CVS - ECGs Flashcards
What is the spread of depolarisation called?
Electrical axis
What is the contraction of each cell triggered by?
Action potential
What do the chest electrodes detect?
A change in membrane potential - ie during depolarisation or repolarisation
What does depolarisation spreading towards an electrode look like in the ECG?
Upwards deflection
What does depolarisation AWAY a from a positive electrode look like?
Downwards deflection
What does repolarisation spreading towards a positive electrode look like?
Downwards deflection
What does repolarisation away from a positive electrode look like on ECGs?
Upwards deflection
What does the amplitude of the deflection depend on?
No of cells changing and how fast
How directly the wave is moving towards the electrode
What does the p wave show?
Atrial depolarisation
What does the QRS complex show?
Q = septal depolarisation (away from lead II electrode) R= main ventricle depolarisation (towards lead II electrode) S = end ventricular depolarisation (away from lead II electrode)
What does the T wave show on the ECG?
Repolarisation of the myocardium (away from lead II electrode)
What is an amplifier?
They take the incoming signal on the negative electrode and invert it to positive before combing the two to form the view.
Where does lead I,II And III view?
I - left side
II - apex view
III - bottom view
What is an augmented lead?
A lead with two negative electrodes and one positive
So they convert the two -ves to a single one then invert it.
How many leads in a full ECG?
12
Where are the positions of the 10 electrodes in a 12 lead ECG?
One on each limb - RYGB (right arm, left arm, left leg, right leg) Then Remember Your Great Big Black Purse 1- 4th ICS right side 2 - 4th ICS left side 3 - inbetween 2 and 4 4 - 5th ICS mid clavicular 5- between 4-6 6- 5th ICS mid Axilla
How is rate seen in ECGs?
Each square - 0.2s
300 squares per minute
When is the p wave absent?
In atrial fibrillation
When is the P-R interval altered?
Prolonged in 1st degree heart block
Erratic in 2nd degree heart block
No relationship between this and QRS complex in 3rd
What does the direction of main ventricular depolarisation (electrical axis) show?
It shows if there is any left/right Hypertrophy
Left axis deviation (left hypertrophy)- larger lead 1
Right axis deviation (right hypertrophy) larger lead 3
What does the shape of the QRS complex show?
Tells you about any damage to the conducting pathway
I.e bundle branch block
What does an ST depression show?
Partial coronary artery occlusion
What does an ST elevation show?
Dying myocardium (MI)
When are pathological Q waves seen?
Present in MI and remain even after resolve
