ECG Flashcards
What is Ohm’s law
Voltage= current X resistance
On as ECG what does a positive deflection show
The net current is travelling towards the lead
What does it mean if there is an isoelectric point on an ECG
The line would be flat showing no net current in direction of a lead
What does it mean if there is a negative deflection on an ECG
The next current flow is travelling away from the lead
What is an ECG
Electrocardiogram
What is an ECG used for
The record the electrical activity of the heart from different angles to identify and locate pathology via placing electrodes on the limps and chest of the patient
What does the P wave represent on a healthy individuals ECG
Atrial depolarisation
What does the PR interval represent in an ECG of a healthy individual
This interval begins at the beginning of the P wave and ends at the beginning of the Q wave and it represents the time taken for the electrical activity to move between the atria and the ventricles
What is the QRS complex
The ORS Complex is 3 closely related waves that show the depolarisation of the ventricles
What is the ST segment on the ECG
This segment start at the S wave and ends at the end of the T wave.
This is shown as an isoelectric line between the depolarisation and the re polarisation of the ventricles in the heart
What is the T wave on an ECG
The T wave show ventricular repolarisation and is shown as a small wave after the QRS complex
What is the QT interval on an ECG
This is begins at the beginning of the QRS complex and finishes at the T wave
This interval shows the depolarisation of the ventricles and then them repolarising
What is an ECG electrode
It is a conductive pad that attaches to the skin that records the electrical activity of the heart
What is an ECG lead
This is a lead that gives a graphical representation of the Hearts electrical activity which is calculated by data from several ECG electrodes
How many chest electrodes are there
6
What is the location of each chest electrodes on the chest wall
V1 is located on the 4th intercostal space at the right side of the sternal angle
V2 is located on the 4th intercostal space at the left side of the sternal angle
V3 is located midway between chest lead v2 and v4
V4 is located in the 5th intercostal space in the midclavicular line
V5 is located in the left anterior axillary line at the same horizontal level as v4
V6 is located in the left mid axillary line at the same horizontal level of v4 and v5
How many limb leads are there
4
Where are the limb leads located
Red lead is located on the right arm on the ulnar styloid process of the right arm
Yellow lead is located on the left arm on the ulnar styloid process of the left arm
Green lead is located on the left leg on the medial/lateral malleolus of the left leg
Black lead is located on the right leg on the medial/lateral malleolus of the right leg
What do each chest lead show
V1 shows a septal view of the heart
V2 shows a septal view of the heart
V3 shows a anterior view of the heart
V4 shows a anterior view of the heart
V5 shows a lateral view of the heart
V6 shows a lateral view of the heart
What does lead I show and how is it calculated
Lead I shows an inferior view of the heart and is calculated by analysing the right arm and left leg
What does lead II show and how is it calculated
Lead II shows an inferior view of the heart and is calculated by analysing the right arm and left leg electrode
What does lead III show and how is it calculated
Lead III shows an inferior view of the heart and is calculated by analysing the Left arm and left leg electrodes
What does the aVR lead show and how is it calculated
This lead shows a lateral view and is calculated by analysing the activity between Left arm and left leg compared with right arm
What does the aVL lead show and how is it calculated
This shows a lateral view of the heart and is calculated by analysing the activity between the right arm and left leg compared to the left arm
What does the aVF lead Show and how is it calculated
This lead shows the inferior view of the heart and is calculated by analysing the activity between the right arm and left arm compared to the left leg
What does a positive deflection on an ECG
A positive deflection shows that the electrical activity within the heart is travelling towards the lead
What does a negative deflection on an ECG show
A negative deflection shows that the electrical activity within the heart is travelling away from the lead =
What is each deflection on an ECG representing
Each deflection is a wave of the average electrical activity is traveling
What does the height of the deflection show
The height of the deflection represents the amount of electrical activity flowing in that direction
What is shown by the lead with the most positive deflection
The lead with the most positive deflection is the most aligned with the direction the hearts electrical activity is travelling
What does it mean if the R wave is greater than the S wave
It suggests the depolarisation is moving towards the lead
What does it mean if the S wave is greater than the R wave
It would suggest that the depolarisation is moving away from the lead
What does it mean if the S and R wave are of equal heights
It means that the depolarisation is travelling at 90 degrees to the lead
Different leads represent different anatomical territories of the heart what does this allow
This allows for pathology to be localised to a particular region of the heart
Which leads show an inferior view of the heart
Leads II, III and aVF
Which leads show a lateral view of the heart
Leads I, aVL, aVR, V5, V6
Which leads show an anterior view of the heart
Leads V3 and V4
Which leads show a septal view of the heart
Leads V1 and V2
If an ECG shows an ST elevation which leads would be affected and what would it suggest
Leads to V3 and V4 which could suggest an anterior myocardial infarction
Where does electrical activity start in the heart
At the sinoatrial node
From the sinoatrial node where does the electrical activity spread to
The atrioventricular node
From the atrioventricular node where does the electrical activity spread to
Spreads down the bundle of HIS and into the purkinje fibres
What does the electrical activity in the purkinje fibres cause
The ventricular contraction
What is a normal cardiac axis in a healthy individual
Lies between -30 degrees and +90 degrees
In a normal cardiac axis in a healthy individual in which leads is overall electrical activity seen
In leads I, II and III
In a normal cardiac axis of a healthy individual which leads has the most positive deflection
Lead II
In a normal cardiac axis of a healthy individual which lead shows the most negative deflection and why
The aVR lead because it has a viewpoint of the heart from the opposite direction
What causes right axis deviation
The direction of depolarisation is been distorted to the right between +90 and +180 degrees
What is the most common cause of right axis deviation and how does it occur
Right ventricular hypertrophy.
This occurs when there is extra right ventricular tissue resulting in a stronger electrical signal been generated by the right side of the heart this causes the deflection in lead I to become negative and the deflection on lead aVF and IIII to become more positive
What is right ventricular hypertrophy most commonly associated with
Pulmonary hypertension but can be seen in very tall people
What causes left axis deviation
Left axis deviation is caused by the direction of depolarisation being distorted to the left between -30 and -90 degrees
How is left axis deviation showing in relation to the lead
The deflection of lead III becomes more negative
When should left axis deviation be considered significant
Left axis deviation should only be considered significant if the deflection of lead II becomes negative
What can cause left axis deviation
Conduction abnormalities
What are the boundaries of a
Normal
Tachycardia
Bradycardia
Heart rates
Normal is 60-100 bpm
Tachycardia is over 100 bpm
Bradycardia is under 60 bpm
How do you calculate a heart rate from an ECG of a regular heart rhythm
Count the number of large squares present in the PR Interval and then divide 300 by the number counted which gives you the heart rate
How do you calculate heart rate from an ECG id the patient has an irregular heart rhythm
Count the number of complexes on the rhythm strip and multiple by 6
There are 2 types of irregular heart rhythm… what are they
Regularly irregular
Irregularly irregular
What is meant when a patient has a regular irregular heart rhythm
The patients hear rhythm has a recurrent pattern of irregularity
What is meant if a patient has a irregularly irregular heart rhythm
This patients heart rhythm is completely disorganised
If P waves are present what should they be followed by
QRS Complex with a normal duration, direction and shape
What happens if P waves are absent with an irregular heart rhythm
Atrial fibrillation
How lon should the PR interval last for
Between 120-200m/s (3-5 small squares)
If there is a prolonged PR interval what does this mean
There would be atrioventricular delay which could cause AV block
How many types of heart block is there
4
What are the 4 types of heart block
First degree heart block
Second degree heart block type 1
Second degree heart block type 2
Third degree heart block
What are the characteristics of first degree heart block
Fixed PR interval longer than 200 m/s (longer than 5 small squares)
What are the characteristics of second degree heart block type 1
Progressive prolongation of the PR interval until the atrial impulse is no longer conducted and the QRS complex is dropped. AV condition resumes with the new beat and the sequence repeats
What are the characteristics of seconds degree heart block type 2
Consistent PR interval duration with the QRS complex intermittently dropped due to a condition failure, this follows a repeating pattern at every 3rd or 4th P waves
What is 3rd degree heart block also known as
Complete heart block
What does complete heart block mean
There is non electrical communication between the atria and the ventricles which results in a complete failure of conduction
How would compete heart block be represented on an ECG trace
There would be a presence of both P waves and QRS Complexes but they have no association with each other due to the atria and ventricles functioning independently
What does it mean if in 3rd degree heart block the QRS complex lasts for less than 0.12s in duration
The signal originated above the bifurcation of the bundle of HIS
WHAT DOES IT MEAN IF THE QRS Complex lasts longer that 0.12s in 3rd degree heart block
The signal originates fro below the bifurcation of the bundle of HIS
What does it mean if a patient has a shortened PR interval
The P wave originated from somewhere closer to the AV node so the conduction takes less time
Or
The atrial impulse is getting to the ventricle by a faster shortcut instead of conducting slowly across the atrial wall, this is known as an accessory pathway associated with the delta wave
