Please note: The following ECGs have all been recorded at 25 mm/sec and gain setting of 10 mm/mVe 26.1
A 54-year-old female walks into the Emergency Department complaining of palpitations for the past hour Her ECG is shown on page 8 (Figure 1). She has no electrolyte abnormalities.
a) Describe the rhythm disturbance. (20% marks)
b) How would you treat this rhythm disturbance? (10% marks)
c) Name two anti-arrhythmic drugs that are contra-indicated for this rhythm disturbance. (20% marks)
Atrial fibrillation with an accessory pathway
AF / SVT with aberrant conduction acceptable answer.(The rapid rate precludes AF with bundle branch block so no marks should be given for AF with bundle branch block).
Electrical cardioversion (flecainide, ibutilide, propafenone acceptable).
Digoxin, calcium channel blocker, beta-blockers, amiodarone, adenosine or other agents that preferentially block AV node and not accessory pathway.
This is WPW, in AF. The conduction rate is roughly 1:1.5; the QRS rate is about 180 to 200. It is hard to tell that its irregularly irregular. The QRS complexes will be a mixture of pre-excited delta-waving ones, and normal-looking narrow ones. If the accessory pathway has a short refractory period, it will conduct more often and therefore there will be more broad complexes than narrow ones. The shorter the refractory period of the accessory pathway, the broader the QRS. And the broader the QRS, the greater the chance of this thing degenerating into ventricular fibrillation.
Management of this acute arrhythmia has several options:
Flecainide or propafenone are used in long term management. Amiodarone also OK - but the side effect profile in long term use is not very nice for younger patients.
What can we say about the safety of AV nodal blockers in WPW?
On this basis, the authorities tend to recommend the use of Class I or Class III agents instead of AV nodal blockers. The model answer to Question 3.1 from the first paper of 2009 lists procainamide and amiodarone as first-line agents, whereas digoxin and verapamil are contraindicated. Digoxin decreases the refractory period of the accessory pathway and verapimil tends to accelerate the ventricular response to AF by a similar mechanism. Since 2009, public opinion has also drifted away from amiodarone. As an acute infusion it is basically a beta-blocker with some AV nodal specificity. It is therefore the wrong drug for acute management of WPW SVT; or rather, it will probably be safe in the narrow-complex-obviously-orthodromic population, with the aforementioned caveats. In the long term, it becomes more useful, as its Class III and Class I effects begin to develop, slowing conduction down the accessory pathway.
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and, somewhat more recently...
Scheinman, Melvin M. "History of Wolff‐Parkinson‐White Syndrome." Pacing and clinical electrophysiology 28.2 (2005): 152-156.
Keating, L., F. P. Morris, and W. J. Brady. "Electrocardiographic features of Wolff-Parkinson-White syndrome." Emergency medicine journal 20.5 (2003): 491-493.