Lidocaine IV (Cardiac Arrhythmia)

How it works

Given intravenously it blocks fast cardiac sodium channels preferentially in ischaemic and depolarised myocardium, shortening the action potential and raising the threshold for ventricular ectopy and re-entry.

Prescribing in practice

• Lidocaine has a narrow therapeutic margin and accumulation causes progressive central nervous system toxicity (perioral numbness, confusion, then seizures) and myocardial depression, so the rate of intravenous administration must be controlled.
• Clearance is reduced in hepatic impairment, heart failure and low cardiac output states, requiring lower infusion rates to avoid toxicity.
• It is contraindicated in severe sinoatrial or atrioventricular conduction disorders unless the patient is paced.

Monitoring

Use continuous ECG and blood pressure monitoring during intravenous administration and watch for neurological signs of toxicity.

Counselling the patient

• This is an emergency injection given and monitored by the resuscitation or critical-care team.
• Tell the team if you notice numbness around the mouth, ringing in the ears, or feel confused or drowsy.
• The dose is adjusted for liver or heart problems to keep blood levels safe.

Evidence & guidelines

Resuscitation Council UK advanced life support guidance lists lidocaine as an alternative antiarrhythmic to amiodarone for shock-refractory ventricular fibrillation or pulseless ventricular tachycardia.