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Learn ECG daily for PGMEE
Left Axis Deviation

If the QRS is upright in lead I (positive) and downward in lead aVF (negative), then the axis is between 0 and -90 degrees. However, recalling that left axis deviation is defined as between -30 and -90, this scenario is not always technically left axis deviation. In this scenario, the QRS axis could fall between 0 and -30, which is within normal limits. 
To further distinguish normal from left axis deviation in this setting, look at lead II. If lead II is downward (negative), then the axis is more towards -120, and left axis deviation is present. If the QRS complex in lead II is upright (positive), then the axis is more towards +60 degrees, and the QRS axis is normal.

The causes of LAD are: (Note that the first three account for almost 90% of ECG tracings with LAD.)

  1. Normal variant
  2. Left anterior fascicular block
  3. Left ventricular hypertrophy (rarely with LVH; usually axis is normal)
  4. Left bundle branch block (rarely with LBBB)
  5. Mechanical shift of heart in the chest (lung disease, prior chest surgery, etc.)
  6. Inferior myocardial infarction
  7. Wolff-Parkinson-White syndrome with “pseudoinfarct” pattern
  8. Ventricular rhythms (accelerated idioventricular or ventricular tachycardia)
  9. Ostium primum atrial septal defect

[Image: axix_deviation.jpg]

Right Axis Deviation

If the QRS is predominantly negative in lead I and positive in lead aVF, then the axis is rightward (right axis deviation). The causes of RAD are listed below.

  1. Normal variant
  2. Right bundle branch block
  3. Right ventricular hypertrophy
  4. Left posterior fascicular block
  5. Dextrocardia
  6. Ventricular rhythms (accelerated idioventricular or ventricular tachycardia)
  7. Lateral wall myocardial infarction
  8. Wolff-Parkinson-White syndrome
  9. Acute right heart strain/pressure overload — also known as McGinn-White Sign or S1Q3T3 that occurs in pulmonary embolus
Who can see the Invisible, Can do the Impossible!

Messages In This Thread
Learn ECG daily for PGMEE - by acrosspg - 23-04-2018, 06:25 PM
The ECG Paper and Normal ECG - by acrosspg - 23-04-2018, 06:51 PM
Left and Right axis deviation - by acrosspg - 29-04-2018, 02:13 PM
Wandering Atrial Pacemaker (WAP) - by acrosspg - 10-05-2018, 03:30 PM
Multifocal Atrial Tachycardia - by acrosspg - 10-05-2018, 04:12 PM


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