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*CVS Jeny > S6) The ECG > Flashcards

S6) The ECG Flashcards

1
Q

What is the ECG?

A
  • The ECG is a device used to measure the electrical activity of the heart by using electrodes placed on the skin
  • This is an extracellular recording of the combined spread of electrical activity across the whole heart
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2
Q

Which structures compose the specialised conducting system of the heart?

A
  • SAN (sinus rhythm)
  • AV node
  • Bundle of His
  • Right and Left bundle branches
  • Fibres of the Purkinje system
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3
Q

In 9 steps, outline how action potentials spread over the heart in a precise pattern

A
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4
Q

Which different complexes can form for depolarisation waves?

A
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5
Q

Repolarisation of the ventricles happens in the reverse order.

Thus, which different complexes can form from repolarisation waves?

A
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6
Q

What determines the nature of the signal?

A

The nature of the signal depends upon the direction of spread of the electric field relative to the position of the recording electrode

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7
Q

How can the nature of the signal be predicted in terms of repolarisation and depolarisation?

A
  • Depolarisation towards a positive recording electrode → upward deflection
  • Depolarisation away from a positive recording electrode → downward deflection
  • Repolarisation towards a positive recording electrode → downward deflection
  • Repolarisation away from a positive recording electrode → upward deflection
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8
Q

Which factors affect the amplitude of the deflection?

A
  • Size and speed of muscle changing potential
  • Direction of wave of activity towards the electrode (directly, obliquely, perpendicular)
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9
Q

Describe the electrical activity in this 5 individual diagrams and the depolarisation complexes they form

A
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10
Q

What is the mechanism behind the P wave?

A

P wave: atrial depolarisation spreads along both atrial fibres & internodal pathways towards the AV node

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11
Q

What is the mechanism behind the Q segment?

A

Q segment: the initial downward deflection after the P wave as the muscle in the interventricular septum depolarises from left to right

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12
Q

What is the mechanism behind the QRS segment?

A

QRS segment: ventricular depolarisation

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13
Q

What is the mechanism behind the R segment?

A

R segment: initial upward deflection after p wave (large as there is greater muscle mass i.e. more electrical activity)

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14
Q

What is the mechanism behind the S segment?

A

S segment: downward deflection after the R as depolarisation finally spreads upwards to the base of the ventricles

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15
Q

What is the mechanism behind the T segment?

A

T segment: ventricular repolarisation (epicardial surface → endocardium) produces medium upward deflection

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16
Q

What is the R-R interval in the ECG and what is its significance?

A
  • Where to measure: from peak to peak of R-waves
  • What does this indicate: shorter interval = faster heart rate
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17
Q

What is the QRS complex in the ECG and what is its significance?

A
  • Where to measure: start of the Q-wave to the end of the S-wave
  • What does this indicate: wider QRS complexes are associated with abnormal ventricular depolarisations
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18
Q

What is the P-R interval in the ECG and what is its significance?

A
  • Where to measure: start of the P-wave to start of the Q-wave
  • What does this indicate: longer P-R intervals indicate slow conduction from the atria to the ventricle (first degree heart block)
19
Q

What is the ST segment in the ECG and what is its significance?

A
  • Where to measure: end of S-wave to start of T-wave
  • What does this indicate: the ST segment should be isoelectric (myocardial infarction/ischaemia if raised/depressed)
20
Q

What is the Q-T interval in the ECG and what is its significance?

A
  • Where to measure: start of Q-wave to end of T-wave
  • What does this indicate: a prolonged Q-T interval suggests prolonged repolarisation of the ventricles, lead to arrhythmias
21
Q

Explain the relationship of the Q-T interval with the heart rate, and how this can be adjusted for

A
  • The faster the heart rate, the shorter the R-R and Q-T interval
  • This can be adjusted to improve the detection of patients with increased risk of ventricular arrhythmia (QTc)
22
Q

How many electrodes are used to record the ECG and where are they placed?

A
  • Limbs: 4 electrodes (A)
  • Chest: 6 electrodes (B)
23
Q

What are the colours of the different limb electrodes?

A

Mnemonic: Ride Your Green Bike

24
Q

What are the colours of the different chest electrodes?

A

Mnemonic: Ride Your Great Big Brown Pony

25
Q

Identify the specific locations of the different chest leads

A
  • V1: 4th intercostal space (right sternal border)
  • V2: 4th intercostal space (left sternal border)
  • V3: Between V2 and V4
  • V4: 5th intercostal space (mid-clavicular line)
  • V5: Between V4 and V6
  • V6: 6th intercostal space (mid-axillary line)
26
Q

How many different views/leads are given of the heart?

27
Q

What are the 6 different views in the vertical plane (limb leads)?

28
Q

Which views are given by limb leads: II, III and aVF?

A

They look at the inferior surface of the heart

29
Q

Which views are given by limb leads: I and aVL?

A

They look at the left side of the heart

30
Q

What are the 6 different views in the horizontal plane (chest leads)?

31
Q

Which views are given by chest leads: V1 and V2 (aka septal leads)?

A

They look at the right ventricle & septum

32
Q

Which views are given by chest leads: V3 and V4 (aka anterior leads)?

A

They look at the anterior wall of the ventricles

33
Q

Which views are given by chest leads: V5 and V6 (aka lateral leads)?

A

They look at the left ventricle

34
Q

Which ECG leads can detect problems in the lateral surface of the heart?

A

I, aVL, V5, V6

35
Q

Which ECG leads can detect problems in the inferior surface of the heart?

A

II, III, aVF

36
Q

Which ECG leads can detect problems in the septum of the heart?

37
Q

Which ECG leads can detect problems in the anterior surface of the heart?

38
Q

In an ECG trace, how much is the following:

  • 1 large square (width)
  • 1 large square (length)
  • 1 small square (width)
A
  • 1 large square = 0.2 seconds (width)
  • 1 large square = 0.5 mV (length)
  • 1 small square = 0.04 seconds (length)
39
Q

How does one determine normal sinus rhythm?

40
Q

Distinguish between sinus bradycardia and sinus tachycardia

A
  • Sinus rhythm with rate < 60/minute = sinus bradycardia
  • Sinus rhythm with rate > 100/minute = sinus tachycardia
41
Q

How does one calculate heart rate from an ECG with a regular rhythm?

A
  • Count the number of large boxes between complexes (R – R interval)
  • How many complexes could be fitted into 300 large boxes ( i.e. 1 minute)?
  • E.g. 300/4 = 75 beats per minute*
42
Q

How does one calculate heart rate from an ECG with an irregular rhythm?

A

Calculate heart rate by counting the number of QRS complexes in 6 seconds, then multiply by 10

E.g. Heart rate = 70 beats per minute

43
Q

With reference to the electrical activity of the heart, describe what is happening at each of the numbered points

A

1 - SAN depolarisation

2 - Atrial depolarisation

3 - AVN delay

4 - Ventricular depolarisation

*CVS Jeny (17 decks)

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