Cardiac Cycle

Question 1

What are resistance vessels

Answer 1

Arterioles that direct blood to where needed (high arterial pressure)

Question 2

What are capacitance vessels

Answer 2

Act as storage which release blood when needed (low venous pressure)

Question 3

What is systole

Answer 3

Contraction and ejection of blood from ventricles

Question 4

What is diastole

Answer 4

Relaxation and filling of ventricles

Question 5

Name the 4 major valves within the heart

Answer 5

Mitral valve, aortic valve, tricuspid valve, pulmonary valve

Question 6

Explain the structure of myocardium

Answer 6

Individual cells but are functional syncytium
Cells connected together through gap junctions so what happens in one cells can quickly be transmitted to adjacent cells - functionally electrically connected

Question 7

Explain structure of heart valves

Answer 7

Cusps of mitral and tricuspid valves attach to papillary muscles via chordae tendineae
Chordae tendineae anchor the valve leaflets to prevent leaflets from inverting on systole

Question 8

Briefly explain the conduction system

Answer 8

1. Special cardiac myocytes of pacemaker cells in sinoatrial node generate action potential
2. Activity spreads over atria - atrial systole
3. Atrioventricular node delays action potential to allow ventricle to contract later (120ms)
4. Excitation spreads down septum between ventricles
5. Then spreads through ventricular myocardium from inner (endocardial) to outer (epicardial) surface
6. Ventricle contracts from the apex up forcing blood through outflow valves

Question 9

List the 7 phases of the cardiac cycle

Answer 9

1. Atrial contraction
2. Isovolumetric contraction
3. Rapid ejection
4. Reduced ejection
5. Isovolumetric relaxation
6. Rapid filling
7. Reduced filling

Question 10

Explain atrial contraction

Answer 10

Ventricle already 80% filled through passive filling with atrial contraction topping up ventricle
Atrial pressure rises due to atrial systole (A wave)
P wave in ECG signifies onset of atrial depolarisation
At the end of Phase 1, ventricular volumes are maximal - termed end-diastolic volume (EDV) - typically 120ml

Question 11

Explain isovolumetric contraction

Answer 11

QRS complex in ECG signifies onset of ventricular depolarisation
Mitral valve closes as intraventricular pressure exceeds atrial pressure
Rapid rise in ventricular pressure as ventricle contracts
Closing of mitral valve causes the C-wave in the atrial pressure curve
Isoventricular since there is no change in ventricular volume (all valves closed)
Closure of the mitral and tricuspid valve results in the first heart sound (S1)

Question 12

Explain rapid ejection

Answer 12

Ejection begins when the intraventricular pressure exceeds the pressure within the aorta - causes aortic valve to open
Rapid decrease in ventricular volume as blood is ejected into aorta
Atrial pressure initially decreases as the atrial base is pulled downward as ventricle contracts (X descent)
Blood continues to flow into the atria from the their respective venous inputs

Question 13

Explain reduced ejection

Answer 13

Repolarisation of ventricle leads to a decline in tension and the rate of rejection begins to fall
Atrial pressure gradually rises due to the continued venous return from the lungs (V wave)
Ventricular repolarisation depicted by T-wave of ECG

Question 14

Explain isovolumetric relaxation

Answer 14

When intraventricular pressure falls below aortic pressure, there is a brief backflow of blood which causes the aortic valve to close
Closure of the aortic and pulmonary valves results in the second heart sound (S2)
Although rapid decline in ventricular pressure, volume remains constant since all valves are closed (isovolumetric relaxation)
Dicrotic notch in aortic pressure curve caused by valve closure
Stroke volume is the amount of blood ejected each beat

Question 15

Explain rapid filling

Answer 15

When the intraventricular pressure falls below atrial pressure, the mitral valve opens and rapid ventricular filling begins
Fall in atrial pressure that occurs after opening of mitral valve (Y descent)
Ventricular filling normally silent - (S3) heart sound in adults may signify heart failure

Question 16

Explain reduced filling

Answer 16

Rate of filing slows down (diastasis) as ventricle reaches its inherent relaxed volume

Question 17

Define stroke volume and give its equation

Answer 17

Stroke volume is the volume of blood pumped from the left ventricle per beat
Stroke volume = end diastolic volume - end systolic volume = EDV - ESV

Question 18

What is normal typical value of stroke volume

Answer 18

At rest, each ventricle pumps ~70mL blood per beat

At a heart rate of 70bpm = 4.9L blood pumped per minute (approximate volume of blood in body)

Question 19

Explain the timings of systole and diastole at rest

Answer 19

Systole occurs between when mitral valve closes to when the aortic valve closes
Occurs when aortic valve closes to when mitral valve closes

Question 20

Explain how systole and diastole change during exercise

Answer 20

Systole gradually increases in exercise

Question 21

Explain the origin of the 1st and 2nd heart sounds in relation to the cardiac cycle

Answer 21

The 1st heart sound is when the tricuspid and mitral valves close in phase 2 of the cardiac cycle
The 2nd heart sound is when the aortic and pulmonary valves close in phase 5 of the cardiac cycle

Question 22

What is stenosis

Answer 22

Valve doesn’t open enough leading to obstruction to blood flow when valve normally open

Question 23

What is regurgitation/incompetence

Answer 23

Valves do not close all the way leading to back flow when valve should be closed

Question 24

What are causes of aortic valve stenosis

Answer 24

Degenerative (senile calcification/fibrosis)
Congenital (bicuspid form of valve)
Chronic rheumatic fever - inflammation - commissural fusion

Question 25

What are the effect of aortic stenosis

Answer 25

Less blood can get through valve:
Increased left ventricle pressure leading to left ventricle hypertrophy as muscle has to work harder against the higher pressure
Left sided heart failure leading to syncope (fainting) or angina (chest pain)

Question 26

What are the causes of aortic valve regurgitation

Answer 26

Aortic root dilation (leaflets pulled apart)
Valvular damage (endocarditis rheumatic fever)

Question 27

What are the effect of aortic valve regurgitation

Answer 27

Blood flows back into left ventricle during diastole
Increases stroke volume as blood flows back to atria for refilling
Systolic pressure increases
Diastole pressure decreases as less volume in aorta
Bounding pulse (head bobbing, Quinke’s sign - light compressions of nail bed)
Left ventricle hypertrophy

Question 28

What is the main cause of mitral valve stenosis

Answer 28

Rheumatic fever

Question 29

What is the effect of mitral valve stenosis

Answer 29

Harder for blood to flow from left atrium to left ventricle leading to increased left atrial pressure
Pulmonary oedema, dyspnea, pulmonary hypertension leading to right ventricle hypertrophy
Left atrium dilation leading to atrial fibrillation causing thrombus formation
May also lead to oesophagus compression causing dysphagia (difficulty/discomfort swallowing)

Question 30

What are the causes of mitral valve regurgitation

Answer 30

Chordae tendineae & papillary muscle normally prevent prolapse in systole
Myxomatous degeneration can weaken tissue leading to prolapse
Other causes - damage to papillary muscle after heart attack
Left sided heart failure leads to left ventricle dilation which can stretch valve
Rheumatic fever can lead to leaflet fibrosis which disrupts seal formation

Question 31

What is the effect of mitral valve regurgitation

Answer 31

As some blood leaks back into left atrium, this increases preload