The Cardiac Cycle Flashcards
What are the 2 phases of the cardiac cycle?
Diastole
- lasts approx. 2/3 of each beat
- ventricular relaxation- ventricles fill with blood
- split into 4 phases
Systole
- lasts approx 1/3 of each beat
- ventricular contraction- ventricles eject blood into arteries
- split into 3 phases
What re the phases of heart contraction?
- Atrial systole
- Isovolumetric contraction
- Rapid ejection
- Slow ejection
- Isovolumetric relaxation
- Rapid passive filling
- Slow passive filling
How is stroke volume calculated?
End diastolic volume- end systolic volume
How is ejection fraction calculated?
Stroke volume/ end diastolic volume
What happens in atrial systole?
P wave on ECG is start of atrial systole
Atria almost full from passive filling driven by pressure gradient
Atria contact to top up amount of blood in ventricle
If a 4th heart sound is heard its abnormal- occurs with cognitive heart failure, pulmonary embolism or tricuspid incompetence
What happens in isovolumetric contraction?
QRS complex of ECG
Interval between AV valves closing and semi-lunar valves opening
Contraction of ventricles with no change in volume
1st heart sound “Lub” due to closure of AV valves and associated vibrations
What happens in rapid ejection?
Between S and T on ECG
Opening of semi-lunar valves
Ventricles contract causing pressure within them to exceed pressure in pulmonary arteries and aorta
Semi-lunar valves open and blood is pumped out decreasing ventricular pressure
No heart sound
What happens in reduced ejection?
T wave on ECG End of systole
Reduced pressure gradient means semi-lunar valves begin to close
Blood flows from ventricles decreases and ventricular volume decreases more slowly
As pressure in ventricles falls, blood begins to flow back causing semi-lunar valves to close
Ventricular muscle cell repolarise forming T wave
What happens in isovolumetric relaxation?
Semi-lunar valves close but AV valves remain shut until ventricular pressure falls below atrial pressure
Rate of pressure decline is determined by rate of relaxation of muscle fibres (aka. lusitropy)
Atrial pressure continues to rise.
Dichronic notch caused by rebound pressure against aortic valve as dissented aortic wall relaxes
2nd heart sound (dub) produced due to SLV closure
What happens is rapid passive filling?
Occurs during isoelectric (flat) ECG between cardiac cycles
Once AV valves open, blood in atria flows rapidly into ventricles
If a 3rd heart sound is produced its abnormal- may signify turbulent ventricular filling, hypertension or mitral incompetence
What happen in reduced passive filling?
Can be called diastisis
Ventricular volume fills more slowly
Ventricles are able to fill considerably without contraction of atria
How does pressure change of left heart compare to right heart?
Patterns of pressure change in right heart are identical to left
Although pressure in right heart is lower, right ventricle ejects the same amount of blood as left
How can we measure left atrial pressure?
We can place a balloon tipped catheter into the right atrium, right ventricle, pulmonary artery
Once balloon is inflated in branch of pulmonary artery, its blocked- pressure measured is approx. same as that of left atrium
What can an increase in left atrial pressure lead to?
Risk of pulmonary oedema- life threatening
What occurs at each letter?
A: ventricular filling- preload
B: Isovolumetric contraction- afterload
C: Ejection
D: Isovolumetric relaxation
A and D are diastolic
B and C are systolic
Stroke work is area in the loop
Stroke volume is end diastolic volume (A) - end systolic volume (C)
Label the following- PV loop for exercise
- Increased venous return aided by muscle and respiratory pump- increased end-diastolic volume
- Sympathetic actiation of myocytes increases ventricular contractility- decrease in end systolic volume
- Increase in arterial pressure increases afterload
- Increased cardiac contractility and increased venous return generates increased SV
