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Cardiovascular system > ECG theory and practice > Flashcards

ECG theory and practice Flashcards

1
Q

What is detected by an ECG?

A

The extracellular current of the myocytes on the skin surface

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2
Q

How many electrodes are used to perform a 12-lead ECG?

A

10

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3
Q

What is an ECG lead?

A

An imaginary line (Lead axis) between 2 or more electrodes, it is NOT the wire that connects the electrode to the recording device

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4
Q

Which electrode acts as a recording electrode?

A

The positive electrode

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5
Q

What is represented by an upward deflection on an ECG?

A

The movement of depolarisation towards the recording electrode or depolarisation away from the recording electrode

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6
Q

What is represented by a downward deflection on an ECG?

A

The movement of depolarisation away from the recording electrode

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7
Q

What is represented by an isoelectric line?

A

No wave of depolarisation

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8
Q

What are the 3 standard limb leads?

A

Lead I - RA (-ve) to LA (+ve)
Lead II - RA (-ve) to LL (+ve)
Lead III - LA (-ve) to LL (+ve)

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9
Q

Which electrode is placed on the right leg?

A

A neutral, earthed electrode

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10
Q

Which electrodes form Einthoven’s triangle?

A

Right Arm
Left Arm
Left Leg

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11
Q

What causes the appearance of the P wave in a Lead II ECG?

A

Atrial depolarisation spreads from the SA node, inferiorly and to the left, so it moves towards the recording electrode (Left Leg) and so shows an upward deflection

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12
Q

What causes the appearance of the Q wave in a Lead II ECG?

A

Left to right depolarisation of the intraventricular septum, which moves slightly away from the recording electrode (Left Leg) and so shows a slight downwards deflection

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13
Q

What causes the appearance of the R wave in a Lead II ECG?

A

Depolarisation of the main ventricular mass, which moves towards the recording electrode (Left Leg) and so shows a large upwards deflection

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14
Q

What causes the appearance of the S wave in a Lead II ECG?

A

Depolarisation of the ventricles at the base of the heart, moving slightly away from the recording electrode (Left Leg) and so shows a slight downwards deflection

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15
Q

What causes the appearance of the T wave in a Lead II ECG?

A

Ventricular depolarisation, which moves away from the recording electrode. This has an opposite effect to depolarisation and so shows an upwards deflection on the ECG

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16
Q

What is a normal QRS duration?

A

<0.1 seconds

17
Q

What is the normal P wave duration?

A

0.08 - 0.1 seconds

18
Q

What is the normal PR interval duration?

A

0.12 - 0.2 seconds

19
Q

What is the normal QT interval duration?

A

0.36 - 0.44 seconds at 60bpm

20
Q

What are the 3 types of leads?

A

Bipolar limb leads
Augmented limb voltage leads
Chest leads

21
Q

What are the 3 types of augmented voltage leads?

A

aVR (Right arm +ve)
aVL (Left arm +ve)
aVF (Left Food +ve)

22
Q

What are the 6 chest leads?

A

V1
V2
V3
V4
V5
V6

23
Q

What leads give a coronal plane view of the heart?

A

I
II
III
aVR
aVL
aVF

24
Q

What leads give a transverse plane view of the heart?

A

V1 - V6

25
Q

In what direction do the limb leads and augmented voltage leads record?

A
26
Q

What is the name given to the system comprising of the 3 bipolar limb leads and 3 augmented voltage leads?

A

Hexaxial reference system

27
Q

Which leads are lateral leads?

A

Lead I and aVL

28
Q

Which leads are inferior leads?

A

II, III and aVF

29
Q

Where should the 6 chest leads be placed?

A

V1 = 4th intercostal space, immediately right of sternum
V2 = `4th intercostal space, immediately left of sternum
V3 = Mid-way between V2 and V4
V4 = 5th intercostal space at mid-clavicular line
V5 = Same horizontal level as V4 at anterior axillary line
V6 = Same horizontal level as V4 at mid-axillary line

30
Q

What colour is the right arm electrode?

A

Red (R)

31
Q

What colour is the left arm electrode?

A

Yellow (L)

32
Q

What colour is the left leg electrode?

A

Green (F)

33
Q

What colour is the right leg electrode?

A

Black (N)

34
Q

To what level should an ECG be calibrated?

A

25mm/second on the time (x) axis
10mm/1mV on the amplitude (y) axis

35
Q

How can you calculate heart rate from an ECG?

A

HR = 300 ÷ Number of big squares between R waves

36
Q

What is the ECG rhythm strip?

A

A prolonged section of an ECG, usually from Lead II

37
Q

What are some examples of conditions that may not show up on an ECG?

A

Myocardial infarction
Intermittent rhythm disturbances
Stable angina

38
Q

What 7 questions should you ask yourself when looking at an ECG?

A
  1. Is electrical activity present?
  2. Is rhythm regular or irregular?
  3. What is the heart rate?
  4. Are P-waves present?
  5. What is the PR interval? (Average 3-5 small squares)
  6. Is each P-wave followed by a QRS complex?
  7. Is the QRS duration normal? (< 2.5 small squares)

Cardiovascular system (45 decks)

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