Practical ECG methods/Understanding the ECG Flashcards
What is an ECG lead?
They are a digital representation of the changes of depolarisation of the heart. it is a view of heart electrical activity.
It is not physical.
Downward deflections are towards the …………
Steepness of line denotes the ‘…………’ of action potential
What does the isoelectric line represent?
What does the sharpnees of turns denote?
Upward deflections are towards the …………
Downward deflections are towards the anode (-)
Steepness of line denotes the ‘velocity’ of action potential
The isoelectric line represents no net change in voltage
Sharpness of turns denote ‘rapid’ changes in direction of action potential
Upward deflections are towards the cathode (+)
Lable the diagram below for a lead 2 trace ( the normal one)- the one true lead- if you look at the angle it is roughly inline with the angle of the heart.- the grey bar represents the fact that the atrium and the ventricles are electrically insulated
Why is the septal depolarisation cause a downwards defelection?
Hint: in the grey pic of the heart below
The ventricular septum depolarises from the bottom to the top. It is rapid due to the purkinje fibers.
The left bundle branches-not the right- insulation terminates and a bit of impulses escape and the first bit of muscle exposed to this is the ventricular spetum then depolarise from the bottom up. Very little muscle.
What is the S wave?
The S wave travels in the opposite direction to the large R wave because, as can be seen on the earlier picture, the Purkinje fibres spread throughout the ventricles from top to bottom and then back up through the walls of the ventricles.
S wave representing depolarisation of the Purkinje fibres.
What does the height of the ECG tell you about the muscle?
The higher the height the more muscle there is
What does the following mean?
P wave
QRS complex
T wave
P wave= atria contraction
QRS complex= ventricle contraction
T wave= ventricle repolarisation
Where does Lead 1 start and end at?
Do the same for the other leads
Where is the neutral lead located?
Where does it always end at?
Remember rules of L’s
Lead I: Right arm to Left arm
Lead II: Right arm to Left Leg
Lead III: Left arm to Left Leg
Neutral: Right leg
Always ends on the Left side
Draw a picture of eithhovens triangle and state where the leads are and if they are psitive or negative?
Draw the sternum and rib cage and annotate it with the locations of the electrodes?
Fill in the summary table below
Bipolar -2 leads
Why does a lead 1 ECG have a posistive QRS?
Name the 3 augmented leads and example how augmeted leads are calculated?
How do you find lead aVR?
How do you find lead aVL?
How do you find lead aVF?
What is the easiest way of calculating the QRS axis?
Remember to angle from the 0 degrees
Essentially you pick two leads that are perpendicular to each other than you find their net deflections and then you use trigonometry
Net= postive deflection - negative deflection
QRS axis is the direction in which the mean QRScurrent flows. The normal axis points mostly downward and to the left because the more muscular left ventricle generates a stronger depolarizing current that overwhelms that generated by the less bulky right.
What is the QRS axis?
Lead II- + 4.5mm net deflection
Lead aVL- + 2mm net deflection
36 degrees
remeber to subtract from 60 degrees
Draw a diagram showing the direction of aVR, aVL, aVF?
aVR=Right
aVL=Left
aVF=foot
Draw a diagram showing lead 1?
Show which arm is posistive or negative?
Draw a diagram showing lead 2?
Show where the possitive and the negative electrodes are?
Draw a diagram showing lead 3?
Show where the positive and negative electrodes are?
Draw Einthoven’s triangle?
Describe how lead aVR is calculated?
The right arm is the true recording posisitve electrode.
The negative electrode is the average potential of the left arm and the left leg.
Draw a diagram showing how aVL is calculated?
State where the positve and negative electrodes are and the direction?
Draw a diagram showing how aVF is calculated?
State where the positve and negative electrodes are and the direction?
Draw how each ECG looks like for each lead
Augmented leads
Obtained by using the average voltage of
two electrodes as the negative pole, and
reading from the remaining electrode as
the positive pole
Reference for ECG
Draw a diagram of a pin wheel with the angle of the leads on it.
Draw on the diagram where a left axis will be, right axis and a normal qrs axis?
Calculating QRS axis
Notice how -14 goes upwards
Calculate the qrs axis in the image below
Calculate the QRS axis
State the location of the v1 to v6 leads?
Remember they are vectors.
Point the two vectors in the direction they go and then find their angle
What is the positive and negative pole in chest leads?
Summary
What precordial leads correspond the the following views?
septal
Anterior
lateral
