Algorithmic approach to tachycardias:
                =====================================
The ACLS guidelines for treatment of 'tachycaridias' that you refer to
seperate them out into the following 4 categories 1) _definite_ atrial
fib/flutter 2) _definite_ PSVT  3) _definite_ VT  and 4) wide complex tach
(WCT) of uncertain type.  Your question pertains to limb #2 of this
algorithm. Failing vagal maneuvers and adenosine, lidcoaine and procaine
are recommended for WCT that are KNOWN to be SVT.  Why is that?  Because
this covers the possibility of antidromic SVT through an accessory pathway
(WPW).  My preference in this case would actually be the opposite (i.e.,
procaine followed by lidocaine) because procaine reliably slows accessory
pathway conduction and lidocaine does so usually but not always.
Also, there have been rare reports of the precipitation of v-fib
in patients with WPW given lidocaine. Bretylium is not a consideration in
this case because it does not slow accessory pathway conduction.
Bretylium is indeed antiarrthmic and is effective for v-tach.  To suggest
that it is not used for this reason in limb #2 but IS used in the v-tach
limb would make absolutely no sense unless it WERE effective for VT.
Bretylium also appears as an option in the WCT (of uncertain origin) limb
of the algorithm because 80+% of WCT is VT and not SVT with aberrency.

In practice you will rarely know, in the ED, much less in the field, that
a WCT is definately supraventricular in origin.  For this reason, and
because of the hemodynamic consequences of guessing wrong.  You would be
wise to assume that ALL WCT is VT and treat accordingly.  For the stable
and 'semi-stable' patient with WCT it is appropriate (contrary to the
algorithm) to reverse the order of administration of lido and adenosine
(i.e., I might try adenosine first) in certian situations. Baring case
reports this drug appears to be safe, though ineffective in most cases of,
VT.

Finally there are rare situations where adenosine may terminate a true VT.
This occurs in right ventricular outflow track tachycardias.


H. Louzon MD