What does the R Peak in the QRS complex correspond to?

Question

Hi!
My question goes as follows: In the QRS complex, normally one has an A-like shape, being q, r, and s wave.

When the R wave gets to its peak, just right in the middle, what does it mean?
does it mean that HALF myocardium is de-polarized? or does it mean something else?

i have search everywhere with no luck, only to obtain the same
answers, being q wave the negative deflection, r the positve and s again negative, but i havent found what im looking for...

any thoughts?? thanks in advance...
PS: If you have the URL source i'll really appreciated.
and the same question goes for the upward and downward braches of the R wave (above baseline)

atte xeonrebel or rickhunter

Answer 1

I have your answer good person. Thank you for this question, because I was stumped for awhile on how to answer this. Here goes...

The QRS complex represents ventricular depolarization. The time it takes for the electrical pulse to travel through the ventricals is measured by the QRS time. Now we have to look at amplitude...at some given time within the QRS complex, the amplitude will be at it's greatest (or lowest if we are using lower leads [except for when the S has the same amplitude]) *let's please only talk about upward deflection*

R represents the exact time the highest amount of electrical impulse was present in the ventricle. Presumably it is when the impulse reaches the apex.

------------------UPDATE---------------
WWD has introduced a facinating topic. I made it to advanced EKG, but WWD sounds waaaaay more qualified to answer your question. Take my answer for what it's worth.

Answer 2

When the wave of depolarization (the electrical trigger for muscle contraction), represented by the QRS complex starts out in the ventricles, it is travelling down the middle (septal) wall, between the ventricles, to the bottom of the ventricles, and then it comes back up around all of the outside walls of the ventricles to the top again. This is graphically represented by the changes in direction of the QRS, but I have not yet seen anything that landmarks exactly where in the myocardium (heart muscle) the wave front is when the direction change of depolarization occurs.

The ECG is a representation of the sum of all depolarizations, moving in all directions, so the timing of the QRS complex direction change may not necessarily match the time the wave of depolarization is located at the point of direction change.

Good question, I'll be interested in others' answers.

Answer 3

The QRS complex is a whole entity that represents the depolarization of the heart's ventricals. The negative and positive deflections represent the direction of electrical activity in the heart. Therefore the positive deflection means that the electical impulse travels from the AV node to the bundle of His and then through the perkinje fibers to cause the heart to beat. the R-wave represents when the impulse reaches the apex of the heart muscle. The negative deflection of the S-wave then represents the bundles being excited in the other direction, and therefore causing a negative deflection on the isoelectric line.

Answer 4

You're going to drive yourself nuts thinking along lines like "exactly half the myocardium [being] depolarized."
I assume since you're pondering this question, you have a text showing lead placements, etc., and probably one of those figures with a PQRSTU cycle and an action-potential curve one drawn above the other.
The QRS complex you're looking at is a vector sum of action potentials when looked at from a particular area. The peak of the R in V6 is exactly the same as the trough of the S in VI, not the R. Not the answer, but I hope it helps you figure it out.