Basics of ECG (including how to set up)

Question 1

List the steps for setting up an ECG

Answer 1

1. Gain consent and position patient lying at 30-40 degrees
2. Confirm patient ID/details and enter this into ECG
3. Attach electrodes and leads (may need to prep skin first)
4. Ensure machine is in the correct settings
5. Make sure patient relaxes and record the ECG

Question 2

If the ECG is taken in anyother position than lying at 30-40 degrees what should be done ?

Answer 2

It should be documented so i.e. if taken when patient is sitting up in a chair say this

Question 3

What may you need to do to prep someones skin for an ECG ?

Answer 3

May need to dry or shave the skin

Question 4

What should the limb electrodes be placed over ?

Answer 4

Bony promineces to minimise electrical interference from muscles

Question 5

How do you remember which limb electrode goes where ?

Answer 5

• Red for right arm
• Lellow(yellow) for left arm
• Green for left leg
• Black for right leg

From red to green is the traffic light

Question 6

What is the correct placement of the chest leads in an ECG ?

Answer 6

• V1 = 4th IC space right sternal edge
• V2 = 4th IC space left sternal edge
• V3 = midway between V2 and V4
• V4 = 5th IC midclavicular line
• V5 = 5th IC space anterior axillary line
• V6 = 5th IC space mid axillary line

Question 7

What differences is done for positioning of the chest electrodes in females ?

Answer 7

• Ideally the bra should be removed
• The electrode should be placed underneath the breast fold in the appropriate intercostal positioning

Question 8

What is AC interference and its appearance on ECG?

Answer 8

It causes a thick baseline - caused by electrical devices

Question 9

What ECG abnormality is shown and its causes ?

Answer 9

Muscle tremor - shivering, movement etc

Question 10

Describe the appearance of wandering baseline and its causes on ECG

Answer 10

Causes a smooth rising and falling baseline - caused by patient movement including breathing

Question 11

What are the 8 aspects of an ECG trace that you need to assess?

Answer 11

1. Rate
2. Rhythm
3. Axis
4. Timings
5. P-wave
6. PR interval
7. QRS complex
8. T-wave

Note - dont ever forget to check the date and time of ECG and identity of the patient

Question 12

How do you calculate the rate on an ECG ?

Answer 12

• If rhythm is regular - count the number of large squares between 2 R waves and divide into 300
• If regular but tachycardiac then count the number of small squares between 2 R waves and divide into 1500
• If irregular rhythm then count the number of ARS complexes in 6 secs/30large squares and multiply by 10

Question 13

When assessing rhythm what are the 6 key things you should check?

Answer 13

1. Is there electrical activity
2. Are there p waves present
3. What is the QRS rate
4. Is the QRS regular/irregular
5. Is the QRS broad/narrow
6. What is the relationship between the P waves and QRS complexes

Question 14

How do you determine the cardiac axis on an ECG?

Answer 14

• Look at leads I and aVF - make lead I your left hand and aVF your right. If QRS complexes are mainly positive in both then raside both hands its normal axis.
• If only lead I QRS is mainly pos then raise left hand and right hand stays down. This is left axis deviation
• If only aVF QRS complex is mainly pos then raise your right hand and keep the left down. This is right axis deviation

Question 15

What happens during the PR interval and state the normal duration of it

Answer 15

• It is measured from the onset of the p-wave to the onset of the QRS complex.
• Its normal duration is 0.12-0.2s
• It is caused by the AV node causinf delay in contraction to prevent rapid contraction of ventricles and to also allow them to fill

Question 16

What is the normal duration of the QRS complex and what occurs in the cardiac cycle here ?

Answer 16

• Normal duration = <0.12s (3 small squares)
• Represents ventricular depolarisation

Question 17

When assessing the QRS complex how do you determine which is the Q, R and S waves ?

Answer 17

• The first upward deflection is termed an R wave wether it is preceeded by a Q wave or not
• First downward defelection following an R wave is termed the S wave
• If the initial defelection is downward for the QRS complex then it is termed a Q wave

Question 18

Describe what is meant to happen to the R waves throughout the chest leads when assesing the QRS complexes

Answer 18

R wave amplitude should increase from V1-5(6) sometimes V6 is a little smaller as it can be past the apex now

Question 19

What is the QT interval and how is its duration calculated ?

Answer 19

• It is measured form the start of the QRS complex to the end of the T wave.
• It represents ventricular repolrisation

Question 20

What does the P-wave represent, what must it follow, what is the normal size of it and where is it normal to see an inverted Pwave ?

Answer 20

• It must preced a QRS complex (1:1)
• Represents atrial depolarisation
• <2.5mm in height and <3mm in width
• Normal to be inverted in aVR

Question 21

What is the general rule for assessing the size of T waves ?

Answer 21

They shouldnt be > 1/2 the size of the preceeding QRS complex

Question 22

What does the P wave, QRS complex and T wave all represent on an ECG ?

Answer 22

• P-wave represents atrial depolarisation
• QRS complex represents ventricular depolarisation
• T-wave represents ventricular repolarisation

Note - atrial repolarisation tends to be hidden in the QRS complex by ventricular depolarisation hence why you cant see it