Cardiac Cycle Flashcards
What are the four major stages of the cardiac cycle
Diastole and the inflow of blood.
The blood volume stays the same and there is isovolumetric contraction.
The outflow of blood phase systole
And then Isovolumetric relaxation for diastole again.
It is isovolumetric because the valves close and the volume stays the same.
How is the cycle initiated
Why do both atria contract together
and what happens after
The P wave occurs and both atria contract together.
Because of fast conduction velocity in the Bachman’s branch.
The blood pressure in the atria increases and blood enters the ventricles which takes 0.1second.
80% of blood flows into the ventricles passively due to gravity and elasticity.
The left atria only contributes to 10% of flow into ventricles. The rest is due to the atrial kick.
After the atria contract their pressure begins to fall and the AV valves shut.
Atrial fibrillation.
The atrial muscles quiver but it doesn’t have a big affect as 80% of blood flow is passive and doesn’t require the atrial muscles.
Phase 1 of the cycle
Ventricles are….
What is the end diastolic pressures and why
The ventricular volumes are maximal (end diastolic volume)
On the left it is 120ml and this represents the ventricular pre load.
LV = 8-12mmHg RV = 3-6mmHg
The RV is smaller so it doesn’t damage the lung capillaries because they are close and very thin.
The alveoli could fill with blood due to many fenestrations and cause a pulmonary oedema (dry drowning)
Phase 2
What are the valves doing and what happens in this phase
What does ventricle contraction trigger
What is the first heart sound
All valves are closed.
This is when there is QRS on the ECG. ventricular depolarisation.
The myocyte muscles will contract.
The rate of pressure development is rapid.
The AV valves close when ventricle pressure exceeds atrial pressure.
Ventricle contraction triggers papillary muscles contraction with their chordate tendinae which are attached to the valves. They stop the AV valves bulging back too far into the atria and becoming incompetent.
Closing of the AV valves is the first heart sound. This sound is normally split because tricuspid closure is slightly after mitral closure.
Phase 3 what happens
C wave
What is the rate of pressure increase in the ventricles determined by
Ventricular pressure rises rapidly without a change in the volume.
The C wave on the graph is due to AV valves bulging back into the atria and causing their pressure to slightly increase due to the volume decrease.
Rate of contraction of the muscle fibres.
Phase 4
What happens and valves
What maximums are achieved
Heart sounds
What happens to the atria
The pressure in the ventricles is sufficient to open the semilunar valves.
The AV valves remain shut.
Blood is pumped out the ventricles as the pressure is higher in the ventricles than the arteries.
Maximum outflow velocity.
Maximum aortic and pulmonary pressure.
No heart sound when healthy valves open.
As the ventricles contract the atria are pulled down and this causes a slight volume increase and pressure decrease. Blood begins to enter the atria from veins and pressure rises again.
What happens after phase 4
Any heart sounds ?
Dicrotic notch and wave
What determines the rate of pressure decline in the ventricles.
Isovolumetric relaxation where the pressure decreases after contraction.
This will cause the semilunar valves to close and give the second heart sound.
There is small backflow of aortic blood into the ventricles causing the dicrotic notch in the graph.
The dicrotic wave is when the aortic pressure increases and then slowly decreases again.
The rate of pressure decline is determined by muscle relaxation rate (lusitrophy). And this relaxation is regulated by the sarcoplasmic reticulum rapidly taking up Ca to stop contraction.
What is the blood called which remains in the ventricles after contraction
End systolic volume
50ml in left ventricle.
What is stroke volume
The difference between the end diastolic volume 120ml
And end systolic volume 50ml.
Which is 70ml.
Phase 6
The ventricles continue to relax until the ventricular pressure falls below the atrial pressure.
Causing the AV valves to rapidly open and the ventricles start to be passively filled again.
A third heart sound
Ventricular filling is normally silent
When a third heart sound is audible it may be because of tensing of chordea tendinea and AV ring during ventricular relaxation and filling.
Picture
Picture
Electrocardiograph =
Electrocardiogram =
Machine
Recording
Where does the impulse spread when it passes through the heart
How can we measure the impulse
To all adjacent tissues surrounding the heart and even to the skin surface.
If electrodes are placed on the skin around the heart we can record the electrical activity on an ECG.
What is a lead used in ECGs.
What happens if the depolarisation is moving towards or away from an electrode
What does each lead do
The tracing of the voltage differences between two electrodes and what is actually produced by the ECG recorder.
If the depolarisation is going towards the electrode the graph will go upwards. If it is moving away from the electrode the graph will have a deflection.
1- difference between the right arm electrode and the left arm one.
2- difference between the right arm and left leg.
3- difference between the left arm and left leg
PICTURE.
What is the ECG like at rest
The direction of depolarisation through the heart determines
Where will the biggest wave be found
There is no net current flow towards any electrode.
And so there are no deflections on the ECG.
Depending on which lead is looked at there will be a normal ECG shape.
The waves on the ECG.
On lead 2 where the impulse reached the bottom of the heart and changed direction to travel back up the sides.
The P wave and which lead sees it.
QRS
T wave
Atrial depolarisation makes a small wave because they are only small. This is picked up on the lead 2.
Ventricular depolarisation begins at the apex and makes a big wave due to the large ventricles.
Ventricular repolarisation begins at the apex.
What is the U wave
It is thought to be the repolarisation of papillary muscles.
How long is each of the intervals
P-R is 0.12-0.2 seconds
QRS is 0.08-0.1 seconds
QT is 0.4-0.43 seconds
ST is 0.32 seconds
What is electromechanical dissociation
The heart is so damaged that it can’t respond to electrical activity and the person has no cardiac output.
Corpses can still have an ECG reading because of this.
Abnormally large P wave means
Low T wave means
Long ST means
The atria are hypertrophied and have too much muscle.
Ventricular hypoxia as there is no enough blood supply to ventricles.
Myocardial infarction
Arrhythmia
Examples
Lack of normal rhythm.
Heart rate should normally vary when we exercise etc.
Non exercise tachycardia- 150-200bpm for short periods of time causing dizziness.
Heart flutter lasting a few seconds 200-300bpm.
Fibrillation is fast non synchronous contraction 300bpm can lead to cardiac arrest.
What are heart blocks
Impairments of conducting pathways
Can be caused by infractions, artery disease or partial blocks of coronary arteries.
First degree heart block and what it causes on the ECG
Interruption somewhere between the SA node and the AV node.
There is slowing down of conduction.
There is an increased PR interval
Second degree heart block
Some of the SA impulses fail to cause a QRS.
Mobitz 1- progressive prolongation of the PR interval and it gets longer and longer until there is a missed QRS.
Mobitz 2- there is no PR interval prolongation but there is the occasional absence of QRS. the PR intervals are normal.
PICTURE
What causes mobitz 2
What do patients also have
Why is it all or nothing
What do patients need ?
Failure of conduction at the level of the bundle of his or purkinje fibres.
Due to structural damage to the conducting system like fibrosis.
LBBB- left bundle branch block.
Part of the left bundle branch has a blockage of conduction.
The conduction in the purkinje or his suddenly fails.
Pacemaker
What causes Mobitz 1
Progressive fatigue of the AV nodal cells.
Third degree heart blocks or complete heart block
What’s the ECG look like
What takes over as the pacemaker and how good is it.
Symptoms and what is AV dissociation
Complete absence of atrioventricular conduction.
No impulses make it to the ventricles.
P waves are fired but no QRS complexes.
The bundle of his acts as the pacemaker and it is very irregular.
It can supply the body until exercise when you need a regular large cardiac output.
The patient May suffer ventricular standstill where cardiac output stops. Syncope occurs or sudden death.
It causes brachycardia with independent atrial and ventricular rates called AV dissociation.
What can be seen under the skin and why in third degree heart block patients
The atria contract against a closed tricuspid valve which causes a pressure wave up the jugular veins and so their jugular vein can be seen pulsing under the skin.
Atrial fibrillation symptoms
And ECG
Usually asymptomatic. But they can have a rapid heart rate and make give angina.
In extreme cases it can cause shortness of breath or odema in the ankles.
No obvious P wave and there’s an irregular distance between the QRS complexes.
Atrial fibrillation treatment
Warfarin
Flecainide and beta blockers.
Need to make sure they aren’t on warfarin or anticoagulants incase it causes them to have too much blood thinning.
They are already likely to have been prescribed warfarin because they will have had a low cardiac output and this will decrease blood flow and make blood clot formation more likely.
Circus movement
How is re excitation normally stopped
Also known as re entry of an action potential.
The electrical signal is not completing the normal circuit and loops back upon itself rapidly.
The refractory muscle normally prevents re excitation.
If a wave meets a non refractory tissue it will be able to travel onwards.
PICTURE
