CVS - Cardiac Cycle Flashcards Preview

Semester 2 > CVS - Cardiac Cycle > Flashcards

Flashcards in CVS - Cardiac Cycle Deck (32):

What does the myocardium consist of?

Individual specialised cells joined by low electrical resistance connections


What is the contraction on each cell produced by?

Action potential - A rise in intracellular calcium triggered by an all or none electrical event in the cell membrane


What produces the action potential in the heart? And where is it located?

Sino-atrial node - specialised pacemaker cells

Right atrium


What is the period when the myocardium is contracting and relaxing?

Contracting - systole (1/3rd of time)

Relaxation between contractions = diastole (2/3rd of time)


What is the cardiac cycle? How many stages are there?
What is the total duration?

Sequence of pressure flow changes and valve operations that occur with each heartbeat
7 stages
0.9 seconds


What are the valves between the atrium and ventricle?

Right side = Tricuspid

Left side = Mitral


Name the outflow valves

Aortic and pulmonary valves


What is cardiac output?

Volume pumped per minute by the left heart

Pumping is intermittent it is the product of the volume ejected per cardiac cycle (stroke volume) and number of cycles per minute (heart rate).


What is stroke volume?

What is it on an average person?

How much each ventricle pumps at rest

70ml blood per beat


What do cells contract in response too?

Action potential in membrane which causes rise in intracellular calcium


What do the valves open or close dependent on?

Pressure on each side


What do valves have to prevent back flow?



What prevents inversion of valves on systole?

Cusps of mitral and tricuspid valves attach to papillary muscles via chordae tendineae


How long is the delay after the action potential reaches the atrioventricular node?

120 ms


What direction does the action potential spread in the ventricular myocardium?

What direction does the ventricle contract from?

Endocardial (inner) to epicardial (outer)

Apex up forcing blood through outflow valves


What is a wiggers diagram?

Which side of heart is it typically plotted for?

Allows us to plot changes that occur in pressure with time

Typically plotted for left side of heart


What is the A wave in cardiac cycle?

Atrial pressure rising due to atrial systole


Describe the pressure and volume changes in atrial contraction.

What valves are open/closed?

Atrial pressure increase
Ventricular volume increase

Provides the last 10-20% of blood to fill ventricles

Tricuspid/mitral valve - open
Aortic/pulmonary valve - closed


What does the P wave in an ECG represent?

Onset of atrial depolarisation


What happens in phase 2 of cardiac cycle, isovolumetric contraction (ventricle start to contract?

Mitral valve closes. Closing of mitral valve = C wave
Isometric volume (no change in volume) as all valves closed
Rapid rise in ventricular pressure


What does the first heart sound signify?

Closing of mitral and tricuspid valves


What signifies the onset of ventricular depolarisation in ECG?

QRS complex


What happens during rapid ejection? Phase 3 of cardiac cycle

What are the state of the valve?

Intraventricular pressure exceeds that of aorta causing aortic valve to open
Atrial pressure initially decreases as atrial base pulled downward as ventricle contracts (X descent)
Rapid decrease in ventricular volume

Mitral/tricuspid - closed
Aortic/pulmonary - open


Why does the rate of ejection fall in the ventricles during 'reduced ejection' phase 4?

What wave on ECG depicts ventricle reploarisation?

What happens to atrial pressure?

Ventricle is repolarised which leads to decline in tension and rate of ejection begins to fall

T wave

Gradually rises due to continued venous return (V wave).

Mitral/tricuspid valve - closed
Aortic/pulmonary valve - open


What halogens in phase 5 of cardiac cycle isovolumetric relaxation?

Are valves open/closed?

Intraventricular pressure falls below aortic pressure, brief back flow of blood which causes aortic valve to close

Rapid decline in ventricular pressure. Volume remains constant since all valves are closed

Mitral/tricuspid - closed
Aortic/pulmonary - closed


What causes the dicrotic notch in aortic pressure curve?

Valve closure


How do you calculate end stroke volume?

End diastolic volume - end systolic volume

Typically 70/80ml


What gives you the second heart sound?

Closure of aortic and pulmonary valves

Only CLOSURE of valves gives heart sounds


What causes the Y descent in atrial pressure during phase 6 of cardiac cycle. Rapid filling stage.

What must occur for mitral valve to open?

Fall in atrial pressure that occurs after mitral valve has opened

Intraventricular pressure must fall below atrial pressure and ventricle begins to fill

Mitral/tricuspid valve - open
Aortic/pulmonary valve - closed


What is the third heart sound occasionally heard?

Filling of ventricles - which is normally silent

Children - normal
Adults - can be a sign of pathology


What is phase 7 of cardiac cycle?

Reduced filling - rate of ventricular filling slows down (diastasis) as ventricle reaches inherent relaxed volume
Further filling driven by venous pressure
Ventricles are 90% full by end of phase 7

Mitral/tricuspid valve - open
Aortic/pulmonary valve - closed


Where does the right and left heart pump blood to?

Right - Lungs (pulmonary circulation)

Left - Body (systemic circulation)