ECG

Question 1

Where are the 10 electrodes placed on the body?

Answer 1

• 4 classic electrodes - right arm, left arm, left leg, right leg (ground)
• 6 precordial electrodes - located on the chest

Question 2

Where are the 3 bipolar leads?

Answer 2

Classic lead I, II, III

Question 3

Where are the 9 bipolar leads located

Answer 3

• Augmented vectors (central terminal → classic electrodes) - aVl, aVr, aVf
• Precordial vectors (central terminal → precordial electrodes) - V1-6

Question 4

If the wave of depolarisation is heading in the the direction of the positive recording electrode, the ECG is programmed to produce a _______ deflection

Answer 4

If the wave of depolarisation is heading in the the direction of the positive recording electrode, the ECG is programmed to produce a positive deflection

Question 5

If the wave of repolarisation is heading in the the direction of the negative reference electrode, the ECG is programmed to produce a _______ deflection

Answer 5

If the wave of repolarisation is heading in the the direction of the negative reference electrode, the ECG is programmed to produce a positive deflection

Question 6

If the wave of depolarisation is heading in the the direction of the negative reference electrode, the ECG is programmed to produce a _______ deflection

Answer 6

If the wave of depolarisation is heading in the the direction of the negative reference electrode, the ECG is programmed to produce a negative deflection

Question 7

If the wave of repolarisation is heading in the the direction of the positive reference electrode, the ECG is programmed to produce a ________ deflection

Answer 7

If the wave of repolarisation is heading in the the direction of the positive reference electrode, the ECG is programmed to produce a negative deflection

Question 8

What does the isoelectric linerepresent?

Answer 8

Period of no net electrical change (i.e. no changes in membrane potential as myocytes are completely depolarised or repolarised)

Question 9

Name the deflections of the ECG graph

Answer 9

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Question 10

What does the P wave represent?

Answer 10

Depolarisation of atrial wall

Question 11

Why do the SA node, AV node, and other major contractile myocyte groups not produce a deflection on the ECG?

Answer 11

Size too small hence electrical signal not strong enough to be read by ECG

Question 12

What does the PQ segment represent?

Answer 12

• Complete depolarisation of atria → atrial contraction
• Isoelectric line

Question 13

What does the Q wave represent?

Answer 13

• Wave of depolarisation travelling down the interventricular septum
• AP travels faster down the left bundle branch than the right (due to greater number of cardiac myocytes) → wave of depolarisation moves from the left to the right → Q wave = negative deflection

Question 14

What does the R wave represent?

Answer 14

Depolarisation of the majority of the free ventricular wall (apex → base; endocardium → epicardium)

Question 15

What does the S wave represent?

Answer 15

• Depolarisation of the final Purkinje fibres
• Negative deflection as Purkinje fibres move into mid-myocardium region, thus change in direction

Question 16

What does the ST segment represent?

Answer 16

• Complete depolarisation of ventricle → ventricular contraction
• Isoelectric line

Question 17

What does the T wave represent?

Answer 17

Repolarisation of the ventricle

Question 18

How is the heart rate (HR) calculated using an ECG

Answer 18

Measure RR interval

• Big squares = 0.2 seconds
• Small squares = 0.04 seconds

Question 19

What regions of the heart do the classic limb leads view?

i.e. Lead I-III

Answer 19

• Lead I - Lateral wall
• Lead II - Inferior wall
• Lead III - Inferior wall

Question 20

What region of the heart do the augmented vectors view

i.e. aVl, aVr, aVf

Answer 20

• aVl - No specific view
• aVr - lateral wall
• aVf - inferior wall

Question 21

Where are the 6 precordial leads placed?

Answer 21

• V1 - placed in the 4th intercostal space, right of the sternum
• V2 - placed in the 4th intercostal space, left of the sternum
• V3 - placed between V2 and V4
• V4 - placed 5th intercostal space in the nipple line. Official recommendations are to place V4 under the breast in women.
• V5 - placed between V4 and V6
• V6 - placed in the midaxillary line on the same height as V4
  
  • (horizontal line from V4, so not necessarily in the 5th intercostal space)

Question 22

What regions of the heart do the precordial leads view?

Answer 22

• V1-4 - Anterior chest
• V5-6 Lateral wall

Question 23

To review, what leads view the:

1. Anterior Chest
2. Lateral Wall of the Left Ventricle
3. Inferior Chest
4. No Man’s Land

Answer 23

1. V1, V2, V3 and V4
2. aVL, Lead I , V5 and V6
3. Lead II, Lead III, and Lead aVF
4. aVR