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1.23.3.11 - ECG Generation - Coggle Diagram
1.23.3.11 - ECG Generation
introdcution
waves of depolarisation and repolarisation
responsible for rhythmic pumping
many cells involved
functional syncytium
can generate action potentials
electrical impulses are conducted to surface
cardiomyocytes are electrically excitable
recorded as the ECG
depolarisation
depolarisation and repolarisation produce an electrical current in opposite directions
dipoles
dipoles exist within the myocardium
a dipole is a negative and positive charge separated b s a short distance
current flows between poles
consequence of ion movement
magnitude of deflection
determined by two main factors
direction of depolarisation
amount of muscle mass that is depolarising
where the elctrodes are located
which lead you are using
other factors
fluid/fat surrounding the heart
insulaton
surface ECG
one pair of electrodes
bipolar leads
+ve and -ve elctrodes
2 = RF and LH (+ve)
1 = RF and LF (+ve)
3 = LF and LH (+ve)
dog and cat
PQRST
Q wave
ventricular depolarisation
begins in septum
variable
typically negative
R wave
ventricular depolarisation
endo to epicardium
largest deflection
biggest +ve in lead 2
T wave
ventricular repolarisation
variable - may be negative positive or biphasic
resting membrane potential heart is -90
indications for ECG
may suggest altered myocardial metabolism
routine - many cases
assessment of rate or rhythm
may provide evidence of chamber enlargement/hypertrophy
electrical activity only pump may have stopped
ventricular depolarisation occurs form the inside out (endocardium to epicardium)
summary
lead 2 is usually most informative
P, QRS, T waves are normally identifiable
positive deflection when depolarisation wave (resultant dipole) moves towards positive electrode
integrity of conduction system is important
ECG measure changes in potential at animal surface
sizes of ECG complexes
p-wave = may be wider with left atrial enlargement
r wave - may be taller with elft ventricular enlargement
p-wave: may be taller with right atrial enlargement
s wave - may be deeper with right ventricular enlragement
large animals
big hearts, wont struggle to pick up the electical signals
typically just two leads
atrial replarisation usually happens within the QRS complex, so is masked and cant be seen
should have an isoelectric baseline
wide and bizarre complexes
damage to one bundle branch of conduction system
p wave initiated but impulse not conducted normally
can happen if conducting system is damaged