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Cardiovascular System > A first look at the ECG > Flashcards

A first look at the ECG Flashcards

1
Q

What are the 3 main recordings made from any pair of electrodes?

A
  • SLL I = left arm wrt right arm
  • SLL II = left leg wrt right arm
  • SLL III = left leg wrt left arm
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2
Q

Basic principles of ECG

A
  • Fast events e.g. depolarisation and repolarisation of the AP, are transmitted well.
  • Slow events, e.g. the plateau of the AP, are not.
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3
Q

What hypothetical triangle is created around the heart when electrodes are placed on both arms and the left leg?

A

Einthoven’s triangle

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4
Q

What does each side of the Einthoven’s triangle represent?

A

Numbered that correspond to 3 leads (or pairs of electrodes) used for recording

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5
Q

What are the 2 leads of SLL I (standard limb lead 1)?

A

Left arm and right arm

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6
Q

What are the 2 leads of SLL II?

A

Right arm and left leg

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7
Q

What are the 2 legs of SLL III?

A

Left leg and left arm

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8
Q

What is the difference between an AP and an ECG recording?

A
  • An AP is one electrical event in a single cell recorded using an intracellular electrode.
  • An ECG is an extracellular recording that represents the sum of multiple action potentials taking place in multiple heart muscle cells.
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9
Q

On SLL II, what occurs when the wave of depolarisation passes the electrode on the left leg?

A

It creates a positive potential relative to the electrode on the right arm.

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10
Q

In SLL II, how is the P wave caused?

A

P wave is caused by atrial depolarisation.

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11
Q

In SLL II, how is the QRS complex caused?

A

QRS complex is caused by ventricular depolarisation.

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12
Q

In SLL II, how is the T wave caused?

A

T wave is caused by ventricular repolarisation.

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13
Q

Why can’t you see atrial repolarisation on the recording from SLL II?

A

Because atrial repolarisation coincides (same time) with ventricular depolarisation.
- Ventricular depolarisation involves much more tissue depolarising much faster so it swamps any signal from atrial repolarisation.

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14
Q

Why is the QRS complex so complex?

A

-Because different parts of the ventricle depolarise so different times in different directions:
1st – the interventricular septum depolarises from left to right
2nd – the bulk of the ventricle depolarises from the endocardial to the epicardial surface
3rd – the upper part of the interventricular septum depolarises

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15
Q

Why is the T wave positive-going?

A

Because the action potential is longer in endocardial cells than in epicardial cells, so the wave of repolarisation runs in the opposite direction to the wave of depolarisation.

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16
Q

Why is the R-wave bigger in SLL II than in SLL I or SLL III?

A

Because the main vector of depolarisation is in line with the axis of recording from the left leg with respect to the right arm.

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17
Q

What would happen to the wave if the heart was rotated to the left, or developed hypertrophy on the left, or atrophy on the right?

A

Causes axis deviation

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18
Q

What extra information do the augmented limb leads give you?

A
  • By recording from one limb lead with respect to the other two combines, it gives you 3 other perspectives on events in the heart.
  • ie recordings from SLLs I, II, III and aVR, aVL, aVF give you 6 different views of events occurring in the frontal (or vertical) plane
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19
Q

What causes an “upward-going blip” in an ECG recording?

A

A wave of approaching depolarisation

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20
Q

How does the wave of depolarisation pass in SLL2 (standard limb lead)?

A

It passes from atria down to the ventricles and through the body fluids towards the electrode on the left leg

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21
Q

What potential does a wave of depolarisation cause?

A

POSITIVE potential

22
Q

What potential does a wave of repolarisation cause?

A

NEGATIVE potential

23
Q

What are the 2 intervals which exists in an ECG recording?

A
  • PR interval (from P to Q)

- QT interval (from Q to T)

24
Q

What does the PR interval tell us?

A

Time from atrial depolarisation to ventricular depolarisation mainly due to transmission through the AV node

25
Q

How long does the PR normally last for?

A

Normally about 0.12-0.2 seconds

26
Q

How long does the QRS complex last for?

A

Normally about 0.08 seconds

27
Q

Function of which fibres are reflected by the QRS complex effectivity?

A

Bundle of His

28
Q

Which interval will be longer in longer Plateau phase?

A

Longer QT interval

29
Q

What are the 3 augmented limb leads?

A
  1. aVR (right arm)
  2. aVF (left leg)
  3. aVL (left arm)
30
Q

What is the most positive limb lead?

A

aVF

31
Q

What is the most negative limb lead?

A

aVR

32
Q

What extra information do the precordial (chest) leads give you?

A
  • These are arranged in front of the heart and therefore look at the same events, but in the horizontal (or transverse) plane
33
Q

What are the 6 precordial (chest) leads?

A

V1,2,3,4,5,6

34
Q

Where is the biggest negative blip in the precordial (chest) leads?

A

V1

35
Q

Where is the biggest positive blip in the precordial (chest) leads?

A

V6

36
Q

Where is the “flip over” part of the precordial (chest) leads?

A

V3 or V4

37
Q

What do limb leads look at?

A

Spread of depolarisation and repolarisation from 6 angles in the frontal plane

38
Q

What do precordial leads look at?

A

Spread of depolarisation and repolarisation from 6 angles in the transverse plane

39
Q

What is the ECG rhythm in terms of time?

A

25mm/sec

40
Q

What is the calibrating pulse?

A

0.2 sec =1 large square (5mm)

41
Q

How many beats per minute is normal?

A

60-100 bpm

42
Q

What is the term for heart rate< 60 beats?

A

Bradycardia

43
Q

What is the term for heart rate> 60 beats?

A

Tachycardia

44
Q

When is the PR interval too short?

A

<0.012 seconds

45
Q

When is the PR interval too long?

A

> 0.02 seconds

46
Q

When is the QRS complex too wide?

A

> 0.12 seconds

47
Q

When is the QT interval too long?

A

> 0.42 seconds at 60bpm

48
Q

What is STEMI?

A
  • ST elevated myocardial infarction (on ECG)
  • Developing complete occlusion of major coronary artery previously affected by atherosclerosis
  • Full thickness damage of heart muscle
49
Q

What is NSTEMI?

A
  • Non-ST elevated myocardial infarction (on ECG)
  • Developing complete occlusion of minor coronary artery or partial occlusion of major coronary artery previously affected by atherosclerosis
  • Partial thickness damage of heart muscle
50
Q

Is STEMI or NSTEMI worse?

A

STEMI is worse

  • STEMI is more damage in tissue/severity of heart attack.
51
Q

What are the 2 types of myocardial infarctions?

A

STEMI and NSTEMI

Cardiovascular System (36 decks)

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