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Cardiovascular System > Lecture 5: Electrical Events of the Heart > Flashcards

Lecture 5: Electrical Events of the Heart Flashcards

1
Q

what is the basis of the electrocardiogram?

A

body = volume conductor
when cardiac muscle cells depolarise, extracellular current between resting and depot causes potential difference that can be measured at the body surface

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2
Q

in what direction does current flow?

A

from -ve to +ve

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3
Q

what a cell depolarises what is the net charge on the OUTSIDE?

A

-ve

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4
Q

what are einthovens 5 hypotheis’

A
  1. heart is located at the centre of a homogenous volume conductor
  2. attachment of arms and legs to trunk = equidistant
  3. limbs behave as linear conductors to trunk
  4. electrodes placed on limb = located at apices of equilateral triangle
  5. differences in potential recorded between electrodes represent projection of vector forces
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5
Q

what are the three main ECG leads?

A

Lead 1: right arm -ve, left arm +ve
Lead 2: right arm -ve, left leg +ve
lead 3: left leg -ve, right arm +ve

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6
Q

which lead is the most accurate vector analysis?

A

lead 2

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7
Q

what are the limitations to einthovens hypothesis in regards to quadrupeds?

A
  • limb arrangement is much less like an equilateral triangle
  • anatomical attachment of forelimbs to body is different
  • moving limbs alter amplitude and direction
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8
Q

describe the general features of an ECG wave

A

P wave = depol of atria
QRS complex = ventricular depot
T wave = ventricular repol
(can’t see atrial repol, hidden behind QRS complex)

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9
Q

What type of contraction is the P-R, and S-T segment?

A

iso-electric

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10
Q

what is the P-R interval?

A

the delay between atrial and ventricular depol due to eh delay in the AV node

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11
Q

what is the S-T segment?

A

plateau of ventricular muscle action potential

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12
Q

Why is the T wave not inverted?

A 
endocardial cells depolarise first, then the epicardial cells
epicardial cells (on the outside) REPOLARISE before the endocardial cells 
ie/ tissue that depol last in the tissue are the first to repol
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13
Q

what can change the mean electrical axis of the heart?

A

change in position of the heart eg/ mass in the thorax

increase in mass in one of the ventricles

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14
Q

what is an arrhythmia?

A

an alteration in rate or rhythm

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15
Q

what is bradycardia?

A

slowing of heart rate

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16
Q

what is tachycardia?

A

increase in heart rate

17
Q

what is sinus bradycardia?

A

slowing of heart rate governed by SA node due to increase in vagal tone eg/ observed in sleeping individuals

18
Q

what is sinus tachycardia?

A

inc of HR governed by SA node due to increase in sympathetic tone, normal during exercise, anxiety feat etc.

19
Q

what is sinus arrhythmia?

A

variations in HR synchronous with respiration
HR increase towards end of inspiration
HR decrease towards end of expiration
disappears with increase Hr

20
Q

what is a sinoatrial block?

A

impulse blocked before it enters atrial muscle = no p wave

21
Q

what is an atrioventricular block?

A

transmission through the AV node either slowed or completed impeded
P wave is not always related to QRS

22
Q

what is premature atrial contractions?

A

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

23
Q

What is a premature ventricular contraction?

A

not proceeded by the P wave
often followed by missed beat as muscle is in refractory
premature beat has decreased SV

24
Q

what is a paroxysmal tachycardia

A

tachycardia arising from ectopic pacemaker
onset and termination normally abrupt, may arise in atria or AV node
may progress to fibrillation

25
Q

what is fibrillation?

A

rapid disorganised conduction pathways

26
Q

what does atrial fibrillation lead to?

A

disorganised atrial activity and conduction
irregular ventricular rhythm
no p wave on trace
reversible with medication

27
Q

what does ventricular fibrillation lead to?

A

loss of consciousness within seconds

can arise from electric shock, handling in surgery

28
Q

how do you resuscitate a patient with ventricular fibrillation?

A

electric shock - place whole heart in refractory and give SA node change to take over again as pace maker

Cardiovascular System (38 decks)

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