-Algorithm
supraventricular	I-Algorithm
tachycardia	I-Algorithm
.	O
</s>
<s>
Diagnosing	O
sinus	B-Algorithm
node	I-Algorithm
dysfunction	I-Algorithm
requires	O
clinical	O
symptoms	O
as	O
well	O
as	O
ECG	B-Application
abnormalities	O
.	O
</s>
<s>
If	O
ECG	B-Application
findings	O
cannot	O
be	O
identified	O
,	O
prolonged	O
cardiac	O
monitoring	O
should	O
be	O
pursued	O
either	O
with	O
a	O
Holter	O
monitor	O
in	O
an	O
outpatient	O
setting	O
or	O
telemetry	O
while	O
inpatient	O
,	O
due	O
to	O
the	O
transient	O
nature	O
of	O
abnormal	O
ECG	B-Application
findings	O
.	O
</s>
<s>
If	O
Holter	O
or	O
telemetry	O
monitoring	O
fails	O
to	O
identify	O
ECG	B-Application
changes	O
and	O
suspicion	O
of	O
sinus	B-Algorithm
node	I-Algorithm
dysfunction	I-Algorithm
remains	O
high	O
due	O
to	O
severe	O
symptoms	O
or	O
episodes	O
of	O
syncope	O
,	O
implantable	O
loop	O
recorders	O
should	O
be	O
considered	O
for	O
extended	O
monitoring	O
up	O
to	O
24	O
months	O
.	O
</s>
<s>
Exercise	O
stress	O
tests	O
can	O
be	O
utilized	O
to	O
identify	O
intrinsic	O
causes	O
of	O
sinus	B-Algorithm
node	I-Algorithm
dysfunction	I-Algorithm
.	O
</s>
<s>
Tilt	O
table	O
tests	O
can	O
be	O
used	O
to	O
discriminate	O
bradycardia	B-Algorithm
caused	O
by	O
dysfunction	O
of	O
the	O
autonomic	O
nervous	O
system	O
.	O
</s>
<s>
Pacemaker	B-Device
implantation	O
is	O
the	O
primary	O
treatment	O
modality	O
of	O
symptomatic	O
sinus	B-Algorithm
node	I-Algorithm
dysfunction	I-Algorithm
.	O
</s>
<s>
The	O
goal	O
of	O
this	O
treatment	O
modality	O
is	O
to	O
relieve	O
symptoms	O
associated	O
with	O
sinus	B-Algorithm
node	I-Algorithm
dysfunction	I-Algorithm
and	O
improve	O
quality	O
of	O
life	O
.	O
</s>
<s>
Dual	O
chamber	O
pacemakers	B-Device
are	O
preferred	O
due	O
to	O
the	O
possibility	O
of	O
developing	O
atrioventricular	B-Algorithm
block	I-Algorithm
as	O
well	O
as	O
long	O
term	O
cost-effectiveness	O
relative	O
to	O
single-chamber	O
atrial	O
pacemakers	B-Device
.	O
</s>
<s>
In	O
tachycardia-bradycardia	O
syndrome	O
,	O
medication-based	O
management	O
can	O
treat	O
atrial	O
tachyarrhythmias	O
.	O
</s>
<s>
However	O
,	O
these	O
medications	O
may	O
exacerbate	O
underlying	O
bradyarrhythmia	B-Algorithm
.	O
</s>
<s>
Therefore	O
,	O
a	O
dual-chamber	O
pacemaker	B-Device
capable	O
of	O
managing	O
atrial	O
tachyarrhythmias	O
as	O
well	O
as	O
bradyarrhythmias	B-Algorithm
is	O
implanted	O
before	O
drug	O
therapy	O
is	O
begun	O
.	O
</s>
<s>
Overall	O
incidence	O
of	O
sinus	B-Algorithm
node	I-Algorithm
dysfunction	I-Algorithm
increases	O
with	O
age	O
with	O
1	O
in	O
1000	O
in	O
adults	O
over	O
45	O
years	O
old	O
and	O
1	O
in	O
600	O
cardiac	O
patients	O
over	O
65	O
years	O
old	O
.	O
</s>
<s>
Sinus	B-Algorithm
node	I-Algorithm
dysfunction	I-Algorithm
is	O
the	O
primary	O
indication	O
for	O
approximately	O
30%	O
-50	O
%	O
of	O
all	O
pacemaker	B-Device
implantation	O
in	O
the	O
United	O
States	O
.	O
</s>
<s>
Sinus	B-Algorithm
node	I-Algorithm
dysfunction	I-Algorithm
is	O
a	O
relatively	O
uncommon	O
syndrome	O
in	O
the	O
young	O
and	O
middle-aged	O
population	O
.	O
</s>
