10-Drugs and arrhythmias

Question 1

Define arrhythmia

Answer 1

Abnormality of heart rate/rhythm

Question 2

What is the threshold for bradycardia?

Answer 2

< 60 bpm

Question 3

What are the types of bradycardic arrhythmias and what causes them?

Answer 3

Sinus bradycardia- caused by intrinsic SAN dysfunction/ extrinsic drugs (beta blockers and calcium channel blockers)
Conduction blocks - slow conduction at AVN due to above drugs

Question 4

What is the threshold for tachycardia?

Answer 4

> 100 bpm

Question 5

What are the types of tachycardic arrhythmias and what causes them?

Answer 5

Ectopic pacemaker - damaged myocardium depolarises, latent pacemaker activated by the ischaemia, dominates over SAN
After depolarisation - abnormal depolarisation following AP, more likely when intracellular calcium too high
Atrial flutter/fibrillation/re-entry loop - too fast conduction to the ventricles

Question 6

What increases the risk of delayed after depolarisations?

Answer 6

High intracellular calcium

Question 7

What increases the risk of early after depolarisation?

Answer 7

Prolonged action potential

Question 8

What happens in normal excitation mechanisms?

Answer 8

Refraction of impulses causes them to meet and cancel out

Question 9

Describe the two re-entrant mechanisms

Answer 9

Damaged region blocks impulse completely, so impulses don’t cancel out
Damaged region blocks impulse unidirectionally, so excitation takes long way round

Question 10

What causes atrial fibrillation?

Answer 10

Multiple re-entrant circuits in atria

Question 11

What causes AVN re-entry?

Answer 11

Fast and slow pathways in the AVN

Question 12

What causes ventricular pre-excitation?

Answer 12

Accessory pathway between atrial and ventricles creating a re-entry loop

Question 13

What kind of arrhythmia is Wolff-Parkinson-White?

Answer 13

Ventricular pre-excitation

Question 14

Which kind of arrhythmia is paraxsysmal?

Answer 14

Wolff-Parkinson-White

Question 15

What are the types of anti-arrhythmic drugs?

Answer 15

Na voltage gates channel blockers
B adrenoreceptor antagonist
K channel blockers
Ca channel blockers

Question 16

Name a Na voltage gated channel blocker

Answer 16

Lidocaine

Question 17

How do Na voltage gated channel blockers work?

Answer 17

Preferentially block damaged, depolarised tissue by blocking Na gates that are open/inactive
Dissociates before the next action potential

Question 18

When would lidocaine be prescribed?

Answer 18

After an MI if ventricular tachycardia present

Question 19

Name a beta adrenoreceptor antagonist

Answer 19

Propanolol/atenolol

Question 20

How do beta adrenoreceptor antagonists work?

Answer 20

Block b1 receptors in the heart which:
Decreases slope of pacemaker potential in SAN
Decreases sympathetic action
Slows conduction at AVN
Reduce O2 demand

Question 21

When would you prescribe propanolol?

Answer 21

After an MI, as MI increases sympathetic output

Question 22

Name a k channel blocker

Answer 22

Amiodorone

Question 23

How do k channel blockers work?

Answer 23

Block k channels, which lengthens the absolute refractory period, prolonging the action potential

Question 24

Why are k channel blockers not commonly used?

Answer 24

Can be pro-arrhythmic

Question 25

When would you prescribe amiodorone?

Answer 25

Post MI if ventricular arrhythmias present

Or in Wolff-Parkinson-White to treat tachycardia

Question 26

Name a Ca channel blocker

Answer 26

Verapamil