When leads I and aVF are used to determine electrical axis, left axis deviation is present if the QRS is:

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Leads I and aVF divide the heart into four quadrants. These two leads can be used to quickly estimate electrical axis. In leads I and aVF, the QRS complex is normally positive. If the QRS complex in either or both of these leads is negative, axis deviation is present.Another popular shortcut using leads I and aVF to determine axis deviation is called the "thumbs method." Hold up your left and right hands and make a thumbs up/thumbs down position in the direction of the QRS in leads I and aVF, respectively. Two thumbs up reflects normal axis. Left thumb up, right thumb down = left axis deviation. Left thumb down, right thumb up = right axis deviation. Both left and right down = extreme right axis deviation.

When Leads I and AVF Are Used to Determine Electrical