<s>
Lown	B-Algorithm
–	I-Algorithm
Ganong	I-Algorithm
–	I-Algorithm
Levine	I-Algorithm
syndrome	I-Algorithm
(	O
LGL	O
)	O
is	O
a	O
pre-excitation	O
syndrome	O
of	O
the	O
heart	O
.	O
</s>
<s>
Those	O
with	O
LGL	B-Algorithm
syndrome	I-Algorithm
have	O
episodes	O
of	O
abnormal	O
heart	O
racing	O
with	O
a	O
short	B-Algorithm
PR	I-Algorithm
interval	O
and	O
normal	O
QRS	B-Algorithm
complexes	I-Algorithm
seen	O
on	O
their	O
electrocardiogram	B-Application
when	O
in	O
a	O
normal	O
sinus	O
rhythm	O
.	O
</s>
<s>
LGL	B-Algorithm
syndrome	I-Algorithm
was	O
originally	O
thought	O
to	O
be	O
due	O
to	O
an	O
abnormal	B-Algorithm
electrical	I-Algorithm
connection	I-Algorithm
between	O
the	O
atria	O
and	O
the	O
ventricles	O
,	O
but	O
is	O
now	O
thought	O
to	O
be	O
due	O
to	O
accelerated	O
conduction	B-Algorithm
through	O
the	O
atrioventricular	B-Algorithm
node	O
in	O
the	O
majority	O
of	O
cases	O
.	O
</s>
<s>
LGL	B-Algorithm
syndrome	I-Algorithm
was	O
originally	O
thought	O
to	O
involve	O
a	O
rapidly	O
conducting	O
accessory	B-Algorithm
pathway	I-Algorithm
(	O
bundle	O
of	O
James	O
)	O
that	O
connects	O
the	O
atria	O
directly	O
to	O
the	O
bundle	B-Algorithm
of	I-Algorithm
His	I-Algorithm
,	O
bypassing	O
the	O
slowly	O
conducting	O
atrioventricular	B-Algorithm
node	O
.	O
</s>
<s>
However	O
,	O
the	O
majority	O
of	O
those	O
with	O
LGL	O
in	O
whom	O
electrophysiological	B-Algorithm
studies	I-Algorithm
have	O
been	O
performed	O
do	O
not	O
have	O
any	O
evidence	O
of	O
an	O
accessory	B-Algorithm
pathway	I-Algorithm
or	O
structural	O
abnormality	O
.	O
</s>
<s>
Whilst	O
in	O
a	O
minority	O
of	O
cases	O
some	O
form	O
of	O
intranodal	O
or	O
paranodal	O
fibers	O
that	O
bypass	O
all	O
or	O
part	O
of	O
the	O
atrioventricular	B-Algorithm
node	O
can	O
be	O
found	O
with	O
subsequent	O
conduction	B-Algorithm
down	O
the	O
normal	O
His-Purkinje	B-Algorithm
system	I-Algorithm
,	O
in	O
most	O
cases	O
the	O
short	B-Algorithm
PR	I-Algorithm
interval	O
is	O
caused	O
by	O
accelerated	O
conduction	B-Algorithm
through	O
the	O
atrioventricular	B-Algorithm
node	O
.	O
</s>
<s>
LGL	B-Algorithm
syndrome	I-Algorithm
is	O
therefore	O
felt	O
to	O
represent	O
a	O
clinical	O
syndrome	O
with	O
multiple	O
different	O
underlying	O
causes	O
.	O
</s>
<s>
LGL	B-Algorithm
syndrome	I-Algorithm
is	O
diagnosed	O
in	O
a	O
person	O
who	O
has	O
experienced	O
episodes	O
of	O
abnormal	O
heart	O
racing	O
(	O
arrhythmias	O
)	O
who	O
has	O
a	O
PR	B-Algorithm
interval	I-Algorithm
less	O
than	O
or	O
equal	O
to	O
0.12	O
second	O
(	O
120	O
ms	O
)	O
with	O
normal	O
QRS	B-Algorithm
complex	I-Algorithm
configuration	O
and	O
duration	O
on	O
their	O
resting	O
ECG	B-Application
.	O
</s>
<s>
A	O
short	B-Algorithm
PR	I-Algorithm
interval	O
found	O
incidentally	O
on	O
an	O
ECG	B-Application
without	O
episodes	O
of	O
tachycardia	O
is	O
simply	O
a	O
benign	O
ECG	B-Application
variant	O
.	O
</s>
<s>
LGL	O
can	O
be	O
distinguished	O
from	O
WPW	O
syndrome	O
because	O
the	O
delta	O
waves	O
seen	O
in	O
WPW	O
syndrome	O
are	O
not	O
seen	O
in	O
LGL	B-Algorithm
syndrome	I-Algorithm
.	O
</s>
<s>
The	O
QRS	B-Algorithm
complex	I-Algorithm
is	O
often	O
normal	O
but	O
can	O
also	O
be	O
narrow	O
in	O
LGL	B-Algorithm
syndrome	I-Algorithm
,	O
as	O
opposed	O
to	O
WPW	O
,	O
because	O
ventricular	O
conduction	B-Algorithm
is	O
via	O
the	O
His-Purkinje	B-Algorithm
system	I-Algorithm
.	O
</s>
<s>
Lown	B-Algorithm
–	I-Algorithm
Ganong	I-Algorithm
–	I-Algorithm
Levine	I-Algorithm
syndrome	I-Algorithm
is	O
a	O
clinical	O
diagnosis	O
that	O
came	O
about	O
before	O
the	O
advent	O
of	O
electrophysiology	B-Algorithm
studies	I-Algorithm
.	O
</s>
<s>
It	O
is	O
important	O
to	O
be	O
aware	O
that	O
not	O
all	O
WPW	O
ECGs	B-Application
have	O
a	O
delta	O
wave	O
;	O
the	O
absence	O
of	O
a	O
delta	O
wave	O
does	O
not	O
conclusively	O
rule	O
out	O
WPW	O
.	O
</s>
<s>
Individuals	O
with	O
LGL	B-Algorithm
syndrome	I-Algorithm
do	O
not	O
carry	O
an	O
increased	O
risk	O
of	O
sudden	O
death	O
.	O
</s>
<s>
The	O
only	O
morbidity	O
associated	O
with	O
the	O
syndrome	O
is	O
the	O
occurrence	O
of	O
paroxysmal	O
episodes	O
of	O
tachycardia	O
which	O
may	O
be	O
of	O
several	O
types	O
,	O
including	O
sinus	B-Algorithm
tachycardia	I-Algorithm
,	O
atrioventricular	B-Algorithm
nodal	I-Algorithm
re-entrant	I-Algorithm
tachycardia	I-Algorithm
,	O
atrial	B-Application
fibrillation	I-Application
,	O
or	O
atrial	O
flutter	O
.	O
</s>
