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 hope 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!

Looking to understand Axis deviation in ECG using the Thumb Rule? We will guide you with the mnemonic and the causes for the same in an ECG. Let’s start with another chapter on the Basics of ECG. Hope you are familiar with the following graph already:

Axis Deviation Graph

Please don’t forget to check some of the posts we crafted for ECG Interpretation:

  1. PSVT vs Atrial Fibrillation
  2. P wave Abnormalities
  3. ECG Quick Review

Thumb Rule Mnemonic of Axis Deviation in ECG

Considering the following, we will interpret axis deviation using Rule of Thumb:

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

Calculating Axis Deviation with Thumb Rule

Interpretation of the thumbs co-relating to ECG are as follows:

Both Thumbs are UP

  • ECG- If QRS in lead I and II are both positive
  • Interpretation- Normal

Thumbs LEFT each other

  • ECG- If QRS in lead I is up (+ve) and in lead II is down (-ve)
  • Interpretation- Left Axis Deviation

Thumbs are RIGHT towards each other

ECG- If QRS in lead I is down (-ve) and in lead II is up (+ve)
Interpretation- Right Axis Deviation

Both Thumbs are Down

  • ECG- If both lead I and II are negative
  • Interpretation- Right Superior Axis Deviation (Extreme Right Axis Deviation)

Still confused? Have a look at the image:

Axis deviation chart ECG

Causes of Axis Deviation

The causes have been categorized depending on type as follows:

Axis deviation ECG

Left Axis Deviation

  1. Inferior MI (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

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

Following are the three common P wave abnormalities found in ECG:

Absent P Wave

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)

Hope you enjoyed our Rule of Thumbs Mnemonic for Axis Deviation in ECG. Have questions? We love solving them!

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