S wave on ECG.. what the heck is it?

[Flopotomist]

OK guys.. I am a bit lost. In lead II (or heck, any lead for that matter), why do you have an upward deflection of an S wave normally? It seems like the QR should just return to the isoelectric line. Can't seem to find the answer. Help!

---

Members don't see this ad.

 

[Mr. Freeze]

I'm going to throw out a total guess, but somewhat based loosely on fact. Believe it or disprove it.

If you're asking what I think you're asking, i.e. essentially, why is there an S wave at all, EKGs are directional. The depolarization has to come down the septum, then up from apex, and at some point will be above the outflow valves. To squeeze out as much SV, you'll have another change in the direction, leading to a vector change on the strip.

But I'm just guessing.

 

[LJDHC05]

Stuff you know already:
The depolarization of the left vent basically sets up a dipole in the chest that is monitored by the leads of the ECG. When the overall depolarization vector of the tissue is moving in a direction perpendicular to a lead, it creates the largest deflection from the 0 line. The direction of the deflection (up/down) depends on the depolarization vector (change from + to - charge outside the cells) orientation relative to the +/- terminals of the lead (maybe someone else can explain that better)

Applied to the situation:
The S segment of the QRS complex should be the last segments of the ventricular myocardium depolarizing (portions of the L/R vents just deep to the epicardium near the AV valves and out towards epicardium). Seeing that that final little depolarization is moving from the apex of the heart towards the AV valves (in the direction of the (-) terminal of lead II, nearly parallel to it) there is a small downward deflection (or atleast in our examples it's usually down). Every lead and heart is a little different in the S wave due to the final depolarization, reason it out based on what you know

Hope that helps, and correct me anywhere I made mistakes...

Now, if you're talking ST elevation--> knee jerk reflex is always MI/ ventricular damage...if you need to know anything more, find a cardiologist.

 

[smq123]

OK guys.. I am a bit lost. In lead II (or heck, any lead for that matter), why do you have an upward deflection of an S wave normally? It seems like the QR should just return to the isoelectric line. Can't seem to find the answer. Help!

Do you mean downward deflection of an S wave, or an upward deflection of a T wave? I'm confused.

 

[Flopotomist]

Do you mean downward deflection of an S wave, or an upward deflection of a T wave? I'm confused.

I am talking about when the S wave deflects upwards to return to the isoelectric line suggesting that there is either a repolarization somewhere moving away from the lead, or a depolarization somewhere moving toward the lead. I am still struggling here... I think I am just slow today.

 

[justsomeguy]

I am talking about when the S wave deflects upwards to return to the isoelectric line suggesting that there is either a repolarization somewhere moving away from the lead, or a depolarization somewhere moving toward the lead. I am still struggling here... I think I am just slow today.

I found this on the internet, hopefully this will help a little.

The R wave is the point when half of the ventricular myocardium has been depolarized. Activation of the posteriobasal portion of the ventricles give the RS line.

-from http://sprojects.mmi.mcgill.ca/cardiophysio/EKGQRScomplex.htm

My understanding is that the entire QRS complex corresponds to depolarization of the ventricles, the ST segment corresponds to the "plateau phase" of repolarization, and the T wave corresponds to the "rapid phase" of repolarization. I remember learning that when the heart contracts, it actually does so in a spiral fashion (like wringing a wet towel) to eject blood more efficiently. Maybe that has something to do with it?

Please correct me if I am wrong. 🙂

 

[Hard24Get]

OK guys.. I am a bit lost. In lead II (or heck, any lead for that matter), why do you have an upward deflection of an S wave normally? It seems like the QR should just return to the isoelectric line. Can't seem to find the answer. Help!

Like the others are saying, remember that you are watching the depolarization from one point of view on any particular lead. Depending on the person's anatomy relative to your leads, some depols/repols will come towards you (up) or away from you (down). Not everyone has a S or Q wave for this reason.

Also know that the EKG has no true baseline, just the lack of electrical CHANGE makes the line flat (which is why ST elevation and depression are due to baseline changes, not real ST segment changes).

It will (eventually) become clear during your cardiology elective (which I'm doing now 😛 )... In the meantime, check out Lilly's Pathophys of heart disease

 

[ambulancedriver]

essentially, the s wave you'll see on leads II and III are because the direction of the heart depolarization vector changes to pointing towards the base of the left ventricle (up and to the right instead of down and to the right). this causes a negative deflection (i.e. s wave) on those two leads b/c it points towards the negative end of those two leads. lead I should still be positive since the general direction of the vector is still towards the positive end of lead I.

for a good explanation, read Guyton's textbook of medical physiology. it helps you understand the basis of EKGs really well.

 

[tacrum43]

I am talking about when the S wave deflects upwards to return to the isoelectric line suggesting that there is either a repolarization somewhere moving away from the lead, or a depolarization somewhere moving toward the lead. I am still struggling here... I think I am just slow today.

I am studying this stuff right now too.

The best I can figure it, it's because the depolarization (-) moving away from the + electrode has reached the top of the ventricles (and therefore stopped), but that the repolarization (+) has not yet begun because of the prolonged refractory period that ventricular cells have. Then you get the T-wave once the repolarization begins, starting at the apex.

...but I could be mistaken. Exam is tomorrow. Guess I'll find out then. 🙂