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Origin of QRS complex on ECG!

9K views 3 replies 3 participants last post by  laithbv 
#1 ·
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.
 
#2 ·
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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