Classic Electrocardiographic Findings in Wolff-Parkinson-White Syndrome
The classic ECG findings in Wolff-Parkinson-White syndrome are: shortened PR interval (<120 ms), delta wave (slurred upstroke of the QRS complex), and widened QRS complex (>120 ms). 1
The Three Pathognomonic Features
The diagnosis of WPW syndrome relies entirely on surface ECG findings that reflect ventricular pre-excitation through an accessory pathway 1:
Short PR interval: Less than 120 ms (or <100 ms in neonates), caused by the accessory pathway bypassing the AV node and conducting the electrical impulse prematurely to the ventricles 1, 2
Delta wave: A slurred, slow upstroke at the initial portion of the QRS complex, representing early ventricular activation through the accessory pathway before normal AV nodal conduction arrives 1, 2
Widened QRS complex: Duration greater than 120 ms, resulting from fusion of two wavefronts—one through the accessory pathway and one through the normal AV node-His-Purkinje system 1, 2
Additional ECG Characteristics
Beyond the classic triad, WPW demonstrates secondary repolarization abnormalities 2:
- ST-segment and T-wave changes: These are typically discordant (directed opposite) to the major delta wave and QRS vector, reflecting abnormal ventricular depolarization 2, 3
Important Clinical Caveats
Intermittent pre-excitation is common, particularly in neonates and infants, where the WPW pattern may only be visible in mid-precordial leads depending on accessory pathway location and AV nodal conduction properties 1. A short PR interval alone without delta wave or QRS widening should not trigger further evaluation in asymptomatic athletes 1.
The most important diagnostic criterion is recognizing the delta wave—the short PR interval or broad QRS may not be present in every case 4. Some patients with WPW can have prominent septal Q waves despite manifest pre-excitation, so physicians should not dismiss the diagnosis based solely on Q wave presence 5.
Why the Other Options Are Incorrect
- Incomplete RBBB with ST elevation in V1-V3 describes Brugada pattern, not WPW 1
- LVH with deep narrow Q waves suggests hypertrophic cardiomyopathy or prior infarction 1
- Sinus tachycardia with low voltage and electrical alternans is classic for pericardial effusion with tamponade physiology
The correct answer from your options is: Shortened PR interval, delta wave, and widened QRS complex 1, 2.