Session 7.1

Question 1

How long should the PR interval be?

Answer 1

3-5 small boxes

Prolonged if more than 1 large box

Question 2

How long should the QRS complex be?

Answer 2

Less than 3 small boxes

If more, prolonged

Question 3

What is normal sinus rhythm?

Answer 3

Heart rate 60-100bpm
P waves present
Leads I and II, leads upright 
PR interval = 3-5 small boxes
QRS complex = less than 3 small boxes

Question 4

What lead do you use to interpret the rhythm?

Answer 4

Lead II rhythm strip at the bottom of the 12 lead ECG

Question 5

What’s a heart block/AV conduction block and what are the causes?

Answer 5

Delay/failure of conduction of impulses from atrium to ventricles via AV node and bundle of His

Causes

• acute myocardial infarction
• degenerative changes

Question 6

What’s a first degree heart block?

Answer 6

PR interval prolonged more than 5 small boxes (0.2 seconds)

If long standing, don’t need to do anything about it.

Question 7

What’s the different between mobitz type 1 and mobitz type 2 second degree heart block?

Answer 7

Type 1 = successively longer PR intervals until one QRS is dropped, then cycle starts again.

Type 2 = PR intervals do not lengthen, but suddenly dropped a QRS complex (higher risk of progression to complete heart block)

Question 8

What’s a third degree heart block?

Answer 8

Complete failure of AV conduction

Atria and ventricles depolarise separately - ventricular pacemaker takes over as sinus control isn’t reaching ventricles

Usually get a wide QRS complex, inverted T waves, and urgent pacemaker insertion is required

Question 9

Where can abnormal rhythms arise from?

Answer 9

Sinus node
Atrium
AV node

These are also called supraventrivcular rhythms (arise above the ventricles)

Also ventricular rhythms

Question 10

What do ventricular rhythms cause?

Answer 10

Ventricular tachycardia

Wide and bizarre QRS complex

Question 11

What it atrial fibrillation?

Answer 11

A supraventricular rhythm
Arises from multiple atrial foci
Rapid, chaotic impulses

No P waves, wavy baseline
Impulses reach AV node at rapid irregular rate and not all are conducted due to AV node refractory period

Ventricles depolarise normally = narrow QRS complex with irregular R-R intervals

Question 12

What are the haemodynamic effects of atrial fibrillation?

Answer 12

Atrial conduction lost, they just quiver
Ventricles contract normally but at an irregular rate
Heart rate and pulse irregular

Question 13

What’s the difference between regularly irregular and irregularly irregular?

Answer 13

Regularly irregular = weird but consistent

Irregularly irregular = weird but inconsistent

Question 14

What is a ventricular ectopic beat?

Answer 14

Ectopic focus in ventricular muscle
Impulse doesn’t spread via his— purkinje system
Therefore much slower depolarisation of ventricular muscle
Therefore wide QRS complex, different in shape to usual QRS

Question 15

How can a ventricular ectopic lead to ventricular tachycardia?

Answer 15

More than 3 consecutive ventricular ectopic = ventricular tachycardia

Question 16

What is risky about ventricular tachycardia?

Answer 16

Can lead to ventricular fibrillation = causes cardiac arrest

Question 17

What is ventricular fibrillation?

Answer 17

Abnormal, chaotic, fast, ventricular depolarisation
Impulses from number ectopic sites in ventricular muscle

No coordinates contraction = ventricles quiver

No cardiac output = cardiac arrest

Question 18

What sequence do you go through when analysing an ECG?

Answer 18

1) regular or irregular
2) rate
3) p waves present
4) PR interval
5) QRS - narrow or broad
6) is every P followed by a QRS
7) Is every QRS preceded by a p wave

Question 19

What are the ECG changes of ischaemia and myocardial infarction?

Answer 19

• coronary artery occlusion = ischaemia or infarction in area supplied by artery
• changes seen in leads facing affected area of ventricle
• look at PQRST in all 12 leads
• need to know which groups of leads look at different parts of the heart

Question 20

What does partial narrowing of the lumen of arteries cause?

Answer 20

Sub endocardial ischaemia/injury
This area is further away from coronary arteries which lie on the surface of the heart

hence the most vulnerable region, involved first

Question 21

What does complete occlusion of the lumen cause?

Answer 21

Full thickness injury

Including sub- epicardial region

Question 22

What’s a STEMI?

Answer 22

• ST elevation myocardial infarction
• Due to complete occlusion of coronary artery by thrombus
• Full thickness of myocardium involved
• Sub epicardial injury causes ST segment elevation in leads facing affected area

Question 23

What do pathological q waves indicate?

Answer 23

Muscle necrosis

Pathological if more than 1 small square wide and 2 small squares deep

Question 24

How do unstable angina and severe ischaemia present on an ECG?

Answer 24

Same ECG changes seen in both unstable angina and NSTEMI

They are differentiated by a blood test = troponin present in NSTEMI

Question 25

What are the physiological changes in hyperkalaemia?

Answer 25

Resting membrane potential is less negative
This inactivates some voltage gated Na+ channels
Heart becomes less excitable
Conduction problems can occur

Question 26

How does hyperkalaemia appear in an ECG?

Answer 26

Missing p wave
ST segment merges with T wave
Widened QRS