ECG reading and understanding Flashcards
What does the ECG detect
Electrical potential changes on the body surface caused by the re and depolarisation of the heart
Benefit of the ECG
Allows you to indirectly and non invasively monitor the heart
Why can the ECG detect electrical potential changes on the surface of the skin
Due to the spread of the electrical current via gap junction in cardiac muscle this causes current flow in surrounding tissue
Describe the propagating current in one beat
Positive wave followed by a negative wave
At what potential is the positive wave
+30mV
What is a lead?
An imaginary line between two electrodes
What is the +ve electrode
This is the reading electrode
What is the -ve electrode
This is the reference electrode
When is an uplift in the ECG produced?
When the wave of depolarisation is towards the +ve reading electrode
When is a down lift in the ECG produced?
When the wave of depolarisation is moving away from the +ve reading electrode
What are the names of the standard limb leads?
I, II and III
What lead is between the right and left arm?
Lead I and the LA is the +ve electrode
What is the lead between the right arm and the left leg?
Lead II and the LL is the +ve electrode
What is the lead between the left arm and the left leg?
Lead III and the LL is the +ve electrode
Why in lead II is the T wave an uplift?
Because its a wave of repolarisation that moves away from the +ve LL electrode which is recorded as an uplift
Why in lead II is the Q wave downwards when its a depolarisation?
Because the wave of depolarisation in the inter-ventricular septum is from left to right which is sightly away from the +ve LL electrode
Why in lead 2 is the S wave downwards?
This is because in ventricular depolarisation the wave propagates from the apex upwards away from the +ve electrode
1 electrode is positive the other to are linked to provide a reference point in the centre of the heart .
Augmented limb leads
What are the three augmented leads?
aVR, right arm aVL, left arm aVF, left foot
What is the point of the augmented limb and standard limb leads?
To provide a vertical/frontal view of the heart
What electrodes when placed give us a horizontal view of the heart?
Precordial leads V1-V6
V1
4th intercostal space directly right of the sternum
V2
4th intercostal space directly left of the sternum
V3
Midway between V2 & V4
