ECG Basics: Axis Deviation and P wave Abnormalities Causes


We are starting a new thread of ECG Basics: Conceptual Understanding Made Easy. To kick start the topic, we will discuss Axis Deviation and P wave abnormalities causes on ECG. Many Students after MBBS (and some Doctors after graduation!) give up hopes on even trying to understand ECG. The simplest mnemonic or trick for Axis Deviation has been given below. We have also simplified P Wave ECG findings below. Stay connected for more updates!

Axis Deviation


  • Left Thumb= Lead I
  • Right Thumb= Lead II

Now once you have identified which thumb is which, simply start pointing them as below:

  • If QRS in lead I and II are both positive
    • Normal
  • If QRS in lead I is up (+ve) and in lead II is down (-ve)
    • Left Axis Deviation (Thumbs LEFT each other)
  • If QRS in lead I is down (-ve) and in lead II is up (+ve)
    • Right Axis Deviation (Thumbs are RIGHT towards each other)
  • If both lead I and II are negative
    • Right Superior Axis Deviation (Extreme Right Axis Deviation) (Both thumbs down)
Axis Deviation Causes
Axis Deviation Causes


  • Left Axis Deviation
    1. Inferior MI or Myocardial Infarction (Lead II negative)
    2. Left Ventricular Hypertrophy (LVH)
    3. Left Anterior Fascicular Block (or Hemiblock)
    4. Obese
    5. Wolf Parkinson White Syndrome (delta wave)
  • Right Axis Deviation
    1. Lateral MI (Lead I negative)
    2. Right Ventricular Hypertrophy (RVH)
    3. Left Posterior Fascicular Block (or Hemiblock)
    4. Thin, Tall, Children
    5. Chronic Lung Disease
    6. Pulmonary Embolism
  • Extreme Right Axis Deviation (No Man’s Land) = (North West Axis)
    1. Congenital Heart Disease
    2. Left Ventricular Aneurysm
Read more-   Pleural Effusion : Diagnosis | Treatment : Video
Axis Deviation Causes 2
Axis Deviation Causes 2

P Wave

P Wave Pathologies Causes
P Wave Pathologies Causes


  • Normal Duration
    • Normal P Wave is less than 0.12 secs (<3 small squares)
  • Normal Amplitude
    • Normal P Wave has an amplitude less than 2.5mm in limb leads (I, II, III, avR, avL, avF)
    • Also, it is less than 1.5mm in precordial/chest leads (V1-V5)

P Wave Abnormalities Causes

  • P Pulmonale (peaked P waves)
    • ECG Finding- 2.5mm in limb leads or >1.5mm in chest leads
    • Cause- Right Atrial Enlargement (Cor Pulmonale- Pulmonary Hypertension in chronic respiratory disease)
  • P Mitrale (bifid P wave)
    • ECG Finding- 0.12 secs/ >3 small squares
    • Cause- Left Atrial Enlargement (MS- Mitral Stenosis)

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