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Cardiovascular System > Session 8 > Flashcards

Session 8 Flashcards

1
Q

What type of signal does a depolarisation moving towards an electrode give on an ECG?

A

Upward signal

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2
Q

What type of signal does a depolarisation moving away from an electrode give on an ECG?

A

Downward signal

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3
Q

What type of signal does a repolarisation moving towards an electrode give on an ECG?

A

Downward signal

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4
Q

What type of signal does a repolarisation moving away from an electrode give on an ECG?

A

Upward signal

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5
Q

What affects the amplitude of a signal on an ECG?

A
  • The amount of muscle depolarising

- How directly the signal is moving towards the electrode

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6
Q

Describe the P wave on an ECG

A
  • Caused by atrial depolarisation

- Small upward deflection

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7
Q

How long is the gap between a P wave and the Q wave on a normal ECG?

A

Around 120ms

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8
Q

Describe the Q wave on an ECG

A
  • Caused by septal depolarisation spreading to the ventricle

- Small and very short downward deflection

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9
Q

Describe the R wave on an ECG

A
  • Caused by the main ventricular depolarisation

- Large, relatively short upward deflection

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10
Q

Describe the S wave on an ECG

A
  • Caused by end ventricular depolarisation

- Small downward deflection

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11
Q

How long is ventricular contraction in a typical person and what is it represented by on an ECG?

A
  • Usually ~280ms

- Represented by the QRS complex on an ECG

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12
Q

Describe the T wave on an ECG

A
  • Caused by ventricular repolarisation

- Medium upward deflection

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13
Q

How does the QRS complex on an ECG change if the viewing electrode is moved around the heart?

A

Direction and amplitude of the complex changes

  • Large upward deflection slightly to the left of the septum
  • Deflection becomes smaller as the electrode moves anti-clockwise around the heart
  • No deflection at the atrioventricular septum as the QRS complex moves at a right angle to the electrode
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14
Q

Which electrode in a 12 lead ECG is neutral?

A

Right lower limb lead

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15
Q

What view of the heart do the limb leads provide?

A

Vertical view

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16
Q

What view of the heart do the chest leads provide?

A

Horizontal view of the heart

17
Q

From what angle does lead 1 view the heart?

A

0 degrees

18
Q

From what angle does lead 2 view the heart?

A

+60 degrees

19
Q

From what angle does lead VF view the heart?

A

+90 degrees

20
Q

From what angle does lead 3 view the heart?

A

+120 degrees

21
Q

From what angle does lead VR view the heart?

A

-150 degrees

22
Q

From what angle does lead VL view the heart?

A

-30 degrees

23
Q

How is a regular heart rate calculated from a rhythm strip?

A

300/(number of squares in the R-R interval)

24
Q

How is an irregular heart rate calculated from a rhythm strip?

A

Using more than one R-R interval and multiplying by the number of beats used; best to use 30 beats if possible

25
Q

What does a ventricular ectopic beat look like on an ECG?

A
  • QRS complex which isn’t preceded by a P wave
  • Wider than a normal QRS complex as the depolarisation doesn’t originate from or flow down the normal conduction pathway
26
Q

How does atrial fibrillation appear on an ECG?

A
  • P wave absent
  • Irregular fibrillation waves present instead of P wave
  • No stimulus reaching AV node so other pacemakers must take over; heart rate may be reduced
27
Q

How does ventricular fibrillation appear on an ECG?

A
  • Uncoordinated ventricular contraction so no QRS complexes

- Completely irregular ECG with no clearly visible waves

28
Q

What is a first degree heart block?

A

Communication problem between the atria and ventricles causing a conduction delay through the AV node

29
Q

How does a first degree heart block appear on an ECG?

A
  • P-R interval is elongated so is longer than 200ms

- All electrical signals eventually reach the ventricles

30
Q

What is a type 1 second degree heart block?

A

Heart block where not all atrial beats get through to the ventricles

31
Q

How does a type 2 heart block appear on an ECG?

A
  • PR interval is erratic

- PR interval elongates until eventually a QRS complex is dropped and the system resets

32
Q

What is a type 2 second degree heart block?

A

Heart block where sometimes electrical excitation fails to pass through the AV node or bundle of His

33
Q

How does a type 2 second degree heart block appear on an ECG?

A
  • Usually a constant PR interval

- Not all atrial contractions are followed by ventricular contractions

34
Q

What is a complete, third degree heart block?

A

Heart block where no electrical conduction is conveyed to the ventricles

35
Q

How does a third degree heart block appear on an ECG?

A
  • No link between atrial and ventricular depolarisations

- Ventricles generate own electrical signal via ectopic pacemakers so ventricular depolarisations are usually slow

36
Q

What is the effect of a bundle branch block on an ECG?

A
  • Lengthens and changes the shape of the QRS complex

- Several variations depending on the location of the block

37
Q

How does an action potential spread through the the heart?

A
  • Action potential generated by pacemaker cells in the SAN
  • Electrical activity spreads over the surface of the heart to the AV node
  • Delay at the AV node of around 120ms
  • Excitation spreads from the AVN down the septum via the right and left bundle branches
  • Excitation spreads out from the apex of the heart over the ventricular myocardium from inside to outside until all ventricular cells are depolarised
  • Repolarisation starts from the outside of the heart to the inside

Cardiovascular System (10 decks)

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