ECG basics

Question 1

PR interval

Answer 1

3-5 small squares (120-200ms)

Question 2

QRS complex length

Answer 2

120ms (3 small squares)

Question 3

1st degree heart block - how long is the PR interval?

Answer 3

Longer than 1 big square i.e. >6 small squares, or bigger than 220ms

Question 4

Mobitz type 1 - ecg findings

Answer 4

PR interval steadily gets longer, then you drop a QRS complex

Question 5

Another name for mobitz type 1

Answer 5

Wenchebach = Weird ONE = type ONE

Question 6

ECG for Mobitz type 2

Answer 6

Constant PR interval but occasional dropped QRS complex

Question 7

What is a fixed block?

Answer 7

Two p waves per QRS complex / three fixed p waves per qrs complex

Sometimes the T wave looks like an M because it’s super imposed with a p

type of mobitz 2

Question 8

Is first degree heart block worrying?

Answer 8

Apparently not

Second degree is worrying

Question 9

What might cause heart block?

Answer 9

Coronary artery disease
Drugs
Electrolyte abnormalities

Question 10

What happens in complete heart block (third degree)?

Answer 10

No relationship between p wave and qrs complex so ventricles decide to autonomously depolarise,

Question 11

QRS in complete heart block

Answer 11

QRS is wide (more than 120ms)

Question 12

What do we call the trigger that causes a wide QRS complex?

Answer 12

Supraventricular trigger

Question 13

Causes of complete heart block

Answer 13

Acute MI
Fibrosis of bundle branch/atria
Blockage of both bundle branches

Question 14

What is the rate of the p wave/qrs complex in complete heart block?

Answer 14

QRS rate is actually really slow

P wave is usually faster

Overall bradycardia

Question 15

How do you look for axis deviation?

Answer 15

Look at leads 1, 2 and 3

Question 16

Right axis deviation

Answer 16

QRS complex in l3 pointing up

l1 pointing down like ‘reaching’

Question 17

What happens to the QRS complex in branch blocks?

Answer 17

QRS widens because it takes forever to depolarise due to the bundle branch block

Also, you end up with TWO qrs complexes because the ventricles are depolarising out of sync

Question 18

What are the causes of a widened QRS complex?

Answer 18

Bundle branch block OR

if ventricles are depolarising of their own accord

Question 19

What does the QRS complex look like in certain leads in RBBB?

Answer 19

RBBB - Marrow

M in V1 - positive deflection in lead V1
W in V6

Question 20

What does the QRS complex look like in certain leads in LBBB?

Answer 20

LBBB - William

W in V1 - negative deflection in lead V1
M in V6

Question 21

Causes of RBBB

Answer 21

Can be normal !!
Atrial septal defect
Right side heart problm

Question 22

Causes of LBBB

Answer 22

If asymptomatic, no problem

If chest pain, MI

Question 23

What happens in WPW?

Answer 23

No AV node so no delay in conduction, so preexcitation occurs via bundle of Kent, so left ventricle depolarises early

Question 24

What can WPW lead to?

Answer 24

Paroxysmal (on and off) tachycardia

also reentry tachycardia

Question 25

ECG changes in WPW

Answer 25

Short PR interval and early QRS

Slow curved upstroke QRS = delta wave

Question 26

How do you identify axis deviation?

Answer 26

Look at leads 1 and 3

If the QRS complexes are Reaching for each other (lead 1 qrs pointing down whilst lead 3 qrs is pointing up), it’s Right BBB

If they’re both ‘leaving’ each other, it’s LEFT bundle branch block

Also thumb method

Question 27

LVH features on ECG

Answer 27

S wave depth in V1 + tallest R wave height in V5-V6 > 35 mm (Sokolov-Lyon criteria)
Leftward axis
Widespread ST depression and T wave inversion