4. Cardiac Cycle Flashcards
Describe the movement of blood around the heart
- Deoxygenated blood will flow from the systemic circulation into the superior and inferior vena where it’ll empty into the right atrium.
- Blood will move through the tricuspid valve into the right ventricles
- Blood will move from the right ventricles through the pulmonary valve into the pulmonary artery to the lungs
- At the lungs the deoxygenated blood is oxygenated
- The oxygenated blood flows from the lungs along the pulmonary veins into the left atrium.
- The blood will move into the left ventricle passing through the mitral valve.
- Blood from the left ventricle then moves into the aorta via the aortic valve
- Blood will then enter into the systemic circulation system
how does the heart act as a pump and describe the pressures of the two sides?
- Two pumps acting in series
- Systemic circulation = High Pressure
- Pulmonary circulation = Low pressure
- Output of left and right sides over time must be equal
- Atria act as “priming pumps” for ventricles
Define the terms systole and diastole
- Systole = Contraction and ejection of blood from ventricles
- Diastole = Relaxation and filling of ventricles
what are the typical pressures of the heart chamber and vessels?
Left Atrium - 8 - 10
Left ventricle - 120 systole / 10 diastole
Aorta - 120 systole / 80 diastole
Right atrium - 0 - 4
Right ventricle - 25 systole / 4 diastole
Pulmonary artery - 25 systole / 10 diastole
what are the valves present in the heart?
- Tricuspid valve
- Mitral valve
- Pulmonary valve
- Aortic valve
Define the terms systole and
which are the vessels linked to the heart and what are their functions?
- Superior vena cava
Carries deoxygenated blood to the right atrium from the upper parts of the body - Inferior vena cava
Carries deoxygenated blood to the right atrium form the lower parts of the body - Pulmonary artery
There are 2 the left pulmonary artery and the right.
Carries deoxygenated blood from the right ventricle to the lungs - Pulmonary veins
There are 4 pulmonary veins
Carries oxygenated blood back from the lungs to the left atrium - Aorta
Carries oxygenated blood to the body
how much blood is pumped by each ventricle in an average man per beat?
At rest each ventricle pumps ~ 70 ml blood per
beat (= Stroke volume)
what is the average volume of blood in a typical adult?
5L
Describe the structure of heart muscle
Cardiac muscle are discrete striated muscles that are interconnected electrically.
They have gap junctions between them that facilitate electrical communication.
describe how the responds to action potential
- Cells contract in response to action potential in membrane
- Action potential causes a rise in intracellular calcium
- Cardiac action potential relatively long – lasts for durations of a single contraction of heart (~280 ms)
- Action potentials are triggered by spread of excitation from cell to cell
What is the Function of chordae tendineae and papillary muscles?
The chordae tendineae (heart strings) are fibrous cords of connective tissue that connect the papillary muscles to the tricuspid valve and the bicuspid valve in the heart.
They work to prevent the prolapse of these valves and backflow of blood into the atria during systole.
what causes the valves to open and close?
- Open or close depending on differential blood pressure on each side.
- Valve cusps are pushed open to allow blood flow and close together to seal and prevent backflow.
- Cusps of mitral and tricuspid valves attach to papillary muscles via chordae tendineae. Prevents inversion of valves on systole.
Describe the conduction system within the heart
- Pacemaker cells in sinoatrial node generate an action potential
- Activity spreads over atria – atrial systole - atria both contract
- Action potential Reaches the atrioventricular node and delayed for ~ 120 ms - this allows atria to finish contracting
- From a-v node excitation spreads down septum between ventricles
- Next spreads through ventricular myocardium from inner (endocardial) to outer (epicardial) surface
- Ventricle contracts from the apex up forcing blood through outflow valves
Where is the SAN located
In the right atrium
what are pacemaker cells?
Specialised cardiac myocytes with muscular origin, not neuronal origin
What is the cardiac cycle?
It’s the sequence of pressure flow changes and valve operations that occur with each heartbeat.
It has a total duration of 0.9s (at 67 bpm).
List 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
What effect does exercise have on systole and diastole of the cardiac cycle?
Our heart beats faster, diastole will get shorter whilst systole stays constant.
What is the Wiggers Diagram?
This diagram shows the pressure changes against the volume changes in the heart. As well as this it can equate the heart sounds and electrical events on the ECG.
The diagram is typically plotted just for the left side of the heart, the diagram for the right side of the heart would be very similar but be at a lower pressure.
what are the two heart sounds and what causes them
> lub (or first sound) when atrial valves close
> dub (or second sound) when semilunar valves close
In the Wiggers diagram, what is one heart beat split into?
One heart beat contains one systole and one diastole. But, by convention, the Wiggers diagram starts at atrial contraction which is 2/3 of the way through diastole. This means that graphically, 1 heart beat is divided into 2/3 of diastole, then systole, then the rest of diastole.
Describe phase 1 of the cardiac cycle- Atrial contraction
- P wave in ECG signifies onset of atrial depolarisation.
- Atrial pressure rises due to atrial systole. This is called the “A wave”
- Mitral/Tricuspid valve: Open
- Aortic/Pulmonary valve: Closed
- Atrial contraction accounts for final ~10% of ventricular filling. This value varies with age and exercise
- At the end of Phase 1 ventricular volumes are maximal: termed the End-Diastolic Volume (EDV) (Typically ~120 ml)
Describe phase 2 of the cardiac cycle- Isovolumetric contraction
- QRS complex in ECG signifies onset of ventricular depolarisation.
- Rapid rise in ventricular pressure as ventricle contracts
- Mitral/tricuspid valve closes as intraventricular pressure exceeds atrial pressure. The Aortic/Pulmonary is also Closed at this point.
- Closing of mitral/tricuspid valve causes the “C wave” in the atrial pressure curve
- Isovolumetric since there is no change in ventricular volume (all valves are closed)
- Closure of the mitral and tricuspid valves results in the first heart sound (S1) - lub.
Mitral/Tricuspid: Closed
Aortic/Pulmonary: Closed
Describe phase 3 of the cardiac cycle- Rapid ejection
•Ejection begins when the intraventricular pressure exceeds the pressure within the aorta. This causes the aortic/pulmonary valve to open
•Rapid decrease in ventricular volume as blood is ejected into aorta
• Atrial pressure initially decreases as the atrial base is pulled downward as ventricle contracts. This is called the
“X descent”
• Blood continues to flow into the atria from their respective venous inputs
Mitral/Tricuspid: Closed
Aortic/Pulmonary: Open
Describe phase 4 of the cardiac cycle- Reduced ejection
- Repolarization of ventricle leads to a decline in tension and the rate of ejection begins to fall
- Atrial pressure gradually rises due to the continued venous return from the lungs. This is called the “V wave”
- Ventricular repolarization depicted by T-wave of ECG
The mitral/tricuspid valves are closed whilst the aortic/pulmonary valves are open.
Describe phase 5 of the cardiac cycle- Isovolumetric relaxation
diastole begins:
• When intraventricular pressure falls below aortic pressure, there is a brief backflow of blood which causes the aortic/pulmonary valve to close
• Closure of the aortic and pulmonary valves results in the second heart sound (S2).
• Although rapid decline in ventricular pressure, volume remains constant since all valves are closed. Hence isovolumetric relaxation
• “Dicrotic notch” in aortic/pulmonary artery pressure curve caused by aortic/pulmonary valve closure
Mitral/Tricuspid: Closed
Aortic/Pulmonary: Closed
what is the atrial kick?
This refers to blood being pushed into the ventricles because of atrial contraction.
Describe phase 6 of the cardiac cycle- Rapid fillling
- When the intraventricular pressure falls below atrial pressure, the mitral/ tricuspid valve opens and rapid ventricular filling begins.
- Fall in atrial pressure that occurs after opening of mitral valve is called the “Y-descent”
- Ventricular filling normally silent. However, third heart sound (S3) sometimes present. S3 heart sound is normal in children but can be sign of pathology in adults. The S3 sound is caused by the rapid entry of blood from the atria to the ventricles
Mitral/Tricuspid: Open
Aortic/Pulmonary: Closed
Describe phase 7 of the cardiac cycle- Reduced filling
Rate of filling slows down (diastasis) as ventricle reaches its inherent relaxed volume. Further filling is driven by venous pressure
At rest the ventricles are ~90%. full by the end of phase 7.
Mitral/Tricuspid: Open
Aortic/Pulmonary: Closed
Describe when in the cardiac cycle each valve in the heart opens and closes, and the pattern of flow through each valve
- Atrial contraction
The mitral/ tricuspid valves are open whilst the aortic/pulmonary valves are closed. - Isovolumetric contraction
The mitral/tricuspid valves are closed and the aortic/pulmonary valves are closed. - Rapid ejection
The mitral/ tricuspid valves are closed whilst the aortic/pulmonary valves are open. - Reduced ejection
The mitral/ tricuspid valves are closed whilst the aortic/pulmonary valves are open. - Isovolumetric relaxation
The mitral/tricuspid valves are closed and the aortic/pulmonary valves are closed. - Rapid filling
The mitral/ tricuspid valves are open whilst the aortic/pulmonary valves are closed. - Reduced filling
The mitral/ tricuspid valves are open whilst the aortic/pulmonary valves are closed.
Explain the origin of the 1st, 2nd and 3rd heart sounds
Sound 1 is due to the closure of the mitral and tricuspid valves in Isovolumetric contraction (Stage 2)
Sound 2 is due to the closure of the aortic and pulmonary valves in Isovolumetric relaxation (Stage 5)
Sound 3 is due to filing of the ventricles in rapid filling (Stage 6)
What are the two abnormal valve functions
Valve doesn’t open enough –>Obstruction to blood flow
when valve normally open –> Stenosis
Valve doesn’t close all the way –> Back leakage when valve should be closed –> Regurgitation
Why would you expect to have more problems with valves on the left side than right?
The left valve is working at a higher pressure than the right
What is aortic valve stenosis?
It refers to the narrowing of the aortic valve meaning that it won’t open properly, therefore less blood can get through the valve.
what are the causes of aortic valve stenosis?
• Degenerative (senile calcification/fibrosis)
• Congenital (bicuspid form of valve instead of tricuspid)
• Chronic rheumatic fever –inflammation- commissural
fusion - autoimmune - antibodies against bacteria attack the valve
what is the effect of aortic valve stenosis?
• Less blood can get through valve –> Increased LV
pressure –>LV hypertrophy
• Less blood can get through valve –>Left sided heart failure –> Syncope(fainting) or/and angina
• Shear stress on RBCs because they are forced through a narrowed valve at high pressure –>Microangiopathic
haemolytic anaemia (RBCs burst open)
what causes aortic valve regurgitation?
- Aortic root dilation (leaflets pulled apart)
* Vlavular damage (endocarditis rheumatic fever)
what is the effect of aortic valve regurgitation?
- Blood flows back into LV during diastole
- Increases stroke volume
- Systolic pressure increases
- Diastolic pressure decreases
- Bounding pulse (head bobbing, Quinke’s sign)
- LV hypertrophy
What is the main cause of Mitral valve regurgitation?
- Chordae tendineae & papillary muscle normally prevent prolapse in systole
- Myxomatous degeneration can weaken tissue leading to prolapse - backflow of blood into atria
What are the other causes of mitral valve regurgitation?
Other causes:
• Damage to papillary muscle after heart attack
• Left sided heart failure leads to LV dilation which can stretch valve
• Rheumatic fever can lead to leaflet fibrosis which disrupts seal formation
What can mitral valve regurgitation lead to?
• As some blood leaks back into LA, this increases preload as more blood enters LV in subsequent cycles…can cause LV hypertrophy
what is the cause of Mitral valve stenosis?
- Main cause = Rheumatic fever (99.9% cases)
- Commissural fusion of valve leaflets
- Harder for blood to flow LA –> LV
What is mitral valve stenosis?
The mitral valve won’t open up as wide as it’s supposed to which causes difficulty in getting blood from the left artery to the left ventricle.
How does Mitral valve stenosis lead to RV hypertrophy?
Increased LA pressure –> Pulmonary oedema, Dyspnea, Pulmonary hypertension –> RV hypertrophy
How does mitral valve stenosis lead to thrombus formation?
Increased LA pressure –> LA dilation –> Atrial fibrillation –> Thrombus formation
How does mitral valve stenosis lead to dysphagia?
Increased LA pressure –> LA dilation –> Oesophagus
compression –> Dysphagia
