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Cardiovasular System > ECGs > Flashcards

ECGs Flashcards

1
Q

true or false: ventricles depolarise from endocardium to epicardium

A

true

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2
Q

at what rate does the SAN depolarise

A

60-100 times a minute

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3
Q

what sets the rhythm of the heart

A

the SAN to give the sinus rhythm

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4
Q

why cant electrical impulses pass from the atria to the ventricles

A

there is a fibrous ring around the valves separating the atria and ventricles meaning that there’s no direct contact between atrial and ventricular myocytes

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5
Q

what are purkinje fibres

A

branches of the bundle of His which allow for a rapid spread of depolarisation

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6
Q

what does the AVN do

A

delays the electrical spread as it depolarises slowly giving time for the atria to finish contracting and the ventricles to fully fill before they begin contracting

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7
Q

which myocytes depolarise first once the impulse spreads from the AVN

A

intraventricular septum myocytes

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8
Q

which myocytes are the last to depolarise

A

the myocytes at the base of the ventricles

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9
Q

true or false: repolarisation of myocytes occurs in the same order as depolarisation

A

false - its actually the reverse

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10
Q

true or false - ECGs record changes of the electrical activity inside cells

A

false - they record electrical activity on the extracellular surface

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11
Q

what deflection is given if a depolarisation occurs towards the positive lead

A

positive deflection

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12
Q

what deflection occurs if a depolarisation travels away from the positive lead towards the reference negative

A

negative deflection

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13
Q

what deflection occurs if a repolarisation is travelling towards the positive lead

A

negative deflection

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14
Q

what wave is given if the wave of the electrical signal is at 90 degrees to the electrode

A

there is no complex formed on the ECG

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15
Q

what wave is given if the electrical signal travels directly towards the electrode

A

very tall complex

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16
Q

what wave is given if the electrical signal travels obliquely towards the electrode

A

there is a smaller complex

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17
Q

where is the SAN situated

A

near to the junction of the superior vena cava and the right atrium

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18
Q

how does the depolarisation of the SAN appear on an ECG

A

there is an insufficient signal so it remains a flat line

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19
Q

what does the p wave represent

A

atrial depolarisation throughout the Left and Right atria towards the AVN

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20
Q

why does the p wave give a positive deflection

A

the depolarisation is travelling towards the electrode at the apex

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21
Q

how is the delay at the AVN and spread of the signal though the bundle of his and purkinje fibres seen on an ECG

A

as a flat line

22
Q

what causes the q wave

A

depolarisation of the interventricular septum

23
Q

why does the q wave have a negative deflection

A

because the signal is moving slightly away from the apex electrode as the signal moves from the left to right

24
Q

what gives the R wave

A

depolarisation of the apex and free ventricular wall. It is large due to the large amount of muscle mass giving more electrical activity

25
Q

what is the deflection of the R wave

A

positive as it moves toward the electrode

26
Q

what will happen to the R wave during left ventricle hypertrophy

A

it will be taller

27
Q

what causes the S wave

A

depolarisation of the base of the ventricles

28
Q

what is the deflection of the S wave

A

negative because its moving away from the electrode

29
Q

why is the S wave small

A

as the depolarisation is not moving directly away from the electrode

30
Q

what causes the T wave

A

repolarisation of the ventricles beginning on the epicardium surface.

31
Q

how many electrodes and leads are there in an ECG

A 
10 electrodes (6 chest and 4 limb)
12 leads/electrical views of the heart
32
Q

where are the 4 limb leads placed and what are their colours

A

right arm = red
left arm = yellow
left leg = green
right leg = black (earth)

33
Q

in what plane are the limb leads

A

vertical plane

34
Q

what are the 6 views in the limb leads

A

Bipolar leads:

  • I = voltage travelling between the right to left arm poles so looks at the heart from the left
  • II = from the right arm to left leg so looks from the inferior left
  • III = from left arm to left leg giving an inferior right angle view

Unipolar leads:

  • aVR = voltage goes towards the right arm from the average/middle of the 2 other electrodes to give a view of the right side
  • aVF = towards Left leg giving inferior wall view
  • aVL = towards left arm giving a left side view
35
Q

which limb leads look at the inferior surface

A

II, III and aVF

36
Q

which limb leads look at the left side of the heart

A

aVL and I

37
Q

what can be detected by looking at the inferior surface of the heart

A

inferior heart problems e.g. necrosis due to an MI

38
Q

in what plane are the chest leads

A

horizontal plane

39
Q

where are the 6 chest leads positioned

A 
V1 = 4th intercostal space just right of the sternum
V2 = 4th intercostal space to the left of the sternum 
V3 = between V2 and V4
V4 = midclavicular line in the 5th intercostal space 
V5 = between V4 and V6
V6 = midaxillary line
40
Q

what do V1 and V2 face

A

right ventricle and septum

41
Q

what do V3 and V4 face

A

apex and anterior wall of ventricles

42
Q

what do v5 and V6 face

A

left ventricle

43
Q

how many large/small squares pass per second on an ECG paper

A

25 small

5 large

44
Q

how do you calculate heart rate from an ECG

A

measure the number of large boxes from p wave to p wave and divide by 300 (300 large boxes per min)

45
Q

how do you calculate heart rate from an ECG of an irregular rhythm

A

count the QRS complexes in 6 seconds then multiple by 10

46
Q

what is the PR interval and what is its usual value

A

time taken between the beginning of the p wave (atria depolarisation) before the beginning of the QRS complex
should be -.12-0.2 seconds or 2-5 small boxes

47
Q

what does a prolongation of the PR interval suggest

A

something is wrong with the AVN or bundle of His giving a delayed conduction (heart block)

48
Q

what does a prolonged QT interval suggest

A

the ventricles are taking longer to repolarise

49
Q

why can the QT interval be a measurement for changes in heart rate

A

as the faster the heart rate, the faster the ventricles will depolarise

50
Q

how long should the QRS interval be

A

0.12 seconds or 3 small boxes

51
Q

what is normal sinus rhythm

A

when depolarisation is initiated by the SAN

it gives a regular rhythm, p wave, heart rate between 60-100, normal PR and QRS

52
Q

what is it called when your sinus rhythm is below 60 or above 100

A

below 60 = sinus bradycardia

above 100 = sinus tachycardia

Cardiovasular System (16 decks)

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