Remember how I said that a lead has a positive electrode? Well this comes into play when looking at a specific lead. The isoelectric line is your baseline so-to-speak. The isoelectric line has no amplitude. Anything above the isoelectric line is considered a positive deflection and anything below it is considered a negative deflection.
- When deflections are positive, the mean electrical current is heading in the general direction of the positive electrode.
- When deflections are negative, the mean electrical current is heading away from the positive electrode.
In the above description, you can replace the word 'deflection' with the word 'wave'.
- Deflections or Waves on an ECG strip are representations of heart chamber depolarization and/or replorization (for definitions see basic cardio 2).
Below is an image from Wikipedia which illustrates what I just said:
Take a look at the ECG strip below. Lets say that this is lead II. The yellow circles and lines point out all the positive deflections. The white circle depicts the single negative deflection and the blue lines in the magnified portion are pointing to the isoelectric line.
The isoelectric line is normally at the beginning and end of all waveforms.