ECG Flashcards
What is an ECG?
This measures the potential difference (difference in concentration of electrons) across the body surface. It represents the spread of depolarisation and repolarisation through the myocardium.
What is the difference between a lead and an electrode?
A lead is a connection between 2 electrodes.
An electrode is one of the pads on an ECG monitor
What does the p wave represent?
Depolarisation of the atria.
Why can’t you see the repolarisation wave for the atria?
It is masked by the QRS complex which is the depolarisation of the ventricles.
Why is the T wave in the same direction as the QRS complex?
This is because the last cells to depolarise in the ventricles are the first to repolarise which results in repolarisation going away from the positive electrode so you get a positive deflection.
What results in a positive deflection and negative deflection on an ECG trace?
Positive deflection= a wave of depolarisation travelling towards a positive electrode. A wave of repolarisation travelling away from a positive electrode results in a positive deflection.
Negative deflection= a wave of depolarisation travelling away from a positive electrode. A wave of repolarisation travelling towards a positive electrode results in a negative deflection.
What is lead 1, 2 and 3
Lead 1= R (Right arm- Negative) to L (Left arm- Positive)= 0 degrees
Lead 2 = R (Right arm- Negative) to F (Left foot- Positive) = 60 degrees
Lead 3= L (Left arm- Negative) to F (Left foot- Positive) = 120 degrees
The ECG machine automatically designates which electrode is positive and negative.
What is the AVF, AVR and AVL?
AVF= Connects R to L (Positive electrode is F)
AVL= Connects F to R (Positive electrode is L)
AVR= Connects F to L (Positive electrode is R)
This is where you combine pairs of electrodes to produce virtual electrodes.
What are the limb leads?
These are leads 1,2 and 3 and the AVF, AVR and AVL leads.
They are vertical leads
What are the Chest leads?
C1-C6
They view the heart in the horizontal plane
How many electrodes are there in a 12 lead ECG?
10
What is the PR segment?
This is the time taken for atrial depolarisation to reach the ventricular myocardium
What is the ST segment?
All ventricular muscle has been depolarised and myocardial contraction occurs
What is the T wave?
Ventricular depolarisation. Positive deflection as last cells in the ventricles to depolarise (epicardium) have a much shorter action potential than endocardium cells so they repolarise first.
What is the Q wave?
This is left to right depolarisation of the interventricular septum (hence it is negative)
