Chapter 12 Wolff-Parkinson-White Preexcitation Patterns
Wolff-Parkinson-White Pattern: Preexcitation and Bypass Tracts
Preexcitation of the ventricles with the classic WPW pattern produces the following characteristic triad of findings on the ECG (Figs. 12-2 to 12-4):
1. The QRS complex is widened, giving the superficial appearance of a bundle branch block pattern. However, the wide QRS is caused not by a delay in ventricular depolarization but by early stimulation of the ventricles. The T wave is also usually opposite in polarity to the wide QRS in any lead, similar to what is seen with bundle branch blocks (“secondary T wave inversions”).
2. The PR interval is shortened (often but not always to less than 0.12 sec) because of the ventricular preexcitation.
3. The upstroke of the QRS complex is slurred or notched. This is called a delta wave.