The ECG

Question 1

Label the ECG

Answer 1

Question 2

How does excitation normally spread through the heart?

Answer 2

1) SAN depolarises,
2) impulse spreads through atria,
3) held up at AVN,
4) spreads to ventricle via Bundle of His,
5) spreads rapidly down R and L bundles and purkinje system,
6) myocytes of IV septum are depolarised first,
7) apex, RV and LV free walls are polarised next,
8) ventricle bases last to depolarise
9) repolarisation of ventricles in reverse order

Question 3

Where is the SAN located in the heart?

Answer 3

Top R hand corner of the R atrium

Question 4

How does SAN depolarisation appear on an ECG

Answer 4

First electrical event: insufficient signal to register on ECG = flat line

Question 5

What does the P wave correspond to?

Answer 5

Atrial depolarisation = upwards as towards +ve electrode = SAN must be setting HR, can be absent in which case AV will be setting pace

Question 6

What does 1b on an ECG correspond to?

Answer 6

AVN delay = time for atria to contract and ventricles to fill = stops simultaneous contraction = flat line. Also depolarisation travelling down Bundle of His

Question 7

How are the atria electrically isolated from the ventricles?

Answer 7

Fibrous ring – 4 heart valves

Question 8

What does the Q wave correspond to?

Answer 8

Septum depolarising L to R = downward deflection because moving away

Question 9

What does the R wave correspond to?

Answer 9

Depolarisation of the apex and ventricular wall – large due to muscle mass

Question 10

What does the S wave correspond to?

Answer 10

Depolarisation of base of ventricles (muscle close to atria)

Question 11

What does the T wave correspond to?

Answer 11

Ventricular repolarisation – upward wave as repolarisation is moving away from +ve electrode

Question 12

State the rules about the signal recorded when depolarisation spread towards the recording electrode

Answer 12

Wave of -ve charge travelling to +ve electrode = upward wave = +ve complex

Question 13

State the rules about the signal recorded when depolarisation spread away from the recording electrode

Answer 13

Wave of –ve charge travelling away from +ve electrode = downward wave = -ve complex

Question 14

State the rules about the signal recorded when repolarisation spread towards the recording electrode

Answer 14

Wave of +ve charge travelling towards the +ve electrode = downward wave = -ve complex

Question 15

State the rules about the signal recorded when repolarisation spread away from the recording electrode

Answer 15

Wave of +ve charge travelling away from the +ve electrode = upward wave = +ve complex

Question 16

Draw the correct positions of the CHEST recording electrodes for performing a 12 lead ECG and the names of the leads

Answer 16

V1 = 4th intercostal space, R sternal border

V2 = 4th intercostal space, L sternal border

V3 = mid-way between V2 and V4

V4 = 5th intercostal space, mid-claviclar line

V5 = 5th intercostal space, beginning of axilla

V6 = 5th intercostal space, mid-axillary line

Question 17

Draw a normal ECG trace from an electrode viewing the heart from the apex

Answer 17

Question 18

What are the 12 different view of the heart?

Answer 18

Limbs: I, II, III, aVR, aVL, aVF.

Chest: V1, V2, V3, V4, V5, V6

Question 19

Describe how the QRS complex will change if the viewing electrode is moved around a circle with the heart at the centre

Answer 19

The transition zone is where the QRS complex changes from predominately negative to predominately positive, this usually occurs at V3 or V4.

It is normal to have the transition zone at V2 (called “early transition”), and at V5 (called “delayed transition”).

Question 20

What is sinus rhythm?

Answer 20

any cardiac rhythm where depolarisation of the cardiac muscle begins at the sinus node = presence of P wave

Question 21

What is normal sinus rhythm?

Answer 21

reg rhythm,

HR 60-100,

p wave present and upright in leads I and II,

PR interval 3-5 small boxes,

every p wave followed by QRS,

QRS <3 small boxes

Question 22

What is the speed of ECG paper?

Answer 22

25mm/sec

Question 23

1 second on ECG paper is = to?

Answer 23

25 small squares, 5 large squares

Question 24

How do you calculate a regular heart rate?

Answer 24

300 divided by how many large boxes between R-R interval:

300/4 = 75bpm

Question 25

How do you calculate an irregular heart rate?

Answer 25

Number of QRS complexes in 6 seconds then x by 10

Question 26

Draw the different intervals present on an ECG

Answer 26

Question 27

What does an abnormal R-R interval indicate?

Answer 27

Shorter = faster HR

Question 28

What does an abnormal QRS complex indicate?

Answer 28

Wider = ventricular depolarisations that are not initiated by the normal conductance mechanism

Question 29

What does an abnormal P-R interval indicate?

Answer 29

Lower = slow conduction from atria to ventricle = heart block

Question 30

What does an abnormal ST segment indicate?

Answer 30

Should be isoelectric (flat line) – if raised or depressed = MI or ischaemia

Question 31

What does an abnormal Q-T interval indicate?

Answer 31

Prolonged = prolonged repolarisation of ventricles = can lead to arrhythmias as occur in long QT syndrome

Question 32

On a 12 lead ECG where are the LIMB electrodes placed?

Answer 32

Ride your green bike

Question 33

What view of the heart does each electrode have?

Answer 33

Inferior: II, III, aVF

Lateral: I, aVL, V5, V6

Anterior: V3, V4

Septal: V1, V2