ECG interpretation

Question 1

1. Rate - how do you calculate rate?

Answer 1

If regular - 300 / number of large squares between 2 complexes
If irregular - number of complexes on the rhythm strip x 6

Question 2

1. Rate - how many seconds are each square?

Answer 2

1 small square = 0.04 secs

1 large square = 0.2 secs

Question 3

2. Rhythm - what does sinus rhythm show?

Answer 3

P waves are present

If P waves are absent / irregular - not in sinus rhythm

Question 4

2. Rhythm - example of a reg irreg rhythm? example of an irreg irreg rhythm?

Answer 4

reg irreg - Mobitz type II heart block (2nd degree)

irreg irreg - AF

Question 5

3. Axis - which leads show axis?

Answer 5

Leads I, II, III, aVR, aVL, aVF (I, II and III normally are positive)

Question 6

4. Axis - what does normal axis look like?

Answer 6

Lead I and aVF are +ve

Question 7

4. Axis - what does left axis deviation look like?

Answer 7

Lead I is +ve and aVF is -ve

Question 8

4. Axis - what does right axis deviation look like?

Answer 8

Lead I is -ve and aVF is +ve

Question 9

4. Axis - what does axis describe?

Answer 9

The average orientation of the heart’s electrical activity

Question 10

5. QRS - what does a narrow QRS signify?

Answer 10

Ventricular depolarisation is well synchronised
Normal is <120ms

Question 11

5. QRS - what does a wide QRS signify?

Answer 11

= bundle branch block
A beat originating in the ventricles (ventricular ectopic)
Impulse spreads slowly across myocardium
Occurs in BBB because one ventricle contracts rapidly as part of normal conduction but impulse has to spread slowly to other ventricle
>120ms = wide

Question 12

6. BBB - what does LBBB look like?

Answer 12

1. WiLLiaM
2. W shaped QRS in V1
3. M shaped in V6

Question 13

6. BBB - what does RBBB look like?

Answer 13

1. MaRRoW
2. M shaped QRS in V1, W in V6

Question 14

6. BBB - what axis do left anterior and posterior hemi-blocks deviate to?

Answer 14

LAH = left axis deviation
RAH = right axis deviation
Bifasicular block = LAH / LPH + RBBB

Question 15

7. Hypertrophy - what features does RV hypertrophy have on ECG?

Answer 15

1. Tall R wave in V1-V4
2. R wave exceeds S wave amplitude in V1
3. RAD common

Question 16

7. Hypertrophy - what features does LV hypertrophy have on ECG?

Answer 16

1. Deep S wave in V1 and V2
2. S wave in V1 / R wave in V6 = >35mm
3. LAD common

Question 17

8. HB - what is a normal PR interval?

Answer 17

<200ms
-If prolonged –> heart block

Prolonged suggests there is AVN block

Question 18

8. HB - what does 1st degree HB look like?

Answer 18

Consistently prolonged PR interval

Block is between SAN and AVN

Question 19

8. HB - what does 2nd degree / Mobitz 1 HB look like?

Answer 19

PR interval gradually increases until there is a dropped beat
Block is in AVN

Question 20

8. HB - what does 2nd degree / Mobitz 2 HB look like?

Answer 20

PR interval is consistently prolonged, but dropped beats occur either in a pattern or randomly

Block is after AVN

Question 21

8. HB - what does 3rd degree / complete HB look like?

Answer 21

P waves and QRS complexes are completely unrelated

Question 22

9. where are delta waves seen and in what patients?

Answer 22

Between P and Q

WPW syndrome or tall, thin patients

Question 23

What does hypokalaemia do to the ECG trace?

Answer 23

Shows prominent U waves

Question 24

In what order should you systematically approach an ECG?

Answer 24

1. Patient ID
2. Time and date
3. Rate
4. Rhythm
5. Axis
6. P waves / sinus?
7. QRS
8. ST
9. QTc/other