Arrhythmia Drugs

Question 1

Amiodarone

Answer 1

MOA: Decrease sinus node and slows atrioventricular bypass tract conduction and prolong refractory period of myocardial tissues.

Indication: treatment and prophylaxis of serious tachyarrhythmias refractory to other treatment.

Side effect: worsen arrhythmia (very long half life), nausea vomiting, constipation

Counsel: Avoid sun exposure, wear protective clothing and use sunscreen.
Avoid grapefruit juice
Monitor blood test, ECG and chest x-ray

Question 2

Digoxin

Answer 2

MOA: Inhibits Na+/K+ ATPase pump
- Causing an increase in intracellular calcium = increase cardiac contraction
- Improve CO leads to reduce sympathetic nerve activity = reduce HR
- Increase parasympathetic effect - slow down conduction velocity through the AV node

Indication: HF and AF

Precautions: hyper/hypothyrodisim and electrolyte imbalance and cardiac

Avoid using with drugs that slow cardiac conduction or inhibit/induce P-gp as it increase ADR or decrease efficacy.

Reduce dose in renal impairment
HALF the dose if CrCl = <60L/min

Question 2

Disopyramide

Answer 2

Prolong refractory period of myocardial tissue and reduce automaticity in Purkinje fibres.

Indication: life threatening VT

Precaution
- Digoxin toxicity—contraindicated.
- Treatment with flecainide—contraindicated.
- Electrolyte disturbances (eg hypokalaemia, hyperkalaemia, hypomagnesaemia)—increase risk of arrhythmias; correct before starting treatment if possible.

ADR: May worsen arrhythmia, dry mouth, constipation, N/V

Question 2

Lignocaine/Lidocaine

Answer 2

MOA: Reduces automaticity of myocardial tissue with little effect on cardiac conduction.

Question 2

Flecainide

Answer 2

MOA: Slows cardiac conduction and to a lesser extent, increases refractory period in all myocardial tissues (including bypass tracts) but particularly in the His-Purkinje (ventricular conduction) system. Also has negative inotropic activity.

May worsen arrhythmia

Question 3

Adenosine

Answer 3

MOA: Depresses sinus node activity and slows conduction through the atrioventricular node; also produces peripheral and coronary vasodilation.

Adenosine has a rapid onset and short duration of action.

Question 4

Atropine

Answer 4

MOA: short acting muscarinic antagonist increase HR by inhibiting parasympathetic system causing an activation of sympathetic system

Question 5

Isoprenaline

Answer 5

MOA: Beta agonist, increase cardiac output, tend to maintain or increase systolic BP and decrease diastolic BP by lowering SVR. It increases automaticity and AVN conduction improving coronary blood flow