Cardiac Cycle Flashcards
Describe what happens at each part of a typical ECG wave
P, atrial depolarization Q, septal depolarization => atria R, ventricular depolarization=> apex S, ventricular depolarization => atria T, ventricular repolarisation => endocardiogram
Name the valves and describe how they are affected by changes in pressure
RA => tricuspid => RV
RV => pulmonary => pulmonary arteries
Pulmonary veins => LA => mitral/bicuspid => LV
LV => aortic semilunar => aorta
Healthy valves have v little resistance so small pressure resistance so small pressure gradient across is enough for them to open
How to interpret a 2D ECG
Black areas = heart chambers
Top of cone, probe
Blue, away from probe
Red, towards probe (color doppler)
How do the valves operate under changing pressures
Opening valves due to pressure differences
AV, anchored to ventricle walls by papillary muscles, chord tendinae to prevent inverting
Bulge back into atria in ventricular systole, causes increase in atrial pressure and pulse of blood into jugular vein
How are the anchoring structures damaged and what happens as a result
After MI, AV valve everts into atrium
Backflow, can be seen as mitral regurgitation in ECG
Describe the pressure and volume changes in the heart
Fractional increase in LA pressure > LV pressure => mitral valve opens
LA contracts but not very much
LV contracts, isovolumic contraction (increase in pressure, no change in volume)
LV pressure increases, aortic valves still closed
Aortic valve opens when V pressure > aortic pressure
V ejection
End systolic pressure falls
LV pressure falls below aortic pressure, shuts => dicrotic notch => isovolumic relaxation
LV pressure falls below atrial pressure => mitral opens, V fills
Describe the steps in the pressure volume loop
Mitral opens, empty ventricles Period of filling Mitral closes Isovolumic contraction Aortic opens Period of ejection Aortic closes Isovolumic relaxes
What information can you get from the pressure volume loop
Volume differences => ventricular volume/stroke volume
Diastolic function
Systolic function
Total area, stroke/work
Describe the peaks and troughs found in jugular venous pressure
A, atrial contraction (systole)
C, carotid pulse (carotid parallel to jugular, crushed jugular => P falls)
X, Atrial relaxation
V, R atrial filling in ventricular systole, closed tricuspid bulging, increasing RA pressure (pushes blood => venous system)
Y, Passive atrial emptying
What are the main characteristics of the jugular venous pulse
Biphasic, low pressure
Easily affected by other factors,
Describe the peaks and troughs found in the peripheral arterial pressures
Peak after ventricular systole
Smaller peak, wave of pressure bounces off peripheral vessels
What are the main characteristics found in the peripheral arterial pressure waves
What is it influenced by?
Monophonic and high pressure
Shape of peak and descending phase influenced by
- Reflected waves
- Resonance
- Compliance
- Interference
- Damping
Shape and magnitude of arterial pulse wave varies along arterial tree
How do hydrostatic influences affect the jugular vein
What is the pressure found here
Will collapse at 5cm above RA due to hydrostatic influences, blood can still flow here
4-8mmHg
How does arterial pressure change
Changes as you move away from heart
Generally high
Increased height, increased BP as gravity moves everything down
How to judge if CVP is normal
Support patient at 45
JVP is height of collapse of internal jugular above manubriosternal angle
Collapse point = 3cm above MBS angle
If above 3cm, something is not right
