Cardiac cycle Flashcards
what is the cardiac cycle?
- all events that occur from beginning of 1 heartbeat to beginning of next heartbeat
- orderly depolarisation / repolarisation sequence triggers a recurring cardiac cycle of atrial & ventricular contractions and relaxations
what is diastole?
heart ventricles are relaxed & fill with blood (relaxation)
what is systole?
heart ventricles are contracting & pump blood into aorta (LV) and pulmonary artery (RV)
what is average heart rate and length of diastole/systole?
75 beats per min
- diastole = 0.5
- systole = 0.3
what are the 5 phases during cardiac cycle?
- passive filling
- atrial contraction
- isovolumetric ventricular contraction
- ventricular ejection phase
- isovolumetric ventricular relaxation
what is the passive filling stage of cardiac cycle?
- pressure of atria and ventricles close to 0
- AV valves open so venous return flows into ventricles
- aortic valve close, AV valve is open
- ventricles become 80% full by passive filling
what side has higher pressure?
left has much higher pressure than right
what is atrial contraction phase of cardiac cycle?
- P wave in ECG signals atrial depolarisation
- atria contracts between P wave and QRS
- after atrial contraction = left with end diastolic volume (usually about 65 mmHg)
what is isovolumetric ventricular contraction phase of cardiac cycle?
- ventricular contraction starts after QRS (signals ventricular depolarisation) in ECG
- ventricular pressure rises and when it exceeds atrial pressure, the AV valves shut
- closure of AV valves makes first sound -LUB which signals end of diastole and start of systole
- aortic valve is shut so no blood can enter or leave ventricle and tension rises around closed volume hence the name
what is the ventricular ejection phase of cardiac cycle?
- ventricular pressure exceeds aorta/pulmonary artery
- aortic/pulmonary artery valves open (silent)
- stroke volume ejected by each ventricle leaving behind end systolic volume
- T wave signals ventricular repolarization on ECG
- ventricles relax & pressure falls
- ventricular pressure falls below aortic/pulmonary artery pressure so valves shut and produces 2nd sound (DUB) = end of systole & start of diastole
- valve vibration makes the dicrotic notch in aortic pressure curve
how to calculate stroke volume?
end diastolic volume - end systolic volume
what is dicrotic notch caused by?
the valve vibration produces the dicrotic notch in aortic pressure curve
what is isovolumetric ventricular relaxation?
- closure of aortic/pulmonary artery valves - signals the start of isovolumetric relaxation
- ventricle is again a closed box, as AV valve is shut
- tension falls around a closed volume (isovolumetric relaxation)
- when ventricular pressure falls below the atrial pressure, AV valves open (silent event) and the heart starts a new cycle
what is the first sound caused by?
S1 = sounds like LUB and signals start of systole
- atrial & tricuspid valves closing
what is the second sound caused by?
S2 = sounds like DUB and signals end of systole and start of diastole
- by closure of aortic & pulmonary artery valves
what areas can you do cardiac ausculatation?
circles on diagram in notes represent the areas, lateral to the sternum and within intercostal spaces, to auscultate the heart valves
aortic area = 2nd right intercostal space
pulmonary area = 2nd left intercostal space
tricuspid area = 4th left intercostal space
mitral area = 5th left intercostal space (mid clavicular)
how does arterial pressure not fall to 0?
reason 1 = elastic recoil of the arteries
reason 2 = continuous blood flow
what is JVP?
estimated jugular venous position
= it’s an indirect estimate of right atrial pressure (central venous pressure)
how do you measure JVP?
patient lies at 45 degree angle between sitting and lying
what is a normal JVP?
no more than 3 cm vertically above sternal angle
what does elevated JVP mean?
= RA pressure elevated
- many causes can result in an elevated RA pressure and hence elevated JVP
- elevated JVP is one of signs of heart failure - but can be caused by other causes
