michael s
(Michael S)
#1
66 What drugs should I use for chemically
cardioverting atrial fibrillation and when is DC
cardioversion preferable?
Suzanna Hardman and Martin Cowie
Drugs are more likely to be effective when used relatively early
following the onset of atrial fibrillation. However, when a clear
history of recent onset atrial fibrillation has been obtained it is
important to establish and treat the likely precipitants. In many
instances this will allow spontaneous reversion to sinus
rhythm. Important precipitants include hypoxia, dehydration,
hypokalaemia, hypertension, thyrotoxicosis and coronary
ischaemia. Whilst these precipitants are being treated rate
control will usually be required. Short acting oral calcium
channel blockers (verapamil or diltiazem) and short acting beta
blockers titrated against the patients response are most effective
in this setting and likely to facilitate cardioversion. Intravenous
verapamil should be avoided. If a patient with new atrial
fibrillation is haemodynamically compromised urgent
cardioversion is required with full heparinisation. Similarly
patients with fast, recent onset atrial fibrillation with broad
complexes are probably best treated with early elective DC
cardioversion with full heparinisation.
With the above provisos there is a role for chemical
cardioversion. Amiodarone (which has class III action and mild
beta blocking activity) given through a large peripheral line or
centrally can be highly effective, though a rate slowing agent may
also be needed. Intravenous flecainide (class I) can also be highly
effective. Like other class I agents (quinidine, disopyramide and
procainamide), flecainide is best avoided in patients with known
or possible coronary artery disease and in conditions known to
predispose to torsade de pointes. Digoxin has no role in the
cardioversion of atrial fibrillation.
The highest likelihood of successful cardioversion in patients
with chronic atrial fibrillation is with DC cardioversion
following appropriate investigation and anticoagulation. It
should be noted that cardioversion is generally safe during
digoxin therapy, so long as potassium and digoxin levels are in
the normal range.
