A History of Palpitations and Dizziness

ANSWER
This ECG is diagnostic for Wolff-Parkinson-White (WPW) syndrome. Criteria for WPW syndrome include a normal P wave with a PR interval generally (but not always) of 0.12 sec (120 ms) or greater, initial slurring of the QRS (delta wave), a wide QRS interval > 0.10 sec (100 ms), and secondary ST/T wave changes.

In WPW syndrome, one (or multiple) accessory pathway between the atria and ventricles allows conduction impulses to bypass the atrioventricular node and activate the ventricles prematurely. This premature ventricular activation is responsible for the initial slurring of the QRS complex and produces the characteristic delta wave. The presence of an accessory pathway allows a reentrant tachycardia circuit to occur and is the source of this patient’s palpitations. Subsequent electrophysiology studies identified a single left lateral accessory pathway.