Physiology 5 ECG
this lecture goes through the theory behind the artistic skill of reading 12 lead ECGs
more practice is needed
polarities
RMP negative charged inside of heart positively charged outside of heart
atrial depolarisation positively charges outside of heart (in the atrial regions) negatively charged outside of heart (in the atrial regions)
ventricular depolarisation positively charges outside of heart (in the ventricular regions) negatively charged outside of heart (in the ventricular regions)
ECG vectors
At any given electrode the polarity of the voltage change depends on the direction in which the wave of potential change is moving (as well as if it is repolarisation or depolarisation
we always look from positive node
- depolarisation towards positive electrode: positive potential (upwards)
- Depolarisation away from positive electrode: negative potential (downwards)
- repolarisation towards positive electrode: negative potential (downwards)
- repolarisation away from positive electrode: positive potential (upwards)
different ecg form based on lead placement
right arm left arm left leg righ led
12 lead ecg
vertical slices I II III aVR aVL aVF
horizontal slices v1 v2 v3 v4 v5 v6
need to properly visualise flow of polarisation / depolarisation to understand the movements of
St segment elevations for myocardial attack