Session 6.1 Flashcards
How does the wave of depolarisation spread through the heart?
1) wave of depolarisation spreads downwards and then to the left
2) pause at A.V node so atria can contract before ventricles contract
3) bundle of His is continuous with AV node
4) spreads trough R and L bundle branches of intraventricular septum
5) goes through purkinje fibres at bottom of heart
What is the fibrous ring/skeleton of the heart?
- Fibrous ring is where all the muscles insert into
- In the plane between the atria and ventricules
- ‘electrical insulator’ allows atria to contract separate from ventricles
- bundle of his crosses fibrous ring and is a passageway for conduction
Which parts of the heart depolarise first?
1) IV septum is depolarised first
2) wave passes down left side faster so septum is depolarised from left to right side
3) base of the ventricles are depolarised last
4) repolarisation of ventricles happens in reverse order
Where be a flat line in an ECG?
When the whole cell is depolarised = no current flow = flatline
How do depolarisation/ repolarisation differ?
Depolarisation = outside of region becomes negatively charged relative to inside. Directed towards positive electrode = upward deflection recorded.
Repolarisation = outside of region becomes positively charged relative to inside. Directed away from positive electrode = downwards deflection
What part of an ECG represents atrial depolarisation?
P wave
Why is there a flat line after the p wave in an ECG?
Represents conduction is slowed down at AV node
What us a q wave?
First downwards deflection after p wave
Shows depolarisation of AV septum, goes down a bit as depolarisation is from left to right
What represents the depolarisation of the apex and free ventricular wall?
A large upwards deflection - the R wave
Upwards as moves directly towards electrode and large as its a large muscle mass (NB: if LV hypertrophies = get a bigger R wave)
What does the PR interval represent?
The time between atrial depolarisation and ventricular depolarisation
What does the S in the QRS complex represent?
Depolarisation spreads upwards through the base of the ventricles = small downwards deflection
Why do you get a T wave?
Ventricular repolarisation spreads in the opposite direction = towards positive electrode = medium upwards deflection
Where would you place the limb electrodes on someone for an ECG?
10 electrodes
1 on each limb = 4, get 6 views in total.
- get leads I, II, III, aVR, aVF, aVL
- I and aVL look at left side of heart: best for problems in lateral ventricle wall e.g muscle necrosis due to occlusion of left coronary artery
- II, III and aVF look at inferior surface of heart e.g occlusion of right coronary artery
Where would you place the chest leads for an ECG?
6 electrodes
V1 = on right side of sternum, 4th intercostal space V2 = on left side of sternum, 4th intercoastal space V3= between v2 and v4 V4 = 5th intercoastal place, mid clavicular line V5 = between v4 and v6 V6 = 5th intercoastal space, mid axillary line
What does each lead give a view of?
Inferior ventricle surface = II, III and AVF
Right ventricle and septum = v1 and v2
Anterior surface of ventricles = v3 and V4
IVS and anterior surface of ventricles = V1 to V4
Lateral surface of ventricles = Lead 1, aVF, V5, V6
