electrocardiography 1 Flashcards
why cant you use a defibrillator when there is a flat line on anm ECG
it is an unshockable rhythm
what are electrodes
the things that you stick on the patient
conductive material in contact with the skin
what are wires
the things that attach to the electrodes
what are leads
perspective of heart activity from a given view
what is a vector
a quantity that has both magnitude and direction
how do you represent a vector
with an arrow in the net direction of movement
size reflects the magnitude
what is represented by an isoelectric line
no net change in voltage
vectors are perpendicular to lead
what does the width of deflection denote
the duration of the event
what is denoted by the steepness of the deflection
the velocity of the AP
which way do downward deflections travel
to the anode
which direction do upward deflections travel
to the cathode
what do you use to measure deflection
the cathode and the anode
when is there no isoelectric line between waves
when they overlap
describe the axis of an ECG
x = time (ECG paper/recording moves at a certain speed)
y = amplitude
one in the function of the other = velocity of wave forms
what do the combination of down and upstrokes denote
a wave
what is donated by P
atrial depolarisation
electrical impulse that propagates through the atrial muscle that causes contraction
why is there no atrial repolarisation
hidden by QRS
what is donated by QRS
electrical signal that stimulates the contraction opf the ventricles
what is donated by T
electrical signal that signifies ventricular relaxation/repolarisation
role of the sinoatrial node
starts conduction
spontaneously depolarising at a given rate
action of atrial myocardium
rapidly conducts
role of the AVN
slow impulse to facilitate the mechanical activity of the heart
protective
describe the bundle of His
common bundle - bificates into L and R bundle branches
insulated
impulse can’t leave
impulse travels to the bottom of the ventricle
the insulation of the L branch is not as far as the R branch - L septum contracts first - right in middle so give rest of myocardium anchor to contract around
fibres go into apex - muscular
role of nodal branches
rapidly conduct impulse through atria, and to AVN
why is it important for the heart to contract upwards
because the great vessels leave at the top of the heart
why is lead 2 the best
it goes from cathode in right arm to left leg
which follows the direction of the heart from SAN to apex
describe the cardiac vectors
SAN causes P wave - not big, but broad - there is little muscle
AVN depolarisation - isoelectric - gap between P and QRS
end of isoelectric line - from impulse down bundle of his to mid septum - insulated and really fast
Q wave - bundle branches - escaping bundle wave from L bundle branch - down because towards the -ve, really fast
R - apex, lots of cells and lots of muscle - really to +ve electrode = massive spike
ST - impulse up the walls of the ventricle - a lot of cavity
T - reset - not big because no specific electrical event, broader than P
which is longer contraction/activation(systole)
contraction
features of the electrocardiogram
details - name and date and time (want to see change over time) where interval and axis each double big square is 1mv running speed - rate it would print 25mm/s 10mm/mv - double big square = 1mv .2 seconds for large square .04 seconds for a small square leads 1, 2, 3 - primary bipolar leads aVF, aVL, aVR - augmented leads V1-6 chest leads rhythm strip - evaluate rhythm HR intervals interpretation
leads that give inferior view of heart
2, 3 aVF
leads that give lateral view of heart
1 aVL V5 V6
leads that give an anterior view of the heart
V3 and V4
what are augmented leads calculated from
principle bipolar leads
which leads give a septal view of the heart
V1 and V2
Where does lead 1 measure
right arm to left arm
where does lead 2 measure
Right arm to L leg
where does lead 3 measure
L arm to L leg
which way do you read a lead
L to R
top to bottom
anode is always first
where are the chest leads placed
V1 - R sternal border (4th intercostal space)
V2 - L sternal border (4th intercostal space)
V3 - halfway between V2 and 4
V4 - midclavicular line level 5th intercostal space
v5 - anterior axillary line - level of V4
v6 - mid axillary line - level of V4
why do you put on conductive spray
so you can read activity
features of the 12 leads
anode is the calculation for 9 leads
which leads are in the coronal plane
1-3 and augmented leads
which leads are in the horizontal plane
chest leads
what does it mean by bipolar leads
both anode and cathode are physical leads
hwo do you work out cardiac axis
calculate the net deflection for lead 2 and lead aVL
use trig to calculate the angle
subtract accordingly to make it from 0degrees
why is aVL small
it goes from bottom right to top left
shows the heart is on the correct side of the body
effect of ECG being subjective
have to make judgement calls
how you act depends on the patient as a whole
might be normal for them
effect of putting cables in a different place
different ECG
what happens during inspiration and expiration if you have arrhythmia
inspiration heart rate up expiration heart rate down this is respiratory sinus arrhythmia - breathing cycle affect heart beat heart rate controlled by PNS - slow down breath in remove inhibition
how many people have respiratory sinus anaemia
50%
which views of the heart link to which coronary arteries
lateral = LCx ( L circumflex) septal = LAD (L anterior descending) anterior = RCA (right coronary artery)
