Cardiovascular Physiology 12 Flashcards
What is the ECG a recording of?
The electrical activity of the heart
What is ECG used to diagnose?
Problems with the hearts conducting system
How many Leads do ECGs use?
12
What is the ECG measuring the electrical changes from?
Many cardiac cells at once
What are the fluctuations in voltage in an ECG known as?
Waves
Why is the depolarization in the SA node not shown on an ECG?
Because the signal is not strong enough to reach the body’s surface where the electrodes are placed
What is the first event seen on an ECG recording?
The P-wave
What does the P-wave represent?
The spread of depolarization across the left and right atria
What does the width of the P-wave tell us?
How long it takes the atrial contractile myocytes to depolarize
What wave comes after the P-wave?
The QRS complex
What kind of deflection is seen in the QRS complex?
Downward, Upward and Downward deflection
What is the labelling of the deflection in the QRS complex?
Down - Q wave
Up - R wave
Down - S wave
What does the QRS complex show?
The electrical activity when the contractile myocytes of the left and right ventricles depolarize
What does the width of the QRS complex tell us?
How long it takes for the ventricular myocytes to depolarize
What does the Q wave represent?
The wave of depolarization the flow down the interventricular septum
What do the R wave and S wave signify?
Depolarization that spread from the apex and then up towards the base of the ventricles
What happens at the same time as the ventricles depolarizing?
The Atrial contractile myocytes repolarize
Why can we not see the repolarization of the atria on an ECG?
It is too small of an event to be recorded at the surface of the skin
What occurs after the QRS complex in an ECG?
The T wave
What does the T wave represent?
Ventricular Repolarization
Which parts of the heart can depolarization not be measured from the surface of the skin?
- SA node
- AV node
- Bundle of His
- Bundle branches
- Purkinje network
Where does the PR interval start and end?
It starts at the beginning of the P wave with atrial depolarization and ends at the beginning of the QRS complex
What does the PR interval signify?
How long it takes an action potential to propagate from the AV node before activating the ventricles
Where does the QT interval span?
The beginning of the QRS complex and goes to the end of the T wave
What does the QT interval indicate?
How long the ventricles remain depolarized and is a rough measure of the duration of the overall action potential
What does the ST segment span?
After the QRS complex until the beginning of ventricular repolarization
What does the ST segment represent?
The time until ventricular repolarization
How can the ST segment be described as?
Flat or Iso electric because it does not change in potential
What does the ST segment correspond to?
The plateau phase of the action potential
