Cardiac Cycle Flashcards
What are the two types of circulation in the heart ?
1) systemic = high pressure
2) pulmonary = low pressure system
Define systole
Contraction and ejection of blood from ventricles
Diastole
Relation and filling of ventricles
Average stroke volume for a 70kg man
70ml blood
Define stroke volume
Volume of blood ejected from each ventricle per beat
Are cardiac action potentials longer or shorter than the usual action potentials in eg neuronal cells ?
Much longer - lasts for 280ms
What are chordae tendineae
They are also known as ‘ heart strings’
- they are tendon resembling fibrous chords of connective tissue that connect the papillary muscles to tricuspid and bicuspid valve.
Functions of the papillary muscles
- they are found in both ventricles
- they attach to the tricuspid and bicuspid values via chordae tendineae.
- they contract to prevents inversion of valves during systole
How many phases can the cardiac cycle be split into ?
7
List all 7 phases of the cardiac cycle
1) atrial contraction
2) isovolumetrric contraction
3) rapid ejection
4) reduced ejection
5) isovolumetric relaxation
6) rapid filling
7) reduced filling
What is the total duration of all 7 phases ?
0.9 s
In one heart beat , there are … systole and … diastole
1 and 1
Wiggers diagram
Insert image
What occurs during atrial contraction : the first phase ?
- atria contract , which causes an increase in pressure
- AV vales are open
- semi lunar valves are closed
- this is called an A wave.
- on an ECG : this is called a P wave.
What percentage of ventricular filling does atrial contraction account for ?
10%
At the end of phase 1, are ventricular volumes maximal or minimal ?
Maximal
- this is termed end diastolic volume ( EDV) - 120 ml
What occurs during isovolumetric contraction ?
1) mitral valve closes because ventricular pressure exceeds atrial pressure
- ventricles contract which causes rapid rise in ventricular pressure
- ALL valves are closed
- QRS complex signifies onset of ventricular depolarisation
- EDV remains the SAME because no change in volume due to ALL valves being the same
What occurs during phase 3: rapid ejection
1) AORTIC VALVE opens because ventricular pressure exceeds aortic pressure
- causes ejection of blood into aorta
- rapid decrease in ventricular volume as blood is ejected into aorta
- atrial pressure initially decreases as atrial base pulled downwards when ventricles contract = X descent
What occurs during phase 4: reduced ejection
1) repolarisation of ventricles lead to a decline in tension and rate of ejection begins to fall
2) atrial pressure gradually rises due to continued venous return from lungs = V wave
3) T wave on ECG
What occurs during phase 5: isovolumetric relation
1) aortic valves close because ventricle pressure falls below aortic pressure
2) dicrotic notch in aortic pressure curved caused by valve closure
3) rapid decline in ventricular pressure, but volume remains the same because all valves close
You get end systolic volume .
WHat occurs during phase 6 : rapid filling
1) mitral valves open because atrial pressure exceeds ventricular
2) fall in atrial pressure after mitral valves open is called Y descent
3) rapid ventricular filling occurs
What occurs during phase 7: reduced filling ?
Rate of filling slows down as ventricle reaches relaxed volume.
- this is called diastatis
What is responsible for the S1 sound in a phonocardiogram ?
Closure of the mitral valves during phase 2: isovolumetric contraction.
What is responsible for the S2 sound in the phonocardiogram?
Closure of the semi lunar valves during phase 5: isovolumetric relaxation
What is responsible for the S3 sound ?
Ventricular filling is normally silent . However m third heart sound sometimes present in children , but could be a sign of pathology in adults. Occurs during phase 6- rapid filling
What are two forms of abnormal valve function ?
1) stenosis
3) regurgitation
What is stenosis ?
Valve doesn’t open enough which results in obstruction to blood flow when valve would normally open
What is regurgitation ?
Valve doesn’t close all the way , leads to back leakage when valve should be closed
What causes aortic valve stenosis ?
1) chronic rheumatic fever which results in inflammation
2) congenital cause eg born with bicuspid form of valve
3) degenerative cause eg calcification
What are the consequences for aortic valve stenosis ?
- less blood can get through to valve
- increased left ventricular pressure due to having to work much harder
- results in left ventricular hypertrophy
OR it could lead to left sided heart failure which is characterised by angina ( tightening of the chest) and syncope ( fainting )
What is the cause of aortic valve regurgitation?
1) aortic root dilation ( leaflets pulled apart)
2) valvular damage due to rheumatic fever
What are the consequences of aortic valve regurgitation?
- blood flows back into left ventricle during diastole
- increases stroke volume as more blood is coming back so more blood to pump
- systolic pressure increases and diastolic pressure decreases
- leads to bounding pulse ( head bobbing , beds of nails go red and pale with each beat - QUINKES sign)
- Left ventricular hypertrophy
What is the main cause for mitral valve stenosis ?
Rheumatic fever (99.9% cases)
What are the consequences for mitral valve stenosis ?
Increased left atrium pressure because harder for blood to flow from left atrium to left ventricle
Left atria dilation is a consequence of increased left atrial pressure due to mitral valve stenosis , what are the consequences of increased left atrial dilation ?
- these leads to left atrium dilation which could lead to oesophagus compression which then leads to dysphagia ( swallowing difficulties)
- or the artrial dilation could lead to atrial fibrillation which would lead to thrombus formation.
What are a few other consequences of increased left atrial pressure ( mitral valve stenosis) - other than left atrial dilation ?
- pulmonary oedema (accumulation of fluid within the air spaces and tissues of the lungs) m
- pulmonary hypertension ( increased blood pressure within the arteries of the lungs)
- dyspnea ( shortness of breath)
What are the causes of mitral valve regurgitation?
1) damage to papillary muscles after heart attack
2) myxomatous ( thickening and weakening of mitral leaflets and tendonae) degeneration can weaken tissue leading to prolapse
3) rhetumatic fever which leads to leaflet fibrosis
4) Left sided heart failure leads to left ventricle dilation which can stretch valve
What are the consequences of mitral valve regurgitation?
- as some blood leaks back into left atrium , this increases preload as more blood enters LV in subsequent cycles .. this causes hypertrophy of LV
