Drugs for Acute, Life Threatening Arrhythmias

Drugs for Acute, Life Threatening Arrhythmias

·        For tachycardias:

o   Ventricular Tachycardia:

§  Lignocaine: dose 1 – 1.5 mg/kg by slow iv bolus, followed by infusion of 1 – 4 mg/min. Reduce dose in heart failure, shock, > 70 years, b blockade & hepatic disease. Side effects include convulsions. Action on sodium channels reduces myocardial excitability, especially in ischaemic myocardium. Raises threshold for VF, and suppresses VT and ventricular ectopy. Should be considered in VF after 3 defibrillatory loops. No evidence of usefulness in converting VF but may prevent return to VF. Reduces blood pressure and slows the heart rate

§  Bretyllium: anti-adrenergic, although initially causes adrenergic stimulation (for 20 minutes), raises VF threshold. Use if lignocaine fails

§  Procainamide: powerful antiarrhythmic and strong negative inotropic agent, but slow to act. Use where lignocaine has failed to suppress recurrent ventricular tachycardia

§  Magnesium: prevention and treatment of refractory ventricular arrhythmias

o   SVTs:

§  Adenosine: slows sinus rate and AV conduction. Use for SVT due to re-entry. Very short T½

§  Verapamil: Ca blocker. Suppresses pacemaker activity in SA and AV nodes. For SVT where adenosine has failed

§  Amiodarone: delays repolarisation with less cardiac depression than other antiarrhythmics. Good for SVT, less so for ventricular arrhythmias. Via central line, long T½

§  b-blockers: useful in treatment of hypertension, supraventricular arrhythmias and recurrent VT where LV function is not severely impaired. E.g. propranolol (unselective), atenolol (b1 selective), metoprolol (relatively b selective), labetalol (a & b selective, short acting, for acute hypertensive crises), sotalol (non-selective b blocker + antiarrhythmic), esmolol (ultra-short acting b block)

·        For bradycardias:

o   Atropine: Competitive anticholinergic at muscarinic nerve endings. Enhances SA discharge and AV conduction. Use in bradycardia or AV block. Care in MI – may increase pulse ® extension of ischaemia

o   Isoprenaline: b agonist - use for significant bradycardia refractory to atropine. Use dopamine or adrenaline first

·        Other supra-ventricular arrhythmias:

o   Digoxin: ­force of contraction and ¯AV conduction – for heart failure and supraventricular arrhythmias (particular AF). Avoid in recent MI, heart block, renal impairment, and hypokalaemia

o  Dopamine: for treatment complete heart block. A catecholamine. Infuse at 5 – 20 mg/kg/min. Adjust to keep heart rate at 60 beats per minute. ­renal blood flow (® ­renal output) through renal vasodilator and due to ­CO and perfusion generally

·        Others:

o  Inotropes: dopamine and dobutamine – for supporting blood pressure once cardiac output has been established. Useful in cardiac failure secondary to ischaemia.

o  Nor-adrenaline: intense vasoconstrictor – use for restoring MAP where vasodilation induced hypotension

o  GTN: venous vasodilator - ¯blood pressure and improve artery blood flow. Preload and afterload reduced

o  Diuretics: frusemide – also causes venodilation (® ¯preload)

o  Antihistamines: H1 antagonists (promethazine / Phenergan), H2 antagonists (ranitidine)