Cardiac Cycle Flashcards
What are resistance vessels
Arterioles that direct blood to where needed (high arterial pressure)
What are capacitance vessels
Act as storage which release blood when needed (low venous pressure)
What is systole
Contraction and ejection of blood from ventricles
What is diastole
Relaxation and filling of ventricles
Name the 4 major valves within the heart
Mitral valve, aortic valve, tricuspid valve, pulmonary valve
Explain the structure of myocardium
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
Explain structure of heart valves
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
Briefly explain the conduction system
- Special cardiac myocytes of pacemaker cells in sinoatrial node generate action potential
- Activity spreads over atria - atrial systole
- Atrioventricular node delays action potential to allow ventricle to contract later (120ms)
- Excitation spreads down septum between ventricles
- Then spreads through ventricular myocardium from inner (endocardial) to outer (epicardial) surface
- Ventricle contracts from the apex up forcing blood through outflow valves
List the 7 phases of the cardiac cycle
- Atrial contraction
- Isovolumetric contraction
- Rapid ejection
- Reduced ejection
- Isovolumetric relaxation
- Rapid filling
- Reduced filling
Explain atrial contraction
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
Explain isovolumetric contraction
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)
Explain rapid ejection
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
Explain reduced ejection
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
Explain isovolumetric relaxation
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
Explain rapid filling
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
Explain reduced filling
Rate of filing slows down (diastasis) as ventricle reaches its inherent relaxed volume
Define stroke volume and give its equation
Stroke volume is the volume of blood pumped from the left ventricle per beat
Stroke volume = end diastolic volume - end systolic volume = EDV - ESV
What is normal typical value of stroke volume
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)
Explain the timings of systole and diastole at rest
Systole occurs between when mitral valve closes to when the aortic valve closes
Occurs when aortic valve closes to when mitral valve closes
Explain how systole and diastole change during exercise
Systole gradually increases in exercise
Explain the origin of the 1st and 2nd heart sounds in relation to the cardiac cycle
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
What is stenosis
Valve doesn’t open enough leading to obstruction to blood flow when valve normally open
What is regurgitation/incompetence
Valves do not close all the way leading to back flow when valve should be closed
What are causes of aortic valve stenosis
Degenerative (senile calcification/fibrosis)
Congenital (bicuspid form of valve)
Chronic rheumatic fever - inflammation - commissural fusion
