What are the differences between sinus Wolff‑Parkinson‑White (WPW) and antidromic Wolff‑Parkinson‑White (WPW)?

Sinus WPW vs. Antidromic WPW: Key Differences

Sinus WPW refers to the baseline ECG pattern during normal sinus rhythm showing ventricular pre-excitation (delta wave, short PR interval, wide QRS), while antidromic WPW is a specific type of reentrant tachycardia where the accessory pathway conducts anterogradely from atrium to ventricle and the AV node conducts retrogradely, producing a wide QRS tachycardia. 1

Sinus WPW (Pre-excitation Pattern)

Electrical Pathway and ECG Features:

• During sinus rhythm, the accessory pathway conducts anterogradely in parallel with the AV node, creating fusion between pre-excited ventricular activation and normal AV nodal conduction 1
• The ECG demonstrates three characteristic features: (1) PR interval <120 ms, (2) delta wave (slurring of initial QRS upstroke), and (3) widened QRS complex >120 ms 1, 2
• The degree of pre-excitation varies based on the relative contribution of conduction through the accessory pathway versus the AV node 3
• This represents a manifest accessory pathway that conducts anterogradely, affecting the resting ECG 1

Clinical Context:

• Occurs in 0.1% to 0.3% of the general population 1
• May be asymptomatic (isolated pre-excitation) or symptomatic (WPW syndrome when associated with documented arrhythmias) 1
• The pattern itself is not a tachycardia—it is the baseline ECG appearance during normal sinus rhythm 3

Antidromic AVRT (Antidromic WPW)

Electrical Pathway and Mechanism:

• This is a reentrant tachycardia where the circuit uses the accessory pathway for anterograde conduction (atrium to ventricle) and the AV node for retrograde conduction (ventricle to atrium) 1
• Rarely, a second accessory pathway may serve as the retrograde limb instead of the AV node, termed "pre-excited AVRT" 1
• The reentrant circuit requires both the accessory pathway and the AV node (or second pathway) to sustain the tachycardia 1

ECG Characteristics During Tachycardia:

• Produces a wide QRS complex tachycardia with maximal pre-excitation because ventricular activation occurs entirely through the accessory pathway 1
• The QRS morphology differs from sinus WPW because there is no fusion with normal AV nodal conduction—all ventricular activation is via the accessory pathway 3
• Can be difficult to distinguish from ventricular tachycardia on surface ECG due to the wide QRS morphology 4

Clinical Significance:

• Accounts for only 5% to 10% of tachycardia episodes in patients with manifest accessory pathways, making it much less common than orthodromic AVRT (which accounts for 90-95% of episodes) 1, 4
• Left lateral pathways are more frequently associated with antidromic AVRT, while septal locations are less common 4
• Clinically documented in less than 5% of WPW patients and inducible in less than 10% during electrophysiology studies 4

Critical Distinction for Clinical Management

Why This Matters:

• Sinus WPW is a baseline ECG finding that may or may not cause symptoms; management focuses on risk stratification for sudden cardiac death based on accessory pathway properties 1
• Antidromic AVRT is an active tachyarrhythmia requiring acute termination and consideration for definitive catheter ablation 1

Acute Management Differs:

• For antidromic AVRT in hemodynamically unstable patients, immediate synchronized cardioversion is indicated (Class I) 1
• For stable antidromic AVRT, intravenous procainamide or ibutilide is recommended as first-line pharmacologic therapy 1, 5
• AV nodal blocking agents (adenosine, beta-blockers, calcium channel blockers, digoxin) are absolutely contraindicated in antidromic AVRT and pre-excited atrial fibrillation because they can precipitate ventricular fibrillation by blocking the AV node while allowing unopposed rapid conduction through the accessory pathway 1, 5

Common Pitfall:

• Clinicians may confuse the wide QRS complex of antidromic AVRT with ventricular tachycardia, potentially leading to inappropriate treatment decisions 4
• The term "antidromic WPW" is sometimes incorrectly used to describe any wide QRS tachycardia in a WPW patient, but it specifically refers to this reentrant mechanism using the accessory pathway anterogradely 1