ECG Theory

Question 1

How can ECG rate be calculated

Answer 1

two ways:

1. number of QRS complexes on the rhythm strip x 6
2. 300/ number of large squares between QRS complexes

Question 2

how many seconds is

• one small square
• one large square

Answer 2

one small square = 0.04s

one large square = 0.2s

Question 3

how do you assess rhythm of ECG

Answer 3

look for P waves followed by QRS complexes

Question 4

which rhythm has no P waves and is irregularly irregular

Answer 4

Atrial fibrillation

Question 5

how do you assess the axis of the ECG

Answer 5

Imagine lead 1 = left hand and AvF = right hand - raise hand if lead is +ve - if both +ve then normal axis

Question 6

what kind of axis deviation is there if lead 1 +ve and AvF -ve

Answer 6

left axis deviation

Question 7

what kind of axis deviation is there if lead 1 -ve and AvF +ve

Answer 7

right axis deviation

Question 8

what does P wave represent

Answer 8

atrial depolarisation

Question 9

normal duration of P wave

Answer 9

0.08 - 0.1s

Question 10

what does QRS complex represent

Answer 10

ventricular depolarisation

Question 11

normal duration of QRS complex

Answer 11

< 0.1 s

Question 12

what does PR interval represent

Answer 12

AV nodal delay

Question 13

normal duration of PR interval

Answer 13

0.12-0.2 s

Question 14

causes of a prolonged PR interval

Answer 14

ischaemic heart disease

hypokalaemia

digoxin toxicity

lyme disease

Question 15

what does T wave represent

Answer 15

ventricular repolarisation

Question 16

what causes peaked T waves

Answer 16

hyperkalaemia

(flattened T waves in hypokalaemia)

Question 17

what leads is it abnormal for T waves to be inverted?

what are some of the causes?

Answer 17

Leads I, II, V4-V6

• Ischaemia, digoxin toxicity, PE, ventricular hypertrophy

Question 18

where do the ventricles contract

Answer 18

ST segment - systole

Question 19

where do the ventricles relax

Answer 19

TP segment - diastole

Question 20

what condition causes widespread saddle shaped ST elevation

Answer 20

pericarditis

Question 21

drugs that can cause long QT

Answer 21

macrolides

amiodarone

tricyclic antidepressants e.g. amitryptilline

SSRI - citalopram

(also metabolic disturbances: hypokalaemia, hypocalcaemia)

Question 22

drugs that can cause short QT

Answer 22

digoxin

beta-blockers

phenytoin

Question 23

when are U waves seen

Answer 23

hypokalaemia

(occur after T waves)

Question 24

causes of J waves

Answer 24

hypothermia

hypercalcaemia

Question 25

easy way to differentiate between right + left bundle branch block

Answer 25

QRS has to be broad in bundle branch block

• QRS will point down in V1 in a LBBB
• QRS will point up in V1 in a RBBB

Question 26

anterior MI affects which leads?

which vessel is affected?

Answer 26

Anterior = V2-V5

• Left anterior descending

Question 27

anteroseptal MI affects which leads?

which vessel is affected?

Answer 27

anteroseptal = V1-V3

• Left anterior descending

Question 28

anterolateral MI affects which leads?

what vessel is affected?

Answer 28

Anterolateral = I, AvL, V4-V6

• left circumflex

Question 29

inferior MI affects which leads?

what vessel is affected?

Answer 29

inferior = II, III, AvF

• right coronary

Question 30

normal QT length in

• males
• females

Answer 30

males = < 430 ms

females = < 450 ms