Lecture 5 Flashcards
when a cell depolarizes…
its more neg on the outside (pos on inside)
Eintonven’s hypothesis (5)
electrical forces of the heart originate in a small area at the centre of a homogenous volume conductor
- attachments of the arms and legs to trunk are equidistant from each other
- limbs behave as linear condutors
- electrodes placed at each arm and a leg are considered to be apices of equilateral triangle with heart at center
- differences in potential recorded between these points represent the projection of vector forces originating from a dipole in the heart
ECG leads (3+1)
lead 1- right arm neg, left arm pos
lead 2- right arm neg, left leg pos (most used)
lead 3- left arm neg, left leg pos
-right leg always the earth
LIMITATIONS to Eintoven’s hypothesis(3 and quadrapeds)
body does not form a true homogenous electrical conductor
heart is often not in center
In quadrapeds:
limb arrangement much less like equilateral triangle
anatomical attachment of forelimbs
moving limbs alters amplitude and direction of potentials
Shape of trace depends on…(2)
net direction of the wave front of depolarization and
the amount of tissue that is depolarizing
p wave
depolarization of the atria
QRS complex
ventricular depolarization
T wave
ventricular repolarization
P-R interval
delay between atrial and ventricular depolarization, due to delay in AV node (prolonged?- AV block or atrial damage)
S-T segemtn
plateau of ventricular muscle AP
MEan electrical axis of the heart
orientation of the ECG vector at its max amplitude
mean electrical axis of the heart will be altered by (2)
change in postition of the heart
Inc in the mass of one of the ventricles
Arrhythmia
alteration in rate or rhythm
Bradycardia
slowing of the HR
tachycardia
increase in HR
Sinus Bradycardia
(can be normal)
slowing governed by SA node(due to inc vagal tone)
sleeping and well trained athletes
sinus tachycardia
increase of HR governed by SA node (due to inc sympathetic tone)
exercise, anxiety, fever
sinus arrhythmia
(normal abnormality in a very fit heart)
variations in HR synchronus with respiration
in end of inspiration and dec end of expiration
disappears with inc HR
Sinoatrial block
impulse blocked before it enters atrial muscle-> no P wave
Atrioventricular block (2)
transmission through AV node either slowed or completely impeded
P waves not always related to QRS complex
premature atrial contractions
an area of the atria escapes normal pacemaker domination and initiates a heart beat
may or may not be followed by ventricular contraction
premature ventricular contractions (VPC) (3)
not preceded by p wave
often followed by missed beat as muscle is refractory when normal impulse arrives
premature beat have reduced stroke volume(next beat will have inc SV)
paroxysmal ventricular tachycardia (3)
ectopic pacemaker in ventricle
ventricular filling and contraction incomplete
may progress to fibrillation
Fibrillation
rapid completely disorganized conduction pathways
Atrial fibrillation leads to: (2)
(compatible to life)
irregular ventricular rhythm
no p waves on the trace
Ventricular fibrillation (2)
(not compatible with life)
loss of consciousness within a few seconds
resuscitate with electric shock (place entire myocardium in refractory state and give SA node to take over as pacemaker again)
