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MEDiscuss • Cardiovascular diseases • How do I easily find the axis in ECG?


  1. #1
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    How do I easily find the axis in ECG?

    I have read this a hundred times, but forget invariably. How do I easily find the axis in an ECG? and remember it??

  2. #2
    Physician - Teacher
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    Thumbs Rule for determining ECG axis

    There are easier methods that are crude and slightly complex methods that are accurate. Since you are looking for the easier option, I will tell you the RULE OF THUMBS (remember that this is crude):

    You need only two leads - Lead I and Lead avF - for this method.

    1. Imagine that your left thumb is Lead I and right thumb is avF.
      • Left thumb - Lead I
      • Right thumb - avF

    2. If QRS is predominantly positive, you will hold the corresponding thumb of that lead up, and if negative, down.
      • Positive - UP Name:  icon14..gif
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Size:  606 Bytes
      • Negative - DOWN Name:  icon13..png
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Size:  3.3 KB

    3. Now, look at the leads and hold your thumbs appropriately.
      • If both Lead I and avF are positive, both thumbs will be up (Name:  icon14..gif
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Size:  606 Bytes Name:  icon14..gif
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Size:  606 Bytes) too and this is NORMAL.
      • If lead I is positive and avF is negative, only the left thumb will be up (Name:  icon14..gif
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Size:  606 Bytes Name:  icon13..png
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Size:  3.3 KB) and indicates LEFT AXIS DEVIATION (LAD)
      • If lead I is negative and avF is positive, only the right thumb will be up (Name:  icon13..png
Views: 20847
Size:  3.3 KB Name:  icon14..gif
Views: 20865
Size:  606 Bytes) and indicates RIGHT AXIS DEVIATION (LAD)
      • If both Lead I and avF are negative, both thumbs will be down (Name:  icon13..png
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Size:  3.3 KB Name:  icon13..png
Views: 20847
Size:  3.3 KB) and this is INDETERMINATE axis.

    4. Easy?
    tharenie likes this.

  3. #3
    New Member
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    Mar 2010
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    When trying to determine the axis, the leads that are important are the limb leads. The basic principle behind finding the axis is that you must look for the lead whose QRS complex is closest to zero or equiphasic (i.e., when the areas under each component of the QRS are added up (with those above baseline being positive and that below baseline negative, you get an approximate negative or positive value or zero).

    This axis represents the lead that is perpendicular to the main axis of the ECG (remember this from the vector discussion above). Then to find the lead which is closest to the axis of the ECG, it is necessary to know how the leads are in relation to each other. This was given in the picture immediately above.

    With this lead (i.e. the lead that was perpendicular to the lead which was equiphasic), you have a general idea of what the axis is. Each lead has a positive and negative pole, and therefore after you look at this lead on the ECG and determine whether the QRS complex is overall negative or positive, you need simply look at this diagram to determine what the axis is (corresponding with the positive or negative pole of that lead).

 

 

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