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Internal Med 2023 > Understanding an ECG > Flashcards

Understanding an ECG Flashcards

1
Q

p waves represent

A

atrial depolarisation

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2
Q

in healthy individuals there should be a p wave

A

preceding each QRS complex

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3
Q

the QRS complex looks. like

A
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4
Q

what is the PR interval

A

begins at the start of P wave and ends at the beginning of the Q wave

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5
Q

what does the PR interval reppresent

A

time taken for electrical activity to move between the atria and the ventricles

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6
Q

what does the QRS complex represent

A

represents the depolarisation of the ventricles

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7
Q

what is the ST segment

A

starts at the end of the S wave and begins at the beginning of the T wave

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8
Q

what does the ST segment represent

A

the ST segment is an isoelectric line representing the time between depolarisation and repolarisatiion of the ventricles (ie. ventricular contractions

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9
Q

what is the T wave

A

the T wave represents ventricular repolarisation
it appears as a small wave after the QRS complex

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10
Q

what is the RR interval

A

the RR interval begins at the peal of one R wave and ends at the peak of the next R wave

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11
Q

what does the RR interval represent

A

the time between two QRS complexes

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12
Q

what is the QT interval

A

begins at the start of the QRS complex and finishes at the end of the T wave

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13
Q

what does the QT interval represent

A

the time taken fo the ventricles to depolarise and then repolarise

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14
Q

where is the PR interval

A

begins at the start of P wave and ends at the beginning of the Q wave

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15
Q

where is the PR interval

A

begins at the start of P wave and ends at the beginning of the Q wave

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16
Q

each small square represents

A

0.04 seconds

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17
Q

each large square represents

A

0.2 seconds

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18
Q

5 large squares represents

A

1 second

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19
Q

300 large squares represent

A

1 minute

20
Q

what is an ECG electrode

A

a conductive pad that is attached to the skin to record electrical activity

21
Q

what is an ECG lead

A

a graphical representation of the heart’s electricaal activity which is calculated by analysing data from several ECG electrodes

22
Q

how does a 12-lead ECG works

A

records 12 leads, producing 12 separate graphs on a piece of paper
only 10 physical electrodes are attached to the patient to generate the 12 leads
there are 6 chest electrodes and 4 limb electrodes

23
Q

what are the chest leads

A

V1: septal view of the heart
V2: septal view of the heart
V3: anterior view of the heart
V4: anterior view of the heart
V5: lateral view of the heart
V6: lateral view of the heart

24
Q

what are the other leads

A

lead I: lateral view (calculated by analysing activity between the RA and LA electrodes)
lead II: inferior view (calculated by analysing activity between the RA and LL electrodes)
lead III: inferior view (calculated by analysing activity between the LA and LL electrodes)
aVR: lateral view (calculated by analysing activity between LA+LL -> RA)
aVL: lateral view (calculated by analysing activity between RA+LL -> LA)
aVF: inferior view (calculated by analysing activity between RA+LA -> LL)

25
Q

if the R wave is greater than the S wave

A

it suggests depolarisation is moving towards that lead

26
Q

If the s wave is greater than the R wave

A

depolarisation is moving away from the lead

27
Q

if the R and S waves are of equal size

A

depolarisation is travelling at exactly 90° to that lead

28
Q

what is a deflection

A

when the electrical activity within the heaart travels towards a kead you get positive deflection
when electrical activity travels away from the lead you get negative deflection
the height of the deflection (wave) on the ECG represents the amount of electrical activity flowing in that direction (toward the lead)

29
Q

how do you localise pathology using ECG

A

leads represent anatomical territory

30
Q

which leads show the inferior view of the heart

A

II, III, aVF

31
Q

which leads show the lateral view of the heart

A

I, aVL, aVR, V5, V6

32
Q

which leads show the anterior view of the heart

A

V3, V4

33
Q

which leads show the septal view of the heart

A

V1, V2

34
Q

in healthy individuals, how does electrical activity flow

A

begins at the sinoatrial node then spread to the atrioventricular (AV) node
it then spreads down the bundle of His and then Purkinje fibres to cause ventricular contraction

35
Q

how is a positive deflection produced

A

when electrical activity moves towards a lead

36
Q

how is negative deflection produced

A

when electrical activity moves away from a lead

37
Q

the cardiac axis

A
38
Q

in healthy individuals, what is the normal cardiac axis

A

between -30° and +90°

39
Q

where should you see a positive deflection

A

the overall direction of electrical activity is towards leads I, II, III, therefore you should see a positive deflection in all of these leads, with lead 2 showing the most positive direction

40
Q

where should you see a negative deflection

A

in the aVR lead
due to the aVR providing a viewpoint of the heart from the opposite direction

41
Q

what is right axis deviation

A

Right axis deviation (RAD) involves the direction of depolarisation being distorted to the right (between +90º and +180º)

42
Q

what causes right axis deviation

A

The most common cause of RAD is right ventricular hypertrophy. Extra right ventricular tissue results in a stronger electrical signal being generated by the right side of the heart. This causes the deflection in lead I to become negative and the deflection in lead aVF/III to be more positive.

43
Q

what is right axis deviation associated with

A

RAD is commonly associated with conditions such as pulmonary hypertension, as they cause right ventricular hypertrophy. RAD can, however, be a normal finding in very tall individuals.

44
Q

what does right axis deviation look like

A

the deflection in lead 1 is more negative and the deflection in lead aVF/III is more positive

45
Q

what does left axis deviation look like

A

Left axis deviation (LAD) involves the direction of depolarisation being distorted to the left (between -30° and -90°). This results in the deflection of lead III becoming negative (this is only considered significant if the deflection of lead II also becomes negative).

46
Q

what causes left axis deviation

A

LAD is usually caused by conduction abnormalities.

Internal Med 2023 (52 decks)

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