Lesson 18: Topic 14 - Electrocardiogram and Cardiac Cycle Flashcards
what is an ECG signal?
measurement of electrical signal in the heart
- sum of all cardiac action potentials (ventricular and atrial)
the electrical activity in the ECG is predominantly coming from?
the cardiac muscle cells because the atrial APs are too small
what is the P-wave in an ECG?
P wave is when you have atrial depolarization
what does the time length of the P-wave mean?
there is cell-to-cell conduction
- prolonged sengment
what is cell-to-cell conduction?
one cardiac muscle cell is going to depolarize and then the next through the gap junctions and sodium influx
what is the PR segment of the ECG?
- happens after atrial depolarization
- atria contraction
why is there a delay from P to PR on the ECG?
electrical signal reaches AV node and there is going to be a delay in the AV node
what is the purpose of the PR delay segment? (AV node delay)
purpose is to ensure that the atria fully contracts and is able to fully eject the blood from the atria into the ventricle before the ventricle begins to contract
what is the QRS-complex on the ECG?
ventricular depolarization
why does the QRS complex occur very quickly (ventricular contraction)?
the ventricular contraction have purkinje fibers that is going to rapidly excite the whole entire ventricle because we can’t afford to have cell-to-cell conjunction
why is there a large amplitude different in the ventricle contraction (QRS) compared to the atria contraction (P)?
this is because the ventricular contraction is stronger and its stronger because there are more cardiac muscle cells
more cardiac muscle cells =
more electrical activity
what does the ST segment of the ECG represent?
ventricular contraction
- the ventricle is going to contract and eject blood into the aorta and pulmonary artery and then is followed by ventricular repolarization
what does the T-wave of the ECG represent?
ventricular repolarization
what does the TP interval represent in the ECG?
ventricular relaxation and filling
since the T-wave represents ventricular repolarization, where does atrial repolarization happen?
during the QRS complex, its just hidden because the ventricular depolarization is stronger
during an ECG recording, the QRS complex is observed to be smaller than normal. what is the most likely physiological explanation for this change in amplitude?
less electrical activity happening in the ventricle than normal
- less electrical activity = less cardiac muscle cells
- means there are thinner and less cardiac muscle cells in the ventricle
what is systole?
ventricular contraction
what is extrasystole?
premature ventricular contraction
- happening at the wrong time
if we see a huge disruption(meaning big amplitude) in the ECG, what can we assume the chamber causing it is?
we can assume its the ventricle because the atria cannot produce that much electrical signal due to low strength
when looking at ventricular fibrillation, how do we know the problem is occurring in the ventricle?
there is no QRS, so there is no ventricular depolarization properly (not sufficient for a strong contraction, not ejecting blood)
what happens if ventricular fibrillation keeps occuring?
someone will die because there is no blood going to the brain
what can fix ventricular fibrillation?
paddles
- restart the heart and synchrony
what is a complete heart block?
SA node is working properly to sync and cause atrial depolarization
- P-wave is depolarization at a regular sequence but we have the QRS that is out of sync
- PQRST segment is not happening in sync
- PROBLEM: AV node has its own pace making ability to make the ventricle contract, so SA and AV node are both working. the problem is BETWEEN them. the communication is not working
what is a cardiac myocardial infarction (heart attack)?
has a PQR and the ST is elevated
- due to ischemic cells are undergoing dysfunction and they can prematurely depolarize and have problems with repolarize.
what are the abnormalities in heart rhythm?
- extrasystole (premature ventricular contraction)
- ventricular fibrillation
- complete heart block
what are the cardiac myopathies is the heart?
myocardial infarction (heart attack)
what is a cardiac cycle?
events of each heartbeat
what is the whole function of the cardiac cycle?
to move blood throughout the whole entire body.
- the heart is contracting, moving blood throughout the whole entire body, moving deoxygenated blood to the lungs, moving oxygenated blood back into your heart
how is the movement of blood dictated?
dictated by blood flow
- F = Pressure gradient / resistance
need ___________ ___________ in order for blood flow to occur.
pressure differences
how are pressure differences generated?
by muscle contraction
what are the two essential phases of the cardiac cycle?
- systole
- diastole
what is systole?
ventricular contraction and ejection
what is isovolumetric ventricular contraction?
iso = same
volumetric = volume
- same volume in this contraction
why is there no volume change in an isovolumetric contraction of the heart?
blood is not moving anywhere so volume stays the same
- ex. like a balloon. if you squish it, the volume stays the same because the air is not leaving
are the valves open or closed in isovolumetric contraction?
always close
why/when would isovolumetric contraction occur?
- because the pressure in the ventricle is going to be less than the volume in the aorta or pulmonary arteries so the blood has no pressure gradient to move across
what is diastole?
ventricular relaxation and filling
what is an isovolumetric ventricular relation?
no volume change, all valves are closed, the ventricle relaxes but pressure it still higher than in the atria so valve stays closed. and aortic and pulmonary pressure is also higher.
what step follows isovolumetric ventricular relaxation?
ventricular filling, because the atria now have a higher pressure so it will fill the ventricle.
whether a valve is open depends on?
a pressure gradient
roughly how long is systole?
0.3s (300msec)
roughly how long is diastole?
0.5s (500msec)
when we measure systolic and diastolic blood pressure, what is it really coming from?
aortic pressures
the lub-dub sound you hear during someone’s heart beat is due to?
valves opening
how do you calculate stroke volume (SV)?
end diastolic volume - end systolic volume = SV
during ventricular relaxation, ventricles fill when?
AV valves open due to atrial pressure being higher than ventricular pressure so blood flows into the ventricle
