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Cardiovascular > ECG > Flashcards

ECG Flashcards

1
Q

What direction does depolarisation spread in the ventricles?

A

From the endocardium to the epicardium

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2
Q

What directions does repolarisation spread in the ventricles?

A

From the epicardium to the endocardium

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3
Q

What is the ECG?

A

A recording of potential changes, detected by electrodes positioned on the body surface, that allows the electrical activity of the heart to be monitored in a manner that is simple to perform and non-invasive

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4
Q

How do potentials at the body surface arise?

A

From currents that flow when the membrane potential of myocardial tissue is changing. Only large masses of cardiac tissue generate sufficient current to be detected at the body surface as potential changes

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5
Q

What does the ECG provide information about?

A

Cardiac rate and rhythm, chamber size, electrical axis of the heart and is the main test for assessment of myocardial ischaemia and infarction

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6
Q

What is an electrical dipole?

A

A vector with components of magnitude and direction (from atria to ventricles). The dipole is a separation of charge, when the positive charge moves towards the apex and the negative charge stays at the atria (wave of depolarisation) a vector is created

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7
Q

Which way does the vector spread in the heart?

A

Inferiorly and to the left

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8
Q

What is the clinical importance of the fact that the vector has components of magnitude and direction?

A

It allows the electrical axis of the heart to be estimated

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9
Q

How is magnitude determined?

A

The mass of cardiac muscle that is involved in the generation of the signal

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10
Q

How is the directions determined?

A

By the overall activity of the heart at any instant in time and varies during the cardiac cycle

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11
Q

What is a lead axis?

A

The imaginary line between two or more electrodes

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12
Q

What causes an upward deflection?

A

When depolarisation (positive charge) moves towards the recording electrode

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13
Q

What causes a downward deflection?

A

When depolarisation (positive charge) moves away from the recording electrode

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14
Q

What is the isopotential?

A

The straight line produced when there is no movement towards or away from the recording electrode - no deflection on the ECG

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15
Q

What comprises the 12 lead ECG?

A

3 standard limb leads - 1, 2, 3
3 augmented voltage (aV) leads - aVR (right), aVL (left), aVF (foot)
6 chest leads V1-V6

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16
Q

What leads provide a vertical/coronal picture of the heart?

A

Leads 1, 2, 3, aVR, aVL, aVF

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17
Q

What leads provide a horizontal (transverse) picture of the heart?

A

Leads V1-V6

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18
Q

What lead does the recording in lead 1?

A

Right Arm (negative) to Left Arm (positive). Left arm does the recording

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19
Q

What lead does the recording in lead 2?

A

Right arm (negative) to Left leg (positive). Left leg does the recording

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20
Q

What lead does the recording in lead 3?

A

Left arm (negative) to Left leg (positive). Left leg does the recording

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21
Q

What lead is used for the rhythm strip commonly?

A

Lead 2

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22
Q

What direction does lead to see the heart from?

A

An inferior direction

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23
Q

What is the P wave?

A

Atrial depolarisation

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24
Q

Why is the p wave positive?

A

Atrial depolarisation spreads from the SA node inferiorly and to the left (depolarisation is moving towards the recording electrode (LL) in lead 2) producing an upward deflection in the lead

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25
Q

What is the duration of the p wave?

A

Less than 0.12s

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26
Q

What does the QRS complex represent?

A

Ventricular activation/depolarisation

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27
Q

What is the duration of the QRS complex?

A

0.1s

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28
Q

Where does ventricular depolarisation start?

A

In the interventricular septum

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29
Q

Why is the Q wave negative?

A

The vector spreads from left to right and therefore the wave of depolarisation does not exactly follow the electrical vector in lead 2

30
Q

Why is the R wave positive?

A

The main free walls of the ventricles depolarise causing a tall and narrow R wave

31
Q

Why is the S wave negative?

A

The ventricles at the base of the heart depolarise (depolarisation is away from the electrical vector in lead 2)

32
Q

How is a Q wave defined?

A

A downward deflection preceding an R wave is a Q wave

33
Q

How is an R wave defined?

A

A deflection upwards is called an R wave, irrespective of whether or not it is preceded by a Q wave

34
Q

How is a S wave defined?

A

A downward deflection following an R wave is called an S wave

35
Q

What does the T wave represent?

A

Ventricular repolarisation

36
Q

Why is the T wave positive?

A

It is upwards because the wave of repolarisation is spreading away from the recording electrode (same as a positive moving towards it)

37
Q

What is the PR interval?

A

It is from the start of the P wave to the start of the QRS complex and reflects the time for the SA node impulse to reach the ventricles (AV nodal delay)

38
Q

How long is the PR interval?

A

0.12-0.2s

39
Q

What is the ST segment?

A

From the end of the QRS complex to the start of the T wave - normally isoelectric - this is ventricular systole

40
Q

What is the QT interval?

A

From the start of the QRS complex to the end of the T wave, reflects the time for ventricular depolarisation and repolarisation

41
Q

What is the time for the QT interval?

A

Needs to be corrected for HR but 0.44s in males and 0.46s in females

42
Q

How is heart rate calculated in ECGs?

A

300/number of large squares between beats

300/number of large squares between R-R intervals

43
Q

What is the ECG rhythm strip?

A

Prolonged recording of one lead - usually lead 2 which allows you to detect rhythm disturbances

44
Q

What is goldberger’s method?

A

One positive electrode (recording) and two others linked as negative. This effectively positions the refernce (linked) electrode in the center of the heart to which the recording electrodes “look”

45
Q

What is aVR?

A

Right Arm (+) to Left Arm and Left Foot (-)

46
Q

What is aVL?

A

Left Arm (+) to Right Arm and Left Leg (-)

47
Q

What is aVF?

A

Left leg (+) to Right Arm and Left Arm (-)

48
Q

What does the “eye” recording see?

A

If it sees a positive waveform coming towards it it will create an upward deflection
If it sees a positive waveform moving away from it, it will cause a downward deflection

49
Q

What way do aVR waves form?

A

The waves are negative, the predominant vector is depolarisation moving away from the recording electrode

50
Q

What way do lead 2 waves form?

A

Positive and well resolved - the predominant vector is depolarisation moving towards the recording electrode

51
Q

What leads are lateral leads?

A

Leads 1 and aVL - each has the recording electrode on the LA and views the heart from the left

52
Q

What leads are inferior leads?

A

Leads 2, 3 and aFV are inferior leads - each has the recording electrode on the left foot

53
Q

What way do the V1-6 leads view the heart?

A

In the horizontal plane

54
Q

What way do the V1 and V2 leads look at the heart?

A

They come from the right and look at the inter-ventricular septum

55
Q

What way do the V3 and V4 leads look at the heart?

A

They look at the anterior of the heart

56
Q

What way do the V5 and V6 leads look at the heart?

A

They look at the lateral aspect (left ventricle) of the heart

57
Q

What way does the R and S wave progress from V1-6?

A

The R wave progressively increases and is accompanied by a progressive decrease in the S wave

58
Q

What is the position of V1 on the chest?

A

Fourth intercostal space immediately right of the sternum

59
Q

What is the position of V2 on the chest?

A

Fourth intercostal space immediately left of the sternum

60
Q

What is the position of V3 on the chest?

A

Mid-way between V2 and V4

61
Q

What is the position of V4 on the chest?

A

Fifth intercostal space in the mid-clavicular line

62
Q

What is the position of V5 on the chest?

A

Same horizontal level as V4 but in the anterior axillary line

63
Q

What is the position of V6 on the chest?

A

Same horizontal level as V4 but in the mid-axillary line

64
Q

What occurs during the ST segment?

A

Ventricular systole

65
Q

What occurs during the TP segment?

A

Ventricular diastole

66
Q

Why are 12 leads needed to take an ECG?

A

Determine the axis of the heart in the thorax
Look for any ST segment or T wave changes in relation to specific regions of the heart - crucial in diagnosing ischaemic heart disease
Any voltage criteria changes - crucial in diagnosing chamber hypertrophy

67
Q

What are the 6 step to analysing an ECG?

A
  1. Verify patient details
  2. Check date and time ECG was taken
  3. Check the calibration of the ECG paper
  4. Detemine the axis, if possible
  5. Workout the rhythm
  6. Look at individual leads for voltage criteria changes or any St or T-wave changes
68
Q

What are the 7 things to look for in working out the rhythm of an ECG?

A 
Is electrical activity present 
Is the rhythm regular or irregular 
What is the heart rate 
P-waves present
What is the PR interval 
Is each P-wave followed by a QRS complex 
Is the QRS duration normal
69
Q

What leads look at the left ventricle?

A

1,2 aVL and V4-6

70
Q

What does the aVR lead detect vectors from?

A

The atria

71
Q

What does the aVL lead detect vectors from?

A

Left lateral surface of he heart

72
Q

What does the aVF lead detect vectors from?

A

Inferior surface of the heart

Cardiovascular (27 decks)

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