ECG Flashcards
what is an ECG
a recording of potential charges, detected by electrodes positioned on the body surface, that allows the electrical activity of the heart to be monitored in a simple and non invasive manner
what is a 12 lead ECG comprised of
three standard limb leads, three augmented voltage (aV) leads and six chest leads
What are standard limb leads also termed
bipolar
what are the names of the three standard limb leads?
I, II and III
what are the names of the three aV leads?
aVL, aVR and aVF
what are the names of the six chest leads?
V1-V6
what are augmented voltage leads also termed?
unipolar
what are chest leads also known as
precordial leads
Why use 12 leads instead of just 1?
12 leads allows you to determinet he axis of the heart, look for any ST segment or T wave changes in relation to specific regions of the heart and look for any voltage criteria changes
which leads allow a vertical view and which leads allow a horizontal view?
veritcal view- standard limb leads and aV leads horizontal- chest leads
How does limb lead I connect?
Either it connects from the negatively charged right arm to the positively charged left arm or it connects from the negatively charged right shoulder to the positively charged right left shoulder
How does limb lead II connect?
Either it connects from the negative charger right arm to the positively charged left leg or it connects from the negatively charged right shoulder to the positively charged groin
How does limb lead III connect?
either it connects from the negatively charged left arm to the positively charged left leg or it connects from the negatively charged left shoulder to the positively charged groin
what is it called when the limb leads form a triangle around the heart?
Einthoven’s triangle
which limb lead passes through the heart inferiorly?
Limb lead II
why is the P wave shaped how it is?
Because the SA node is located at the top right of the heart and so atrial depolarisation occurs from the top right of the heart and moves down and to the left following the same direction of neg to pos of limb lead II causing a small upward deflection
how long should a P wave last?
0.12 s or less
what does the P wave represent
atrial depolarisation
why is the Q wave shaped how it is?
because the AV node is located in the interventricular septum meaning that depolarisation starts in the interventricular septum and spreads down from left to right instead of following the neg to pos direction of limb lead II, causing a small negative deflection on the ECG
how long does the QRS complex usually last?
0.1 s or less
Why is the R wave shaped how it is?
because the free walls of the ventricles are depolarised downwards from right to left , following the direction of the neg to pos direction of limb lead II, causing a positive upwards deflection on the ECG
why is the S wave shaped how it is shaped?
because the base of the ventricles are depolarised upward from left to right going against the direction of the neg to pos limb lead II, causing a small negative deflection in the ECG
what does the T wave respresent?
ventricular repolarisation
why is the T wave shaped the way it is?
repolarisation is negative and the ventricle is repolarised from the positive to the negative end of limb lead II, the negative moving in the negative direction is the same as a positive moving in a positive direction and so the T wave appears as a small positive deflection on the ECG
What does the PR interval represent?
the time taken for the electrical impulses to reach the ventricles from the SA node
how long is the PR interval usually?
0.12-0.2s
when does the PR interval start and end on an ECG?
it starts at the start of the P wave and ends at the start of the QRS complex
What influences the PR interval time?
time taken for action potential to pass through AV node and bundle of HIS fibres
Where is the ST segment on an ECG?
from the start of the QRS complex to the end of the T wave
what does the ST segment normally look like and why?
it is normally a flat line because the ventricles are fully depolarised and there is no real large changes going on (plateau phase 2)
what will the ST segment look like during pathological changes?
the ST segment will not be on the isoelectric line, there may be ST depression or elevation
where is the QT interval seen on an ECG
from the start of the QRS complex to the end of the T wave
what does the QT interval represent?
this represents the time taken for ventricle depolarisation and repolarisation
how long should the QT interval be?
0.44s in males and 0.46s in females
what does prolongation of the QT interval suggest?
disturbances of cardiac rhythm, which may be due to drugs patient is on
what is it called when there are six different views of the heart when the frontal leads are put together?
the hexaxial reference system
what do aV leads allow you to see?
the heart from different angles than the standard limb leads
why do the waves appear upside down for aVRv lead?
because during depolarisation means the electrical conduction is moving away from its recording electrode
what are the lateral limb leads and why?
aVL and lead I because they both have a recording electrode on the left arm, giving a view of the heart from a lateral view
what are the inferior limb leads and why?
aVF, lead II and lead III because they all have a recording electrode on the left foot, giving a view of the heart from an inferior direction
what happens to the R and S waves as you go from V1-V6
R wave increases and S wave decreases
where is V1 positioned
at the fourth intercostal space immediately right of the sternum
where is V2 positioned
at the fourth intercostal space immediately left of the sternum
where is V3 positioned
mid way between V2 and V4
where is V4 positioned
at the fifth intercostal space at the mid clavicular line
where is V5 positioned
same horizontal level as V4 anterior axillary line
Where is V6 positioned
same horizontal level as V4 mid axillary line
how many sticky pads are used for 12 lead ECG
10
where are the sticky pads that aren’t V1-V6 placed?
on the four limbs
which lead is usually the rhythm strip
lead II
