Cardiac Cycle Flashcards
How is heartbeat split?
systole (1/3rd of each beat)
diastole (2/3rd of each beat)
What is diastole?
ventricular relaxation heart goes through during passive filling
- represents 4 of total 7 phases
What is systole?
where filling pressure overrides pressure post aortic valve to the point where now blood can be ejected
- represents 3 of total 7 phases
What are the stages of the cardiac cycle?
- atrial systole
- isovolumetric contraction
- rapid ejection
- slow ejection
- isovolumetric relaxation
- rapid passive filling
- slow passive filling
What stages of the cardiac cycle are diastole and which are systole?
diastole:
atrial systole
isovolumetric relaxation
rapid passive filling
slow passive filling
systole:
isovolumetric contraction
rapid ejection
slow ejection
Why does the heart spend more time in diastole?
to allow the heart to maintain its own blood supply from its coronary arteries
What are the lub dub sounds from the heart?
S1=> lub
- when atrioventricular valves snap shut during left and right ventricle contraction
- After aortic and pulmonary valve open up allowing blood to the rest of the body-> systole
S2=> dub
- aortic and pulmonary valves shutting shut to prevent blood back flowing into ventricles after S2 mitral and tricuspid valves open to allow filling of ventricles-> diastole
Do you know this graph?
Describe the stages of the cardiac cycle: atrial systole.
- Atrial pressures override those beyond atrioventricular valves, so blood is ejected into the ventricles.
- P wave on ECG signifies start of atrial systole
- Atria are already almost full from passive filling driven by pressure gradient
- Atria contract to “top-up” the volume of blood in ventricle
Describe the stages of the cardiac cycle: Isovolumetric contraction.
- all valves closed-> as blood fills into ventricles there is a stage where the pressures in the ventricles are equal post atrioventricular and pre semilunar
(isovolumetric= equal volume)
- QRS complex marks the start of ventricular depolarisation
- The interval between AV valves closing and semilunar valves opening
- Contraction of ventricles with no change in volume
- Pressure increase due to excitation
Describe the stages of the cardiac cycle: rapid ejection.
- when pressure in the ventricles overrides pressure post semilunar valves, blood is ejected quickly
- Opening of the aortic and pulmonary valves
- As ventricles contract, pressure within them exceeds pressure in aorta and pulmonary arteries
- Semilunar valves open, blood pumped out and the volumes of ventricles decrease (isotonic contraction= decrease the length in the muscles and push blood out into aorta)
Describe the stages of the cardiac cycle: slow ejection.
- as pressure gradient falls, filling becomes slower.
- End of systole
- Reduced pressure gradient means aortic and pulmonary valves begin to close
- Blood from ventricles decreases and ventricular volume decreases more slowly
- As pressure in ventricles fall below that in arteries, blood begins to flow back causing semilunar valves to close
- Ventricular muscle cells repolarize producing T wave
Plateau and repolarise phase (T phase)
Describe the stages of the cardiac cycle: isovolumetric relaxation.
- all valves are closed-> when aortic valve closes this marks dichrotic notch on pressure-volume loop, both aortic and pulmonic valves are closed
- Aortic and pulmonary valves shut, but AV valves remain closed until ventricular pressure drops below atrial pressure
- Atrial pressure continues to rise
- Dichrotic notch caused by rebound pressure as distended aortic wall relaxes
Describe the stages of the cardiac cycle: rapid passive filling.
- Occurs during isoelectric (flat) ECG between cardiac cycles
- Once AV valves open blood in the atria flows rapidly into the ventricles
describe the stages of the cardiac cycle: reduced passive filling.
- Aka DIASTASIS
- Ventricular volume fills more slowly
- The ventricles are able to full considerably without the contraction of the atria
What are the normal requirements of an ECG?
Pr interval= 120-200ms
QRS< 120ms
cardiac axis= (-30) - (+90) degrees
QT< 420ms in Females, <450ms
ST no depression/ elevation of </> 2mm
What is incompetence when it comes to the heart?
backflow of blood, faulty valve
What is an abnormal 3rd heart sound?
turbulent ventricular filling- mitral incompetence (valve not shutting properly)
The 3rd heart sound is due to incompetency of the valves, due to the valves being restricted, they are calcified and narrow up, so they don’t close properly
What is an abnormal 4th heart sound?
congestive heart failure, pulmonary embolism, tricuspid incompetence
What is a pulmonary embolism?
blocked vessel in lungs
What is a turbulent sound in the heart?
noisy, multi-directional flow as opposed to laminar flow (one direction)
What are the 4 corners of the pressure-volume loop representative of?
a= ventricular filling (mitral valve closes)
b= isovolumetric contraction (aortic valve open)
c= ejection (aortic valve closes)
d= isovolumetric relaxation (mitral valve opens)
What happens at A, B and C?
a= end-diastolic volume
b= aortic pressure encountered
c= end-systolic volume
What are the differences between (A and D) and (C and B)?
A and D are diastolic phases- left ventricular pressures are lowest
B and C are systolic phases- higher left ventricular pressures
How do you calculate stroke volume from pressure-volume loops?
stroke volume= end diastolic volume - end systolic volume
How do you calculate ejection fraction?
(stroke vol/ end diastolic vol) x 100
How would this normal graph change when preload is increased?
Increase in preload results in increased stroke volume (the Frank-Starling relationship)
On graph – increased stroke volume, no changes in end systolic volume if afterload and contractility kept constant
How would this normal graph change when afterload is increased?
Increased afterload results in decreased stroke volume
- as afterload increases, the amount of shortening that occurs decreases
What happens when preload increases?
increased stretching of myofiber→more ventricular filling – more force for ejection and higher stroke volume
On graph – increased left ventricular pressure, increased end systolic volume and decreased stroke volume
What happens when afterload increases?
so volumetric contraction phase is prolonged because ventricle has to generate higher pressures to overcome elevated aortic diastolic pressures
Afterload reduces myofiber shortening so stroke volume will decrease
What happens when contractility increases?
when contractility (inotropy) increased e.g. during exercise, then there is an increase in stroke volume and ejection fraction and decrease in end systolic volume
What are the units for stroke volume and ejection fraction?
mL
%
What is systolic volume?
the volume that is retained in ventricles once contraction is over (residual volume)
What is diastolic volume?
volume, at rest, in ventricles just before contraction
What is the ejection fraction used for?
Assesses cardiac function, it is higher when you are fitter
What is the cause of this bump?
Small bump is due to elasticity and compliance of the aorta
The aorta expands to take blood from the ventricles
During isovolumetric relaxation
Are you comfortable with this diagram?
How do pulmonary circuit pressures change between left and right ventricles?
The left has higher pressures
the pressures in the right heart and pulmonary circulation are much lower (peak of systole- 25mmHg in pulmonary artery)
What are the similarities between the left and right ventricles in pulmonary circuit pressures?
Ventricles eject the same volume of blood
Patterns of pressure changes are identical
What is the systemic circuit?
Systemic circulation carries oxygenated blood from the left ventricle, through the arteries, to the capillaries in the tissues of the body.
What is the pulmonary circuit?
Transports oxygen-poor blood from the right ventricle to the lungs, where blood picks up a new blood supply. Then it returns the oxygen-rich blood to the left atrium.
What is high pressure, the systemic or pulmonary circuit?
Systemic= high pressure= 120/80 mmHg
Pulmonary= low pressure= 25/5 mmHg
Out of all the blood vessels what has the highest pressure?
What does a pressure volume loop link to?
a volume time graph
What increases contractility?
sympathetic stimulation
- because change in sympathetic stimulation= change in Ca2+ delivery to myofilaments
What is contractility?
Contractile capability (or strength of contraction) of the heart
What is the extrinsic mechanism of contractility?
Changes of Ca2+ delivery to myofilaments
What factors affect stroke volume/ cardiac output?
preload, afterload, contractility
How does cardiac contractility affect steepness of the frank-starling relationship?
What are ESPVR lines?
The end-systolic pressure-volume relationship represents the maximal pressure developed by the LV at any given volume and is a measure of cardiac contractility.
What does tachycardia mean in terms of ventricular filling?
less time to fill ventricles
What happens to pressure volume loops during exercise?
Draw the following loops.
Does hardening and narrowing (stenosis) of the pulmonary valve affect preload?
No
What can affect preload?
Right atrial pressure,
Decreased central venous pressure
Decreased ventricular compliance
Increased adrenaline secretion
What is the longest phase of the cardiac cycle?
Reduced passive filling
When is the parasympathetic stimulation present, and what does it do?
Parasympathetic stimulation is present at rest, which slows the SA node rate from 110 bpm to 70 bpm
How does the sympathetic stimulation increase bpm?
Sympathetic stimulation increases SA node rate via:
Hormonal: Circulating adrenaline from adrenal gland
Neural: Noradrenaline released from nerves
In terms of the PV load, what does the afterload affect?
height and left border
In terms of PV load, what does the preload affect?
width
What are preload and afterload affected by?
Preload is affected by volume of blood returning to the heart
Afterload is affected by volume of blood capable of being ejected, due to obstruction of pressure gradient
What is a pressure volume loop?
A graphical representation of how ventricular pressures and volumes change during the cardiac cycle
- Has typically ‘box-like’ profile bordered at the top left by end-systolic pressure volume relation (ESPVR)
