SESSION 2 LECTURE 1 : The Cardiac Cycle Flashcards
Describe the basic anatomy of the heart, naming all valves, chambers and major blood vessels.
- Right and left atrium
- Right and left ventricles
- The tricuspid valve between the right atrium and ventricle
- The mitral valve (bicuspid valve) between the left atrium and ventricle
- The aortic valve between the aorta and left ventricle
- The pulmonary valve between the pulmonary trunk and right ventricle
What are the mitral and tricuspid valves attached to, to prevent inversion of valves during systole?
Papillary muscle via chordae tendineae
Explain the term systole
Contraction and ejection of blood from ventricles
Explain the term diastole
Relaxation and filling of ventricles
Define the term stroke volume and how is it calculated
The volume of blood pumped from the ventricles per beat which is approximately 70 ml
End diastolic volume - End systolic volume
Explain the conduction system of the heart
- Pacemaker cells in the SAN generate an action potential
- Activity spreads over atria; atria systole
- Reaches the AVN and delayed for 120ms
- Excitation spreads down the septum between ventricles via Bundle of His
- Next spreads through ventricular myocardium from the inner (endo) to outer (epi) via Purkinje fibres
- Ventricles contracts from the apex up
The cardiac cycle can be split into 7 phases. State these phases
- Atrial contraction
- Isovolumetric contraction
- Rapid ejection
- Reduced ejection
- Isovolumetric relaxation
- Rapid filling
- Reduced filling
Features of Atrial contraction and its effect on the Wiggers diagram
- Atrial pressure rises due to atrial systole; “A wave” on the atrial pressure curve
- Mitral/tricuspid valves are open
- Pulmonary/aortic valves are closed
- Only accounts for 10% of ventricular filling
Features of Isovolumetric contraction and its effect on the Wiggers diagram
- All valves closed
- A rapid rise in ventricular pressure as ventricle contracts
- isovolumetric since there is no change in ventricular volume
- closing of the mitral valve causes the c wave in the atrial pressure curve
- the onset of ventricular depolarisation depicted by the QRS complex
- closure of the mitral/tricuspid valves results in the first heart sound S1
Features of Rapid ejection and its effect on the Wiggers diagram
- ejection begins when the intraventricular pressure is bigger than the aortic pressure
- Mitral/Tricuspid valves are closed
- Aortic/Pulmonary valves are open
- a rapid decrease in ventricular volume as blood is ejected into the aorta
- atrial pressure initially decreases as the atrial base is pulled downwards as ventricles contract; “X descent”
Features of Reduced ejection and its effect on the Wiggers diagram
- repolarization of ventricles leads to a decline tension, intraventricular pressure decreases and the rate of ejection begins to fall
- Mitral/Tricuspid valves are closed
- Pulmonary/aortic valves are open
- atrial pressure gradually rises due to the continued venous return from the lungs; V wave
- ventricular repolarisation depicted by T wave
Features of Isovolumetric relaxation and its effect on the Wiggers diagram
- All valves are closed
- aortic valve closes due to the brief backflow of blood as intraventricular pressure fall below aortic pressure
- Dicrotic notch in aortic pressure curve caused by valve closure
- volume remains constant
- closure of the aortic and pulmonary valves result in the second heart sound S2
Features of Rapid filling and its effect on the Wiggers Diagram
- Mitral/tricuspid valves are open
- Aortic/pulmonary valves are closed
- fall in atrial pressure that occurs after opening of the mitral valve is called the “Y decent”
- intraventricular pressure falls below the atrial pressure which causes mitral valves to open and ventricular filling begins
- the ventricular filling is normally silent but a third heart sound sometimes present “S3”. this is normal in children but can be a sign of pathology in adults
Features of Reduced filling and its effect on the Wiggers Diagram
- Mitral/Tricuspid valves are open
- Pulmonary/Aortic valves are closed
- rate of filling slows down as ventricles reaches its inherent relaxed volume. the further filling is driven by venous pressure.
At rest, the ventricles are 90% full by the end of phase 7
State 2 abnormal valve function
- Stenosis
- Regurgitation
How does stenosis occur?
- valve doesn’t open enough
- obstruction to blood flow when valve normally open
How does regurgitation occur?
- valve doesn’t close all the way
- back leakage when the valve should be closed
Causes of Aortic valve stenosis
- Degenerative
- Congenital (a bicuspid form of the valve)
- Chronic rheumatic fever due to streptococcal infection which can lead to inflammation and then commissural fusion
Symptoms of Aortic valve stenosis and how they arise
- less blood can get through valve thus leading to increased LV pressure thus hypertrophy of LV
- less blood also leads to left-sided heart failure which can lead to syncope (fainting) or angina
Which type of anaemia can result from aortic valve stenosis?
-Microangiopathic haemolytic anaemia
Shear stress on RBC passing through a stenotic valve can cause damage to the cells as they pass through the narrow opening under pressure
Causes of Aortic Valve regurgitation
- Aortic root dilation (leaflets pulled apart)
- Valvular damage (endocarditis rheumatic fever)
Consequences 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: nails bed flushing w pulse)
- LV hypertrophy
Causes of Mitral Valve regurgitation
- Myxomatous degeneration (problems with collages structure of valve) can weaken tissue leading to prolapse
- damage to papillary muscle after a heart attack
- left-sided heart failure leads to LV dilation which can stretch the valve
- rheumatic fever can lead to leaflet fibrosis which disrupts seal formation
Causes of Mitral Valve Stenosis
- Rheumatic fever (99% cases)
- Commissural fusion of valve leaflets
Symptoms of Mitral Valve Stenosis
-Increased LA pressure leads to LA dilation which can lead to atrial fibrillation and Oesophagus compression
- atrial fibrillation can lead to thrombus formation
- oesophagus compress can lead to dysphagia(problems eating)
- increased LA pressure can also lead to Pulmonary oedema, Dyspnea(difficulty breathing) and pulmonary hypertension.
- all 3 stated above can lead to RV hypertrophy
