3. A First Look At The ECG Flashcards
What hypothetical triangle is created around the heart when electrodes are placed on both arms and the left leg?
Einthoven’s triangle
What does each side of the Einthoven’s triangle represent?
Numbered that correspond to 3 leads (or pairs of electrodes) used for recording
How many leads are used at a time when an ECG is recorded?
1 lead at a time
How many electrodes are there per lead?
2 electrodes; positive electrode and negative electrode (third one is inactive)
Leads look at events in the heart activity in what planes?(2)
vertical or frontal planes
What 3 body parts make up the Einthoven triangle?
- left arm
- right arm
- left leg
What are the 2 leads of SLL I (standard limb lead 1)?
- left arm
2. right arm
What are the 2 leads of SLL II (standard limb lead 2)?
- right arm
2. left leg
What are the 2 leads of SLL III (standard limb lead 3)?
- left leg
2. left arm
What is the difference between an AP and an ECG recording?
- An AP is one electrical event in a single cell recorded using an intracellular electrode
- An ECG is an extracellular recording that represents the sum of multiple action potentials taking place in multiple heart muscle cells
What does an ECG tracing show?
It shows a summed electrical potential generated by all cells of the heart
What causes an “upward- going blip” in an ECG recording?
A wave of approaching depolarisation
Are fast or slow events transmitted better across the heart?
fast events are transmitted better
When recording from SLL II for example, what is actually recorded?
the DIFFERENCE in potential between the left leg and right arm which counts
How does the wave of depolarisation pass in SLL2 (standard limb lead)?
passes from atria down to the ventricles and through the body fluids towards the electrode on the left leg
What is meant by ECG electrodes?
- They are wires that are attached to patients to record the ECG.
- These electrodes allows leads to be recorded
What potential does a wave of depolarisation cause?
POSITIVE potential
What potential does a wave of repolarisation cause?
NEGATIVE potential
What does the standard limb lead tell you?
- lead refers to imaginary line between two ECG electrodes
- electrical activity of this lead is measured and recorded as part of the ECG
What allows leads to be calculated?
electrodes
What is P wave caused by?
atrial depolarisation
What is QRS complex caused by?
ventricular depolarisation
What is T wave caused by?
ventricular repolarisation
What are the 2 intervals which exists in an ECG recording?
- PR interval (from P to Q)
- QT interval (from Q to T)
What does the PR interval tell us?
time from atrial depolarisation to ventricular depolarisation mainly due to transmission through the AV node
How long does the PR normally last for?
normally about 0.12-0.2 seconds
What does the QRS complex show us?
the time for the whole of the ventricle to depolarise