Lecture 7

Question 1

Why is there a delay at the AV node?

Answer 1

Because the depolarisation from the SA node takes longer to spread across atrial muscle cells.

Question 2

P wave

Answer 2

Atrial depolarisation

Question 3

P-R interval

Answer 3

Time between beginning of atrial excitability and ventricular excitability.

Question 4

How long is a normal P-R interval?

Answer 4

0.16 seconds

Question 5

What is QRS?

Answer 5

Ventricular depolarisation. Atrial repolarisation occurs here too but is obscured.

Question 6

Q-T interval

Answer 6

Contraction occurs here

Question 7

How long is a normal Q-T interval

Answer 7

0.35 seconds

Question 8

What shape should the S-T segment be?

Answer 8

A flat line- there is no change in electrical currents.

Question 9

What is the T wave?

Answer 9

Ventricular repolarisation.

Question 10

How would an ECG diagnose 1st degree heart block?

Answer 10

A longer P-R interval of about 0.28 seconds.

Question 11

What can cause 1st degree heart block?

Answer 11

Verapamil or rheumatic heart disease

Question 12

How can you see 2nd degree heart block on an ECG?

Answer 12

Dropped beat, not every P wave is followed by a QRS. 2:1 is where every second P wave has a QRS. 3:1 is where every 3rd P wave has a QRS.

Question 13

What is an example of a 2nd degree heart block?

Answer 13

Atrial flutter

Question 14

What would an ECG show for 3rd degree heart block?

Answer 14

Complete dissociation of P waves from QRS complexes. QRS still regular at 40 per minute due to auto rhythmicity of AV node.

Question 15

What does 3rd degree heart block lead to?

Answer 15

Severe myocardial ischemia

Question 16

What is bradycardia?

Answer 16

Slow heart rate below 60bpm

Question 17

What is tachycardia?

Answer 17

Fast HR above 100bpm

Question 18

Name a regular arrhythmia?

Answer 18

Flutter

Question 19

Name an irregular arrythmia?

Answer 19

Fibrillation.

Question 20

What does an ECG show for atrial fibrillation?

Answer 20

no P wave, narrow QRS complex.

Question 21

Describe atrial fibrillation

Answer 21

No coordinated electrical activity in SA node. AV node fires occasionally.

Question 22

What are the symptoms of atrial fibrillation?

Answer 22

Tiredness, shortness of breath, inability to exercise

Question 23

Describe atrial flutter

Answer 23

Atria contract faster than normal, up to 300 times a minute. Atria and ventricle contract at different speeds. Can see second degree heart block.

Question 24

What is seen on an ECG for ventricular tachycardia?

Answer 24

A not obvious P wave and abnormally fast heart rate.

Question 25

What are the symptoms of ventricular tachycardia?

Answer 25

Chest pain, weak, breathless, lightheaded.

Question 26

What is seen on an ECG with ventricular fibrillation?

Answer 26

No p wave, broad QRS.

Question 27

What is a class 1 antiarrythmic drug?

Answer 27

Na+ channel blockers

Question 28

What is class II?

Answer 28

Beta-blockers (anti-sympathetic)

Question 29

What is class III?

Answer 29

K+ channel blockers

Question 30

What is class IV?

Answer 30

Ca2+ channel blockers

Question 31

What is class V?

Answer 31

Cardiac glycosides.

Question 32

What do class Ia treat? Give an example

Answer 32

Atrial tachycardia or atrial fibrillation. e.g. quinidine. These are moderate blockers

Question 33

What do class 1b treat and give an example?

Answer 33

Ventricular tachycardia or fibrillation. These are very weak blockers. E.g. lidocaine.

Question 34

What do class 1c treat and give an example?

Answer 34

Life threatening ventricular fibrillation. e.g. flecainide

Question 35

How do class II work?

Answer 35

Beta blockers that increase the time between each AP. they prolong phase 4.

Question 36

Why are class III preferred drugs to use?

Answer 36

They only slow repolarisation rate, no risk in blocking depolarisation. e.g. amiodarone

Question 37

What is HR set by?

Answer 37

The sinus rhythm of the SA node

Question 38

What does the sympathetic system do to the heart?

Answer 38

Increases HR by innervating nodal tissue and ventricular muscle increases contractility. Positive ionotropic and chronotropic effects. Depolarisation of cell is quicker.

Question 39

What is a class II drug?

Answer 39

Beta-blocker- propranolol.

Question 40

What does the parasympathetic system do to the heart?

Answer 40

Right side nerves innervates the SA node, Left side to AV node. Has a negative chronotropic effect.

Question 41

What neurotransmitter and mechanism is involved in the parasympathetic system?

Answer 41

Ach on M2 muscarinic receptors. causes hyperpolarisation which slows depolarisation. Calcium channels open more slowly. Gi has inhibitory effect on adenyl cyclase. G-beta and gamma open K+ channels.