Electrocardiogram and Cardiac Cycle: Lecture 6 Flashcards
What is an ECG signal?
the sum of all cardiac action potentials
Where do we get cardiac action potentials from?
SA node and muscle cells
Where does the electrical activity come from predominantly?
cardiac muscle cells
What happens at P-wave?
Atrial depolarization
What happens during the PR wave?
contraction, atrial contraction and AV delay
How long is the P-wave typically?
200msec
True or False
The longer the amplitude of the signal = the more cardiac muscle cells will be activated
True
What is Q representing?
a lag/delay in time due to AV nodal delay
What is the purpose of the Q stage?
to ensure that the atria fully contract and can fully eject the blood from the atrial into the ventricles before the ventricles contract
What is the QRS?
ventricular depolarization
True or False
Ventricular contraction occurs quickly.
True
Why is QRS all happening so rapidly?
due to Purkinje fibres, they can’t wait for cell-to-cell conjugation therefore, it needs to happen quicker
Why is there a larger amplitude in ventricular electrical activity compared to the atria?
it is stronger because there are more cardiac muscle cells
True or False
More cardiac muscle cells = more electrical activity
True
What is happening between the S and T segments?
ventricular contraction, eject blood into the aorta or pulmonary artery
What is happening at the T-wave?
ventricular repolarization
What is happening at the T-P interval
ventricular relaxation
Why is atrial repolarization not seen in the ECG image?
we cannot see it because it is dominated by the RS wave generated by ventricular depolarization
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?
due to smaller and thinner ventricles, because cardiac muscle cells are responsible for generating electrical activity, meaning fewer cells will equal less activity
What is Extrasystole?
premature ventricular contraction
What is ventricular fibrillation?
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
What can fix ventricular fibrillation?
paddles
What is complete heart block?
- 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
What is a Myocardial infarction aka Heart Attack?
- ST elevation
- due to a clot there is not sufficient oxygen, and depolarizations are off-sync
What is the blood flow formula?
Flow = delta Pressure/Resistance
Do we need pressure difference to move blood in the body?
YESSIR
What are the 2 important phases of the cardiac cycle?
- Systole
- ventricular contraction and ejection - Diastole
- ventricular relaxation and filling
What is an isovolumetric ventricular contraction?
same volume contraction
- meaning there is no volume change in the heart but the heart is contracting
True or False
In isovolumetric contraction, all the valves are always closed?
True
What is happening with pressure in the isovolumetric ventricular contractions?
- 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
What is happening at isoventricular relaxation?
- all the valves are closed
- ventricle is relaxing
- pulmonary and aortic pressure is still higher than inside the ventricle
What is the step that follows isoventricular relaxation?
Ventricular filling, where blood flows into the ventricles
What is happening at the ventricular filling?
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
What is the time associated with systole?
0.3 sec or 300 msec
What is the time associated with diastole?
0.5 sec or 500 msec
How can we calculate stroke volume?
end diastolic volume - end systolic volume
STEP 1
What is happening at Ventricular diastole?
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
STEP 2
What is happening at Isovolumetric systole?
All the blood is in the ventricles now, all the valves are shut
- Ventricles go through an isovolumetric contraction as pressure builds
QRS complex
STEP 3
What is happening at ventricular systole?
Pressure is built in the ventricles
- Semilunar valves open
- Blood is being pushed into the aorta or pulmonary arteries
QRS complex
STEP 4
What is happening at Isovolumetric diastole?
Blood is going to the rest of the body or the lungs
- all valves are shut again
- ventricles are relaxing
T wave
