4 - The Heart as a Pump Flashcards
The heart is two pumps acting in ………..
Series
The systemic circulation is under …….. pressure
The pulmonary circulation is under …….. pressure
Systemic - high pressure
Pulmonary - low pressure
Overtime, ……….. ………… of the left and right sides of the heart is equal
Cardiac output
What is systole?
Contraction and ejection of blood from the ventricles
What is diastole?
Relaxation and filling of the ventricles
What is the average stroke volume?
~70ml blood per beat
Heart muscle cells operate in a …………. ………….. as they are electrically coupled by ……. junctions.
Functional syncytium
Gap
How long is a cardiac action potential?
~280 ms
How do the cusps of the mitral and tricuspid valves attach to the ventricular wall?
Valve cusps attached to papillary muscles on the ventricular wall via the chordae tendineae
What is the benefit of attachment of the AV valve cusps to the ventricular wall?
Prevent inversion of the valves and regurgitation of blood on systole
Where is the sinoatrial node?
In the wall of the right atrium - of muscular origin, not neuronal
How long is the conduction delay at the AV node?
~120 ms
Electrical excitation spreads through the ventricular myocardium from the …………….. surface to the ……………….. surface
Endocardial (inner) to epicardial (outer)
How long is systole at rest?
~0.35 s
How long is diastole at rest?
~0.55 s
What are the 7 phases of the cardiac cycle?
- Atrial contraction
- Isovolumetric contraction
- Rapid ejection
- Reduced ejection
- Isovolumetric relaxation
- Rapid filling
- Reduced filling
How do the relative durations of systole and diastole change during exercise?
Heart rate increases by decreasing the length of diastole, the time for systole is constant.
What wave of the ECG signifies atrial contraction?
The P wave
- Onset of atrial depolarisation
The small increase in pressure in the atria and ventricles associated with atrial contraction produces what section of the Wiggers diagram curve?
The A wave
Atrial contraction accounts for the final …….% of ventricular filling. The body can survive without this (e.g. in ………. ………………….)
10%
Atrial fibrillation
At the end of diastole, the ventricular volume is at its maximum, what is this called? What is the typical value in ml?
End-Diastolic Volume (EDV)
~120 ml
What occurs in isovolumetric contraction?
- Ventricle begins to contract causing rapid rise in ventricular pressure
- Mitral/tricuspid valve closes as the ventricular pressure exceeds atrial pressure
- No change in volume (isovolumetric) as all valves are closed
What heart sound is caused by closure of the tricuspid and mitral valves?
S1
During what phase of the cardiac cycle does the QRS complex of the ECG occur? What does it signify?
Isovolumetric contraction
Onset of ventricular depolarisation
What wave is seen on the atrial pressure curve of a Wiggers diagram when then mitral valve closes?
C wave
- Small and transient increase in atrial pressure as the valve snaps shut
What occurs during the rapid ejection phase of the cardiac cycle?
- Ventricular pressure exceeds the aortic pressure and causes the aortic valve to open
- Rapid decrease in ventricular volume as blood is ejected into the aorta
There is a small drop in atrial pressure during the rapid ejection phase (X descent), what causes this?
The atrial base is pulled down toward the apex of the heart during ventricular contraction creating negative pressure in the atria
What occurs in the reduced ejection phase?
- Repolarisation of the ventricle leads to a decrease in tension
- Rate of ejection falls
During reduced ejection the atrial pressure gradually rises. What wave does this produce on a Wiggers diagram? Why does this occur?
V wave
- Atrial pressure rises due to venous return into the atria
What ECG wave depicts ventricular repolarisation?
T wave
What occurs during isovolumetric relaxation?
- Ventricular pressure falls below aortic pressure
- Brief backflow of blood closes the aortic valve
- Rapid decline in ventricular pressure but all valves are closed so volume remain constant (isovolumetric)
What part of the aortic pressure curve is caused by aortic valve closure?
Dicrotic notch
There is always some residual blood left in the ventricles after contraction, what is this called?
End-Systolic Volume (ESV)
What can the End-Diastolic Volume (EDV) and End-Systolic Volume (ESV) be used to calculate?
Stroke volume (SV) SV = EDV-ESV
What heart sound is caused by closure of the aortic and pulmonary valves?
S2
What occurs during the rapid filling phase of diastole?
- When ventricular pressure falls below the atrial pressure the atrioventricular valves open
- Rapid ventricular filling begins
When the atrioventricular valves open, a small drop in atrial pressure occurs, what does this produce on the Wiggers diagram?
The Y descent on the atrial pressure curve
Ventricular filling is usually silent. What heart sound can sometimes be heard? What causes this?
S3
Caused by rapid entry of blood from atria to ventricles (not a valve)
When is the presence of S3 more likely to be pathological?
- S3 is normal in children
- A sign of pathology (heart failure) in adults
What occurs during the reduced filling phase of diastole?
- Rate of filling slows down (diastasis)
- Ventricle reaches its relaxed volume with further filling driven by venous pressure
At the end of the reduced filling phase the resting ventricles are …… % full. How does the remaining blood fill?
90%
- Remaining 10% from atrial contraction in the next cycle
What is stenosis?
Obstruction to blood flow as the valve does not open enough
What is regurgitation?
Valve doesn’t close all the way leading to backflow of blood when it should be closed
What side of the heart is more likely to get abnormal valve function?
Left side - under higher pressures
What causes aortic valve stenosis?
- Degeneration with age (senile calcification/fibrosis)
- Congenital (bicuspid form of valve)
- Chronic rheumatic fever (inflammation and commissural fusion)
What effect does aortic valve stenosis have on the heart?
- Increased LV pressure = LV hypertrophy
- Left heart failure = syncope and angina
What effect does aortic valve stenosis have on blood cells?
- Shear stress due to turbulent flow moving through the aortic valve
- Microangiopathic haemolytic anaemia
What murmur can be heard due to aortic stenosis?
Crescendo-decrescendo murmur during systole (between S1 and S2)
What causes aortic valve regurgitation?
- Aortic root dilation (leaflets pulled apart)
- Valvular damage (e.g. endocarditis, rheumatic fever)
What are the effects of aortic valve regurgitation on the heart?
- Blood flows back into LV during diastole
- Increases the stroke volume
- Systolic pressure increases, diastolic pressure decreases (increase PP)
- Bounding pulse
- LV hypertrophy
What murmur can be heard due to aortic valve regurgitation?
Decrescendo murmur in diastole (immediately after S2)
What occurs in mitral valve regurgitation?
- Chordae tendineae and papillary muscles fail to prevent prolapse of valve leaflets in systole
- Blood leaks back into LA, increases preload as more blood will enter LV in the next cycle - leads to LV hypertrophy
What causes mitral valve regurgitation?
- Myxomatous degeneration - weakens leading to prolapse
- Damage to papillary muscle after heart attack
- Left heart failure = LV dilation - can stretch the valve
- Rheumatic fever can lead to leaflet fibrosis
What type of murmur can be heard is mitral valve regurgitation?
Holosystolic murmur (between S1 and S2)
What occurs in mitral valve stenosis?
- Commissural fusion of valve leaflets
- Flow impaired between LA and LV
- Increased LA pressure leads to pulmonary oedema, dyspnoea and pulmonary hypertension = RV hypertrophy
- LA dilation leads to atrial fibrillation and oesophagus compression (dysphagia)
What is the main cause of mitral valve stenosis?
- Rheumatic fever (99.9% cases)
What murmur is heard due to mitral valve stenosis?
Snap as the mitral valve opens and diastolic rumble
