ECG Topic - Lown–Ganong–Levine (LGL)

Last updated 10/1/25

Introduction

Lown–Ganong–Levine (LGL) describes paroxysmal tachyarrhythmias associated with a short PR interval but normal QRS duration — historically thought to reflect an accessory pathway (James fibers) that bypasses the AV node but rejoins the Bundle of His, allowing rapid conduction without ventricular pre-excitation. Modern understanding (Chou 2018) considers LGL primarily a descriptive ECG pattern — most cases represent enhanced AV nodal conduction or concealed accessory pathways, not a single anatomic syndrome.

Classic ECG Features

• PR interval <120 ms (short AV conduction)
• Normal QRS morphology and duration (no delta wave, no slurring)
• No secondary ST/T changes
• Sinus rhythm baseline; paroxysmal SVT often documented separately

ECG Example - Short PR, no delta wave

ECG Example - Short PR, no delta wave

From LITFL

ECG Example - Short PR with delta wave (WPW)

ECG Example - Short PR with delta wave (WPW)

Pathophysiology

• James fiber hypothesis: atrial-Hisian tract bypasses the AV nodal delay but enters His bundle normally → rapid conduction, no ventricular pre-excitation.
• Modern EP studies (Chou 2018): many “LGL” patterns revealed enhanced AV nodal conduction or atypical AVNRT; discrete bypass tracts are rarely proven.

ECG Examples - Short PR, no delta wave

ECG Example - same patient as above now in SVT

Differential Diagnosis

• Most patients present with paroxysmal AVNRT, AVRT, or rapid AF.
• Asymptomatic elderly may show short PR simply due to fast AV nodal conduction — not true LGL.
• Other short-PR causes: junctional rhythm, low/ectopic atrial rhythm, hyperthyroidism, catecholamine surge, normal variant.

ECG Example - Ectopic Atrial Rhythm

Note the borderline short PR and abnormal P wave axis. The P waves are inverted in the inferior leads and upright in aVR which suggests a pacemaker outside the SA node. In this case, lower down in the atria.

ECG Example - Junctional rhythm

From LITFL

Note the very short PR and abnormal P wave axis. The P waves are inverted in the inferior leads and upright in aVR which suggests a pacemaker outside the SA node. In this case, it’s located in the AV node / Bundle of His.

Clinical Context & Key Points

• Short PR + SVT: think “possible LGL physiology,” but management is same as AVNRT/AVRT.
• No increased sudden death risk compared to general SVT (vs. WPW which has an increased risk)
• Not all short PR with no delta wave is LGL

References

• Chou TC, Surawicz B. Chou’s Electrocardiography in Clinical Practice. 7th ed. Philadelphia, PA: Elsevier; 2018.
• Davila C. The ECG. Updated ed. Self-published; 2024.
• Garcia TB, Garcia DJ. 12-Lead ECG: The Art of Interpretation. 2nd ed. Burlington, MA: Jones & Bartlett Learning; 2013.
• Podrid PJ. Podrid’s Real-World ECGs: A Master’s Approach to the Art and Practice of Clinical ECG Interpretation. Vol 6. Minneapolis, MN: Cardiotext Publishing; 2016.
• Brady WJ, Mattu A, Tabas JA. Critical Decisions in Emergency and Acute Care Electrocardiography. Hoboken, NJ: Wiley-Blackwell; 2009.
• Burns E, Buttner R. Lown–Ganong–Levine Syndrome. Life in the Fast Lane ECG Library. Published October 2024. Accessed September 30, 2025. https://litfl.com/lown-ganong-levine-syndrome/

This post is for education and not medical advice.