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Cardio Med Res 2 > ECG pt.2 > Flashcards

ECG pt.2 Flashcards

1
Q

How many electrodes are used in ECG?

A

Standard ECG is done by putting 10 electrodes, 6 on the chest (horizontal/transverse plane) and 4 on the extremities (Vertical plane) which allows recording of the ECG signal on 12 leads

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2
Q

Where are the electrodes placed on the chest?

A

V1: Placed in the 4th right intercostal space at the sternal border (parasternal line)
V2: Placed in the 4th left intercostal space at the sternal border (parasternal line)
V3: Placed halfway between V2 and V4
V4:Placed in the 5th left intercostal space in the midclavicular line
V5: Placed in the anterior axillary line (AAL) at the same horizontal plane as V4 (just more lateral)
V6: Placed in the midaxillary line (MAL) at the same horizontal plane as V4

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3
Q

Name of peripheral leads and where are they positioned

A

Lead 1/D1 = right arm and left arm (the axis is directed toward the positive electrode)
* Lead 2/D2 = right arm and left foot
* Lead 3/D3 = left arm and left foot
* AVL = left arm
* AVR = right arm
* AVF = foot
In fact, the active electrodes of the peripheral recording
are only 3 (right arm, left arm and left foot)

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4
Q

Axes of peripheral leads

A

Based on an orthogonal system of axes (axis is directed towards positive electrode):
Lead D1 corresponds to an axis of 0° (x axis, horizontal)
Lead D2 corresponds to an axis of 60°
Lead D3 corresponds to an axis of 120°
aVR: 210°
aVL: 330° (or -30°)
aVF: 90° (perpendicular to D1)

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5
Q

Orthogonal system of axes

A

Axis system in which the lines of the leads pass through the electrical center of the heart

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6
Q

What does the signal direction on an ECG depend on?

A
  • What we record in each lead at any time depends on
    the projection of the ECG signal on each lead
  • If the ECG signal generated by the heart is projected on the positive part of the lead we have a positive wave = directed upward on the recording of the ECG
  • If the ECG signal generated by the heart is projected on the negative part of the lead we will have a negative wave = directed downward on ECG recording
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7
Q

Difference electrical measurement (plane) between leads on the chest and leads on the extremities

A

These leads record the projections of the cardiac electrical activity on a horizontal plan
whereas the peripheral leads record it on a frontal plane.

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8
Q

What are the leads on the chest called?

A

Precordial lead

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9
Q

Types of peripheral leads

A

Peripheral (limb) bipolar leads and peripheral (limb) unipolar leads

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10
Q

How many electrodes does each lead use?

A
  • First 3 leads use 2 electrodes, 1 negative and 1 positive making them bipolar leads
  • Last 3 leads only use positive electrodes, making them unipolar leads
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11
Q

Describe a wave on ECG formed by depolarization heading towards a positive electrode

A

Upward spike

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12
Q

Describe a wave on ECG formed by depolarization heading away from a positive electrode

A

Downward spike

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13
Q

Describe a wave on ECG formed by repolarization heading away from a positive electrode

A

Upward spike

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14
Q

When would see a flat line on an ECG

A
  • No net movement of electrical activity
  • Electrical activity moving perpendicular to the axis
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15
Q

Why would see a downwards spike in Q wave in V2?

A
  • Left bundle of his depolarizes the interventricular septum (axis is thus moving to the left and slightly upward, so kind of a superolateral axis moving to the left)
  • This makes the axis of activation move slightly away from the positive electrode and thus the downward spike
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16
Q

Why is the ST segment flat?

A

All of the ventricle is already depolarized so there is no net movement of electrical charges happening at this point, thus the flat line

17
Q

P wave amplitude direction with different leads

A

The P wave must be positive meaning directed upwards in D1, D2 and aVF
* Negative in lead aVR
* Positive in all precordial leads apart from V1 which is usually biphasic (small
initial positive wave followed by a small negative wave)

18
Q

QRS complex wave amplitude direction with different leads?

A
  • Mainly positive in ⇢ leads D1, D2, aVF
    Negative ⇢ in aVR
  • A progressive increase from V1 to V6 of the positive wave (R wave)
  • A progressive reduction from V1 to V6 of the negative wave (S wave
  • Therefore:
    In V1-V2 ⇢ predominance of S waves (negative)
    In V5-V6 ⇢ predominance of R waves (positive)
    In V3-V4 ⇢ we can have intermediate aspects (since we have a progressive increase of R wave and a progressive decrease of the S wave)
18
Q

QRS complex wave amplitude direction with different leads?

A
  • Mainly positive in ⇢ leads D1, D2, aVF
    Negative ⇢ in aVR
  • A progressive increase from V1 to V6 of the positive wave (R wave)
  • A progressive reduction from V1 to V6 of the negative wave (S wave
  • Therefore:
    In V1-V2 ⇢ predominance of S waves (negative)
    In V5-V6 ⇢ predominance of R waves (positive)
    In V3-V4 ⇢ we can have intermediate aspects (since we have a progressive increase of R wave
    and a progressive decrease of the S wave)
19
Q

T wave amplitude direction with different leads

A

Always positive in ⇢ D1, D2, aVF
Always negative in ⇢ aVR
Always positive in ⇢ V3,V4,V5,V6
Negative in ⇢ V1

20
Q

Normal P wave height and width

A

Generally <0.12 sec (three small boxes) and the amplitude <0.25 mv (2.5 small boxes)

21
Q

Normal PR interval duration

A

0.12 to 0.20 s (3 - 5 small squares)

22
Q

QRS interval duration

A

0.06 to 0.10 sec (1.5 to 2.5 small boxes) and is not influenced by heart rate

23
Q

What does the R wave represent?

A

It represents depolarization of the left ventricular myocardium. Right ventricular depolarization is obscured because the left ventricular myocardial mass is much greater than that of the right ventricle

24
Q

What does the S wave represent?

A

Represents terminal depolarization of the high lateral wall

25
Q

What is ventricular systole represented by in ECG?

A

QT interval

26
Q

What is diastole represented by?

A

Period that goes from the end of the T wave to the onset of the subsequent QRS

27
Q

QT interval duration

A

The QT (or JT) interval is dependent upon the heart rate; it is shorter at faster heart rates and longer when the rate is slower

28
Q

Formula used to calculate QT interval

A

Many formulas exist, most frequently used is Bazett formula

29
Q

Bazett formula equation

A
  • QTc = QT interval / square root of the RR interval (both measured in seconds); or equivalently
  • QTc = QT interval / square root of (RR interval/1000) (both measured in milliseconds)
  • QTc = QT interval / square root of the RR interval (in seconds)
30
Q

Normal corrected QT interval

A

a corrected QT interval >460 msec in men and >470 in
women is considered prolonged
* a corrected QT interval <330(M)/340 (F) msec is
considered a short QT interval

Cardio Med Res 2 (3 decks)

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