Electrocardiogram and Cardiac Cycle: Lecture 6

Question 1

What is an ECG signal?

Answer 1

the sum of all cardiac action potentials

Question 2

Where do we get cardiac action potentials from?

Answer 2

SA node and muscle cells

Question 3

Where does the electrical activity come from predominantly?

Answer 3

cardiac muscle cells

Question 4

What happens at P-wave?

Answer 4

Atrial depolarization

Question 5

What happens during the PR wave?

Answer 5

contraction, atrial contraction and AV delay

Question 6

How long is the P-wave typically?

Answer 6

200msec

Question 7

True or False
The longer the amplitude of the signal = the more cardiac muscle cells will be activated

Answer 7

True

Question 8

What is Q representing?

Answer 8

a lag/delay in time due to AV nodal delay

Question 9

What is the purpose of the Q stage?

Answer 9

to ensure that the atria fully contract and can fully eject the blood from the atrial into the ventricles before the ventricles contract

Question 10

What is the QRS?

Answer 10

ventricular depolarization

Question 11

True or False
Ventricular contraction occurs quickly.

Answer 11

True

Question 12

Why is QRS all happening so rapidly?

Answer 12

due to Purkinje fibres, they can’t wait for cell-to-cell conjugation therefore, it needs to happen quicker

Question 13

Why is there a larger amplitude in ventricular electrical activity compared to the atria?

Answer 13

it is stronger because there are more cardiac muscle cells

Question 14

True or False
More cardiac muscle cells = more electrical activity

Answer 14

True

Question 15

What is happening between the S and T segments?

Answer 15

ventricular contraction, eject blood into the aorta or pulmonary artery

Question 16

What is happening at the T-wave?

Answer 16

ventricular repolarization

Question 17

What is happening at the T-P interval

Answer 17

ventricular relaxation

Question 18

Why is atrial repolarization not seen in the ECG image?

Answer 18

we cannot see it because it is dominated by the RS wave generated by ventricular depolarization

Question 19

During the ECG recording, the QRS is seen to be smaller than normal. what is most likely the physiological explanation for this change in amplitude?

Answer 19

due to smaller and thinner ventricles, because cardiac muscle cells are responsible for generating electrical activity, meaning fewer cells will equal less activity

Question 20

What is Extrasystole?

Answer 20

premature ventricular contraction

Question 21

What is ventricular fibrillation?

Answer 21

when there is no QRS consistently, the ventricle is not depolarizing sufficiently to pump enough blood into the body
- ventricle can’t pump blood properly

Question 22

What can fix ventricular fibrillation?

Answer 22

paddles

Question 23

What is complete heart block?

Answer 23

• SA node is working properly, meaning the P-wave is depolarizing at a regular sequence
• QRS is present so the ventricle is depolarizing
• AV node is working
• Communication between SA and AV node is lost

Question 24

What is a Myocardial infarction aka Heart Attack?

Answer 24

• ST elevation
• due to a clot there is not sufficient oxygen, and depolarizations are off-sync

Question 25

What is the blood flow formula?

Answer 25

Flow = delta Pressure/Resistance

Question 26

Do we need pressure difference to move blood in the body?

Answer 26

YESSIR

Question 27

What are the 2 important phases of the cardiac cycle?

Answer 27

1. Systole - ventricular contraction and ejection 2. Diastole - ventricular relaxation and filling

Question 28

What is an isovolumetric ventricular contraction?

Answer 28

same volume contraction - meaning there is no volume change in the heart but the heart is contracting

Question 29

True or False In isovolumetric contraction, all the valves are always closed?

Answer 29

True

Question 30

What is happening with pressure in the isovolumetric ventricular contractions?

Answer 30

- ventricle has greater pressure than inside the atria - pulmonary artery pressure or aortic pressure is greater than ventricular pressure because the ventricular pressure is not sufficient enough to open the pulmonary or aortic valve

Question 31

What is happening at isoventricular relaxation?

Answer 31

- all the valves are closed - ventricle is relaxing - pulmonary and aortic pressure is still higher than inside the ventricle

Question 32

What is the step that follows isoventricular relaxation?

Answer 32

Ventricular filling, where blood flows into the ventricles

Question 33

What is happening at the ventricular filling?

Answer 33

after the heart has had a ventricular contraction - Now the ventricle is an area of low pressure - atria pressure is higher than ventricle causing ventricular filling AV valve is opened

Question 34

What is the time associated with systole?

Answer 34

0.3 sec or 300 msec

Question 35

What is the time associated with diastole?

Answer 35

0.5 sec or 500 msec

Question 36

How can we calculate stroke volume?

Answer 36

end diastolic volume - end systolic volume

Question 37

STEP 1 What is happening at Ventricular diastole?

Answer 37

blood comes into the heart to the atria - AV vales sense the high pressures in the atria forcing them to open to allow for blood to fall into ventricles - SA node signals atria to contact any remaining blood from the atria to the ventricle P wave

Question 38

STEP 2 What is happening at Isovolumetric systole?

Answer 38

All the blood is in the ventricles now, all the valves are shut - Ventricles go through an isovolumetric contraction as pressure builds QRS complex

Question 39

STEP 3 What is happening at ventricular systole?

Answer 39

Pressure is built in the ventricles - Semilunar valves open - Blood is being pushed into the aorta or pulmonary arteries QRS complex

Question 40

STEP 4 What is happening at Isovolumetric diastole?

Answer 40

Blood is going to the rest of the body or the lungs - all valves are shut again - ventricles are relaxing T wave