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QRS complex

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QRS complex

Postby ramichow » Tue Oct 02, 2012 3:34 pm

Why does the size and other features of the QRS complex vary according to the orientation of the electrodes?

one is positive(active) electrode in left leg , negative(reference) electrode in the left arm and the earthing in the Right arm.
second one is with positive(active) electrode in right arm, negative(reference) electrode in the left arm and the earthing in the left leg
the third one is with positive(active) electrode in right arm, negative(reference) electrode in the left leg and the earthing in the left arm.
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Re: QRS complex

Postby david23 » Fri Mar 15, 2013 11:22 pm

remember your vectors back in physics. The heart is in a tilted position. the action potential moves accordingly.
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Postby daniel.kurz » Tue Mar 19, 2013 1:29 pm

Go back to looking at physics of vectors of electrical charge. Vectors never cross and they are vectors that can be summed based on their components. If you think of the heart, electricity flows from the SA node, through the AV node, and then down the septum through the Bundle of His. As the electricity moves, the direction of flow at any given instant is defined by the vector. All the individual vectors from each cell of the heart are summed together to give the overall vector of the electrical flow. We see that on an EKG and talk about the QRS complex as a result. That is only made possible by the fact that an electrical engineer that made the EKG has cunningly made one recording lead the primary. When the vector is moving in that direction we see upwards direction movement on the EKG. When the vector is moving away we see downwards direction movement on the EKG. Assuming that the EKG recording leads were put on correctly.

In most cases, the heart is pointing down and to the anatomical left at an angle of about 5-10°. In rare cases, the heart can point to the anatomical right or in extremely rare cases can be inverted and pointing to the anatomical right.
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