Abrupt Onset Palpitations

ANSWER
The ECG reveals a short PR interval (< 120 ms), a slurred upstroke (delta wave) of the initiation of the QRS complex indicating ventricular preexcitation, a broad QRS (> 110 ms) as a result of the delta wave, and secondary ST- and T-wave changes consistent with Wolf-Parkinson-White (WPW) syndrome. The delta wave is an indicator of an electrical impulse that bypasses normal AV nodal conduction through one or more accessory pathways that allow direct antegrade conduction between the atria and ventricles.

If the delta wave is positive in lead V1, the accessory pathway is located between the left atrium and left ventricle. If the delta wave is negative in aVF, as indicated in this ECG, the accessory pathway can be further located to the lateral wall of the left atrium. This localization aids in estimating the location of the accessory pathway prior to electrophysiology study and ablation.