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Atrial Fibrillation > ECG > Flashcards

ECG Flashcards

1
Q

What is an ECG concerned with?

A

collection of cells

rapid conduction between cells via intercalated discs

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2
Q

In a unipolar electrode, what deflection would depolarisation moving towards a positive electrode give?

A

Upward deflection

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3
Q

In a unipolar electrode, what deflection would depolarisation moving away from a positive electrode give?

A

Downward deflection

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4
Q

When is amplitude maximal?

A

When positive electrode is on the vector

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5
Q

When is amplitude minimal/biphasic?

A

When positive electrode is perpendicular

No charge

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6
Q

In a unipolar electrode, what deflection would depolarisation moving towards a negative electrode give?

A

Downward deflection

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7
Q

In a unipolar electrode, what deflection would depolarisation moving away from a negative electrode give?

A

Upward deflection

Ie. Focally positioned negative electrode records same thing as diametrically opposite positive electrode

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8
Q

Describe a model for unipolar electrode

A

Strip of cells in bath with conducting fluid
Focally positioned positive electrode
Corners of bath connected to negative electrode

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9
Q

How is the strip affected in a unipolar electrode when it depolarises?

A

Inside positive, outside negative
Cells closest to electrode most influenced
Indifferent electrode sees average potential of strip

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10
Q

What does the potential difference reflect?

A

Movement of current in relation to positive electrode

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11
Q

Describe bipolar electrode

A

2 recording electrodes
Strip of cells in bath with conducting fluid
Focally positioned positive and negative electrode

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12
Q

How is the strip affected in a bipolar electrode when it depolarises?

A

Inside positive, outside negative
Wave of depolarisation moving towards positive - upward
Also moving away from negative - upward
Combined means bipolar deflection is larger than unipolar potential difference

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13
Q

How is the strip affected in a unipolar electrode when it repolarises?

A

Potential change is opposite to depolarisation - inside negative, outside positive
Towards positive - downward deflection
Away from positive - upward deflection

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14
Q

How does electrical current flow in the heart?

What does this allow?

A

Flows as if between 2 termInals in a volume conductor
Intra-thoracic contents also act as volume conductors

This allows surface recordings of potential differences provide 3D picture of electrical events in the heart

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15
Q

What is the recorded potential difference at any instant?

A

Vectorial resultant (mean vector) of several differently directed wavefronts

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16
Q

What would be recorded on ECG I if the positive electrode is at apex at atrial depolarisation?

A

Upward deflection - toward positive electrode

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17
Q

What would be recorded on ECG I if the positive electrode is at apex afteratrial depolarisation?

A

No deflection, due to delay as current passes through AV node

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18
Q

What would be recorded on ECG I if the positive electrode is at apex at ventricular depolarisation?

A
  1. Septum (LV to RV) - small negative, away from electrode (small number of cells)
  2. Main ventricular depolarisation - large upward, towards electrode (left bias, more cells, endo to epi)
    Repolarisation
  3. Base of ventricles - small negative, away from electrode
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19
Q

What would be recorded on ECG I if the positive electrode is at apex at ventricular repolarisation?

A

Away from electrode, therefore positive deflection

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20
Q

Which ventricular cells are first to repolarise?

A

Those which are last to depolarise (epicardial cells) - shorter action potentials

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21
Q

Limb leads of unipolar

A

One focally positioned positive electrode, others are indifferent (RL earth)

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22
Q

aVR

A

Right shoulder

Positive RA

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23
Q

aVL

A

Left shoulder

Positive LA

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24
Q

aVF

A

Feet (groin direction)

Positive left leg

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25
Q

Chest leads

A

One focally positioned positive electrode in 6 specific positions on the chest
V1-V6
4th intercostal space at right margin of sternum to 5th intercostal space at mid-axillary line

26
Q

Bipolar limb leads

A

Two focally positioned electrodes (positive and negative)

Records PD between them

27
Q

Limb lead I bipolar

A

Positive - LA (-30)
negative - RA (-150)
Lead - 0 degrees

28
Q

Limb lead II bipolar

A

Positive - LL (groin)
Negative - RA (-150)
Lead - 60 degrees

29
Q

Limb lead III bipolar

A

Positive - LL (90)
Negative - LA (-30)
Lead - 120 degrees

30
Q

What is the p wave?

A

First wave, irrespective of polarity

31
Q

What is the T wave?

A

Final wave

Unless U waves (rare) are present

32
Q

What is the R wave?

A

First positive wave after P wave

33
Q

What is a Q wave?

A

Any negative wave after P wave but before R wave

34
Q

What is an S wave?

A

Any negative wave after R wave

35
Q

What is a R’ wave?

A

Any positive wave after S wave

36
Q

What does a P wave show?

A

Atrial depolarisation

37
Q

What does QRS show?

A

Ventricular depolarisation

38
Q

What does T show?

A

Ventricular repolarisation

39
Q

P duration

A

Around 0.08s

40
Q

P-R interval

A

<0.2s

Wave of excitation through AV node

41
Q

QRS duration

A

Around 0.1s

42
Q

What occurs during S-T?

A

Ejection of blood

43
Q

What would be diagnosed if S-T duration is above baseline?

A

Recent heart attack

44
Q

What occurs in T-P interval?

A

Ventricles filling with blood

45
Q

In a normal ECG where would the largest QRS wave be detected?

46
Q

Is there is a left axis deviation, where would this be detected?

47
Q

Cause of left axis deviation

A

Hypertension
Valvular heart disease
LV hypertrophy

48
Q

Where would right axis deviation by detected?

49
Q

Cause of right axis deviation

A

COPD

Pulmonary hypertension

50
Q

What would 1st degree heart block look like?

51
Q

What would 2nd degree heart block look like?

A

Some P with no QRS

52
Q

What would 3rd degree heart block look like?

A

Complete block

No AV conduction

53
Q

Examples of ectopics

A

Ventricular extrasystole
Tachycardia
Atrial fibrillation
Ventricular

54
Q

Ventricular extrasystole

A

No preceding P wave

Next p missed, therefore gap before next complex

55
Q

Tachycardia

A

Atrial/ventricular

Lots of P, not as many QRS

56
Q

Atrial fibrillation

A

Rhythm not set by SA node, uncoordinated
QRS complex irregular, gaps between
No defined P wave

57
Q

What else can influence electrical activity ?

A

Anti-arrythmic drugs

58
Q

How are dysrythmias classified?

A

Site of origin of abnormality (atrial, junctional, super ventricular)
Rate of change (tachycardia, bradycardia)

59
Q

4 basic phenomena that cause changes

A
  1. Abnormal pacemaker activity
  2. Heartblock - unstable/inappropriate conduction via AV node
  3. Delayed after depolarisation - XS Ca2+ -> Na+ influx
  4. Re-entry - no extinction collision
60
Q

Classes of drugs

A
  1. Block Na+ channels eg. Lidocaine , reduce max rate of depolarisation
  2. Beta-adrenoceptor antagonists eg. Atenolol
  3. Block K+ channels eg. Amiodarone, slow repolarisation, prolong AP, increase refractory period
  4. Ca2+ channel antagonists eg. Verapamil, slow conduction in nodes

Atrial Fibrillation (9 decks)

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