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