ECG Topic - Atrial Enlargement (LAE, RAE, BAE)

Last Updated 7/2/25

Overview

Atrial enlargement reflects chronic pressure or volume overload of the atria — often from valvular, hypertensive, or pulmonary disease. It can alter P wave amplitude, duration, and morphology, especially in leads II and V1.

Atrial Depolarization Vectors

Normal Physiology

The P wave on ECG reflects atrial depolarization:

1. The right atrium depolarizes first, followed by the left atrium.
2. These depolarizations generate distinct electrical vectors based on the heart’s orientation.

Left Atrial Enlargement (LAE)

Pathophysiology

Results from volume or pressure overload of the left atrium, typically due to:

• Mitral stenosis or regurgitation
• Aortic stenosis
• Chronic systemic hypertension
• Hypertrophic cardiomyopathy (HOCM)
• Restrictive cardiomyopathy

Electrophysiology

• The left atrium lies posteriorly, so its depolarization moves away from anterior leads (e.g., V1) leading to a terminal negative deflection in V1 in LAE
• The depolarization spreads superiorly, away from inferior leads leading a wider notched P wave in lead II reflecting prolonged left atrial activation

ECG Findings

LAE example ECGs

ECG 1

• Lead II - P mitrale present
• Lead V1 - biphasic V1 (there is a positive component if you zoom in)
• The negative component is well over 1mm deep (1 small box) and 0.04 s (1 small box) wide.
• If you do the math - the depth (2.5mm) x width (0.08s) ≥ 0.03 mms which is consistent with LAE

ECG 2

Pregnant patient in respiratory distress from pulmonary edema, found to have critical mitral valve stenosis

• Biphasic V1 (there is a positive component if you zoom in)
• The negative component is well over 1mm deep (1 small box) and 0.04 s (1 small box) wide.
• The depth (2.5mm) x width (0.08s) ≥ 0.03 mms which is consistent with LAE

ECG 3

Patient presenting with hypertension and chest pain found to have aortic dissection.

• Lead II - P mitrale present
• Lead V1 - biphasic V1 (there is a positive component if you zoom in)
• The negative component is well over 1mm deep (1 small box) and 0.04 s (1 small box) wide.
• The depth (2.5mm) x width (0.08s) ≥ 0.03 mms which is consistent with LAE

Right Atrial Enlargement (RAE)

Pathophysiology

Occurs due to chronic pressure overload of the right atrium, often from:

• Pulmonary hypertension
• COPD, PE
• Tricuspid stenosis or regurgitation
• Congenital heart disease (e.g., TOF, Ebstein anomaly)

Electrophysiology

• The right atrium is located more anteriorly in the chest, closer to the precordial leads (especially V1–V2) which leads to early positivity in V2
• The depolarization spreads downward toward the inferior leads (II, III, aVF) leading to peaked p waves in those leads

ECG Findings

RAE Example ECGs

ECG 1

Patient with history of RVH

• Lead II clearly shows p-pulmonale (≥2.5 mm)
• There may also be LAE (see V1)

ECG 2

• Lead II clearly shows p-pulmonale (≥2.5 mm)
• V1 shows biphasic p wave - Positive component ≥ 1.5mm and ≥ p wave in V6

ECG 3

• Lead II clearly shows p-pulmonale (≥2.5 mm)
• V1 shows biphasic p wave - Positive component ≥ 1.5mm and ≥ p wave in V6

Biatrial Enlargement (BAE)

Pathophysiology

BAE implies dual atrial remodeling, usually from:

• Combined left + right valvular disease (e.g., mitral stenosis + tricuspid regurgitation)
• Infiltrative cardiomyopathy
• Chronic pulmonary disease + LVH

ECG Findings

Example ECGs

ECG 1

• LAE - p-mitrale in lead II and negative component of biphasic P in V1 appears 1 box wide and deep
• RAE - p-pulmonale / tall p wave in lead II (≥2.5 mm)

ECG 2

• LAE - negative component of biphasic P in V1 appears 1 box wide (0.04s) and deep (1mm)
• RAE - p-pulmonale / tall p wave in lead II (≥2.5 mm)

ECG 3

• LAE - negative component of biphasic P in V1 appears 1 box wide (0.04s) and deep (1mm)
• RAE - positive component of biphasic P in V1 appears ≥ 1.5mm and ≥ P wave in V6

Quick Comparison Table

Conclusion

ECG findings of atrial enlargement offer valuable insight into underlying cardiac pathology — especially valvular, hypertensive, and pulmonary disease. By mastering P wave morphology in leads II and V1, you can:

• Detect early signs of RAE (tall, peaked P waves)
• Identify LAE (notched or biphasic P waves with terminal negativity)
• Recognize BAE as a marker of advanced or mixed cardiac disease

Always interpret P wave abnormalities in clinical context — including rhythm, axis, voltage, and structural risk factors. Subtle waveform clues can be the first signal of significant atrial remodeling.

References

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3. Davila E. The ECG Handbook. 2nd ed. EM-Ronin Publishing; 2024.
4. Garcia TB. 12-Lead ECG: The Art of Interpretation. 2nd ed. Jones & Bartlett Learning; 2013.
5. Life in the Fast Lane (LITFL). ECG Library – Right Atrial Enlargement, Left Atrial Enlargement, Biatrial Enlargement. https://litfl.com/ecg-library/. Updated 2024.
6. Mattu A, Brady WJ. ECGs for the Emergency Physician. Vols 1 & 2. Blackwell Publishing; 2003, 2008.
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