ECG interpretation

Question 1

What is the normal width of the P wave

Answer 1

<120 ms wide (3 small squares)

Question 2

What is the normal height of the P wave

Answer 2

<1.3 mV (3 small sqaures)

Question 3

What could cause a P wave to have low amplitude

Answer 3

Atrial fibrosis
Obesity (fat between SAN and ECG electrodes)
Hyperkalaemia (can inhibit sodium channels)

Question 4

What could cause a tall P wave?

Answer 4

Right atrial enlargment

Question 5

What could cause a bifid p wave?

Answer 5

Left atrial enlargement (delayed depolarisation of different parts of atrium)

Question 6

What could cause focal atrial tachycardia?

Answer 6

Alternative pacemaker foci (ectopic pacemaker, excitable cells outside of SAN)

Question 7

What is the normal time for PR interval?

Answer 7

120-200 ms

Question 8

What could cause a longer PR interval?

Answer 8

Disorders of AV node
Disorders of specialised conducting tissue

Question 9

What could cause a shorter PR interval?

Answer 9

Younger patients
Wolf-Parkinson-White syndrome

Question 10

What is Wolf-Parkinson-White syndrome?

Answer 10

There is an abnormal accessory electrical pathway called the Bundle of Kent between the atria and ventricles. Signals travel more quickly than through AV node leading to premature activation of ventricles

Delta wave characteristic feature - initial part of ventricular contraction before main pathway contraction.

Rapid and irregular heartbeat, supraventricular tachycardia.

Question 11

Symptoms of Wolf-Parkinson-White Syndrome

Answer 11

Palpitations, raid heartbeat, chest pain, dizziness, fainting.
Can be asymptomatic.

Question 11

How fast is normal QRS complex?

Answer 11

<120ms

Question 12

What is the normal frontal axis between

Answer 12

-30 and +90

Question 13

What can cause QRS >120 ms?

Answer 13

ventricular conduction delay
Bundle branch block
Pre-excitation (delta wave in WPW syndrome)

Question 14

What can cause small amplitude QRS complex

Answer 14

Obese patients (fat between ventricles and ECG electrode)

Pericardial effusion (fluid between ventricles and ECG electrode, may compress heart and hinder transmission through myocardium)

Infiltrative cardiac disease (disorders which deposit abnormal substances into heart eg amyloids. can cause fibrosis and impaired myocardial conduction)

Question 15

What can cause tall QRS complexes?

Answer 15

Left ventricle hypertrophy
Thin patient (minimal fat between ventricles and ECG electrodes)

Question 16

What can cause an elevated ST segment?

Answer 16

Myocardial infarction (convex, damaged myocardial cells have influx of calcium ions which shows on ECG)

Pericarditis (concave, electrical changes due to irritated epicardium)

Question 17

Inversion of the T wave may indicate…

Answer 17

Ischaemia or infarction (influx of calcium, leads to delayed repolarisation, T-wave changes)

Myocardial strain/hypertrophy (increased stress on heart, increased calcium influx, delayed repolarisation)

Myocardial disease/ cardiomyopathy

Question 18

What is the normal range for heart rate?

Answer 18

60-100 bpm

Question 19

What are types of tachycardias?

Answer 19

Atrial fibrillation
Atrial flutter
Supraventricular tachycardia
Ventricular tachycardia
Ventricular fibrillation

Question 20

What is atrial flutter?

Answer 20

Regular, organised and rapid heartbeat originating in the atria due to reentrant circuits, typically has a regular ventricular response

Question 21

What is the characteristic ECG of atrial flutter?

Answer 21

Sawtooth pattern

Question 22

What are some causes of bradycardia?

Answer 22

Conduction tissue fibrosis
Ischaemia
Inflammation/infiltrative disease
Drugs

Question 23

What is the difference between AV block and Bundle Branch block?

Answer 23

AV block refers to delay or interruption between atrial and ventricles at AV node

BBB refers to delay or blockage along a bundle branch in the ventricle

Question 24

What is first degree AV block?

Answer 24

Slow conduction between atria and ventricles, all impulses still conducted

Question 25

What is second degree AV block?

Answer 25

Slow conduction with some of the signals being blocked between the atria and the ventricles

Question 26

What is third degree AV block?

Answer 26

No atrial impulses reach the ventricles so independent rhythm for atria and ventricles.

Question 27

What does Mobitz type 1 refer to?

Answer 27

Type of second degree AV block. Progressive prolongation of PR until a P wave is not followed by QRS

Question 28

What does Mobitz type II refer to?

Answer 28

Type of second degree AV block consistent PR interval but intermittent non-conducted P wave without QRS. May progress to complete heart block.

Question 29

What are ECG findings for right bundle branch block?

Answer 29

MaRrow V1 = M shape V6 = W shape

Question 30

What are ECG findings for left bundle branch block?

Answer 30

WiLliam V1 = W shape V6 = M shape

Question 31

Which leads show high lateral side of heart?

Answer 31

I, aVL

Question 32

Which leads show the inferior wall of the heart?

Answer 32

aVF, II, III

Question 33

Which leads show septal activity?

Answer 33

V1,V2

Question 34

Which leads show anterior wall of heart?

Answer 34

V2, V3, V4

Question 35

Which leads show the lateral wall of heart?

Answer 35

V5, V6

Question 36

What does hyperkalaemia show on ECG?

Answer 36

Flattened P waves, broad QRS, tall T waves Flat p waves - decreased excitability of atrial cells Broad QRS - reduced resting potential of ventricular cells slowing conduction Tall T waves - increase in K+ as it leaves the cell during repolarisation and already high concentration

Question 37

What does hypokalaemia show on ECG?

Answer 37

QT prolongation (longer for ventricles to depolarise and repolarise) and flat T waves

Question 38

What does hypercalcaemia show on ECG?

Answer 38

QT shortening

Question 39

What does hypocalcaemia show on ECG?

Answer 39

QT prolongation