The 12-lead ECG

Question 1

What does an ECG detect?

Answer 1

The electrical current flowing through the heart

Question 2

PQRST: What does P show?

Answer 2

Electrical activity during atria contraction

Question 3

PQRST: What do QRS show?

Answer 3

Current causing contraction of L and R ventricles

Question 4

Why does QRS have a larger deflection?

Answer 4

Ventricles have larger muscle mass

Question 5

PQRST: What does T show?

Answer 5

Ventricle repolarisation

Question 6

Why is atria repolarisation not visible?

Answer 6

Hidden in QRS complex

Question 7

How many electrodes in the 12-lead ECG?

Answer 7

6 chest and 4 limb

Question 8

What can a 12-lead ECG determine?

Answer 8

Where abnormality in heart may be by viewing heart from different directions

Question 9

How is a ‘lead’ obtained?

Answer 9

Using signals from different combinations of electrodes

Question 10

What are the unipolar leads?

Answer 10

6 chest leads (leads 1-6)

Question 11

What are bipolar leads?

Answer 11

3 limb leads made from signals of 2 electrodes each (leads 1,11,111)

Question 12

What are augmented leads?

Answer 12

The other 3 limb leads made from signals of 3 electrodes each (aVF,aVR,AVL)

Question 13

What is the electrode placed on the right foot for?

Answer 13

Electrical earth

Question 14

Why may an ECG be performed?

Answer 14

• Chest pain
• History of chest pain / MI
• Hypertension
• Palpitations
• Patient at risk
• Prior to some drug treatments
• Shortness of breath

Question 15

How is an ECG performed?

Answer 15

1) Confirm ID
2) Explain process, informed consent
3) Privacy, comfort (chaperone?)
4) Lying down, head well supported. If breathing difficulties may need to sit upright. Document any variation
5) Unrestricted access to chest, arms, legs. Dignity blanket for females.
6) Reassure anxious patient (affects heart beat)
7) Clean sweaty/oily skin with alcohol wipe for good contact. If chest hair, shave with disposable 1-use razor. If exfoliation needed, rub lightly with abrasive tape
8) Discourage talking/movement (involves use of other muscles) and fists unclenched
9) Position electrodes, ensure good contact
10) Press button to start, record 12-lead ECG at 25mm/sec with a gain setting of 10mm/mv. Filter settings should only be used if interference from other muscle movement and marked clearly on recording.
11) Ensure correct recording labeling, show to requesting practitioner
12) Scan onto PC, store paper reading safely (confidentiality)

Question 16

If rhythm irregular during 12-lead ECG, what should be done?

Answer 16

Additional rhythm strip should be recorded, usually on lead V2 for minimum of 10s (done manually)

Question 17

What are the recommended positions for the limb leads?

Answer 17

• RED - inside R wrist
• YELLOW - inside L wrist
• GREEN - inside L ankle
• BLUE - inside R ankle

Question 18

What are the recommended positions for the chest leads?

Answer 18

• V1 - 4th R intercostal space at sternal border
• V2 - 4th L intercostal space at sternal border
• V3 - Midway between V2 and V4
• V4 - 5th L intercostal space in mid clavicular line
• V5 - L anterior auxillary line at same horizontal level as V4
• V6 - L mid axiullary line at same horizontal line as V4

Question 19

What are two other factors to consider when performing an ECG?

Answer 19

• Infection control (hand decontamination, couch, razors etc.)
• Health and safety ( couch height, check & calibrate electrical equipment annually etc.)