electrocardiography/reading ecg Flashcards
is the sa node acted on by other cells
no
Spontaneously active cells
what is the p wave
Conducts current down atria & internodal pathways
function of av node
Current slows down more time for atrial muscle contraction
how does current travel down the septum
His-Purkinje system
Rapid conduction through left & right bundles -> Purkinje fibres -> ventricular contraction
how is that complex shown on an ecg
QRS complex of ECG
what is the t wave
Cardiac muscle relaxes & membrane potential recovers/repolarises
T-wave of ECG
what does lead II read
electrical currents from right shoulder to left leg
which lead would have the largest current (biggest deflection of the qrs)
lead II
Electrical current flowing away from the positive electrode results in a negative (downward) waveform display. In Lead II, the R wave is therefore positive. … The closer the mean QRS axis is to the electrical axis of Lead II, the larger the amplitude of the R wave.
qrs is going the exact same direction as the positive component of lead 2
how would the qrs change if lead II wasn’t perfectly parallel with the direction of the current
a lower qrs
less deflection in qrs as not parralell
what is axis deviation
- change in heart position
- change in position of electrical conduction ( one of the right or left bundle branches can de damaged or one more dominant that the other- current goes in a different direction)
where does lead 1 measure
horizontal
ii
right shouled to left lef
iii
left shoulder to right leg
aVF
down the middle
aVR
right leg to left shoulder
how would the p wave chnage if a pacemaker is producing currents in mixed directions
absent p wave
lots of small signal drown our the larger signal to av node
what is this condition known as
Atrial fibrillation - loss of p-wave
what is Atrial flutter
- saw-tooth pattern
what would happen if we had a barrier or problem at the av node
- longer pr interval
Type I Heart Block
Type II Heart Block
from what 2 points is the qr interval measured from
from start of p to start of q not R
what is a type 1 heartblock
delay in conduction
calcium channel heart block
increase p r interval duration
what is type 2
and cause
loss of conduction
more of an actual block
missing qrs complex ans thus t
due to damage to cells or drugs
what is the Wolff-Parkinson-White
is caused by an extra electrical pathway in the heart. This allows electrical signals to bypass the usual electrical system route and form a short circuit, resulting in an abnormally fast heart rhythm.
accessory pathway
what is it shown on an ecg
shorter pr complex
pre excitation
biphasic t wave
what causes a biphasic t wave
currents are going thru faster
alight depolarisation due to accessory pathway
what causes pre excitation
accessory pathway allows the current to get from atria to ventrciles faster
what is the bottom graph in the ecg
rythm strip
so one lead shown for a longer period of time normally lead ii
what atrcuture do you use to read ecgs
rate ryhthm and axis
what is the rate
r r interval
how to work it out
300/ number of large swuares e.g. 3,3
what is the rhythm
p r interval
qrs duration
st segment
what is the st segment
the straight part from s to t
how do you work them out
each small square is 40ms
how do you work out axis
guestimate using the diagram
what is the point of multiple leads
greater resalution
more detail abouts whats going on
