A 32-year-old man presents with palpitations that had started suddenly while he was playing and running after his son. He said he had Wolff-Parkinson-White syndrome with an ablation about four years before. He said he had no chest pain, trouble breathing, syncope or near-syncope, or other complaints except that he was hungry.
His vital signs were normal except for a pulse of 128 bpm, as was his physical exam except for a regularly irregular tachycardia. There are no rales and no peripheral edema.
The initial differential diagnosis was atrial fibrillation, atrial flutter, and sinus tachycardia with premature beats.
His CBC, troponin, magnesium, and BMP were all normal, and his ECG is shown.
The ECG shows atrial fibrillation with a rapid ventricular response. The next step should be to call cardiology and keep him NPO for now. You want to consider cardioversion, and start with procainamide if you use drugs.
Wolff-Parkinson-White syndrome is caused by an abnormal myoelectrical tract in the heart that bypasses the AV node and its built-in delay. It typically presents clinically as recurrent episodes of tachycardia, most commonly with a narrow complex, but may also be picked up incidentally on ECGs performed for other indications. WPW rarely presents as a wide complex tachycardia, which can be deadly, especially if improperly treated with any agents that block the AV node.
The baseline ECG in an asymptomatic patient will show a short PR in all leads and a delta wave in at least one lead. The delta wave is a slurred beginning to the R-wave. A symptomatic patient may have one of a variety of findings, usually causing a tachycardia. Orthodromic conduction of atrial dysrhythmias occurs in 70 percent of cases, and manifests as other narrow complex tachycardias, such as SVT, atrial flutter, and atrial fibrillation, and is indistinguishable from their non-WPW counterparts. They should be treated the same as patients with and without WPW.
Antidromic conduction occurs in 30 percent of cases and results in wide-complex tachycardias that can look bizarre because some beats use the bypass tract and others the AV node. They can be fast enough that they appear regular and therefore can be mistaken for ventricular tachycardia or torsades de pointes. These tachydysrhythmias are best treated with cardioversion because any medications that can block the AV node can lead to all of the beats going down the bypass tract, which can sustain rates approaching 300 bpm, which can prove fatal. If medication is tried, one should use procainamide, which does not block the AV node.
Definitive treatment of WPW is with cardiac electro-ablation performed by an electrophysiologist in the cath lab.
The patient was successfully cardioverted at 120 joules using etomidate for sedation. A post-cardioversion ECG showed a computer read of a short PR interval at 100 milliseconds but without a delta wave. The measured PR interval was closer to 120 milliseconds, which is actually normal.
Excerpt on Wolff-Parkinson-White from The Emergency Medicine 1-Minute Consult Pocketbook:
Source: The Tarascon Emergency Department Quick Reference Guide