Cardiovascular Physiology 12

Question 1

What is the ECG a recording of?

Answer 1

The electrical activity of the heart

Question 2

What is ECG used to diagnose?

Answer 2

Problems with the hearts conducting system

Question 3

How many Leads do ECGs use?

Answer 3

12

Question 4

What is the ECG measuring the electrical changes from?

Answer 4

Many cardiac cells at once

Question 5

What are the fluctuations in voltage in an ECG known as?

Answer 5

Waves

Question 6

Why is the depolarization in the SA node not shown on an ECG?

Answer 6

Because the signal is not strong enough to reach the body’s surface where the electrodes are placed

Question 7

What is the first event seen on an ECG recording?

Answer 7

The P-wave

Question 8

What does the P-wave represent?

Answer 8

The spread of depolarization across the left and right atria

Question 9

What does the width of the P-wave tell us?

Answer 9

How long it takes the atrial contractile myocytes to depolarize

Question 10

What wave comes after the P-wave?

Answer 10

The QRS complex

Question 11

What kind of deflection is seen in the QRS complex?

Answer 11

Downward, Upward and Downward deflection

Question 12

What is the labelling of the deflection in the QRS complex?

Answer 12

Down - Q wave
Up - R wave
Down - S wave

Question 13

What does the QRS complex show?

Answer 13

The electrical activity when the contractile myocytes of the left and right ventricles depolarize

Question 14

What does the width of the QRS complex tell us?

Answer 14

How long it takes for the ventricular myocytes to depolarize

Question 15

What does the Q wave represent?

Answer 15

The wave of depolarization the flow down the interventricular septum

Question 16

What do the R wave and S wave signify?

Answer 16

Depolarization that spread from the apex and then up towards the base of the ventricles

Question 17

What happens at the same time as the ventricles depolarizing?

Answer 17

The Atrial contractile myocytes repolarize

Question 18

Why can we not see the repolarization of the atria on an ECG?

Answer 18

It is too small of an event to be recorded at the surface of the skin

Question 19

What occurs after the QRS complex in an ECG?

Answer 19

The T wave

Question 20

What does the T wave represent?

Answer 20

Ventricular Repolarization

Question 21

Which parts of the heart can depolarization not be measured from the surface of the skin?

Answer 21

• SA node
• AV node
• Bundle of His
• Bundle branches
• Purkinje network

Question 22

Where does the PR interval start and end?

Answer 22

It starts at the beginning of the P wave with atrial depolarization and ends at the beginning of the QRS complex

Question 23

What does the PR interval signify?

Answer 23

How long it takes an action potential to propagate from the AV node before activating the ventricles

Question 24

Where does the QT interval span?

Answer 24

The beginning of the QRS complex and goes to the end of the T wave

Question 25

What does the QT interval indicate?

Answer 25

How long the ventricles remain depolarized and is a rough measure of the duration of the overall action potential

Question 26

What does the ST segment span?

Answer 26

After the QRS complex until the beginning of ventricular repolarization

Question 27

What does the ST segment represent?

Answer 27

The time until ventricular repolarization

Question 28

How can the ST segment be described as?

Answer 28

Flat or Iso electric because it does not change in potential

Question 29

What does the ST segment correspond to?

Answer 29

The plateau phase of the action potential