ECG Flashcards
In which direction does the ventricles depolarise in term of layers ?
Endocardium to Epicardium
What is normal sinus rhythm ?
- Depolarisation initiated by SA node
- 60-100 heart rate
- Regular
- P wave before each QRS
- QRS< 3 small boxes (0,12s)
Why is the bundle of His the only path from atria to ventricles for the current ?
Because of the fibrous ring (containing the 4 valves) which prevents direct contact between atrial and ventricular myocytes
Describe the wave of depolarisation toward the electrode
Positive complex (up then down)
Describe depolarisation going away from electrode
Negative complex
Describe Repolarisation towards electrode
Negative complex
Where is the SA node ?
- top right corner of right atrium
- near junction of SVC and right atrium
Can we see SA node depolarisation on an ECG ?
NO
Insufficient signal to register
What causes the P wave ?
Atrial depolarisation : spread through atrial muscles fibres and internodal pathways
In which direction does the atrial depolarisation occur ?
Downwards and to the left
Towards AV node
What happens at the AV node and why ?
Delay of current to allow time for atrial contraction
What contribute to the isoelectric segment 1b of an ECG ?
- Delay of current at AV node
- Current traveling through Bundle of His and Purkinje system
With part of the myocardium depolarises first ? And in which direction ?
- Interventricular septum
- from Left to right
What does the Septum depolarisation look like on an ECG and why ?
- Q wave :small downward deflection
- Depolarisation from left to right , away from electrode so down , but oblique so small
What does the R wave represent ?
Depolarisation of Apex and Free ventricular wall
Describe the R wave , why does it look like that ?
- Large upward deflection
- upward because towards electrode
- large because large muscle mass
What does the S wave represent ?
End of depolarisation .
Of base of ventricles
Why does Repolarisation cause an upward T wave ?
Repolarisation occurs in opposite direction of depolarisation , so away from electrode (double negative)
What does QRS represent ?
Ventricular depolarisation
How many electrodes are needed for the recording of an ECG ?
10
4 limbs
6 chest
In which plane are the limb leads (views)?
Vertical
In which plane are the chest leads ?
Horizontal
How many views are given by the limb electrodes ? Which one?
6
aVF, aVR, aVL
I, II, III
Which limb lead are looking at the inferior surface of the hear ?
II, III, aVF
Lead I ,II and III are obtained thanks to which limb electrodes ?
I: right arm (-) to left arm (+)
II : right arm(-) to left leg (+)
III: left arm(-) to left leg (+)
Which lead are the best to look at inferior myocardial infarction ?
II, III, aVF
Lead I and aVL are looking at which side of the heart ?
Left
Where are electrodes 1 and 2 located ?
4th intercostal space , on each side of the sternum
Leads V1 and V2 face which part of the heart ?
Right ventricle and septum
Where is the 4th chest lead ?
5th intercostal space , mid clavicle
Where is the 6th chest electrode ?
5th intercostal space , below axilla
Chest leads V3 and V4 face which part of the heart ?
Apex and wall of ventricles
Which chest lead face the left ventricle ?
V5 and V6
True or False : V1 and V6 have opposite traces ?
True , Q upwards for V1 and downwards for V6 because depolarisation from left to right (septum)
How many seconds is a small square ?
0,04 s= 40ms
2 large boxes up is womanly mV ?
1
1 second is …large squares
5
How do you calculate the heart rate (regular) ?
(300 squares = 1 minute)
300 / nbr of large boxes between 2 cardiac cycle (R-R)
How do you calculate the heart rate for an irregular rhythm ?
Count nbr of QRS complex in 6 seconds (6x5 large boxes ) then multiply by 10
What does PR represent? Where to measure ?
- Time between atrial and ventricular depolarisation
- Start of P wave -Start of Q wave
What does a longer PR interval indicates ?
Slow conduction from atria to ventricle = First degree heart block
What is the ST segment and where do you measure ?
- Isoelectric segment between end of depolarisation and Repolarisation
- End of S to start of T wave
What does raised or depressed ST segment indicates?
MI or Ischaemia
What does a prolonged QT segment indicates ?
Prolonged Repolarisation > can lead to arrhythmias
