Arrythmias

Question 1

What causes arrythmias

Answer 1

Structural cardiac disease

Drugs

Toxins

Metabolic diseases
e.g. renal disease

Systemic diseases
e.g. sepsis

Sympathetic tone
Increased epinephrine release
e.g. pain, fear

Question 2

How are sympathetically mediated arrythmias treated

Answer 2

Sympathetically mediated arrythmia – adrenoreceptor

Supraventricular tachycardia (SVT)

Beta blockers (antagonists)
Propanolol
Esmolol

Adenosine
Blocks adenylyl cyclase & increases potassium efflux

Question 3

How are parasympathetically mediated arrythmias treated

Answer 3

Acetylcholine mediated
Blocks adenylyl cyclase & reduces cAMP
Reduces calcium effects
Reduces automaticity
Reduced contraction
Slow conduction at AV node

Atropine – muscarinic antagonist
Reduces parasympathetic (vagal) tone
Increases heart rate by reducing suppression

Muscarinic agonists – toxins
Muscarine found in mushrooms
Bradycardia & hypotension

Question 4

What are sodium channel blockers used for in arrythmias

Answer 4

Lidocaine – sodium channel blocker

Raises depolarisation threshold – slows Na channels

Slows AP generation

Treatment for Ventricular tachycardia

Question 5

What are potassium channel blockers used for in arrythmias

Answer 5

Increase refractory period & duration of action potential as repolarisation takes longer

Amiodarone, sotalol

Ventricular tachycardia

Question 6

What are calcium channel blockers used for in arrythmias

Answer 6

Block voltage gated Ca2+ channels in cardiac muscle

Slows conduction, reduces contraction force & causes coronary vasodilation

Verapamil & diltiazem

Symapthetic ventricular tachycaria & diastolic dysfunction