ECG Topic - Wolff Parkinson White (WPW) Pattern

Last updated August 17, 2025

Introduction

Wolff Parkinson White is a pre-excitation syndrome caused by an accessory atrioventricular pathway (the Bundle of Kent). Recognition of this ECG pattern is an important skill as it predisposes patients to tachyarrhythmias and potentially sudden cardiac death.

Classic Triad

Across all 12 leads, WPW is characterized by:

Short PR interval (<120 ms): due to atrial impulse bypassing the AV node.
Delta wave: slurred upstroke of the QRS as the ventricle is activated early through the accessory pathway.
Widened QRS: typically >120 ms, though may be narrower in subtle cases

Not every beat will manifest pre-excitation; intermittent or concealed pathways can hide the diagnosis.

Example: WPW

Source: LITFL

Electro-Pathophysiology

The Normal Pathway

Atrial impulse → AV node (delays conduction ~120 ms) → His-Purkinje → rapid, synchronized ventricular activation.
The AV node is the “gatekeeper” that both slows conduction and prevents rapid ventricular rates during atrial arrhythmias.

What Changes in WPW

An accessory pathway (the bundle of Kent) directly connects atrium to ventricle, bypassing the AV node.
This pathway is fast-conducting (like myocardium, not specialized conduction tissue) and non-decremental (doesn’t slow with faster atrial rates).
Result: Pre-excitation — ventricles get activated earlier than they should.

Adapted from LITFL

How this creates the ECG findings

Short PR	Because the impulse doesn’t pause at the AV node, the atrium quickly conducts to the ventricle, shortening the PR interval
Delta Wave	The accessory pathway activates a portion of the ventricle slowly via myocyte-to-myocyte spread (instead of the fast His-Purkinje). This creates the slurred upstroke of the QRS.
Wide Qrs	Fusion of two activation waves: Early slurred delta wave from the accessory pathway and the normal wave from AV node/His-Purkinje. Combined, this makes the QRS longer.

Types of WPW

Type A (Left-sided pathway)

Location of accessory pathway: left atria —> left ventricle
Precordial leads: Positive in V1-V6
QRS axis: Normal or rightward.
Mimic: Looks like LVH or LBBB with tall R waves across precordium.
Teaching Pearl: Easy to confuse with true LVH or LBBB; delta wave slurring is the giveaway.

Approximately 9–10% of patients with Wolff-Parkinson-White (WPW) pattern have a normal PR interval on surface ECG. This atypical presentation is most commonly associated with left lateral accessory pathways

Example: Type A WPW

Type B (Right-sided pathway)

Location of accessory pathway: right atria —> right ventricle
Precordial leads: Negative in V1 (dominant S wave).
QRS axis: Leftward or normal.
Mimic: Anterior infarct with poor R wave progression.
Teaching Pearl: The pseudo-infarct pattern in anterior leads (Q waves or absent R in V1–V3) can be mistaken for ischemia.

Example: Type B WPW

Type C (Multiple pathways)

Location of accessory pathway: posteroseptal or multiple pathways of origin
Precordial Leads: Positive in V1 and negative in V5/V6
Axis: Often extreme axis deviation.
Teaching Pearl: Rare compared to A and B, but important—can simulate bizarre intraventricular conduction delay. Often linked with multiple accessory pathways and higher arrhythmia risk.

Example: Type C WPW

Tachyarrhythmias

Epidemiology

Prevalence

WPW pattern is found in about 0.1–0.3% of the population.

Progression to SVT

Roughly 50–60% of patients with a WPW ECG pattern will develop paroxysmal tachyarrhythmias most often atrioventricular reentry tachycardia (AVRT)
Approximately 15% will develop atrial fibrillation
The remaining 40–50% may remain asymptomatic for life.

Sudden death risk (if untreated): Rare but real, estimated around 0.1x–0.6% per year in high-risk patients (younger age, multiple pathways, short anterograde accessory pathway, atrial fibrillation).

Example: Orthodromic AVRT (narrow)

Example: Antidromic AVRT (wide)