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QRS is normally inverted in aVR: why?

Discussion in 'Allopathic' started by ilovelanguages, Jun 1, 2012.

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  1. ilovelanguages

    ilovelanguages

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    I'm looking at augmented limb leads (studying for a medical school exam, this is my advanced notice that this is not premed homework help), and my textbook asks me instead of telling me why the QRS in aVR is inverted.

    I know that in aVR the positive terminal is connected to the right arm... and the negative terminal is a connection (sum?) of the left foot and left arm? So perhaps because the base of the heart (the more negative portion) is closer to the right arm, and an area in between the left arm and left leg is more towards the apex of the heart (the more positive portion), the negative portion has the positive terminal and the positive portion has the negative terminal, and that is what produces the inversion? Amidoinitrite? If I seem confused or am using incorrect terminology for anything, any explanations are appreciated
  2. joeDO2

    joeDO2

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    when the direction of current flow is opposite to the axis of the lead, a negative deflection is produced. since the direction of current is basically down and to the patients left, this is opposite the axis of the lead (as shown by the fact that you correctly identified the positive terminal on the right arm). hope that was clear.
  3. ilovelanguages

    ilovelanguages

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    That makes total sense. Thanks.

    I have a follow up question, and it's probably a dumb one :oops: Hope someone can help me out.

    I just got done with a chapter of Guyton Physio regarding EKG's (unfortunately in spanish...)

    It explained to me

    1. EKG lead placements on the left arm right arm and left leg

    2. Augmented lead placements (aVR, aVL, aVF)

    3. Precordial leads

    I open up to my class's scribed lecture notes and the first thing stated is, "The electrocardiograph is an electronic device that captures and expands the heart's electrical activity through electrodes placed in the 4 limbs and 6 precordial positions."

    I thought I just read a chapter describing electrodes being placed on three limbs? Yet, in lab we certainly used four...what is the difference? Why are there so many permutations of this? This question probably seems a bit elementary but I appreciate any and all help.
  4. Limetime

    Limetime

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    The fourth lead is a grounding lead. You ignore it during interpretation.

  5. SpecterGT260

    SpecterGT260 Catdoucheus

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    This kinda gets me too.... we only ever were told left leg right arm and left leg..... no mention of a 4th lead. In addition I am under the impression that the augmented leads are not leads at all but just alternate circuitry for the standard leads, correct?
  6. Limetime

    Limetime

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    Yes, the aV leads are not separate leads physically, they use the same limb electrodes, but look at the heart from a different angle. Totally ignore the fourth grounding limb lead unless you are physically doing a ECG and you have to stick it on, but there is no information on the printout for interpretation. In a 12 lead ECG there are 10 physical electrodes, 6 precordial and 4 limb, that record electrical activity from 12 different angles, 6 pre cordial, 3 limb and 3 aV.
    Last edited: Jun 2, 2012

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