Lecture 5

Question 1

when a cell depolarizes…

Answer 1

its more neg on the outside (pos on inside)

Question 2

Eintonven’s hypothesis (5)

Answer 2

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

Question 3

ECG leads (3+1)

Answer 3

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

Question 4

LIMITATIONS to Eintoven’s hypothesis(3 and quadrapeds)

Answer 4

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

Question 5

Shape of trace depends on…(2)

Answer 5

net direction of the wave front of depolarization and

the amount of tissue that is depolarizing

Question 6

p wave

Answer 6

depolarization of the atria

Question 7

QRS complex

Answer 7

ventricular depolarization

Question 8

T wave

Answer 8

ventricular repolarization

Question 9

P-R interval

Answer 9

delay between atrial and ventricular depolarization, due to delay in AV node (prolonged?- AV block or atrial damage)

Question 10

S-T segemtn

Answer 10

plateau of ventricular muscle AP

Question 11

MEan electrical axis of the heart

Answer 11

orientation of the ECG vector at its max amplitude

Question 12

mean electrical axis of the heart will be altered by (2)

Answer 12

change in postition of the heart

Inc in the mass of one of the ventricles

Question 13

Arrhythmia

Answer 13

alteration in rate or rhythm

Question 14

Bradycardia

Answer 14

slowing of the HR

Question 15

tachycardia

Answer 15

increase in HR

Question 16

Sinus Bradycardia

Answer 16

(can be normal)
slowing governed by SA node(due to inc vagal tone)
sleeping and well trained athletes

Question 17

sinus tachycardia

Answer 17

increase of HR governed by SA node (due to inc sympathetic tone)
exercise, anxiety, fever

Question 18

sinus arrhythmia

Answer 18

(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

Question 19

Sinoatrial block

Answer 19

impulse blocked before it enters atrial muscle-> no P wave

Question 20

Atrioventricular block (2)

Answer 20

transmission through AV node either slowed or completely impeded
P waves not always related to QRS complex

Question 21

premature atrial contractions

Answer 21

an area of the atria escapes normal pacemaker domination and initiates a heart beat
may or may not be followed by ventricular contraction

Question 22

premature ventricular contractions (VPC) (3)

Answer 22

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)

Question 23

paroxysmal ventricular tachycardia (3)

Answer 23

ectopic pacemaker in ventricle
ventricular filling and contraction incomplete
may progress to fibrillation

Question 24

Fibrillation

Answer 24

rapid completely disorganized conduction pathways

Question 25

Atrial fibrillation leads to: (2)

Answer 25

(compatible to life)
irregular ventricular rhythm
no p waves on the trace

Question 26

Ventricular fibrillation (2)

Answer 26

(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)