A 43-year-old patient arrives to the ED complaining of palpitations. Vitals are HR 298, BP 107/74, SpO2 100% RA, RR 18. The patient is diaphoretic, uncomfortable appearing, and heart sounds are fast and irregular. You obtain an EKG which shows the following:

What’s your differential?

  • Atrial fibrillation with bundle branch block
  • Atrial fibrillation with accessory pathway (as in Wolff-Parkinson-White)
  • Polymorphic VT (as in Torsades de pointes)

Your diagnosis is atrial fibrillation with WPW!

In contrast to a fib with bundle branch block, atrial fibrillation with WPW:

  • Has a rate of 200-300 bpm
  • QRS complexes change in shape and morphology

In contrast to polymorphic VT:

  • Axis remains stable

Why is this important?

AV nodal blockers can cause for these patients to decompensate into ventricular fibrillation. AV nodal blockers include calcium channel blockers, adenosine, beta blockers, and amiodarone – most of which are common treatments for atrial fibrillation. This would allow for the selective conduction of atrial impulses through the accessory pathway which does not have a refractory period.

So now what?

If patients are stable, procainamide is a good choice for antiarrhythmic agent as it will selectively block the accessory pathway. In unstable patients, electrical cardioversion is ideal as procainamide has been shown to cause profound hypotension.

Pearl 1 - a Fib with Wpw

For more information on WPW, check out http://lifeinthefastlane.com/ecg-library/pre-excitation-syndromes/