CVS - Cardiac Cycle Flashcards
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?
Cusps
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
