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Yr 3 - Skills & Extras > Understanding an ECG > Flashcards

Understanding an ECG Flashcards

1
Q

What is the purpose of an ECG?

A

to record the electrical activity of the heart from different angles to both identify and locate pathology

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2
Q

What do P waves represent?

A

Atrial depolarisation

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3
Q

In healthy individuals, what precedes each QRS complex?

A

A p wave

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4
Q

What does the PR interval represent?

A

The time taken for the electrical activity to move between the atria & ventricles

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5
Q

Where does the PR interval start and end?

A

Start - beginning of the P wave
End - beginning of the Q wave (NOT at R peak)

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6
Q

What does the QRS complex represent?

A

Ventricular depolarisation

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7
Q

What does the ST segment represent?

A

Time between depolarisation and repolarisation of the ventricles

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8
Q

Where does the ST segment start and end?

A

Start - end of the S wave
End - beginning of the T wave

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9
Q

What does the T wave represent?

A

Repolarisation of the ventricles

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10
Q

What appears after the QRS complex?

A

T wave

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11
Q

What does the RR interval represent?

A

Time between the two QRS complexes (i.e. duration of cardiac cycle)

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12
Q

Where does the RR interval begin and end?

A

Begin - peak of one R wave
End - peak of next R wave

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13
Q

What does the QT interval represent?

A

The time taken for the ventricles or depolarise and then repolarise

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14
Q

Where does the QT interval start and end?

A

Start - beginning of QRS complex
End - end of T wave

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15
Q

Which part of the ECG represents atrial depolarisation?

A

P wave

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16
Q

Which part of the ECG represents ventricular depolarisation?

A

QRS complex

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17
Q

Which part of the ECG represents the time between depolarisation and repolarisation of the ventricles?

A

ST segment

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18
Q

Which part of the ECG represents the time taken for the electrical activity to move between the atria and ventricles?

A

PR interval

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19
Q

Which part of the ECG represents the repolarisation of the ventricles?

A

T wave

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20
Q

Which part of the ECG represents the time between the two QRS complexes?

A

R-R interal

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21
Q

Which part of the ECG represents the time taken for the ventricles to depolarise and repolarise?

A

QT interval

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22
Q

What does each small square of an ECG represent?

A

0.04 seconds

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23
Q

What does each large square of an ECG represent?

A

0.2 seconds

24
Q

how many large squares on an ECG represent 1 second?

A

5

25
Q

How many large squares on an ECG represents 1 minute?

A

300

26
Q

How does an ECG electrode differ from an ECG lead?

A

Electrode → A conductive pad that is attached to the skin to record electrical activity

Lead → A graphical representation of the heart’s electrical activity which is calculated by analysing data from several ECG electrodes

27
Q

How many ECG electrodes are there in a 12-lead ECG?

A

10 (6 chest 4 limb)

28
Q

Describe the position of the chest electrodes

A
  • V1 → 4th intercostal space at right sternal edge
  • V2 → 4th intercostal space at left sternal edge
  • V3 → Midway between V2 and V4 electrodes
  • V4 → 5th intercostal space in left midclavicular line
  • V5 → Left anterior axillary line at same level as V4
  • V6 → Left mix-axillary line at same level as V4/V5
29
Q

Describe the position of the 4 limb electrodes

A
  • Red (RA) → on ulnar styloid process of right arm
  • Yellow (LA) → on ulnar styloid process of left arm
  • Green (LL) → on medial or lateral malleolus of left leg
  • Black (BL) → on medial or lateral malleolus of right leg
30
Q

What 12 leads doe an ECG consist of?

A
  • Three bipolar limb leads (I, II and III)
  • Three unipolar limb leads (IV/aVR, V/aVL and VI/aVF)
  • 6 unipolar chest leads
31
Q

What view of the heart does each chest lead give you?

A
  • V1 → septal
  • V2 → septal
  • V3 → anterior
  • V4 → anterior
  • V5 → lateral
  • V6 → lateral
32
Q

What does a bipolar ECG lead mean?

A

A lead composed of two electrodes of opposite polarity is called bipolar lead.

33
Q

What does a unipolar ECG lead mean?

A

A lead composed of a single positive electrode and a reference point is a unipolar lead.

34
Q

Leads I, II and III are bipolar. Which 2 electrodes does each lead analyse activity between?

A
  • Lead I → calculated by analysing activity between RA (right arm) and LA (left arm) electrodes
  • Lead II → calculated by analysing activity between RA and LL electrodes
  • Lead III → calculated by analysing activity between LA and LA electrodes
35
Q

Which view of the heart does lead I → aVF give?

A

1 → lateral

II → inferior

III → inferior

aVR → lateral

aVL → lateral

avF → inferior

36
Q

What causes positive deflection in an ECG trace?

A

When the electrical activity within the heart travels towards a lead

37
Q

What type of deflection do you get in an ECG trace when electrical activity travels away from a lead?

A

Negative

38
Q

How do deflections appear on an ECG?

A

Waves

39
Q

What does each deflection (i.e. wave) on the ECG represent?

A

the average direction of electrical travel

40
Q

What does the height of each deflection/wave on an ECG represent?

A

The amount of electrical activity flowing in that direction (i.e. the higher the deflection, the greater the amount of electrical activity flowing towards the lead).

41
Q

What is the lead with the most positive deflection aligned with?

A

The direction the heart’s electrical activity is travelling

Example:

  • If the R wave is greater than the S wave it suggests depolarisation is moving towards that lead.
  • If the S wave is greater than the R waves it suggests depolarisation is moving away from that lead.
  • If the R and S waves are of equal size it means depolarisation is travelling at exactly 90° to that lead.
42
Q

What does the cardiac axis give us an overall idea of?

A

the overall direction of electrical activity

43
Q

Describe a brief order of electrical activity in healthy individuals in the heart

A
  1. The electrical activity of the heart begins at the sinoatrial (SA) node
  2. Spreads to the atrioventricular (AV) node
  3. Spreads down the bundle of His
  4. Spreads to Purkinje fibres → causes ventricular contraction
44
Q

Where should the cardiac axis lie between?

A

-30 degrees and +90 degrees

45
Q

Towards which leads (in healthy individuals) is the overall direction of electrical activity?

A

Leads I, II and III → you will therefore see a positive deflection in all these leads

46
Q

In a healthy individual, which lead will show the most positive deflection? Why?

A

Lead II → as it is the most closely aligned to the overall direction of electrical spread

47
Q

In a healthy individual, which lead will show the most negative deflection? Why?

A

Lead IV/aVR → due to aVR looking at the heart in the opposite direction

48
Q

Right axis deviation involves the direction of depolarisation being distorted how?

A

To the right (between +90 and +180 degrees)

49
Q

How are the leads affected in right axis deviation?

A

Lead I becomes negative

Lead aVF/III becomes more positive

50
Q

What is the most common cause of right axis deviation?

A

Right ventricular hypertrophy

51
Q

How does right ventricular hypertrophy lead to right axis deviation?

A
  • Extra right ventricular tissue results in a stronger electrical signal being generated by the right side of the heart
  • This causes the deflection in lead I to become negative and deflection in lead aVF/III to be more positive
52
Q

When is right axis deviation a normal finding?

A

In very tall individuals

53
Q

Give one other condition that causes right axis deviation

A

Pulmonary hypertension as causes right ventricular hypertrophy

54
Q

Left axis deviation results in the direction of depolarisation being distorted how?

A

To the left (between -30 and -90 degrees)

55
Q

Left axis deviation results in the deflection of lead III becoming negative. When is this finding only considered significant?

A

If the deflection of lead II also becomes negative

Yr 3 - Skills & Extras (7 decks)

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