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Use amplitude of vibration method to calculate ECG Axis

Use amplitude of vibration method to calculate ECG Axis:

1) Calculate lead I and III’s QRS amplitude algebraic sum.
To measure R wave, 0.1mv = +1, 0.2mv=+2, and so on.
To measure q or s waves, 0.1=-1, 0.2= -2, and so on.
2) After got the algebraic sum, find the point on the lead axis I and III and make a perpendicularity line to Axis.
3) These two line will joint at some point “A”.
4) The “OA” line’s direction will be the Axis’s direction.
5) Measure the angle formed by line “OA” and Lead I, the degree is the mean Axis, clock-wise is positive and counter-clock wise is negative.

Using this rule, the above ECG example is:
I: +4
III: +9-1 = +8
Find the point +4 on lead I and the point +8 on Lead III, Make a perpendicularity line from the point to both of the leads.
The joint point of these two lines are the “A” point.
Make a line from “O” to “A”, that is the mean Axis.
Measure the angle formed by line “OA” and lead I. It is approximately +70o.

So in this example, the mean electrical axis is approximately +70o .

The mean electrical axis for the heart normally lies between -30 and +90o. (Some textbooks say the normal range is 0 to +90o.) Less than -30o (or less than 0o) is termed a left axis deviation and greater than +90o is termed a right axis deviation.







By Dreamer
Saturday, September 22, 2007