ECG Flashcards
describe how repolarisation spreads through the heart tissue
epicardium to endocardium
describe how depolarisation spreads through the heart tissue
endocardium to epicardium
what is an ECG
recording of potential changes detected by electrodes positioned on the body surface, allows monitoring of heart activity
where do the potentials detected arise from
currents that flow when the membrane potential of myocardial tissue is changing (de/repolarisation)
why does the left ventricle have a bigger influence on the ECG
as bigger mass
can you detect the electrical activity in the nodes
no too small
is it the intra and extracellular current that is detected by an ECG
extra
what is an electric dipole
electrical vector-separated charges, move from atria to ventricles, positive charge first
what are the components of the vector electrical dipole
magnitude and direction
what allows the electrical axis of the heart to be estimated
lines of potential created by the cardiac dipole and their direction
what determines the mass of the electrical vector
the mass of the cardiac muscle
what determines the direction of the electrical vector
overall activity of the heart
describe the direction of depolarisation during the P wave on an ECG
atrial depolarisation moving towards the recording electrode
describe the direction of depolarisation during the Q wave on an ECG
left to right depolarization of the interventricular septum moving slightly away from the recording electrode
describe the direction of depolarisation during the R wave on an ECG
depolarization of the main ventricular mass moving towards the recording electrode
describe the direction of depolarisation during the S wave on an ECG
depolarization of ventricles at the base of the heart moving away from the recording electrode
describe the direction of repolarisation during the T wave on an ECG
ventricular repolarization moving in a direction opposite to that of depolarization accounts for the usually observed upward deflection
what is an ECG lead
the electrical picture obtained of the heart, not the wire
what type of deflect does depolarisation cause when moving towards the electrode
upward deflect
what type of deflect does depolarisation cause when moving away from the electrode
downward deflection
describe an isopotential deflection
no movement of current, no deflection
what are the bipolar leads
standard limb leads (I,II and III)
decsribe the reletionship between the augmented voltage leads
one recording two linked as reference (three all together)
what are the three augmented voltage leads
aVright, aVleft, aVfoot
are the aV leads unipolar or bipolar
unipolar
are the chest leads unipolar or bipolar
unipolar
what leads provide a picture of the heart from a vertical plane
I, II, III, aVR, aVL, and aVF
what leads provide a picture of the heart from a horizontal plane
V1 to V6 (chest leads)
what is the recording electrode for lead 1
RA-ve to LA+ve
what is the recording electrode for lead 2
RA-ve to LL+ve
what is the recording electrode for lead 3
LA-ve to LL+ve
what is bipolarity
A lead composed of two electrodes of opposite polarity is called bipolar lead
what is unipolarity
A lead composed of a single positive electrode and a reference point is a unipolar lead
what is the right legs role in an ECG
is earthed
from which direction does lead 2 see the heart
from an inferior direction
why is the p wave an positive deflection when shown in lead 2
as depolarisation spreads from SA node inferiorly and to the left
what is a normal duration for a P wave in an ECG and what does it represent
time for atrial muscle depolarisation. normally less than 0.120s
what is the downward deflection preceding and R wave called
Q wave
what is an R wave
an upwards deflection irrespective of whether it is proceeded by a Q wave
what is an s wave
a downward deflection following an R wave
what does the QRS complex represent
ventricular depolarisation
how long does a normal QRS complex last
0.1s or less
what causes the Q wave as seen via lead 2
as ventricular depolarisation starts in the inter ventricular septum and spreads from left to right
describe the R wave and what causes it
following the Q wave the main free walls of the ventricles depolarise causing a tall and narrow R wave