Among patients with Wolff-Parkinson-White (WPW) syndrome who develop atrioventricular reentrant tachycardia (AVRT), which is the most common anatomical location of the accessory pathway?

Explanation

## Anatomical Location of Accessory Pathways in WPW **Key Point:** The left lateral wall is the most common site for accessory pathways in WPW syndrome, accounting for 40–50% of all cases. ### Distribution of Accessory Pathways **High-Yield:** Accessory pathway locations follow a predictable anatomical distribution: | Location | Frequency | Clinical Notes | |----------|-----------|----------------| | **Left lateral** | 40–50% | Most common; includes left free wall | | **Posteroseptal** | 15–20% | Second most common; near coronary sinus | | **Right anteroseptal** | 10–15% | Third most common; near AV node | | **Right lateral** | 10–15% | Least common; right free wall | | **Anterior/anterolateral** | 5–10% | Rare | ### Anatomical Basis Accessory pathways are embryologic remnants of myocardial tissue that failed to be separated from the ventricular myocardium during development of the fibrous annulus. The distribution reflects: 1. **Embryologic development** — the left lateral wall is the last region to develop fibrous separation 2. **Anatomical vulnerability** — the left lateral wall has the largest circumference of the AV groove 3. **Frequency of congenital anomalies** — left-sided pathways are more common in the general population ### Clinical Significance of Pathway Location ```mermaid flowchart TD A[Accessory Pathway Location]:::outcome --> B{Location?}:::decision B -->|Left lateral| C[Delta wave in V1-V2 negative]:::action B -->|Posteroseptal| D[Delta wave in II, III, aVF positive]:::action B -->|Right anteroseptal| E[Delta wave in aVR positive]:::action B -->|Right lateral| F[Delta wave in V5-V6 negative]:::action C --> G[Most common AVRT mechanism]:::outcome D --> H[Risk of sudden cardiac death]:::urgent E --> I[Proximity to AV node]:::outcome ``` **Clinical Pearl:** The delta wave polarity on the 12-lead ECG can help localize the accessory pathway. A negative delta wave in V1–V2 suggests a left lateral pathway, while positive delta waves in the inferior leads (II, III, aVF) suggest a posteroseptal pathway. ### Posteroseptal Pathways and Sudden Cardiac Death **Warning:** Although posteroseptal pathways are less common (15–20%), they carry a higher risk of sudden cardiac death because they are located near the AV node and may conduct rapidly during atrial fibrillation, leading to ventricular fibrillation. Left lateral pathways, while most common, typically have slower conduction properties and lower risk of sudden death. ### Why Left Lateral Is Most Common The left lateral wall represents the largest uninterrupted segment of the mitral annulus, making it the most likely site for embryologic separation failure. Additionally, the left lateral pathway is the most frequently encountered in both symptomatic and asymptomatic WPW populations.