EM Vivas · Peri-arrest arrhythmias
The irregular broad-complex tachycardia — the WPW trap
A clinical viva on the irregular broad-complex tachycardia of pre-excited atrial fibrillation and the avoidance of the AV-nodal blocker trap.
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The irregularly irregular broad-complex tachycardia with varying QRS morphology is the signature of atrial fibrillation conducting down an accessory pathway — pre-excited AF in WPW — until proven otherwise. ANZCOR 11.9 also lists AF with bundle-branch block and polymorphic VT in this differential; seek expert help.[1]
The trap is the AV-nodal blocker. If pre-excited AF (or flutter) is suspected, avoid adenosine, digoxin, verapamil and diltiazem. These block the AV node and cause a relative increase in pre-excitation. Electrical cardioversion is usually the safest treatment option. ANZCOR allows that amiodarone may be considered for haemodynamically stable AF over an accessory pathway (Class C) — that is not permission to give an AV-nodal blocker. Pads stay on because the rhythm can degenerate; if it becomes pulseless VT/VF, defibrillate (ANZCOR default 200 J biphasic is a Guideline 11.4 arrest figure, not a cardioversion recipe).[1][2]
Do not quote flecainide or procainamide as the ANZCOR 11.9 treatment of pre-excited AF.[1]