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Physiology Hilary > 3. The ECG > Flashcards

3. The ECG Flashcards

1
Q

Do pacemaker cells have a resting potential?

A

No

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2
Q

What occurs instead of a resting potential for pacemaker cardiac cells?

A

The membrane potential slowly depolarises toward threshold (pacemaker potential).

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3
Q

What is the first half of the pacemaker potential the result of?

A

Simultaneous opening of unique funny channels, which permits inward Na+ current, and closure of K+ channels, reducing outward K+ current.

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4
Q

What is the second half of the pacemaker potential the result of?

A

Opening of T-type Ca2+ channels

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5
Q

Once the threshold is reached, what is the rising phase of the action potential the result of?

A

Opening of L-type Ca2+ channels, whereas the falling phase is the result of opening of K+ channels.

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6
Q

What is the cardiac pacemaker?

A

Sinoatrial Node (SA node)

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7
Q

Where is the SA node located?

A

Within right atrial wall at junction with superior vena cava

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8
Q

What is the intrinsic rate of the SA node?

A

70-80 A.P. per min

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9
Q

What is the conduction speed of the SA node?

A

0.05m/sec

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10
Q

Where is the atrioventricular node (AV node) located?

A

Above cardiac septum at junction of atria and ventricles.

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11
Q

What is the intrinsic rate of the AV node?

A

40-60 A.P. per min

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12
Q

What is the conduction speed of the AV node?

A

0.05m/sec

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13
Q

Where is the bundle of His located?

A

Left & right Branches run down ventricular septum to apex

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14
Q

What is the intrinsic rate of the bundle of His?

A

20-40 A.P. per min

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15
Q

What is the conduction speed of the bundle of His?

A

1m/sec

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16
Q

Where are the Purkinje fibres located?

A

Throughout ventricular myocardium from apex to base

17
Q

What is the intrinsic rate of Purkinje fibres?

A

15-40 A.P. per min

18
Q

What is the conduction speed of Purkinje fibre

A

4m/sec

19
Q

Electrical conduction in heart steps

A
  • SA node depolarises
  • Electrical activity goes rapidly to AV node via internodal pathways
  • Depolarisation spreads more slowly across atria. Conduction slows through AV node.
    4. Depolarisation moves rapidly through ventricular conducting system to the apex of the heart.
    5. Depolarisation wave spreads upward from the apex.
20
Q

What are the two phases that cardiac contractile cell APs exhibit?

A

Prolonged plateau phase - accompanied by prolonged period of contraction.

21
Q

What do the plateau phase and prolonged period of contraction allow for?

A

Ensures adequate ejection time

22
Q

What is the prolonged plateau phase due to?

A

Activation of slow L-type Ca2+ channels

23
Q

Is tetanus of cardiac muscle possible and why?

A

No due to refractory period

24
Q

What is an ECG useful for? x 4

A
  • Assessment of orientation of the heart
  • Localisation of areas that do not conduct electrical activity normally
  • Assessment of myocardial hypertrophy or atrophy (current amplitudes are proportional to electrically active tissue mass)
  • Accurate measurement of heart rate (60/ R-R interval)
25
Q

P wave

A

Atrial depolarisation

26
Q

PR segment

A

AV nodal delay

27
Q

QRS complex

A

Ventricular depolarisation (atria repolarising simultaneously)

28
Q

ST segment

A

Time during which ventricles are contracting and emptying

29
Q

T wave

A

Ventricular repolarisation

30
Q

TP interval

A

Time during which ventricles are relaxing and filling

31
Q

ECG diagram

A
32
Q

P wave timing

A

80-100 ms

33
Q

PR segment timing

A

100-180 ms

34
Q

QRS complex timing

A

80-100 ms

35
Q

ST segment

A

70-80 ms

36
Q

T wave

A

~200 ms

37
Q

ECG lead arrangements

A
38
Q

ECG lead diagrams

A
39
Q

ECG heart conditions diagram

A

Physiology Hilary (12 decks)

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