ECG

Question 1

ECG

Answer 1

Voltage against time graph

Typical settings
Speed = 25 mm/sec
Voltage=10 mm/mV

y axis: 2 big squares= 1mV
x axis: 5 big squares= 1s

Question 2

Methods of rate calculations

Answer 2

Rate (bpm) = 300/no. of large squares between cardiac cycles

Rate (bpm) = (cycles in 10 secs) x 6

Question 3

Fatstest depolarizing part of heart

Answer 3

Sinoatrial node

Question 4

ECG Waves

Answer 4

P wave – atrial depolarization

QRS complex– ventricular depolarization and atrial repolarisation

T wave – ventricular repolarisation

Positive deflection= net current flow towards lead

Negative deflection= net current flow away from lead

Question 5

Atrial flutter

Answer 5

Organised atrial activity ~300/min

Ventricular capture at ratio to atrial rate (usually 2:1 so 150 bpm)

Usually regular

Can be irregular if ratio varies

Question 6

Atrial fibrillation

Answer 6

Random atrial activity

Random ventricular capture

Irregularly irregular rhythm

Question 7

PR Interval- P to start of QRS

Answer 7

Normal values

120 – 200 ms
(3 to 5 small squares)

Normal QRS<120ms
QRS> 120ms
Bundle branch block most common cause

Question 8

QT Interval

Answer 8

Measure of time to ventricular repolarization
Time from onset of QRS to end of T

Normal values

Men 350-440 ms
Women 350-460 ms

Question 9

3 lead ECG

Answer 9

Looks at rhythm but not particularly anything else

Question 10

Electrode

Answer 10

Physical connection to patient in order to measure potential at that point

10 electrodes to record a 12 lead ECG

Question 11

Lead

Answer 11

Graphical representation of electrical activity in a particular ‘vector’

Calculated by the machine from electrode signals

12 leads for a 12 lead ECG (I-III, aVL, aVF, aVR, V1-6)

Question 12

Negative

Answer 12

Current flowing away from the electrode

POSITIVE- current flowing towards the electrode

Question 13

Bipolar lead

Answer 13

Measures the potential difference (voltage) between two electrodes
One electrode designated positive, the other negative

3 bipolar limb leads – I, II, III

Question 14

Unipolar lead

Answer 14

Measures the potential difference (voltage) between an electrode (positive) and a combined reference electrode (negative)
Sometimes known as augmented leads

3 unipolar limb leads – aVL, aVF, aVR

Question 15

Right leg

Answer 15

Neutral electrode
- Reduces artefact – not directly involved in ECG measurement

Left leg= positive

Question 16

Right arm

Answer 16

Negative

Question 17

Left arm

Answer 17

Positive

Question 18

Unipolar limb leads

Answer 18

Measure potential from a single electrode (designated as positive) using a combined reference electrode as negative
Use same electrodes as the bipolar limb leads

Question 19

Rules of thumb – Leads I + II

Answer 19

Lead I + II positive -> normal axis

Question 20

Rules of thumb – Leads I + II

Answer 20

Lead I positive, lead II negative -> Left axis deviation

Leaving each other = Left axis deviation

Question 21

Rules of thumb – Leads I + II

Answer 21

Lead I negative, lead II positive -> right axis deviation

Reaching towards each other = Right axis deviation

Question 22

What you need to know for exam?

Answer 22

ECGs record voltage over time
Show us magnitude of collective electrical impulse in specified directions
Standard set up parameters

P-QRS-T corresponds to electrical (and therefore mechanical) cardiac cycle

12 lead ECG = 10 electrodes

3 bipolar limb leads – I, II, III

3 unipolar limb leads – aVL, aVF, aVR

6 unipolar chest leads (V1-6)

Provide information on rate, rhythm, axis, conduction, myocardial health

More about abnormalities in later phases but it’s important to grasp the basics first