Irregular wide complex tachycardia –> Afib in the setting of WPW
AHA suggested the use of amiodarone to convert the rhythm.
- Other drugs to consider are procainamide and sotalol.
Now the question arises: does amiodarone really work?
- Most Afib with WPW will be unstable. So shock will be used to convert the rhythm. And with the small number of patients with WPW presenting with Afib, it is hard to do a RCT comparing the use of amiodarone vs other anti-arrhythmic drug.
- Most of the evidence are derived from case control studies.
From these case reports:
- Amiodarone infusion leads to more rapid ventricular rate and Vfib.
- Case reports using procainamide are also little (with 2 unknown outcomes). But at least in these very little cases procainamide did not seem to lead to deterioration into ventricular rate.
Why did amiodarone cause more rapid ventricular rate?
- Amiodarone, besides being K+ channel blocker, also blocks Ca2+ channel in AV node. This may lead to preferential anterograde conduction of impulses down the AP.
– AV node and SA node have a similar action potential curve.
– By blocking Ca2+ channel, the conduction through AV node is slowed.
– AP has more chance to conduct the impulses now.
– Note, although SA node could be suppressed as well, impulses from Afib originate from multiple ectopic foci !
- Procainamide is a pure Na+ channel blocker.
– SA node and AV node do not have sodium channels (well, funny current channels conduct sodium ions but are not blocked by sodium channel blockers)
– By prolonging the depolarization (phase 0) in Purkinje fibers, it leads to lower HR.
- Amiodarone should not be used in WPW with Afib.
- It’s not easy to have procainamide in ED. Electrical cardioversion should be the way to go for these patients.
- Marius A. Tijunelis, MD; Mel E. Herbert, MD. Myth: Intravenous amiodarone is safe in patients with atrial fibrillation and Wolff–Parkinson–White syndrome in the emergency department. Can J Emerg Med 2005;7(4):262-5
- Sharis M. Simonian, Shahram Lotfipour, Christopher Wall, Mark I. Langdorf. Challenging the superiority of amiodarone for rate control in Wolff-Parkinson-White and atrial fibrillation. Intern Emerg Med (2010) 5:421–426