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CVS > 12. ECG Methods > Flashcards

12. ECG Methods Flashcards

1
Q

What is the difference between cables/wires and leads?

A
  • Cables/wires - connects electrodes to the device

* Leads - digital representation of the changes of depolarisation in the heart

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2
Q

What is the deflection on an ECG is an impulse is moving towards an anode or a cathode?

A
  • Anode - positive deflection

* Cathode - negative deflection

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3
Q

Why does the ECG look at many views?

A
  • Sometimes the impulse is moving at a right angle to the electrodes
  • This shows no deflection
  • Looking at different views allows you to see these impulses
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4
Q

What does the steepness of a line and sharpness of turns show?

A
  • Steepness - velocity of action potential

* Sharpness - denotes rapid changes in direction of action potential

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5
Q

What is the main lead and why?

A
  • Lead II
  • From Right Arm to Left Leg
  • Angle of lead is roughly the same as the angle of the heart
  • Deflections will be large
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6
Q

Why does the SAN only produce a small deflection?

A
  • Small amount of muscle (autorhythmic myocytes)

* P wave

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7
Q

Why does the AVN lag the impulse?

A
  • Prevents the impulse from immediately going to the ventricles
  • Allows the atria to empty so the ventricles can fill as much as possible
  • Limits the rate of contraction for ventricles too
  • Isoelectric ECG (flat line)
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8
Q

What is the line on the ECG at the Bundle of His?

A
  • Short isoelectric ECG just before QRS (PR segment)
  • Rapid conduction
  • Insulated
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9
Q

What happens at the bundle branches and how is this represented on the ECG?

A
  • Common bundle branch splits into left and right bundle branches
  • Heavily insulated
  • Insulation on the LEFT bundle branch terminates - some impulses escape
  • Ventricular septum is exposed to the impulse and depolarises
  • This wave of depolarisation moves from the bottom up through the septum - towards the negative electrode
  • Small amount of muscle
  • Fast
  • Short, sharp downwards spike on ECG - Q wave
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10
Q

What happens at the Purkinje fibres before the apex and how is this represented on the ECG?

A
  • Ventricular depolarisation
  • Quickl depolarisation - muscle can contract simultaneously for efficient contraction
  • Towards positive electrode - positive deflection - R wave
  • Large deflection due to large amount of muscle at the apex
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11
Q

What happens at the Purkinje fibres after the apex and how is this represented on the ECG?

A
  • Late ventricular depolarisation
  • Ventricles contract up the sides
  • Towards negative electrode - negative deflection - S wave
  • Less muscle - smaller deflection
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12
Q

What happens on the ECG when the ventricles are fully depolarised and why?

A
  • Isoelectric ECG (ST segment)

* Muscle fibres are in tetany - contracted

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13
Q

What happens on the ECG during repolarisation and why?

A
  • Ventricle repolarisation allows ventricles to relax
  • Opposite direction to contraction - positive deflection
  • T wave
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14
Q

Why do you not see atrial repolarisation on an ECG?

A
  • Same time as the ventricle contraction

* More muscle mass in ventricles - hides the repolarisation on the ECG

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15
Q

Why does Lead II usually have a longer recording?

A
  • Look for anomalies

* May not occur on every heartbeat

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16
Q

How many leads are there?

A

12

17
Q

What does LCx, RCA and LAD stand for?

A
  • Left Circumflex Artery
  • Right Coronary Artery
  • Left Anterior Descending Artery
18
Q

What is Lead I, II and III?

A

I - right arm to Left arm (1 L)
2 - right arm to Left Leg (2 Ls)
3 - Left arm to Left Leg (3 Ls)

All form ‘Einthoven’s Triangle’ with the heart in the centre

19
Q

Where are the chest leads attached (in order)?

A
  • V1 - right sternal border, 4th intercostal space
  • V2 - left sternal border, 4th intercostal space
  • V4 - mid-clavicular line, 5th intercostal space
  • V5 - anterior axillary line, level of V4
  • V6 - mid-axillary line, level of V4
  • V3 - halfway between V2 and V4
20
Q

How are unipolar leads different from bipolar leads, and which ones are unipolar?

A

• Unipolar - one physical electrode compared to a virtual electrode
- augmented leads
- chest leads
• Bipolar - two physical electrodes compared

21
Q

What is the PR, ST and QT interval?

A
  • PR interval - start of the P wave to the last isoelectric part before Q deflection
  • ST interval - start of isoelectric segment after S to the end of the T wave
  • QT interval - start of Q deflection to the end of the T wave
22
Q

If one square on an ECG is 0.04s, how long is one big square?

A

0.2s

23
Q

How many milliseconds is 0.04s?

A

40ms

24
Q

What do you need to work out the QRS axis?

A
  • 2 leads

* 90 degrees apart

25
Q

What are the 3 augmented leads and in which direction do they point from the heart?

A
  • aVF - downwards from the heart
  • aVR - 120° (to the top right of the heart) from aVF
  • aVL - 120° (to the top left of the heart) from aVF
  • All point at a coronal view
26
Q

Which Lead is at 0°?

A

Lead I (horizontal from the left of the heart) - reference point

27
Q

At what angle are aVL, Lead II, aVF and Lead III to the reference point?

A
  • aVL: -30°
  • Lead II: 60°
  • aVF: 90°
  • Lead III: 120°
28
Q

How many degrees apart are Lead II and aVL?

A

90°

29
Q

How do you measure net deflection on Lead II?

A
  • Measure positive deflection (Q to the start of the S downward deflection)
  • Take away the negative deflection (start of the negative S deflection down to S)

• e.g. positive = +6.5mm, negative = -2mm, so net = +4.5mm

30
Q

How do you measure net deflection on Lead aVL?

A
  • Measure positive deflection on left side of the complex

* Take away the negative deflection on the right side of what seems to be the S deflection

31
Q

What is the QRS axis (cardiac axis) if the Lead II net deflection is +4.5mm and aVL net deflection is +2mm?

A
  • +4.5 is on the Lead II heart vector (adjacent)
  • +2 is towards aVL (opposite)
  • Tan θ = 2 / 4.5
  • θ = tan^−1
  • θ = 36°
  • So the QRS axis is 36°
32
Q

What is the normal range for cardiac axis?

A

-30° to 90°

CVS (21 decks)

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