Page 11, Electrocardiography, Dr. D. Penney
The ECG (continued...)
To summarize, mean electrical axis of the heart can be estimated in a number of ways (Table 18).
Find the lead with greatest (+) deflection; it points to the axis.
Conversely, find the lead with the greatest (-) deflection - it is 180 degrees to the axis.
Another method is to find a lead with equal voltages in the R and the S waves; the axis is 90 degrees to the lead.
Axis deviation can be caused by a number of conditions: obesity, pregnancy, pulmonary vascular obstructive disease, left or right ventricle hypertrophy, and myocardial infarction. (Table 23)
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