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Cardiovascular lectures > Electrical conduction > Flashcards

Electrical conduction Flashcards

1
Q

Where is the SAN?

A

Superior right atrium

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2
Q

Why can any cell in the heart be a pacemaker?

A

Can spontaneously depolarise

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3
Q

Which node is the pacemaker of the heart?

A

Sinoatrial node - has the highest rate of depolarisation

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4
Q

Describe how electrical impulse is propagated through the heart?

A

Action potential initiated in SAN and propagated to AVN through intermodal pathways in the atria
Cells of AVN delay the impulse by 100ms because they transmit the action potential more slwoly
Impulse spreads down to the ventricles along the bundle of His, which splits into the left and right bundles which give off the Purkinje fibres
The left and right bundles supply the left and right ventricles
Impulses spread tot he contractile cells of the ventricles through the Purkinje fibres, starting in the apex to push blood up
Heart returns to resting state

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5
Q

What connect cells in the heart to allow rapid transmission of electrical impulse?

A

Gap junction - directly connects the cytoplasm

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6
Q

Why is there a delay at the AVN?

A

To allow the ventricles to fully fill

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7
Q

If the SAN is damaged (e.g. scarring from heart attack), why will the patient not become asystolic? What will be different?

A

SAN is not the only pacemaker cell - the AVN will take over

However this will be a slower intrinsic rate

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8
Q

If the AVN becomes the pacemaker cell what will the heart rate be?

A

40-60bpm

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9
Q

If both SAN and AVN are damaged, what will control the electrical conduction of the heart? Will its be normal?

A

Bundle of His or Purkinje fibres

Slower and more unstable

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10
Q

What is a syncytium?

A

Single cell with multiple nuclei

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11
Q

What are intercalated discs?

A

Junctions between cardiac cells that connect them to each other
Contain 3 different types of cell-cell junctions to allow spread of electrical impulse - adherens, gap junctions, desmosomes

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12
Q

Where are intercalated discs found?

A

ONLY in cardiac muscle

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13
Q

Which type of cell-cell junctions do intercalated discs have?

A

Gap junctions (provide direct contact between cells)
Adherens Junctions
Desmosomes (keeps muscle connected when it contracts)

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14
Q

What is the resting membrane potential of pacemaker cells?

A

-70mv

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15
Q

What is the resting membrane potential of non-pacemaker cells?

A

-90mv

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16
Q

What mediates the initial flow of current (spontaneous electrical activity) into the cells? What is this flow?

A

Funny channel

Sodium influx

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17
Q

What is the membrane threshold of a pacemaker cell?

A

035mv

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18
Q

When the membrane threshold is reached, what happens?

A

Rapid opening of channels and influx of ions
mainly calcium
Overshoot to +15mv mediated by L type calcium channels

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19
Q

How is the cell repolarised after the overshoot to +15mv?

A

Efflux of predominantly potassium leaving the cell to return to its normal resting potential

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20
Q

State how a pacemaker cell is depolarised and repolarised

A 
Na+ gates open and Na+ flow in
Depolarisation to -35mv
L type calcium channels open (slow channels), causing influx of calcium and depolarisation to +15mv
Ca2+ channels close and K+ channels open
Cell repolarises
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21
Q

What happens in phase 4 of an action potential of a pacemaker cell? What mediates this?

A

Sodium influx into the cell

Funny channel

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22
Q

What happens in phase 0 of an action potential in a pacemaker cell? What mediates this?

A

When membrane threshold (-35mv) is reached, there is an all or nothing phenomenon.
Calcium influx into the cell
Overshoot to +15mv
Long-type calcium channels

23
Q

What happens in phase 3 of an action potential in a pacemaker cell? What mediates this?

A

Efflux of potassium out of the cell, and cell is repolarised back to resting membrane potential -70mv
Potassium ions

24
Q

What mediates sodium influx into pacemaker cells?

A

Funny channel

25
Q

What mediates calcium influx into pacemaker cells?

A

Long-type calcium channels

26
Q

What mediates repolarisation of pacemaker cells?

A

potassium efflux

27
Q

why is resting membrane potential lower in non-pacemaker cells?

A

less likely to be spontaneously depolarised

28
Q

What are the three differences between non-pacemaker and pacemaker cell action potentials?

A

Shape of action potential is different -

main influx of ions into non-pacemaker cell is mediated by fast sodium channels instead of L-type calcium channels

phase 2 (plateau phase) in non-pacemaker cells

29
Q

What is phase 2 in non-pacemaker cells?

A

Plateau phase where polarisation doesn’t change much
Mediated by calcium influx, which mediates excitation contraction coupling and allows cells time to contract (v important in muscle cells; this is the point of electrical conduction)

30
Q

What is the phase of action potentials in non-pacemaker cells?

A

Na+ channels open and Na+ flows in
Na+ channels close
Ca2+ channels open and fast K+ channels close
Ca2+ channels close and slow K+ channels open
resting potenital

31
Q

What is electrical activity on an ECG determined by?

A

WHERE the lead is anatomically on the heart - characteristic impulses relative to heart

32
Q

How will electrical activity toward an electrode show on an ECG?

A

Positive deflection (upwards)

33
Q

How will electrical activity away from an electrode show on an ECG?

A

negative deflection (downwards)

34
Q

Which two anatomical planes are looked at when interpreting an ECG?

A

Coronal and transverse

35
Q

What plane are V1 to V6 chest leads in?

A

Transverse
V1-V2 = right ventricle
V3-V4 = septum
V5-V6 = left ventricle

36
Q

What does axis on an ECG refer to?

A

Overall direction of depolarisation, determined by left ventricle

37
Q

Which leads determine the direction of depolarisation (axis)?

A

Lead 1, 2 and 3

if these are positive, then the axis is normal - should be coming toward the electrodes in the right ventricle

38
Q

What does P wave show

A

atrial depolarisation

39
Q

what is PR interval

A

delay at AVN

40
Q

What is the QRS wave?

A

ventricular depolarisation

Q = depolarisation of intraventricular septum form left to right
R = depolarisation of main mass of ventricles
S = depolarisation of the base
41
Q

What is the T wave?

A

ventricular repolarisation

42
Q

What is the U wave?

A

Pathological - usually caused by electrolyte abnormality

43
Q

What is ST segment?

A

Full ventricular depolarisation

44
Q

How would you determine a regular heart rhythm from an ECG?

A

Count the number of big squares between each QRS complex to see if it is regular

45
Q

How would you determine heart rate from an ECG?

A

Count the number of big squares between each QRS complex
1 square = 300bpm
4 square = 75bpm

46
Q

How long is a normal PR internal?

A

120ms

47
Q

What is the quiescent period of an ECG?

A

After T wave when all chambers are relaxed

AV valves are open and blood flows into ventricles

48
Q

What is sinus arrhythmia?

A

physiological slowing of SA node during expiration caused by an increase in vagal activity

heart rate increases on inspiration which helps to preserve cardiac output because stroke volume falls during inspiration

49
Q

What is sinus bradycardia?

A

Bradycardia when all electrical impulses are coming from SAN

50
Q

What can cause sinus bradycardia?

A

Athletes

Medication e.g. beta blockers

51
Q

What is ventricular ectopy? What will be the changes in ECG?

A

Extra electrical impulse generated from somewhere else in the myocardium other than normal electrical conducting system
Depolarisation spreads but is not as efficient because there are not gap junctions

there will be an extra electrical bear in ECG and wide QRS complex because slower conduction

52
Q

What is complete heart block?

A

AVN dissociation causes atrial and ventricular activity to be completely separate from each other
Electrical activity will be spread by another pacemaker

53
Q

What can cause heart block?

A

Disease of AVN e.g. scarring from MI

54
Q

How long is normal PR interval?

A

200ms

Cardiovascular lectures (6 decks)

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