Chamber enlargement patterns

Right Atrial Enlargement - The Tall P Wave

• ECG Finding: Tall, peaked P wave (>2.5 mm) in inferior leads (II, III, aVF).
  • Often called P pulmonale due to its association with pulmonary disease.
  • P wave width remains normal (<0.12s).
• Pathophysiology: Increased electrical forces from the right atrium, often due to hypertrophy or dilation from pressure/volume overload.
• Common Causes: COPD, pulmonary hypertension, tricuspid stenosis, congenital heart disease (e.g., Ebstein anomaly).

⭐ Look for this pattern in patients with chronic respiratory conditions presenting with new-onset arrhythmia or syncope.

Left Atrial Enlargement - The Notched P Wave

• Also known as P mitrale, classically seen in mitral valve disease.
• Lead II Criteria:
  • Wide P wave > 0.12s (3 small squares).
  • Notched, M-shaped P wave with inter-peak duration > 0.04s.
• Lead V1 Sign:
  • Biphasic P wave with a deep, wide terminal negative portion.
  • Negative deflection must be ≥ 1 mm deep and ≥ 0.04s wide.

⭐ The biphasic P-wave in V1 with a terminal negative portion >1mm deep and >0.04s wide is more specific for LAE than P mitrale in lead II.

📌 Mnemonic: Think "M" for Mitrale and the "M-shaped" P wave.

Right Ventricular Hypertrophy - Axis Goes Right

• Right Axis Deviation (RAD): QRS axis > +90°.

• Precordial Lead Changes:

  • Dominant R wave in V1 (R > S ratio > 1; R wave > 7 mm).
  • Dominant S wave in V5/V6 (R/S ratio < 1).

• RV "Strain" Pattern: ST depression and T-wave inversions in right-sided leads (V1-V3, inferior leads II, III, aVF).

• Common Etiologies:

  • COPD
  • Pulmonary Hypertension
  • Pulmonic Stenosis
  • Tetralogy of Fallot

⭐ The most common cause of RVH is pulmonary hypertension, often secondary to chronic lung disease (cor pulmonale) or left-sided heart failure.

Left Ventricular Hypertrophy - The Voltage King

• Pathophysiology: Increased LV muscle mass, typically from pressure overload (e.g., systemic hypertension, aortic stenosis). This larger muscle mass generates more electrical signal, leading to ↑ QRS voltage.
• Primary Voltage Criteria (Sokolow-Lyon):
  • S wave in V1 + R wave in V5 or V6 ≥ 35 mm.
  • R wave in aVL > 11 mm.
• Associated Findings:
  • Left Axis Deviation (LAD).
  • LV “Strain” Pattern: ST depression and T-wave inversion in lateral leads (I, aVL, V5, V6).

⭐ Voltage criteria for LVH are specific but not sensitive. Cornell criteria (R in aVL + S in V3 > 28 mm for men, > 20 mm for women) can improve diagnostic accuracy.

High‑Yield Points - ⚡ Biggest Takeaways

• Right Atrial Enlargement (RAE) is defined by tall, peaked P waves (P pulmonale) > 2.5 mm in lead II.
• Left Atrial Enlargement (LAE) shows broad, notched P waves (P mitrale) > 0.12s in lead II and a biphasic P in V1.
• Right Ventricular Hypertrophy (RVH) typically presents with right axis deviation and a dominant R wave in V1.
• Left Ventricular Hypertrophy (LVH) is suggested by voltage criteria, like Sokolow-Lyon (S in V1 + R in V5/V6 > 35 mm).
• LVH often includes a “strain pattern”: ST depression and T-wave inversion in lateral leads.