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Old 12-21-2009
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EKG Origin of QRS complex on ECG!

This is probably more in-depth than required for the Step 1, but I'd like someone to explain:

1- Why does the QRS complex have two downward waves (Q & S) if it's just depolarization?

2- Why is the T wave in the same recorded direction (upwards) as the R wave, even though the R wave denotes depolarization and the T wave denotes repolarization?

It's easy to just memorize, but since I have some time before I give the exam, I'd like to understand better.

Thanks in advance.
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Old 12-21-2009
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The downward deflections of the QRS are there because you have depolarization of the septum before you have depolarization of the ventricles.
The direction of deplorization of the septum is the reverse of the depolarization of the ventricle and therefore Q and S are always the reverse of R wave.
The T wave is in the same direction of the R because depolarization starts in the endocardium and spreads to epicardium while replorazation starts in the epicardium and ends in the endocardium so they'll will ultimately go in the same direction.

Hope that makes sense
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Old 12-22-2009
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Quote:
Originally Posted by laithbv View Post
The downward deflections of the QRS are there because you have depolarization of the septum before you have depolarization of the ventricles.
The direction of deplorization of the septum is the reverse of the depolarization of the ventricle and therefore Q and S are always the reverse of R wave.
The T wave is in the same direction of the R because depolarization starts in the endocardium and spreads to epicardium while replorazation starts in the epicardium and ends in the endocardium so they'll will ultimately go in the same direction.

Hope that makes sense
so the q wave stands for depolarisation of the septum (which direction?) what do the r and s waves represent? kindly explain, please.
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Old 12-22-2009
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Originally Posted by memory View Post
so the q wave stands for depolarisation of the septum (which direction?) what do the r and s waves represent? kindly explain, please.
depolarization of the left part of the septum starts before the right side, therefor it's away from your lead II direction therefore it's responsible for the downward deflection of your Q wave.
Then as the depolarization spreads from up to down towards the apex you'll have the upstroke of the R wave.
Then the depolarization will proceed from the apex back to the base which is responsible of the down stroke of the R wave.
Then you have little further depolarization of the last part of the base of the left ventricle which is again toward your lead II and this is responsible for the upstroke of the S wave back to baseline.
Look at this image and you'll understand it very well:


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Cardiovascular-, EKGs-, Figures-, Physiology-

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