PBL 4 - ECG and detection of abnormal rhythm Flashcards
what does an ECG record?
the electrical activity of the heart
why would an ECG be carried out?
many reasons:
- chest pain
- SOB
- abnormal rhythm
- collapse
what is the SAN?
a collection of pacemaker cells at top right of atrium
briefly describe how electrical activity spreads through the heart
- electrical impulse generated in SAN and spreads throughout both atria, reaching the AV node
- impulse reaches AV node before the LA has finished contracting
- the impulse is slowed down through the AV node — allows the LA to finish contracting
- from the AVN, the impulse goes down the Bundle of His and the wave of depolarisation will go down through the left and right bundle branches and then they’ll spread through both ventricles via the Purkinje fibres
why is the wave produced on an ECG for the atria smaller than for the ventricles?
atria are smaller in size than ventricles
what does each of the 3 wave represent?
- atrial contraction (depolarisation)
- ventricular contraction (depolarisation)
- ventricular relaxation (repolarisation)
what about atrial repolarisation?
it also occurs but it is hidden by the magnitude of the QRS complex
any movement above or below the baseline is called what?
a wave or deflection
what does the p wave represent?
the spread from the SAN throughout the atria = atrial contraction
what does the P-R interval represent?
the onset of atrial depolarisation until the onset of ventricular depolarisation (conduction from the SAN through the AVN)
= time taken for excitation to spread through the ventricles (0.12-0.2s)
on ECG paper, what does one large square represent?
5mm = 0.2 seconds
ECG chest leads ‘look at’ the heart in what plane?
transverse plane
how many electrodes are placed onto the chest wall?
6 electrodes
where are each of the 6 chest leads placed?
1st = 4th IC space on right 2nd = 4th IC space on left 4th = 5th IC space on midclavicular line 3rd = half way in between 2nd and 4th 5th = anterior axillary line 5th IC space 6th = 5th IC space in mid axillary line
what are the 3 different intervals at the bottom?
what are the chest leads named?
V1-V6
what do V1 and V2 ‘look at’?
RV
what do V3 and V4 ‘look at’?
anterior, septum
what do V5 and V6 ‘look at’?
lateral (left), LV
ECG limb leads ‘look at’ the heart in what plane?
vertical plane
each limb lead gives how many readings?
2
how many limb leads are there and where are the limb leads placed?
4
- one on a bony point of the right shoulder or wrist
- one on the left shoulder or wrist
- one on the left ankle or hip
- an earth electrode on the right ankle or hip
what is the role of the earth electrode?
it doesn’t pick up electrode activity, it just makes the whole procedure safe
which limb lead picks up electrical activity from the RA and what is the reading called?
R electrode — aVR reading
which limb lead picks up electrical activity from the left lateral surface and what is the reading called?
L electrode — aVL reading
which limb lead picks up electrical activity from the inferior surface of the heart and what is the reading called?
F electrode — aVF
what do the limb leads look like on a diagram?
show leads 1, 2 and 3 on a diagram
what do leads 1 and 2 look at, and what does lead 3 look at?
1+2 —> left lateral aspect of the heart
3 —> inferior aspect of the heart
show leads 1, 2, 3 and aVR, aVL and aVF on a diagram
how many traces are there on a normal ECG?
12
- 6 chest leads
- 3 on the limbs — each produce 2 traces
(1 earth electrode — no trace)
what term is used to describe normal HB and a normal pattern of HBs?
sinus rhythm (because electrical impulse starts at the SAN)
what is meant by the term sinus arrhythmia?
HB still originates at the SAN but the rhythm isn’t regular
what is not present on an ECG in someone in atrial fibrillation?
no p wave
what is the QRS complex like in atrial fibrillation?
normal
how is the pulse described in atrial fibrillation?
irregularly irregular
why does atrial fibrillation occur?
atria are not beating in harmony — not emptying properly so no good input into ventricles — danger of clot formation — can lead to lots of different problems eg. stroke
what are 2 common causes of atrial fibrillation?
myocardial ischaemia and myocardial infarction
where do you listen on the chest for the aortic valve?
2nd right IC space
where do you listen for pulmonary valve?
2nd left IC space
where did you listen for tricuspid valve?
4th left sternal edge
where do you listen for biscupid valve?
5th IC space mid-clavicular line
what is information between aVR and aVL known as?
lead 1
what is information between aVR and aVF known as?
lead II
what is information between aVL and aVF known as?
lead III
in general, what do the different sections on an ECG look at?
what are the inferior limb leads? what do they primarily observe?
II, III, aVF (primarily observe the inferior wall of the LV)
