Cardiac Cycle Flashcards
What are the two phases of each heart beat
Diastole, lasts 2/3rds of each beat, ventricular relaxation, fill with blood, split into 4 phases
Systole, lasts 1/3rd of each beat, ventricular contraction, ventricles generate pressure and eject blood into arteries, split into 3 phases
What are the 7 steps of the cardiac cycle (note whether they are part of S or D)
Atrial systole (D) Isovolumetric Contraction (S) Rapid ejection Slow ejection Isovolumetric relaxation (D) Rapid passive filling Slow passive filling
What is the end diastolic volume and when is it reached
Max vol of blood in heart just before ventricles start to contract (at max relaxation point, just before systolic period starts)
What is end systolic volume and when is it reached
Amount of blood in the heart after contraction is completed/ residual volume. Occurs just before diastolic period
How do you calculate stroke volume (mL), and what are these values approximately
End diastolic volume - end systolic volume
EDV= 120mL, EsV = 50mL, SV= 70mL
What is a clinically relevant indicator of cardiac function and how is it calculated
What is its normal range, vs someone with heart failure
Ejection fraction (%) = 100StrokeVol/ endDiastolicVol
Normal is 52-72%, heart failure may be 30-35%
What does the P wave on an ECG signify
What occurs at this stage
Start of atrial systole
Atria already almost full from passive filling driven by pressure gradient. Atria contract to ‘top up’ volume of blood in ventricle
Why may the contribution of atrial systole to ventricular filling vary
Around 10% normally, but when HR is high, diastolic period is shorter, and passive filling is too slow so AS may account for 40%
Why may a 4th heart sound be heard and is this normal
May occur during atrial systole (p wave), abnormal, occurs with congestive heart failure, pulmonary embolism or tricuspid incompetence
What occurs during the QRS complex
Phase, electrical activity, valves, volume, sound
Isovolumetric contraction
QRS complex marks start of ventricular depolarisation
Interval between AV valves closing and semi lunar valves opening
Contraction of ventricles with no change in volume
As AV valves close, 1st heart sound (lub) occurs
What phase is marked by the opening of the aortic and pulmonary valves
Rapid ejection
As ventricles contract, pressure exceeds Ao and Pu arteries, SL valves open, blood pumped out, vol of ventricles decreases
What phase is represented by the T wave, what does it mark and what occurs
What electrical event produces the T wave
Reduced ejection
End of systole
Reduced pressure gradient means Ao and Pul valves begin to close, blood flow from ventricles decreases, vol decreases more slowly,
Pressure flows, blood begins to flow back, causes semilunar valves to close
Ventricular muscle cells depolarise producing T wave
What phase occurs during the 2nd heart sound and what causes this sound, what occurs during this phase?
Isovolumetric relaxation
SL valves shut, but AV valves remain closed until ventricular pressure drops below atrial pressure
Atrial pressure continues to rise
Dichroic notch caused by rebound pressure against aortic valve as distended aortic wall relaxes
What occurs during the isoelectric (flag) ECG between cardiac cycles
What may cause a 3rd heart sound during this phase
Rapid passive filling
Once AV valves open, blood flows rapidly from atria to ventricles
3rd heart sound usually abnormal and may signify turbulent ventricular filling, due to severe hypertension or mitral incompetence
When does reduced passive filling (diastasis) occur
Ventricular vol fills more slowly, able to fill considerably without contraction of atria, cardiac cycle starts again
