## Most Common Site of Accessory Pathway in WPW Syndrome **Key Point:** The left lateral wall (left free wall) is the most common location for accessory pathways in Wolff–Parkinson–White (WPW) syndrome, accounting for approximately 40–50% of all cases. ### Anatomical Distribution of Accessory Pathways in WPW | Location | Frequency (%) | Anatomical Region | ECG Delta Wave Polarity | |----------|---------------|-------------------|------------------------| | **Left lateral** | 40–50 | Between LA and LV (free wall) | Negative in V1–V2, positive in II, III, aVF | | Right anteroseptal | 20–25 | Between RA and RV (near AV node) | Positive in V1–V2, negative in inferior leads | | Posterior (right posteroseptal) | 15–20 | Between RA and RV (posterior) | Biphasic or negative in V1–V2 | | Anteroseptal (left) | 5–10 | Between LA and LV (septal) | Variable | **High-Yield:** Left lateral pathway is the most common site — this is a high-yield fact for NEET PG exams. ### Mechanism of ECG Changes in WPW 1. **Shortened PR interval:** The accessory pathway bypasses the AV node, allowing faster conduction from atrium to ventricle 2. **Delta wave:** The initial slurred upstroke of the QRS complex represents early ventricular depolarization via the accessory pathway 3. **Wide QRS:** Fusion of conduction through both the AV node and the accessory pathway produces a wider QRS complex ### Clinical Pearl The **location of the delta wave** on the 12-lead ECG can help localize the accessory pathway: - **Left lateral:** Negative delta in V1–V2, positive in inferior leads - **Right anteroseptal:** Positive delta in V1–V2, negative in inferior leads - **Posteroseptal:** Biphasic or isoelectric delta in V1–V2 ### Mnemonic **LRAP** — **L**eft lateral (most common), **R**ight anteroseptal, **A**nteroseptal, **P**osteroseptal — in rough order of decreasing frequency.
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.