Cardiovascular System Lecture 5- Observing The Electrical Activity Of The Heart

Front 1

when the cardiac muscles ...., extracellular currents between... and... cells causes potentials that can be measured at the body surface

Back 1

deplorises
depolorised
resting

Front 2

einthovens hypothesis

Back 2

1. body is volume conductor
2. heart is at center of volume conductor
3. trunk is equilateral triangle
4. limbs are at point of triangle
5. limbs are linear conductors

Front 3

limitations of einthovens hypothesis

Back 3

body not true homogenous conduction, so dispersion of electrodes not uniform.
heart not at center of equilateral triangle, so recording electrodes not equidistant from the heart.
in quadrupeds arrangement is a lot less like a triangle so that movement of limbs can alter amplitude and direction of potentials.

Front 4

lead 1

Back 4

right arm negative, left arm positive

Front 5

lead 2

Back 5

right arm negative, left leg positive

Front 6

lead 3

Back 6

left arm negative, left leg negative

Front 7

wave form of ECG represents

Back 7

the net vector of depolarisation and repolarisation of the heart over time

Front 8

the shape of the trace of an ECG depends on the

Back 8

net direction of the wave front of depolarisation and the amount of tissue that is depolarising

Front 9

p wave

Back 9

depolorisation of the atria

Front 10

QRS complex

Back 10

ventricular depolarisation

Front 11

T wave

Back 11

Ventricular repolarisation
extreamly variable in domestic animals. can be positive, negative or notched in normal animals

Front 12

Back 12

Front 13

repolarisation of atria is

Back 13

lost in the QRS complex

Front 14

P-R and S-T segment

Back 14

normally isoelectric.
ie no current flowing because tissue ( either atria of ventricles) are with all depolorised or all at rest

Front 15

P-R interval

Back 15

delay between atria and ventricular deppolarisation, due to delay in AV node.

Front 16

prolonged P-R interval suggests

Back 16

atrial damage or AV block

Front 17

S-T segment

Back 17

plateau of ventricular muscle AP

Front 18

electrical axis of the heart

Back 18

the orientation of the ECG vector at the maximum amplitude

Front 19

the electrical axis of the heart corresponds to

Back 19

depolarisation of the main mass of ventricles

Front 20

the mean electrical axis of the heart can be altered by

Back 20

change in the position of the heart
increase in the mass of one of the ventricles

Front 21

the mean electrical axis of the heart can calculated by

Back 21

mathematical anlysis of three bipolar leads

Front 22

arrhythmia

Back 22

alteration in rate or rhythm

Front 23

bradychardia

Back 23

slowing of HR

Front 24

tachychardia

Back 24

increase in HR

Front 25

sinus brachycardia

Back 25

due to increased vagal tone, slowing governed by SA node
seen during sleep and in well trained athletes

Front 26

sinus tachycardia

Back 26

increased HR goverened by SA node due to release from vagal tone and increased sympathetic tone. normal during exercise, anxiety states, fevers etc

Front 27

sinus arrythmia

Back 27

variations in heart rate synchronus with respiration due to altered vagal tone on SA node with respiration. normal in DOGS. HR increases towards end of respiration, decreases towards end of expiration, disappearing with increased HR

Front 28

sino-atrial block

Back 28

impulse blocked before it enters atrial muscle. this results in CESSESION OF P WAVES. the ventricle pick up new rhythm so the QRS and T are not altered. this may be due to action of vargus nerve on SA node or potassium disturbance.

Front 29

atrio-ventricular block

Back 29

impeded conduction through AV node that may vary in degrees

Front 30

atrio-ventricular block first degree

Back 30

unusually slow conduction through AV node, detected abnormally long PR interval

Front 31

atrio-ventricular block second degree

Back 31

some but not all impulses transmitted through AV node. the atrial rate is often faster than ventricular rate by a certain rate (ie 2:1, 3:1)

Front 32

atrio-ventricular block third degree

Back 32

complete block with complete dissociation of P wave and QRS complex. an area of conducting tissue in the ventricles (often in bundle branch) assumes pacemaker role. the ventricular rate is likley to be slower than normal.

Front 33

premature atrial contractions

Back 33

caused when an area of atria escapes normal pacemaker domination and initiates heartbeat ( becomes an ectopic pacemaker). this causes early and irregular contraction that may or may not be followed by a ventricular contraction

Front 34

premature ventricular contractions

Back 34

not preceded by a P wave
quite common in small animals
often followed by missed beat as muscle is refractory when normal impulses arrive
premature beat has a reduced stroke volume, the delayed beat larger then normal stroke volume.

Front 35

paroxymal tachycahrdia

Back 35

tachycardia arising from an ectopic site in the heart, with an onset and termination that are normally abrupt.

Front 36

paroxymal tachycahrdia arising from AV node

Back 36

aka supraventricular
are indistinguishable

Front 37

paroxymal tachycahrdia arising from ventricles

Back 37

develop as a result of ectopic pacemaker in the ventricle. this is much more serious than atrial tachychardia as ventricular filling and contraction impaired. may progress to fibrillation.

Front 38

fibrillation

Back 38

refers to completely disordered conduction pattern in either atria or ventricles.

Front 39

atrial fibrillation

Back 39

leads to an irregular ventricular rhythm with an absence of P waves on ECG. compatible with life because atrial contraction not necessary for ventricular filling and can be reversed by drugs

Front 40

ventricular fibrillation

Back 40

more serious than atrial
may result from electrical shock, major myocardial infraction, loss of blood supply, certain anestetic agents or handling of heart during surgery
it results in loss of conciousness within a few seconds
requires resuscitation with electric shock
this places entire myocardium in refractory state and gives SA node chance to take over as pacemaker again