ECGs Flashcards
What is the electrical axis of the heart?
The overall direction of the wave of depolarisation of the heart
Normally its a diagonal line running from top right of the heart (SAN) to the left of the interventricular septum
If depolarisation is spreading towards a positively recording electrode what direction will the deflection be?
Upward deflection
If depolarisation is spreading away from a positively recording electrode what direction will the deflection be?
Downwards
If repolarisation is spreading towards a positively recording electrode what direction will the deflection be?
Upwards
If repolarisation is spreading away from a positively recording electrode what direction will the deflection be?
Downwards
What contributes to the amplitude of a deflection?
Size of muscle changing potential and how fast it changes
How directly the wave of activity is travelling towards the electrode
If a wave of activity is heading directly towards/away from an electrode how big will the deflection be?
Large signal
If a wave of activity is heading obliquely towards/away from an electrode how big will the deflection be?
Smaller signal
If a wave of activity is spread at right angles from an electrode how big will the deflection be?
NO signal
What does the P wave represent?
Atrial depolarisation
What does the QRS complex represent?
Ventricular depolarisation
What does the T wave represent?
Ventricular repolarisation
What is the PR interval?
The start of the P wave to the start of the Q wave
It is the time it takes for the initiated depolarisation in the atria to reach/be conducted to the ventricles
What does a prolonged PR interval indicate?
Delayed conduction through the AV Node to the ventricles
What can cause a prolonged PR interval/delayed conduction via the AVN to the ventricles?
Heart block
Ischaemic heart disease
Hypokalaemia
What is the PR segment?
Isoelectric section before Q wave where the impulse reaches the AVN and it initiates a time delay
In the QRS complex why is the Q wave deflecting downwards?
Depolarisation of septum happens right to left which is moving away from the positive electrode
In the QRS complex why is the R wave deflecting upwards?
Depolaristion spreading down bundle of His in direction of the positive electrode
In the QRS complex why is the S wave deflecting downwards?
Depolarisation spreads from the apex of the heart upwards via the Purkinje fibres AWAY from the positive electrode
What is the ST segment?
Isoelectric segment following the end of the S wave and before the start of the T wave
If the ST segment is Raised or Depressed (NOT isoelectric) what does this indicate?
Myocardial Infarction
Ischaemia
What is indicated by the QRS interval/complex being wider?
Depolarisations not indicated by normal conductance mechanisms
(Depolarisations arising ectopically in ventricles)
What can lead to the QRS interval being wider?
Bundle branch block
Hyperkalaemia
Ventricular ectopics
What is the QT interval?
Start of the Q wave to the end of the T wave?
What does a prolonged QT interval suggest?
Prolonged ventricular depolarisation/delayed repolarisation
What can cause a prolonged QT interval?
Certain drugs:
-Amiodarone (K+ channel blocker)
-Antidepressants
When taking an ECG, how many electrodes are put on them?
10
How many electrodes are placed on the limbs in an ECG?
4
(1 on each limb)
How many electrodes are placed on the chest in an ECG?
6
What phrase is used to remember what electrodes go on which limbs in an ECG?
Ride
Your
Green
Bike
What does Ride Your Green Bike mean?
Corresponds to the colour of the electrodes put on the limbs
Where is the Red electrode put on the limbs for an ECG?
Right arm
Where is the Yellow electrode put on the limbs for an ECG?
Left arm
Where is the Green electrode put on the limbs for an ECG?
Left thigh
Where is the Black electrode put on the limbs for an ECG?
Right thigh
How do you use the “Ride your green bike” phrase to remember where you put the 4 limb electrodes?
The first letter corresponds to the colour of the electrode
Start at right arm and go clock wise to the left arm, left leg then right leg when you’re looking at the patient
Where do you place the V1 electrode?
4th intercostal space to the right of the sternum
What is an intercostal space?
Space below the corresponding rib
Where do you place the V2 electrode?
4th intercostal space to the left of the sternum
Where do you place the V4 electrode?
5th intercostal space at the midclavicular line on the left side
Where do you place the V3 electrode?
Directly between the V2 and V4 electrode
Where do you place the V5 electrode?
Level with V4 at left anterior Axillary line
Where do you place the V6 electrode?
Level with V5 at left midaxillary line (directly under the midpoint of the armpit
How do you find the 4th intercostal space?
Palpate the great sternal notch
Go across and your inline with the second costal (Rib)
Space underneath that is the second intercostal space
Out of the right arm, left arm and left leg electrodes which is always most negative?
RA
Out of the right arm, left arm and left leg electrodes which is always most positive?
LL
Out of the right arm, left arm and left leg electrodes which electrode can be positive or negative depending on which electrode connects to it?
LA
Where is Lead 1?
Runs from RA to LA
Where is Lead II?
Runs from RA to LL
Where is Lead III?
Runs from LA to LL
Which way do cables look at the heart from?
Look from the positive end
What other type of wave can be present in an ECG?
What does it indicate and what can cause it?
U waves
Pathology like hypokalaemia
How do you calculate the heart rate from an ECG:
For a sinus rhythm?
For a non sinus rhythm?
What lead do you normally use for this?
For a sinus rhythm count the number of large squares between each peak of the R wave.
Then do 300/num of large squares between
For a non sinus rhythm count the number of QRS complexes in 30 large squares. This will tell you the number of beats per 6 seconds. Then multiply it by 10.
Lead II normally used for HR
How long is a normal PR interval?
3-5 small boxes, anything over 1 large box is prolonged
What condition is there likely to be a shortened PR interval?
Why?
What additional features are expected to be seen on the ECG?
Wolff-Parkinson-White syndrome
There’s a faster conduction pathway between the atria and ventricles where the time delay from the AVN is bypassed
DELTA WAVES expected which make PR interval short
How long is a normal QRS interval/complex?
2-3 small boxes
Roughly how long is a normal QT interval?
Between 10-12 small boxes but it varies with heart rate
Roughly how long is a normal QT interval?
Between 10-12 small boxes but it varies with heart rate
What is classified as a sinus rhythm?
Regular rhythm
HR between 60-100bpm
P waves present
P waves upright in leads I and II
Normal PR interval
Every P wave followed by QRS
Every QRS happens after a P wave
Normal QRS width
How should you approach analysing an ECG?
Rate (HR)
Rhythm (regular or irregular, check distance between peaks of QRSs)
Axis
Intervals
Is there P waves (atrial activity)
Is there QRS complexes (ventricular activity)
What should be considered if the QRS complex is large and encroaching on other leads traces?
LV Hypertrophy
What should be considered if the QRS is broad?
Bundle branch block
How long is a whole ECG strip?
How can you use this to calculate heart rate?
10s
Count number of QRS complexes and multiply by 6
What leads do you look at to determine the axis of an ECG?
Only the limb leads
So Leads I, II, III, aVR, aVL and aVF
What leads are the most positive with a normal axis?
If Leads I or II largest/most +ve axis is normal
What changes are seen in the electrodes when there is right axis deviation?
Lead III will be the most +ve out of the 3 limb leads
(Normally lead I or II is most +ve)
Causes avL and lead I to become negative
What changes are seen in the limb lead electrodes with Left Axis Deviation?
aVL will be the most +ve
And Lead II, III and aVF will be -ve
What usually causes Left Axis Deviation?
Can be normal or seen in hypertension and hypertrophy
Left bundle branch block
LV hypertrophy
Complete inferior wall MI
Wolff-Parkinson-white syndrome
Where can Right Axis Deviation be seen?
Can be normal in kids/ young people
Left posterior branch blocks
Complete lateral MI
RV Hypertrophy
Wolff-Parkinson-white syndrome (it depends on where the access pathway is)
