Session 6 Lectures - The ECG Flashcards
In what direction to
ventricles depolarise?
From endocardium to epicardium
What is the normal rhythm of the heart referred to as?
Sinus rhythm
Where do the right and left bundle branches lie?
Subendocardially in intraventicular septum
When current is carried from the Bundle of His - what depolarises first and in what direction?
The atrioventricular septum
Depolarises left to right
What is last in the ventricles to be depolarised?
The base of the heart (towards the atria)
Where does the ECG record changes?
On the extracellular surface of the cardiac myocytes
In what direction is a wave travelling to cause a positive deflection? (moving up)
The wave is travelling towards the electrode
In what direction should a wave be travelling to cause a negative deflection? (DOWN)
Away from the electrode
What will you see on the voltmeter if the heart was at resting state?
A flat line Positive charge (because the intracellular environment is more negative and we are measuring extracellular environment)
Does the depolarisation of the SA node register on the ECG?
No! The depolarisation is too small to register on the ECG
What causes the first current on the ECG and what is this called?
Depolarisation of the atria
It causes the P wave which is a positive deflection as the current is moving in the direction of the positive electrode
What causes the flat line after the P wave?
The delay at the AV node (which allows for the atria to finish emptying into the ventricles)
What causes the Q wave?
Depolarisation of the intraventricular septum
It causes a small negative deflection because the depolarisation is travelling left to right (moving away from the view at apex)
What causes the R wave - why is it the largest deflection?
Depolarisation of the apex of the ventricles
It is so large because there is a large muscle mass so greater electrical activity
The R wave is a large positive deflection because the wave is moving towards the electrode
What will happen to the R wave in LV hypertrophy?
The R wave will increase - greater deflection because there will be more muscle mass so greater electrical conductivity
What causes the S wave?
What direction is the deflection?
The depolarisation of the base of the ventricles
It produces a small downwards deflection because moving slightly away from view
What part of the wave is atrial depolarisation and which is ventricular depolarisation?
Atrial = the P wave Ventricular = the QRS complex Q = iv septum R = apex S = base
How many electrodes are placed on the body and how many views does this give?
10 electrodes = 4 on the limbs and 6 on the chest
12 views of the heart
- 6 from the limb electrodes (AVR, AVL, AVF, 1, 2 and 3)
- 6 from the electrodes on the chest
Which limb leads are looking at the heart inferiorly?
Leads 2,3 and AVF
Which limb leads are looking at the left side of the heart?
Lead 1 and AVL
On ECG paper what is the size of the small squares and large squares?
Small = 1mm x 1mm
Large = 5mm x 5mm
5 small squares = width of 1 large square
On the ECG paper what are along the axis?
Horizontal = time (ms) Vertical = voltage (mv)
What is the normal ECG speed?
How many squares does this equal?
25mm/second If small square = 1mm 25 small squares = 25mm 25 small squares = 5 large squares So it will travel 5 large squares or 25 small squares a second
How long does it take to travel 1 small square and 1 large square?
How many squares can you travel in a second?
1 small square = 0.04 seconds
1 large square = 0.2 seconds
So in 1 second you can travel 5 large squares or 25 small squares
How many large squares can you travel in 3 seconds on an ECG?
1 large square = 0.2 seconds
5 large squares in 1 seconds
15 large squares in 3 seconds
(as there are 5 small squares in 1 large square you can also travel 75 small squares in 3 seconds)
How many squares in 6 seconds?
1 large square = 0.2 seconds
5 large squares = 1 second
30 large squares = 6 seconds
(there are 5 small squares in 1 large square so 150 small squares in 6 seconds)
Which waves on the ECG make up 1 cardiac cycle?
PQRST complex = 1 cardiac cycle or Heartbeat
If you count 4 squares between an R-R interval, what is the heart rate?
300 large squares (no for 1 minute) divided by 4 = 75
So the patient has a heart rate of 75 BPM
What should you count on an ECG if heart rate is irregular?
Count the number of QRS complexes in 6 seconds and then multiply by 10
30 large squares = 6 seconds
Count for 30 large squares and the number of QRS complexes x 10
What is the PR interval?
What is the normal length?
The start of the P wave until the flat line afterwards changes (to either the Q wave or the R wave if there is no Q wave)
The PR complex should be 3-5 small boxes
What is the QRS interval?
What is the normal length?
It is the start of Q until the end of S
It should be less than 3 small boxes
What is the QT interval?
What is the normal length?
The start of Q until the end of T
It should be 11-12 small boxes
What HR = sinus tachycardia and which = sinus bradycardia?
Sinus tachycardia = over 100BPM
Sinus bradycardia = under 60BPM
