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
How long is QT interval normally?
0.35 ms
An abnormal QT interval can be caused by what?
Abnormal phase 2
-issues with calcium or potassium channels
What can be the underlying problem for a longer PR interval?
Maybe issue with AV node
Where are leads normally placed?
Right Arm
Left Arm
Left Leg
Which chest/precordial leads tend to be negative and positive?
Negative: V1 and V2
Positive: V4-V6
Which electrodes look at inferior regions of the heart?
II
III
aVF
Which electrodes look at the right ventricle of the heart?
V1
V2
Which electrodes look at anterior regions of the heart?
V3
V4
Which electrodes look at lateral regions of the heart?
V5
V6
I
aVL
Which electrodes look at interventricular septum of the heart?
V3
V4
