Last updated 1/28/26
Introduction
The transition zone is the point in the precordial leads where the QRS complex changes from predominantly negative (S > R) to predominantly positive (R > S). It marks where the horizontal plane depolarization vector becomes perpendicular to the chest lead axis (the QRS is isoelectric).
In most adults, the normal transition occurs at V3–V4.
Rather than a single lead, the transition is a continuum between two adjacent leads:
- One mostly negative
- The next mostly positive
- The true transition lies between them
Adapted from Tomas Garcia’s 12 Lead ECG - Art of Interpretation
ECG: Normal transition from S to R waves occurs between V3 and V4
ECG: Normal transition from S to R waves occurs between V3 and V4
Rotation Terminology
Clockwise or counter-clockwise terminology is used because the precordial transition point shifts around the chest in the same direction the hands of a clock would move when the heart is viewed from the feet, reflecting anterior–posterior rotation of the heart’s electrical axis relative to the chest leads.
Adapted from Tomas Garcia’s 12 Lead ECG - Art of Interpretation
Counter-Clockwise Rotation (Early Transition)
Transition at V1–V2 or V2–V3
Common causes:
- Right ventricular hypertrophy (RVH)
- Posterior MI (loss of posterior forces)
- Young / thin chest wall
- Vertical heart
- Acute RV strain (PE)
- Dextroposition / lead misplacement
ECG: RVH with early transition at V1
ECG Example: Inferior/Posterior MI with early transition between V2 and V3
ECG: Submassive pulmonary embolism with early transition between V2 and V3
Clockwise Rotation (Late Transition)
Transition at V4–V5, V5–V6 or beyond
Common causes:
- Left ventricular hypertrophy
- Hyperinflated lungs (COPD)
- Horizontal heart
- Anterior MI (loss of anterior forces)
- Pericardial effusion (global voltage + delayed transition)
- Poor R-wave progression from lead misplacement
ECG: Anterior MI with late transition between V4 and V5
ECG: LVH with late transition between V4 and V5
ECG: Pericardial Effusion with low voltage and late transition at V4 or V5
Clinical Interpretation Framework
The transition zone is not diagnostic by itself, but it localizes anterior–posterior electrical forces and serves as a pattern-recognition trigger prompting you to actively look for conditions that shift ventricular dominance or cause regional loss of forces and seek additional ECG findings that may help make a diagnosis.
Practical algorithm (ED):
- Locate where R/S ≈ 1 (the isoelectric point) → define early/normal/late.
- Check R-wave width in V1 (narrow vs wide).
- Integrate axis, ST-T pattern, voltage, and clinical context
Transition Zone | Rotation | Typical Lead Pattern | Common Causes |
V1–V2 / V2–V3 | Counter-clockwise (Early) | Tall R appears early; R/S ≥1 by V1–V2 | RVH, acute RV strain (PE), posterior MI (loss of posterior forces), young/vertical heart, lead misplacement |
V3–V4 | Normal | R and S equal around V3–V4 | Normal adult pattern |
V4–V5 / V5–V6 | Clockwise (Late) | Dominant S persists into V4–V5; R becomes dominant late | LVH, COPD/hyperinflation, horizontal heart, anterior MI (loss of anterior forces), pericardial effusion, lead misplacement |
Key Points
- Normal transition: V3–V4
- Early transition (V1–V2): think RV forces or posterior loss
- Late transition (V5–V6): think LV dominance or anterior loss
- The transition zone reflects anterior–posterior vector balance, not ischemia by itself.
- Always interpret with:
- R-wave width
- Axis
- ST-T morphology
- Clinical context
Resources
- Brady WJ, Harrigan RA. Critical Decisions in Emergency and Acute Care Electrocardiography. 2nd ed. Wiley-Blackwell.
- Burns E, Buttner R. “Poor R Wave Progression & Precordial Rotation.” LITFL ECG Library.
- Chou TC, Knilans TK. Electrocardiography in Clinical Practice. 6th ed. Elsevier.
- Davila E. The ECG. 2025.
- Garcia TB. 12-Lead ECG: The Art of Interpretation. 2nd ed. Lippincott Williams & Wilkins.
- Mattu A, Brady WJ. ECGs for the Emergency Physician, Vols 1–2. Lippincott Williams & Wilkins.
- Podrid PJ. Podrid’s Real-World ECGs.
This post is for education and not medical advice.