This weeks ECG puts the Scary in Sunday Scaries…
Wide complex tachycardias rightfully scare most residents (and probably a fellow or two as well). Hopefully this post lets you focus on the ‘proven otherwise’ part of “VT until proven otherwise”.
ECG pattern: A fib with pre-excitation, aka an accessory pathway linking atria to ventricle outside the AV node leads to depolarization of the ventricle via myocyte to myocyte conductance rather than via the purkinje system. The accessory pathway and AV node are bombarded with impulses from the atria leading to an irregular pattern with frequent QRS morphology changes.
a fib occurs in ~20% of WPW patients
Rates tend to be >200 (as opposed to a fib with aberrancy which are still slowed through the AV node)
tend to be younger patients
delta waves will NOT be present while conducting down the accessory pathway, look at EKG at baseline (aka when conducting down AV node) to find WPW triad of short PR, delta wave, and widened QRS
how to differential from VT
QRS changes in morphology/shape
NO concordance in the precordial leads
Axis remains normal (as opposed to NW axis in VT)
A-flutter with pre-excitation can be more difficult to differentiate, as it often will be at a regular interval
do NOT give AV nodal blockade agents (BB, CCB, adenosine) as this exacerbates the problem (further blocks AV nodal conduction and promotes accessory pathway use)
this INCLUDES Amiodarone.
Procainamide/ ibutilide (same dose for both)
100 mg every 5 minutes until arrhythmia is controlled, hypotension occurs, QRS complex widens by 50% of its original width, or total of 17 mg/kg is given
Maintenance infusion: 1 to 4 mg/minute
Notably a fib with pre-excitation is a high risk rhythm for devolving into VT or VF, prompt treatment should be pursued.
A nice review of WPW as a whole with small part on pre-excitation
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