The correct answer is 1, procainamide, since patients with atrial fibrillation secondary to WPW should not be treated with atrioventricular (AV) nodal blockers.
In the hearts of patients with WPW, there is an accessory pathway (known as the Bundle of Kent) that conducts depolarization directly from the atria to the ventricles, bypassing the AV node (Illustration A). This pathophysiology explains why AV nodal blockers should be avoided in WPW patients. AV nodal blockers (e.g. beta blockers, calcium channel blockers) only increase conduction across the accessory pathway, which can degenerate into lethal rhythms (e.g. ventricular fibrillation).
As Colucci et al. explain, once a diagnosis of WPW is suspected, urgent referral to a cardiologist is necessary. This is not only because the arrhythmia can be dangerous, but also because cardiac ablation is a potentially curative option.
WPW is frequently diagnosed based on an EKG. A key finding is the delta wave, a slurred upstroke in the QRS complex that results in a shortened PR interval (see illustration B). However, as Katoh et al. note, these classic findings are not always apparent, and further diagnostic workup may be necessary.
Illustration A shows the accessory pathway in WPW. Illustration B shows the key EKG findings in WPW.
Answers 2-5: These drugs all block the AV node in some capacity and, therefore, are contraindicated in WPW.
Colucci RA1, Silver MJ, Shubrook J. Common types of supraventricular tachycardia: diagnosis and management. Am Fam Physician. 2010 Oct 15;82(8):942-52.
PMID:20949888 (Link to Abstract)
Katoh T, Ohara T, Kim EM, Hayakawa H. Non-invasive diagnosis of concealed Wolff-Parkinson-White syndrome by detection of concealed anterograde pre-excitation. Jpn Circ J. 2001;65(5):367–370.
PMID:11348037 (Link to Abstract)
USMLE World Step 2 QBank Question #3069. Copyright © USMLEWorld, LLC 2012