Why does atrial depol cause upward deflection on EKG?

In summary: So when a cell depolarizes, it creates a change in voltage which the electrodes pick up on, leading to an upward deflection on the EKG. In summary, the EKG is measuring voltage, not current, and when a cell depolarizes it creates a change in voltage which the electrodes pick up on, resulting in an upward deflection on the EKG.
  • #1
drana91
3
0
Given a standard 3-lead ekg where the leads are read as below:
ecg_534.gif

Why does atrial depolarization cause an upward deflection? Assuming the EKG is being read from Lead II, I believe that if the current flowing from the negative terminal at RA (right arm) to the positive terminal at LL (left leg) is positive, then atrial depolarization (whose current moves parallel to this vector from upper right heart to lower left heart) would cause a positive summation of currents leading to the upward deflection. However, why would Lead II (which runs from negative terminal to positive) cause a positive current? Doesn't convention state that current is defined as the apparent movemnt of positive charge, in this case, in a direction opposite to what is shown in the graphic above? Am I even thinking about this correctly?? Thank you!
 
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  • #2
drana91 said:
Assuming the EKG is being read from Lead II, I believe that if the current flowing from the negative terminal at RA (right arm) to the positive terminal at LL (left leg) is positive,

I'm not familiar with the details of an EKG setup, but a positive current cannot flow from a negative terminal to a positive terminal. Is there really a current flowing here, or are the leads measuring a voltage change?
 
  • #3
Ah, I guess I assumed current was flowing. You're right, the leads are simply measuring voltage change. Just to make sure this makes sense then... if a positive current causes an upward deflection on an EKG, the recording terminal must be the positive one, correct?
 
  • #4
Errr, I thought you just said that an EKG doesn't measure current...
 
  • #5
So when the heart cell depolarizes, positive ions are let out. Because this propogates down the heart this causes the positive current. I believe what the ekg is measuring is the change in voltage, over time, across a lead. Does that make sense? Sorry, I'm trying to make it make sense!
 
  • #6
drana91 said:
So when the heart cell depolarizes, positive ions are let out. Because this propogates down the heart this causes the positive current. I believe what the ekg is measuring is the change in voltage, over time, across a lead. Does that make sense? Sorry, I'm trying to make it make sense!

Based off of what the wikipedia article is saying about EKG's, I believe that is correct. The electrodes are measuring voltage, not current.
 

Related to Why does atrial depol cause upward deflection on EKG?

1. Why does atrial depolarization cause an upward deflection on an EKG?

Atrial depolarization is the electrical activation of the heart's upper chambers, the atria. This activation causes the atria to contract, which is represented on an EKG as a P wave. The movement of electrical impulses from the atria towards the ventricles creates an upward deflection on the EKG due to the direction of the electrical current flow.

2. How is atrial depolarization different from ventricular depolarization on an EKG?

Atrial depolarization occurs first and is represented by the P wave on an EKG. Ventricular depolarization, which is the electrical activation of the heart's lower chambers, follows and is represented by the QRS complex on an EKG. Atrial depolarization is typically a smaller and shorter wave compared to the QRS complex.

3. Can atrial depolarization be seen on an EKG if the P wave is absent?

In some cases, such as in individuals with heart block, the P wave may be absent on an EKG. This does not necessarily mean that atrial depolarization is not occurring. In these cases, the atria are still being activated, but the electrical signal is not strong enough to produce a visible P wave on the EKG.

4. What can cause changes in the amplitude or duration of the P wave on an EKG?

Changes in the amplitude or duration of the P wave on an EKG can be caused by various factors, including changes in heart rate, electrolyte imbalances, or underlying heart conditions such as atrial enlargement or conduction disorders. These changes can provide important information about the health and function of the heart.

5. Is the direction of the P wave on an EKG always the same?

The direction of the P wave on an EKG can vary depending on the lead placement. In most cases, the P wave will have an upward deflection, but in some lead placements, it may appear inverted. This is due to the different angles at which the electrical activity of the heart is being recorded on the EKG.

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