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MPharm 2 - PH2113 > Unit 6 - Cardiovascular - ECG > Flashcards

Unit 6 - Cardiovascular - ECG Flashcards

1
Q

What is the path taken by the electrical activity of the heart?

A
  1. Action potential (AP) generated in the sino-atrial node (SAN)
  2. Atrial depolarisation
  3. AP delayed at the atrioventricular node (AVN)
  4. AP travels down the septum to the apex of the heart and around the ventricles
  5. Wave of AP causes wave of contraction
  6. Wave of depolarisation follows wave of depolarisation
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2
Q

What does depolarisation of cardiac muscle cause?

A

Contraction of cardiac muscle

- negative to positive

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3
Q

What does repolarisation of cardiac muscle cause?

A

Relaxation

- positive to negative

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4
Q

What is depolarisation of cardiac muscle followed by?

A

Repolarisation

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5
Q

What are the different forms of cardiac action potential?

A 
Pacemaker/nodal/slow response
- If
- ICa
Non-nodal/fast response
- INa
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6
Q

Why is direction considered on an ECG?

A

Cells may repolarise in the same order in which they were depolarised
The order may be reversed

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7
Q

What does the P wave on an ECG show?

A

Atrial depolarisation

- delay between P and Q

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8
Q

What does the QRS wave on an ECG show?

A

Ventricular depolarisation

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9
Q

What does the T wave on an ECG show?

A

Ventricular repolarisation

- delay between S and T

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10
Q

What does the ECG measure?

A

The electrical activity of the heart

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11
Q

What is used to measure an ECG?

A

An array of electrodes placed on the body surface

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12
Q

What initiates the cardiac cycle?

A

Action potentials propagate from the sinoatrial node (SAN) through the myocardium

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13
Q

How is the ECG measured?

A

The spread of action potentials results in an electromagnetic force vector being generated

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14
Q

How quickly does the trace on an ECG move?

A

Trace moves at 25 mm/s

- 300 big squares/minute

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15
Q

How is heart rate calculated from an ECG?

A

Intervals between waves

- normally R-R

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16
Q

What does the PR interval on an ECG show?

A
  1. 12 - 0.20 seconds
    - represents the time between onset of atrial and ventricular depolarisation
    - if > 0.20 seconds, possible AV conduction block
17
Q

What does the QRS wave on an ECG show?

A
  1. 06 - 0.1 seconds
    - represents ventricular depolarisation
    - if prolonged (> 0.1s) conduction is impaired within the ventricles
    - bundle branch block
    - movement of pacemaker site
18
Q

What does the QT interval on an ECG show?

A

0.2 - 0.4 seconds depending on heart rate
- gets shorter as heart rate increases
- can be correct for heart rate (QTc)
- represents the time for both ventricular depolarisation and repolarisation to occur
- rough estimate of ventricular AP duration
Prolonged QT intervals (> 0.44s) are diagnostic of certain types of tachyarrhythmia

19
Q

What does the ST interval on an ECG show?

A 
Indicator of myocardial infarction
- depression
- elevation
AP conduction is affected by ischaemia
- level will be elevated is transmural
Also used to diagnose other conduction defects
20
Q

When is there no movement on an ECG?

A

Resting polarised state

  • no current
  • no measurement
21
Q

Which direction does the action potential travel on an ECG?

A

Action potential is stimulated and conducted left to right

- movement of positive charge towards positive electrode

22
Q

What causes an upward deflection on an ECG?

A

A positive voltage

23
Q

What happens on an ECG once depolarisation has finished?

A

No more movement of charge

- no potential difference again

24
Q

What does lead 2 measure on an ECG?

A

On the cardiac axis to measure the P wave

  • depolarisation from SA to AV node
  • positive deflection on ECG
25
Q

How is repolarisation of atria measured on an ECG?

A

It is not seen on an ECG

  • negative trace following P wave
  • hidden by QRS complex
26
Q

Which direction does depolarisation of the ventricles take place?

A

Endocardium to epicardium

  • lining of chambers outwards
  • generally in the direction of the electrode
27
Q

Why is the depolarisation of the ventricles a larger wave (R wave) than the depolarisation of the atria (P wave)?

A

Larger

- more cells to depolarise

28
Q

Which cells are the first to repolarise in the ventricles?

A

The last cells to depolarise

- repolarisation is from epicardium to endocardium

29
Q

Why is the T wave a positive wave?

A

The action potential is moving away from the electrode

30
Q

What is the result of a wave of depolarisation traveling towards a positive electrode?

A

A positive deflection in the ECG trace

31
Q

What is the result of a wave of depolarisation traveling away from a positive electrode?

A

A negative deflection in the ECG trace

32
Q

What is the result of a wave of repolarisation traveling towards a positive electrode?

A

A negative deflection in the ECG trace

33
Q

What is the result of a wave of repolarisation traveling away from a positive electrode?

A

A positive deflection in the ECG trace

34
Q

When is there no net deflection in an ECG?

A

A wave of depolarisation or repolarisation travelling perpendicular to an electrode axis

MPharm 2 - PH2113 (50 decks)

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