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Cardiovascular > Interpreting ECGS: Lecture 1 > Flashcards

Interpreting ECGS: Lecture 1 Flashcards

1
Q

Define depolarisation

A

Change within cell of electric charge distribution leading to a less negative charge inside the cell. This happens through movement of ions eg Na+ , K+ , Ca2+

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2
Q

Define repolarisation

A

Change within cell of electric charge distribution leading to more negative charge inside cells.

This happens through movement of ions - Na+ , K+ , Ca2+

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3
Q

What does the resting membrane potential measure ?

A

How much more negative the inside of the cell cell compared with the outside.

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4
Q

How does propagation of cell depolarisation spreads from cell to cell ?

A

X

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5
Q

How does the electrical activity spread throughout the heart at tissue level ?

A
  1. Pacemaker cells located within the SA node depolarise , generating an electrical impulse which spreads across the atria and causes the atria to contract.
  2. There is a fibrous band of tissue ( Annulus fibrosis) that separates the atria from the ventricles. This prevents the impulse from spreading directly to the ventricles.

3, instead the impulse reaches the AV node which is located between the atria ( INTER- ATRIAL SEPTUM)

4, the Av node delays the pulse for a short period of time before transmitting the impulse down the Bundle of His.

  1. The bundle of his divides into the right bundle branch which travels along the right side of the inter ventricular septum. And the left bundle branch which travels along side the left side of the inter ventricular septum.
  2. The right and left bundle branch terminate into the extensive network of Purkyne fibres which would depolarise the ventricles.
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6
Q

Which has a faster rate of depolarisation- the SAN or the AVN ?

A

The SAN has the fastest rate of depolarisation in the heart.

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7
Q

What is the intrinsic firing rate of the SAN ?

A

60-100 times / minute

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8
Q

What is the intrinsic firing rate of the AVN ?

A

40-60 times / minute

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9
Q

What is the intrinsic firing rate of the left bundle and right bundle branch ?

A

20-40 times / minute

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10
Q

What does an ECG measure ?

A

Changes in electrical potential produced in successive areas of myocardium during the cardiac cycle - measures and records these changes over time.

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11
Q

What do we use to measure an ECG ?

A
  1. An electrode which is a conductive pad that attaches to the skin and enables recording of electrical currents.
  2. Leads : which is a cable used to connect the electrode to the ECG recorder. BUT a lead ALSO means the electrical view of the heart obtained from any one combination of electrodes.
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12
Q

When recording an ECG , how many electrodes and cables do we use ? And how many views does this produce ?

A

10 electrodes ( 6 on the chest and 4 on the limbs )

Connected by 10 cables to ECG machine

This gives us 12 VIEWS / LEADS

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13
Q

What does limb lead 1 measure the voltage difference between ?

A

Voltage difference between the electrode on the right arm and left arm. The positive electrode is on the left arm.

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14
Q

What dies limb lead 11 measure the voltage difference between ?

A

Voltage difference between right arm and left leg. The positive electrode is on the left leg.

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15
Q

What does limb lead 111 measure the voltage difference between ?

A

The voltage difference between electrode on the left arm and left leg. The positive electrode is placed on the left leg.

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16
Q

What is important about the right leg electrode ?

A

It is a grounding electrode - it is it actually used for any views/leads.

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17
Q

Are limb leads 1,11,111 unipolar or bipolar ?

A

They are bipolar because they have both positive and negative electrodes.

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18
Q

What is different between the augmented limb leads and limb leads 1,11,111 ?

A

Augmented limb leads are unipolar - they only have a positive electrode

19
Q

What are augumented limb leads ?

A

They are termed unipolar leads because they have a single positive electrode that is. Referenced against combination of the other limb electrodes.

The positive electrodes for these augmented leads are located on the : aVl ( Left arm ) , aVR ( right arm ) and the aVf ( left leg / foot)

20
Q

Depolarisation spreading towards a positive electrode would yield what type of deflection ?

A

Upward deflection from the isoelectric point.

21
Q

Depolarisation spreading away from the positive electrode would yield what type of deflection ?

A

Downwards deflection

22
Q

Repolarisation spreading towards a positive electrode would yield what type of deflection ?

A

Downwards deflectiom

23
Q

Repolarisation spreading away from a positive positive electrode would yield what type of deflection?

A

Upwards

24
Q

Using a view from ECG lead 11 , what does the P wave represent ? And outline why there is an upwards deflection ?

A

P wave represents depolarisation of the atria.

  • this is where the electrical impulses spread along the atrial muscle fibres and intermodal ( between SA -AV nodes) pathways.
  • the direction of impulses is downwards and to the left - towards the AV node.
  • this produces a small upwards deflection because the electrical impulses are travelling towards the positive electrode ( Left Leg).
  • this lasts 80-100 ms.
25
Q

Using a view from ECG lead 11 , what does the isoelectric segment after the P wave indicate ?

A

The delay at the AV node.

This allows time for atrial contraction to fill the ventricles.

26
Q

What produces the downwards deflection ( Q wave) using an ECG view of lead 11 ?

A

Depolarisation of the interventricular septum

There is a downwards deflection because electrical impulses are not moving straight towards the positive electrode - some depolarisation spreads from the left to the right septum.

27
Q

Using a view from ECG lead 11, what produces the large upwards deflection - termed the R wave ?

A

Upwards because depolarisation moving Directly towards the positive electrode ( LL ) as the apex and free ventricular walls become depolarised.

R wave larger than other waves because there is large muscle mass therefore more electrical activity.

28
Q

Using a view from ECG lead 11, why does depolarisation of the ventricles produce a small downwards defection - known as the S wave

A

Downwards deflection because the electrical impulses are moving away from the positive electrode as they move upwards to the top of the ventricles.

29
Q

Using a view from ECG lead 11 , why is. There an upwards deflection for the repolarisation of the ventricles ?

A

Because it is a wave of repolarisation moving away from the positive electrode. When repolarisation moves away from lead produces upwards deflection.

This is termed the T wave

30
Q

What does the T wave indicate ?

A

Ventricular repolarisation

But relaxation of the ventricles immediately follows the T wave.

31
Q

Leads 11, 111 and AVF are best at looking at what view of the heart ?

A

INFERIOR surface of the heart

AND

Muscle necrosis due to occlusion of the right coronary artery.

32
Q

Leads 1 ,aVL , V5 and V6 are best at looking at what view of the heart ?

A

Lateral wall of the left ventricle..

Muscle necrosis due to occlusion branch left coronary artery - lateral wall MI.

33
Q

Where do we place the chest electrodes ?

A

V1 = fourth intercostal space ( right)

V2 = 4th intercostal space ( left )

V3 = in between the V2 and V4

V4 = 5th Left intercostal space ( mid clavicular )

V5 = between V4 and V6

V6= 5th intercostal left space : mid axillary line.

34
Q

What is the mnemonic to remember the colour of the limb leads ?

A

RIDE ( red limb lead for right upper limb )

YOUR ( yellow limb lead for left upper limb )

GREEN ( green limb lead for lower left limb)

BIKE ( black limb lead for right lower limb)

35
Q

Chest leads V5 and V6 are good at giving us what view of the heart ?

A

Lateral left view of the heart

36
Q

Which ECG leads give the view of the apex and anterior surface of the ventricles ?

A

V3 and V4

37
Q

Which ECG leads give a view of the septum and right ventricle ?

A

V1 , V 2 and AVR

38
Q

How many large boxes represent 60s?

A

300 large boxes = 60s

39
Q

How to calculate heart rate if the rhythm is regular ? ( ie. the R-R intervals are consistently the same )

A

If 300 boxes = 60s

You count the number of boxes between R-R peaks. You then do 300 divided by the number of boxes between R-R. This should give you heart rate.

If there was 1 box and 4 mini boxes - you would do 300/1.8. This is because If 1 Box = 5 mini boxes then 4 mini boxes would mean 0.8 Boxes. So 1.8.

40
Q

How to calculate the heart rate is the rhythm is irregular ?

A

REMEMBER: 39 large boxes in 6s.

You have to count the number of QRS complexes in 6s.

You then multiply the number of QRS complexes by 10. This will give you the total heart beats in 60s.

41
Q

What is the P-R interval ?

A

Start of the P Wave to the start of the Q wave.

It is usually 3-5 small boxes. It is prolonged if it is greater than one large box.

42
Q

What is the QRS. Interval ?

A

Start of the Q wave to the end of the S wave.

Wider QRS complexes are assosiated with ventricular depolarisations that are not initiated by the normal conductance mechanisms (His-purkyne system)

Normal = less than 3 small boxes.

43
Q

What is the QT interval ?

A

Start of the Q wave to the end of the T wave.

Prolonged QT interval indicates prolonged ventricular repolarisation

Longer than 11 small boxes

Cardiovascular (18 decks)

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