Lecture 7 - ECG 1 Flashcards
P wave?
electircal activation of atria
QRS wave?
electrical activation of ventricles - muscle activation
T wave?
repolarisation of ventricles
PR segment?
little to no electrical activity occurring
QT segment?
isoelectric period, ventricles polarised
Propogating wavefront charges?
resting: inside negative outside positive; active: vice versa - extracellular current flows opposite direction of wavefront movement (positive to negative)
Isopotential lines are?
lines of equal potential
Vector representation?
direction = direction of dipole (negative to positive), length proportional to strength of dipole
Dipole projections?
electrode recording shows the projection on the lead axis, rather than the full dipole
Measured dipole depends on?
magnitude of charges (dipole), orientation of dipole and electrodes, distance between dipoles and electrodes
Origin of QRS - Q?
top left of IV septum innervated to th right, electrodes record small negative deflection
Origin of QRS - R?
progressive innervation to bottom of ventricles, electrodes record big positive charge
Origin of QRS - S?
innervation spreads to base of heart, electrodes record slightly bigger negative charge than q
Why is T wave positive?
repolarisation changes direction, occuring from epithelium to endothelium due to difference in action potential duration (long on inside), resulting in reversed wavefront movement causing a positive measured dipole
Einthoven’s triangle?
1 = LA-RA; II=LL-RA, III= LL-LA
