ECG

Question 1

What is an ECG

Answer 1

Record of the depolarisation and repolarisation cycle of cardiac muscle obtained from the skin surface

Question 2

Standard Limb Leads

Answer 2

Lead I - RA -> LA
Lead II - RA -> LL
Lead III - LA -> LL
Right leg is earthed - reduces electrical interference

Question 3

Augmented leads

Answer 3

One recording electrode (+ve) linked to 2 reference electrodes (-ve)
aVR - RA (+) recording against LA and LL
aVL - LA (+) recording against RA and LL
aVF - LL (+) recording against RA and LA

Question 4

Chest leads

Answer 4

Labelled V1-V6
Covers the horizontal plane of the heart
V1 - 4th ICS, right sternal edge
V2 - 4th ICS, left sternal edge
V4 - 5th ICS, mid clavicular line
V3 - between V2 and V4
V5 - same level as V4 but anterior axillary line
V6 - same level as V4 but mid axillary line

Question 5

Rhythm strip

Answer 5

Usually obtained from lead II 
Allows you to detect any rhythm disturbances 
Paper speed = 25mm/sec 
each large square (5mm) = 0.2 secs
each small square (1mm) = 0.04 secs

Question 6

Calculating regular heart rate

Answer 6

300 / number of large squares between R-R interval

Question 7

Calculating irregular heart rate

Answer 7

Number of QRS complexes in 30 large squares multiplied by 10

Question 8

ECG deflection

Answer 8

Wave of depolarisation moving towards recording electrode (+) gives an upward deflection, moving away gives a downward deflection

Wave of repolarisation moving towards recording electrode (+) gives a downward deflection, moving away gives an upward deflection

Question 9

Lead axis

Answer 9

When lead axis is parallel to dipole, the measured potential difference if greatest
When lead axis perpendicular to dipole, there is no change in potential

Question 10

Electrical vector

Answer 10

Magnitude - determined by mass of cardiac muscle that is involved in the generation of the signal

Direction - determined by the overall activity of the heart at any instant in time and varies during the cardiac cycle

Question 11

P wave

Answer 11

Atrial depolarisation

normal range: 0.08-0.1 secs

Question 12

QRS complex

Answer 12

Ventricular depolarisation

normal range: <0.1 secs

Question 13

T wave

Answer 13

Ventricular repolarisation

Question 14

PR interval

Answer 14

Atrial contraction

Normal range: 0.12-0.2 secs

Question 15

QT interval

Answer 15

Depolarisation and depolarisation of ventricles

Question 16

ST segment

Answer 16

Duration of ventricular depolarisation (systole)

Question 17

TP interval

Answer 17

Diastole

Question 18

ECG steps

Answer 18

1. verify patient’s name and DOB
2. Verify date and time ECG was taken
3. Check the calibration of the ECG
4. Determine the axis
5. 1 Electrical activity present? - (if straight line then no)
6. 2 Regular/irregular rhythm? - (spaces between R-R)
7. 3 What is the heart rate?
8. 4 P waves present? - (if yes, then atrial activity present)
9. 5 PR interval?
10. 6 Each P wave followed by QRS complex? - (sinus)
11. 7 QRS duration normal?
12. Look at individual leads for any other abnormalities

Question 19

Normal axis

Answer 19

-30 -> +90 degrees

Question 20

Normal axis deviation

Answer 20

Lead 1 upright

Lead aVF upright

Question 21

Left axis deviation

Answer 21

Lead 1 upright

Lead aVF down

Question 22

Right axis deviation

Answer 22

Lead 1 down

Lead aVF upright

Question 23

Inferior leads

Answer 23

Lead II
Lead III
Lead aVF

Question 24

Anterior leads

Answer 24

Precordial leads (V1-V6)

Question 25

Antero-septal leads

Answer 25

V1-V4

Question 26

Lateral leads

Answer 26

Lead I
Lead aVL
V5-6

Question 27

Q waves

Answer 27

Pathological

Indicates previous MI as it is an indicator of irreversible death

Question 28

ST elevation criteria

Answer 28

More than or equal to 1mm ST elevation (1 small box) in 2 limb leads that supply the same area of the heart (i.e.: RCA, LAD)

More than or equal to 2mm ST elevation (2 small box) in 2 precordial leads that supply the same area of the heart (i.e.: RCA, LAD)