6.5: Cardiac cycle Flashcards
Systole is
Contraction - ventricles generate pressure then eject blood into arteries
Diastole is
Relaxation - ventricles fill with blood
Each heart beat is split into two main phases
Diastole and systole
Diastole is split into how many phases
4 distinct phases
Systole is split into how many phases
3 distinct phases
7 stages of the cardiac cycle
Atrial systole (D)
Isovolumetric contraction (S)
Rapid ejection (S)
Slow ejection (S)
Isovolumetric relaxation (D)
Rapid passive filling (D)
Slow passive filling (D)
P wave on an ECG signifies
Start of atrial systole
In atrial systole
Atria are almost full from passive filling, driven by pressure gradient.
Atria contract to “top-up” volume of blood in ventricle
What 3 diseases can cause a 4th heart sound to arise (abnormal)
Congestive heart failure
Pulmonary embolism
Tricuspid incompetence
What does the QRS complex mark the start of
Ventricular depolarisation
During Isovolumetric contraction
[Contraction of ventricles with no change in volume (isometric)]
Interval between AV valves closing and semi-lunar valves opening
1st stage of cardiac cycle
Atrial systole
2nd stage of cardiac cycle
Isovolumetric contraction
Isovolumetric contraction produces
1st heart sound - ‘lub’ due to closure of AV valves and associated vibrations
What marks the start of the rapid ejection phase
Opening of the aortic and pulmonary veins
During the rapid ejection phase
Ventricles contact, pressure within them exceeds pressure in aorta and pulmonary arteries
Semilunar valves open, blood is pumped out and volumes of ventricles decrease - isotonic contraction
(No heart sounds)
3rd phase of the cardiac cycle
Rapid ejection
4th phase of cardiac cycle
Slow ejection / reduced ejection
5th phase of cardiac cycle
Isovolumetric relaxation
6th phase of cardiac cycle
Rapid passive filling
7th phase of cardiac cycle
Slow passive filling
Calculation for stroke volume
End diastolic volume - end systolic volume = stroke volume (mL)
Calculation for ejection fraction (%)
100x (stroke volume / end diastolic volume ) = ejection fraction
Reduced ejection marks
The end of systole
During reduced ejection
Reduced pressure gradient means aortic and pulmonary valves being to close.
Blood flow 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
What produces the T wave on an ECG
Ventricular muscle cells repolarizing - during reduced ejection
During Isovolumetric relaxation
Aortic and pulmonary valves shut,
AV valves remain closed until ventricular pressure drops below atrial pressure.
Atrial pressure continues to rise
What causes the Dichrotic notch on an ECG
Rebound pressure as distended aortic wall relaxes - Isovolumetric relaxation
What is the 2nd heart sound caused by
Closure of semi-lunar valves
Rapid passive filling on and ECG is represented by
Isoelectric (flat) between cardiac cycles
During rapid passive filling
Once AV valves open blood in the atria flows rapidly into ventricles
3rd heart sound can be due to
Usually abnormal
May signify turbulent ventricular filling
Can be due to hypertension or mitral incompetence
Reduced passive filling is also known as
Diastasis
During reduced passive filling
Ventricular volume fills more slowly
Ventricles are able to fill considerably without the contraction of the atria
What are the patterns of pressure changes like in the right heart compared to the left
Identical in the right heart as in the left
Comparison of heart pressures quantitativley
Pressures in right heart and pulmonary circulation are much lower in the right heart but ejects same volume of blood as left
Pressures in the systemic circuit
High pressure
120/80 mmHg
Pressures in the pulmonary circuit
Low pressure
25/5 mmHg
Preload is determined by
Volume of blood returning to the heart (blood filling ventricles during diastole , stretching resting ventricular muscle)
Afterload is
Pressure heart has to work against
What is afterload determined by
Diastolic blood pressure (BP in great vessels - aorta, pulmonary artery)
What is preload
Stretch
What do Changes in preload and afterload affect
Shape of the PV loop
What does increased sympathetic stimulation result in
Increased cardiac myocyte [cAMP]
Allows delivery of more Ca2+ to myofilaments
Delivery of more Ca2+ by increased sympathetic stimulation results in
Activation of sympathetic beta receptors by:
Circulating catecholamines from adrenal gland
Noradrenaline released from nerves
What affects the width of the PV loop
Changes in preload
What affects the height and left border of the PV loop
Changes in afterload
Upper left point follows the ESPVR
What stimulation is present at rest
Parasympathetic
What happens to the heart rate at rest
Slowing of SA node due to parasympathetic stimulation
From 110bpm to 70bpm
How does the sympathetic stimulation increase SA node rate (2)
Hormonal : circulating adrenaline from adrenal gland
Neural : noradrenaline released from nerves
What is the longest phase of the cardiac cycle
TBA…
