Lecture 16: Physiological Basis of ECG Flashcards
The ECG measures ____ potential.
Extracellular
Why does the ECG not report a difference between the atria and ventricles?
Due to insulation between atria and ventricles
-no current flow
What are the normal charges of the base and apex of the heart?
Base: negative
Apex: positive
What is the pathway of depolarization of the heart?
SA Node –> atrial muscles –> AV node –> bundle branches –> purkinje fiber –> ventricular muscles
SA nodes cause atria to depolarize in what direction?
Right to left
Ventricles depolarize in what direction?
Right to left
Base to apex
Interior to exterior
Ventricles repolarize in what direction?
Left to right
Base to apex
Where is the u wave seen?
After T wave but not normal
-unsure what causes it
When are timed potassium gates opened in ventricles?
T wave (phase 3)
When is sodium most permeable?
P wave (phase 0)
What is a segment?
Duration of single event on ECG
- P wave
- QRS complex
- T wave
What is an interval?
Duration of two or more events
- PR interval
- QT interval
- ST interval
How many large boxes make up 1 second on an ECG?
5 boxes (horizontal) -each box is 0.2 seconds
How many large boxes make up 1 mv on an ECG?
2 boxes (vertical) -each box is 0.5 mv
How long is PR interval normally?
0.16 ms
