Why does atrial depol cause upward deflection on EKG?

  • Context: Graduate 
  • Thread starter Thread starter drana91
  • Start date Start date
  • Tags Tags
    Cause Deflection
Click For Summary
SUMMARY

Atrial depolarization causes an upward deflection on an EKG primarily due to the positive summation of currents flowing from the right arm (RA) to the left leg (LL) in Lead II. The leads measure voltage changes rather than current flow, which clarifies the apparent contradiction regarding positive current direction. As heart cells depolarize, positive ions are released, leading to a measurable voltage change across the leads. This understanding aligns with the principles outlined in EKG literature.

PREREQUISITES
  • Understanding of EKG lead placement and function
  • Basic knowledge of cardiac physiology, specifically depolarization
  • Familiarity with voltage versus current measurements in electrical systems
  • Knowledge of the standard EKG waveform interpretation
NEXT STEPS
  • Research the principles of EKG lead configurations and their implications
  • Study cardiac depolarization and repolarization processes in detail
  • Learn about the differences between voltage and current in electrical measurements
  • Explore advanced EKG interpretation techniques and common abnormalities
USEFUL FOR

Medical students, healthcare professionals, and anyone interested in understanding EKG mechanics and cardiac electrical activity.

drana91
Messages
3
Reaction score
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!
 
Physics news on Phys.org
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?
 
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?
 
Errr, I thought you just said that an EKG doesn't measure current...
 
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!
 
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.
 

Similar threads

  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 3 ·
Replies
3
Views
8K
  • · Replies 10 ·
Replies
10
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 6 ·
Replies
6
Views
6K
Replies
12
Views
2K
  • · Replies 4 ·
Replies
4
Views
6K
Replies
1
Views
2K