S4 Cardiac Cycle Flashcards
What are the key structures of theLeft side of the Heart.
Pulmonary veins Left atrium Mitral valve Left ventricle Aortic valve Aorta
What are the key structures of the Right side of the Heart.
Superior Vena Cava Inferior Vena Cava Right atrium Tricuspid valve Right ventricle Pulmonary valve Pulmonary artery
Define systole
Contraction and ejection of blood from ventricles
Define diastole
Relaxation and filling of ventricles
What is the stroke volume of the heart? (Inc. volume)
Stroke volume in the amount of blood ejected from the ventricle per beat.
Approx 70ml per beat
What is the average Heart rate?
Between 60-100
At 70bpm 4.9l of blood pumped per minute (approx the amount in the body)
What are the four valves and how do they open or close?
Right- tricuspid, pulmonary valves
Left- mitral valve, aortic valve.
They open/close by differential pressures.
How are Mitral and tricuspid valves linked to the heart?
They are attached to papillary muscles via the chordae tendonae which prevents inversion during systole.
What is the hearts pacemaker?
The sinoatrial node
Describe the Heart’s conduction system.
Action potential generated by the SAN.
Spreads over The atria (atrial systole)
Reaches the Atrioventricular node and is delayed for 120ms
AVN spreads the excitation down the septum via the Purkinje fibres which spread through the ventricular myocardium from inner (endocardial) to outer (epicardium) surface
Ventricles contact from the apex up forcing the blood up through the up flow valves.
What are the 7 phases of the cardiac cycle.
1 - Atrial contraction 2 - Isovolumetric contraction 3 - Rapid ejection 4 - Reduced ejection 5 - Isovolumetric relaxation 6 - Rapid filling 7 - Reduced filling
repeat
What is a Wiggers diagram?
A diagram showing the events of the cardiac cycle through pressure changes (mmHg) and volume (ml).
Typically in the Left side of the heart.
Describe phase 1 of the cardiac cycle.
Atrial contraction.
Atrial pressure rise called “A wave”
Accounts for the final 10% of ventricular filling
P wave of ECG signifies onset of atrial depolarisation.
At the end of Phase one ventricle volumes are maximal termed the End-diastolic volume (EDV) ~120ml
Describe Phase 2 of the cardiac cycle.
Isovolumetric contraction.
Mitral valve closes as pressure in ventricles>atria
Rapid rise in ventricular pressure as their contract
Closing of Mitral valve causes “C wave” in atrial pressure curve.
Isovolumetric as no change in ventricular volume and valves are shut.
QRS wave in ECG signifies onset of ventricular systole.
Closure of heart signifies first heart sound (S1)
Describe Phase 3 of the cardiac cycle.
Rapid ejection.
As pressure in ventricle>aorta, aortic valve OPENS to allow ejection to begin.
Atrial pressure decreases called an “X descent”
Rapid blood decrease in ventricular volume as blood enters aorta.
Blood continues to flow into the atria from veins.
Describe Phase 4 of the Cardiac cycle.
Reduced ejection.
Repolarisation of ventricles, decline in tension and rate of ejection falls.
Atrial pressure gradually increases due to venous return, called “V wave”
Ventricular repolarisation shown by T wave on ECG
Describe Phase 5 of the Cardiac cycle
Isovolumetric relaxation
When ventricular pressure
Describe Phase 6 of the Cardiac cycle.
Rapid filling.
Fall in atrial pressure after opening of mitral valve called “Y descent”
Intraventricular pressure falls below atrial pressure
Mitral valve opens ventricles begin to fill ( volume increases)
Ventricular filling is usually silent but can be present (S3).
S3 normal in children but can be a sign of pathology in adults.
Describe Phase 7 of the Cardiac cycle.
Reduced filling.
Rate of filling slows down (diastole) as ventricles reach the inherent relaxed volume. Further filler is driven by venous pressure.
Ventricles 90% full at the end of Phase 7
What is Stenosis?
Valve doesn’t open enough
Obstruction to blood flow when valve normally opens
What is regurgitation?
Incompetence/Insufficiency
Valve doesn’t close all the way
Back leakage when valve should be closed.
What causes Aortic valve stenosis?
Degenerative - senile calcification or fibrosis
Congenital - bicuspid form of valve
Chronic rheumatic fever - inflammation, commiserate fusion.
What are the possible consequences of aortic stenosis?
Path 1
Less blood through valve - increase LV pressure ->LV hypertrophy
Less blood through valve - left sided heart failure -> syncope or angina.
Path 2
Shear stress - microangiopathic haemolytic anaemia
What causes aortic valve regurgitation?
Aortic root dilation (leaflets pulled apart)
Valvular damage (edocharditis rheumatic fever)
What are the consequences of aortic valve regurgitation?
Blood flows back into LV during diastole.
Increase SV
Systolic pressure increases
Diastolic pressure decreases
Bounding pulse (head bobbing, Quinke’s sign)
LV hypertrophy.
What causes mitral valve regurgitation?
Myxomatous degeneration can weaken papillary muscle and chordae tendonae causing a prolapse in systole.
Damage to papillary muscle following an MI
Left sided heart failure leads to LV dilation which can stretch valve.
Rheumatic fever can lead to leaflet fibrosis which disrupts seal formation.
What are the consequences of mitral regurgitation?
Some blood leaks back into LA which increases preload as more blood enters LV in subsequent cycles… can cause LV hypertrophy.
Causes a holosystolic murmur.
What causes Mitral valve stenosis?
Mainly Rheumatic fever (~99.9% of cases.)
Commissural fusion of valve leaflets.
Harder blood flow from LA to LV
What are the consequences of Mitral Valve stenosis?
Increased LA pressure - Pulmonary oedema/Dyspnea/pulmonary hypertension —> RV hypertrophy
Increased LA pressure - LA dilation —> atrial fibrillation —> Thrombus formation
Increased LA pressure - LA dilation —> oesophageal compression—> dysphagia
What changes occur to systole and diastole if the heart rate is increased?
Systole stays the same,
Diastole decreases.
