Determination of the electrical axis of the heart

The rapid, accurate determination of the electrical axis of a patient's heart is very useful for diagnosis. This determination can be made readily by using six electrocardiographic leads. The procedure for interpreting the data from these leads and determining the electrical axis of the heart is charted. This method uses key leads I and aVF to determine the quadrant where the axis is located and secondary leads II, III, aVR, and aVL to find the axial position within the quadrant. When either I or aVF is isoelectric, only one key lead is used.