Week 3 Heart Axis And Cardiac Flow Flashcards
What is one lead
A set of TWO electrodes
What does a lead measure
Records a voltage shift
As waves spread over the heart
How are direction and strength of a signal related in a lead
When a wave is parallel (same direction) it sis stronger
Perpendicular - no signal
Why is einthovens triangle formation used
A wave travelling in any direction will be parallel to at least one of the three leads
Ground electrode - purpose
Acts as a baseline
Looks at the natural voltage of the ground
By convention - what are the ECG directions for depol and repol
Depol - positive (up)
Repol - negative (down)
Waves travelling away from the positive electrode - opposite ^
Why is lead 2 normally used in a single lead trace
Lead 2 has the strongest response to a healthy heart
Several issues can be detected on lead 2 - other leads can then be assessed
Q of QRS
Depolarisation in the direction of the negative electrode - downward slope
small magnitude
Upwards slope R of QRS
Ventricle is being depolarised
Happens in the direction of lead 2
Huge wave in the positive direction
Downward slope R of QRS
Ventricle is still depol
But wave points less at the positive electrode
So is seen returning to 0
S of QRS
Opposite direction to positive electrode
Wave travels toward atria
Small magnitude
Trace is negatice
What is the heart axis
The mean vector
Describing direction of voltage in the heart
Heart axis calculation
Calculates mean of each mean electrical wave
Normal is 0-90 degrees
what causes ventricular fibrillation
- AP keeps circling back on itself
- or cardiomyocytes are repeatedly contracting
- or contracting irregularly so ventricle is out of synch
when to use a defibrillator
- not for a flatline
- is used for ending FIBrillation
how does a defib work
depolarises all cardiac cells at once
to create a fresh signal from myogenic pacemaker cells
to bring back synchrony in beating
what are the two valves
mitral/bicuspid - 2 cusps
tricuspid - 3 cusps
what is the wiggers diagram
a method to visualise several aspects of the heart at once
systole
period of contraction of the ventricles
diastole
relaxation of heart muscle + then chamber fills with blood
phases of systole
- isovolumetric contraction
- rapid ejection phase
- slow ejection phase
phases of diastole
- isovolumetric relaxation
- rapid filling phase
- slow filling phase
- atrial contraction
what phase of diastole is the P wave
atrial contraction / depol
what phase of systole is QRS
ventricular contraction
what phase of systole is the T wave
ventricular relaxation / repol
aortic pressures in
1) diastole
2) ejection phase
3) isovolumetric phase
1) diastole - 80mmHg
2) ejection phase - 120
3) isovolumetric relaxation - aortic valve closes, causes dicrotic notch
ventricular pressure
1) isovolumetric contraction
2) ejection phase
3) isovolumetric relaxation
1) ventricle contracts, closed chamber so pressure increases
when ventricular pressure crosses (is higher) the aortic pressure, the aortic valve opens
2) ejection phase is the top peak ◠ curve
when VP decreases and drops below the aortic pressure, the aortic valve closes
3) isovolumetric relaxation starts - pressure decreases - slope downwards
when VP falls below atrial pressure (1-7 mmHg) - mitral valve opens - rapid and slow filling ventricle phase starts
Atrial pressure
starts high than VP
mitral valve closes when ven pressure raises -> raises atrial pressure
ejection phase - atrium is filled + pressure rises
when pressure is higher than VP - mitral valve opens and filling phase of ventricle starts
ESPVR
end systolic pressure volume relationship
the max pressure of left ventricle at any volume
a measure of cardiac contractility
EDPVR. passive filling curve of the left ventricle during diastole and is a measure of passive chamber stiffness
end diastolic pressure volume relationship
passive filling curve of the left ventricle during diastole
measure of passive chamber stiffness
factors affecting cardiac output:
- preload
- frank starling mechanism
- afterload
- compliance
- inotropy
what is cardiac output
amount of blood that the heart pumps in a minute
what is preload
how much blood is in the chamber at the end of diastole
more blood entering heart = more preload
so heart increases stroke volume
stroke volume
The volume of blood pumped out of the left ventricle of the heart during each systolic cardiac contraction
factors that increase preload
these factors increase ventricular filling time
- increased atrial contractility
- increased central venous pressure
- decreased heart rate
frank starling mechanism
when the heart is stretched
the heart contracts more
so end systolic volume is maintained
more contracting = more preload = increased stroke volume
afterload
the pressure the heart has to pump to push blood out during ventricular contraction (systole)
aortic pressure
the pressure at the root of the aorta
caused by blood pushed from the LV to the aorta
how does afterload determine end systolic volume
increased aortic pressure - increased afterload
- higher aortic pressure = aortic valve closes earlier
- less ventricular emptying
- volume is at the end of systole
what is compliance
the inverse of stiffness
ie. MORE stiff, LESS compliant
how does compliance contribute to preload
it alters EDVPR
hypertrophy:
preload is reduced by having a stiffer heart
ventricle walls do not stretch as far in response to more blood volume
what is inotropy
increases the speed of contractility
lowers end systolic volume (ESV)
affects ESPVR
inotropes
make the heart beat with more or less power
between which phases does ejection occur
spans from the end of isovolumic contraction to the beginning of isovolumic relaxation
