Title: Identifying Wolff-Parkinson-White in the Absence of Pre-excitation on Electrocardiogram
Case Report Body
Introduction: Wolff-Parkinson-White (WPW) is a syndrome characterized by ventricular pre-excitation via an accessory pathway between the atrium and the ventricle. Classically, a delta-wave on a baseline electrocardiogram (ECG) can assist with identifying the syndrome. However, under certain circumstances this delta wave is less prominent and various pharmacologic interventions may assist in the diagnosis of WPW.
Description: A 21-year-old male with no past medical history presented with palpitations. Vital signs revealed tachycardia with heart rates that would intermittently accelerate to greater than 200 BPM. Blood pressure was within normal limits. ECG demonstrated a wide complex monomorphic tachycardia. Family history was notable for a history of WPW in his brother. Given this family history, he received two separate boluses of IV procainamide 100mg and was then started on a continuous infusion. His rate and rhythm had no response to procainamide. Then, with defibrillator pads in place, he received a 12mg IV bolus of adenosine, which also did not alter his rate or rhythm. Patient subsequently underwent direct current cardioversion with successful restoration of sinus rhythm. Post-cardioversion ECG had no evidence of delta wave or ventricular pre-excitation. Low dose beta blockade was then initiated to suppress a presumed left sided ventricular tachycardia. One day later follow-up ECG now had evidence of small delta waves in leads V3 and V4. To confirm the presence of an accessory pathway, the patient again had defibrillator pads placed and was then challenged with 12mg of IV Adenosine while in sinus rhythm and undergoing continuous ECG monitoring. This confirmed the presence of a prominent delta wave. Patient then underwent electrophysiology study and radiofrequency ablation of a left free wall accessory tract.
Discussion: Left lateral accessory tracts may be electrically silent on ECG under baseline physiologic conditions due to the distance of these tracts from the SA node. This increases the likelihood that the AV node will have more rapid conduction than the accessory tract resulting in the lack of a delta wave on ECG. With close ICU level monitoring, patients may undergo challenge with AV nodal blocking agents to confirm the presence of a pre-excitation tract.