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    On an ECG machine, i know that lead 1 and lead 3 add together to form lead 2 but i dont know why lead 2 is bigger than the other two? please
    help! 😁
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    Hi,

    Instead of trying to "add" 2 or more leads, it is easier to understand the ECG by interpreting the direction from which each lead "looks" at the heart. The diagram below illustrates this principle for the unipolar (leads I, II, III) and bipolar (leads aVR, aVF and aVL).

    Name:  Frontal_leads ECG.png
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    You can see that lead II looks at the heart from the left and below (as you face the patient) - this is one of the most active or powerful direction of the vectors generated by the heartbeat [in particular the largest chamber, the left ventricle] - a positive deflection is produced by electrical activity approaching the electrode and a negative deflection by activity travelling away from the electrode. As there is a large electrical potential travelling in the direction that runs from the cardiac apex (which is to the left and downwards), this activity is picked up by lead II as coming towards it i.e. displayed as a large, positive deflection.

    I hope this makes things easier to understand.

    M (former medic)
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    Ahh ok, yeah it makes more sense, thanks
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