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Cardiovascular System (Milly's) > ECG > Flashcards

ECG Flashcards

1
Q

How do the ventricle depolarise?

A

From endocardium to epicardium

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2
Q

What are the purkinje fibres?

A

Fine branches of the bundle of His

Which allow rapid spread of depolarisation throughout ventricular myocardium

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3
Q

Where can you fin the Bundle of His?

A

In the intra-atria septum of the heart

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4
Q

Briefly describe how the heart depolarises

A
  1. SAN depolarises
  2. Impulses spreads through atria
  3. Held up at AVN (want atria to finish contraction)
  4. Spreads to ventricle via Bundle of His (endocardium to epicardium)
  5. Spreads rapidly down R and L bundles and purkinje system (septum is depolarised first)
  6. Myocytes of intra-ventricular septum depolarised first
  7. Apex and RV and LV free walls are depolarised next
  8. Base of the ventricles are last to be depolarised
  9. Repolarisation of the ventricles happens in the reverse order
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5
Q

How do we see negative and positive complexes on an ECG?

A

If the signal is going from negative to positive then it will give a positive complex (ie a Hill) and then the reverse for a negative complex (a trough)

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6
Q

How are negative and positive complexes formed on an ECG during repolarisation?

A

If the signal goes form positive to negative you get a negative complex and vice versa

*it is the opposite of depolarisation

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7
Q

When viewing electively activity form the apex of the heart, what causes the difference in the size of the positive and negative complexes and why, at points, would you see both together?

A

If the depolarisation/repolarisation is heading in the same direction as the electrodes then the peaks/troughs will increase in size

Movement at 90 degrees gives both positive and negative complexes

(Ie if the depolarisation wave is going directly away from the electrode- +ive to -ive then you see a large trough)

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8
Q

Where is SAN located?

A

In the top right hand corner of the RA

Near junction of SVC and RA

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9
Q

Why does the SAN depolarisation not register on an ECG?

A

Because the signal is insufficient

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10
Q

What is the P wave of an ECG?

A 
Atrial depolarisation 
(Spreads along atrial muscle fibres and internodal pathways

This is a small positive complex because the movement is towards the positive electrode

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11
Q

What is the point of the delay of signal at the AV node?

A

Allows time for atrial contraction to fill ventricle

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12
Q

What separate the atria and ventricles in electrical terms? How is this bridged?

A

A fibrous ring

Bundle of His bridges the gap between them

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13
Q

What makes up the flat line after the p wave on an ECG?

A

The AVN impulse delay and the depolarisation of the Bundle of His

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14
Q

How does the intra-ventricular septum depolarise? (In which direction)
How is this seen on an ECG?

A

From left to right

Produces a small downward deflection (called the Q wave) because the signal is moving away from the positive electrode but not directly towards the negative electrode so the negative complex is only small

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15
Q

What causes the R wave seen on an ECG?

A

The depolarisation of the apex and free ventricular wall

The signal is moving directly towards the positive electrode so there is a large positive complex (large becuase large muscle mass-more electrical activity)

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16
Q

In what situation will the R wave be even taller than normal?

A

If LV was hypertrophied

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17
Q

What causes the s wave of the QRS complex of an ECG?

A

The depolarisation of the base of the ventricles

Signal going away from positive electrode so negative complex is formed

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18
Q

What surface does repolarisation occur from?

A

Begins on epicardial surface

Spreads in opposite direction to depolarisation

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19
Q

What causes the T wave of the ECG?

A

Ventricular repolarisation

Because signal is towards the negative electrode then we see a positive complex (medium wave)

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20
Q

What is the QRS wave representing?

A

Ventricular depolarisation (NOT CONTRACTION)

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21
Q

When recording an ECG how many electrodes are there and where do they go? How many views/leads does this give of the heart?

A

10 electrodes: 4 on limbs, 6 on chest

Gives 12 views/leads

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22
Q

What are the 6 limb leads?

A 
aVR
aVF
aVL
I
II
III
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23
Q

Which limb leads are best for looking at the inferior surface of the heart?

A
  • aVF
  • II
  • III
24
Q

Which limb leads are best for looking at the lateral LV?

A
  • I

- aVL

25
Q

In what plane do the chest leads view the heart?

A

Transverse plane

26
Q

What are the septal leads?

A

V1 and V2

27
Q

What are the anterior leads?

A

V3 and V4

28
Q

What are the lateral leads?

A

V5 and V6

29
Q

What does lead V1 face?

A

RV and septum

30
Q

What does lead V2 face?

A

RV and septum

31
Q

What does lead V3 face?

A

Apex and anterior wall of ventricles

32
Q

What does lead V4 face?

A

Apex and anterior wall of ventricles

33
Q

What does lead V5 face?

A

LV

34
Q

What does Lead V6 face?

A

LV

35
Q

Why does lead V1 show a negative complex during ventricular depolarisation even though there is electrical signal coming towards it?

A

The ventricular walls depolarise simultaneously and the electrical signals recorded look at the sum of the opposing effects in the 2 ventricles. LV is much thicker so determines curve and the LV depolarisation is moving away from V1 so it creates a negative complex

36
Q

What is the normal ECG paper speed?

A

25 mm/sec

25 small squares=1 second

5 large squares = 1 second

37
Q

If 5 large boxes= 1 second, how long is 1 large square? And how long is 1 small square?

A

1 large square = 1/5 of a second= 0.2 seconds (200ms)

1 small square =1/5th of 0.2 seconds= 0.04 seconds (40 ms)

38
Q

How many squares on an ECG chart represent 6 seconds and then 1 minute?

A

6 sec= 30 large squares

1 min= 300large squares

39
Q

How do you calculate heart rate from an ECG?

A

Count the number of large boxes between complexes (easier to count R-R intervals)

How many complexes could be fitted into 300 large boxes (ie in 1 minutes?)
Eg 300/(number of large boxes you count) = HR

Eg 300/4=75 bpm

40
Q

How do you calculate the heart rate if rhythm is irregular?

A

Count the number of QRS complexes in 6 seconds (30 large boxes), then x by 10

*this method can be used for regular heart rhythms too

41
Q

How long should the PR interval be?

A

0.12-0.20 seconds

Or

3-5 small boxes

Prolonged if >1 large box

**PR interval starts just before the P wave and just ends just before the Q wave

42
Q

How long should the QRS complex be?

A

<0.12 seconds

Or

<3 small boxes

Prolonged=might show ischaemic bundle of His or purkinje fibres

43
Q

How long should the QT interval be?

A

Varies with heart rate

Show us how long the heart is taking to repolarise

Upper limits are:
0.45/0.47 (m/f) seconds

Or

11-12 small boxes

44
Q

What is normal sinus rhythm?

A

Depolarisation is initiated by SA node

The bottom strip of an ECG gives the rhythm- reading from apex

45
Q

How do you determine if a heart beat is in sinus rhythm?

A
  • is the rhythm regular?
  • heart rate? (60-100)
  • are there p waves (shows that sinus node has depolarised)
  • are P waves upright in leads I and II?

-is PR interval normal? (3-5 small boxes)

  • every P wave followed by QRS?
  • every QRS preceded by a P wave?

-normal QRS width (<3 small boxes)

46
Q

It is possible to be in sinus rhythm with a heart rate outside of 60-100bpm?

A

Yes, it is call sinus bradycardia or sinus tachycardia

47
Q

What causes the normal delay between the P wave and the QRS complex?

A

AVN delay

48
Q

Which might cause a prolonged PR interval? (6)

A

Prolonged PR-AV block

AV nodal disease
Enhanced vagal tone
Myocarditis 
Acute myocardial infarction 
Electrolyte disturbances
Medication
49
Q

What does the QT interval show?

A

Ventricular depolarisation and repolarisation

50
Q

What forms the inferior border of the heart and which coronary artery usually supplies this region?

A

RV

Right marginal artery

51
Q

NB:

A

QT interval gets shorter with increasing heart rate and to assess this accurately it needs to be corrected for heart rate

52
Q

Why are leads II and aVR ECG traces all but mirror images of one another?

A

Because they’re travelling in opposite directions but aren’t quite going in the same plane

53
Q

Why, when looking at different leads on an ECG, will the deflections be smaller/bigger?

A

Because the leads are looking from different angles so the depolarisation that they experience may be bigger/not as big

54
Q

What region of the heart face the anterior of the chest wall?

A

RV, septum and little bit of the LV

55
Q

What coronary artery supplies the anterior aspect of the heart?

A

LAD (left anterior descending)

Cardiovascular System (Milly's) (28 decks)

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