ECG

Question 1

Which direction does repolarisation spread in relation to depolarisation?

Answer 1

The opposite direction, epicardial – endocardial (outside - inside)

Question 2

Where are leads 1,2,3

Answer 2

1: L side
2. apex
3. Right bottom

Question 3

What 2 factors determine the amplitude of the signal?

Answer 3

Muscle mass proportional, position of electrode in relation to the ‘moving excitation’

Question 4

Define a heart lead

How many cables are there and how many leads in an ECG?

Answer 4

Lead: electrical view of the heart

10 cables, 12 views/leads

Question 5

How many leads are there in the chest and limbs?How many limb and chest cables are there?

Answer 5

6 limb leads, 6 chest leads (V1-V6)

*4 limb cables, black one generates no signal it is the ‘earth electrode’

Question 6

How could you calculate an irregular heart rate using an ECG?

Answer 6

1. Count the number of peaks in 30 squares (equal to 6 seconds) and multiply that number by 10 to give you bpm
2. Count the number of peaks in the bottom segment representing 10 seconds and X by 6

Question 7

How many seconds is represented in each square on an ECG usually? What is the normal bpm?

Answer 7

0.2 seconds larger square, 0.04 seconds little square

Normal bpm is 60-100 bpm

Question 8

Which wave is absent in atrial fibrillation?

Answer 8

P wave (atrial depolarisation)

Question 9

What can be indicated by a broad QRS complex?

Answer 9

More time for excitation to pass through ventricles, indicates AP being generated elsewhere (may be AV node or bundle of HIS)

Question 10

What does the segment between P-R represent? How many seconds and squares long is it usually and what does it mean if its longer?

Answer 10

Time for an AP to cause ventricular systole, typically 280 ms, 3-5 squares.

> 280 ms indicates a block

Question 11

Explain the sinus arrhythmia phenomenon

Answer 11

HR increases: inspiration
HR decreases: expiration

Appears ‘regularly irregular’ on ECG

Question 12

If part of the myocardium is temporarily short on oxygen, what can be seen on an ECG?

Answer 12

an ST-depression (reduced blood flow)

Question 13

Which limb lead looks like the opposite of lead 2?

Answer 13

aVR is inverted

Question 14

How long should the ST segment be? What does it represent?

Answer 14

5-150ms, (1.25-3.75 small squares), represents amount of time between ventricular depolarisation and ventricular repolarisation