What is the recommended dosage and administration of lidocaine (intravenous anesthetic) for treating ventricular arrhythmias, such as ventricular tachycardia?

Lidocaine for Ventricular Arrhythmias

For ventricular tachycardia in the setting of acute myocardial infarction, administer an initial IV bolus of 1 mg/kg (maximum 100 mg), followed by additional 0.5 mg/kg boluses every 8-10 minutes as needed up to a total of 3-4 mg/kg, then maintain with a continuous infusion of 1-4 mg/min (20-50 mcg/kg/min). 1, 2, 3

Initial Bolus Dosing

• Give 1 mg/kg IV bolus (not exceeding 100 mg) as the first dose 1, 2, 3
• Administer additional boluses of 0.5 mg/kg every 8-10 minutes if the initial dose fails to suppress the arrhythmia 1, 2, 3
• Maximum cumulative bolus dose is 3-4 mg/kg 1, 2, 3
• For VF/VT cardiac arrest, use only bolus therapy (100 mg initially), which may be repeated every 2-3 minutes 3

Maintenance Infusion

• After successful bolus therapy, start continuous infusion at 1-4 mg/min (or 20-50 mcg/kg/min, which equals 1.4-3.5 mg/min in a 70 kg patient) 1, 2, 3
• Patients requiring multiple boluses to achieve suppression need higher maintenance doses (40-50 mcg/kg/min) 1, 3
• Reduce the infusion rate by 1 mg/min at 12 hours, but no later than 24 hours, as lidocaine's half-life increases after 24-48 hours of continuous infusion 3

Critical Dose Reductions Required

This is where most errors occur. Lidocaine clearance is dramatically reduced in certain cardiac conditions, making standard dosing dangerous 1, 4:

• Heart failure: Half-life increases from 1-2 hours to >4 hours 1
• Cardiogenic shock: Half-life exceeds 20 hours 1, 4
• Acute MI with complications: Significantly prolonged elimination 1

You must reduce both bolus and infusion doses substantially in these patients to avoid toxicity 4, 3. The guidelines emphasize this is "appropriate reduction" without specifying exact percentages, but given the 10-20 fold increase in half-life, consider reducing maintenance infusions by at least 50% in heart failure and 75% or more in cardiogenic shock 1, 4.

When to Use Lidocaine vs. Alternatives

Lidocaine is second-line therapy for stable monomorphic VT because it is less effective than procainamide, sotalol, and amiodarone at terminating the arrhythmia 1, 2, 5:

• Procainamide terminated 80% of VTs vs. lidocaine's 21% in head-to-head comparison 5
• Amiodarone is superior to lidocaine for recurrent sustained VT or VF 1

However, lidocaine remains appropriate as first-line therapy in the acute MI setting when VT or VF treatment is indicated 1, 2. The European Society of Cardiology specifically states: "If the estimated risk for (recurrent) ventricular fibrillation is high, lidocaine is usually the drug of first choice" 1.

Specific Indications for Lidocaine in Acute MI

Use lidocaine for 1:

• Frequent VPCs (>6/min)
• Closely coupled VPCs (R-on-T phenomenon)
• Multiform VPCs
• Short runs of 3 or more VPCs in succession
• Sustained ventricular tachycardia
• VF resistant to defibrillation

Hemodynamically Unstable VT

Immediate synchronized cardioversion is the primary intervention for unstable VT with pulse, not pharmacologic therapy 2. Lidocaine can be used if the patient is somewhat stable, but electrical cardioversion should not be delayed 3.

Monitoring for Toxicity

Watch for these signs of lidocaine toxicity 2, 3:

CNS symptoms (most common):

• Perioral numbness
• Dizziness and drowsiness
• Confusion and slurred speech
• Muscle twitching
• Seizures
• Respiratory depression

Cardiovascular effects:

• Bradycardia
• Sinus arrest
• Hypotension
• Myocardial depression 1

There is an increased incidence of asystole with lidocaine, which may obscure its favorable effects on VF suppression 1.

Common Pitfalls to Avoid

1. Using standard doses in heart failure or cardiogenic shock without significant reduction - this is the most critical error and can lead to severe toxicity 1, 4, 3

2. Relying on lidocaine as first-line therapy for stable VT in non-MI settings - procainamide (10 mg/kg at 100 mg/min) or amiodarone are more effective 1, 2, 5

3. Increasing maintenance infusion without an additional bolus - this results in a very slow increase in plasma concentration (>6 hours to reach new plateau) 3

4. Prophylactic use beyond 24 hours - trials have failed to demonstrate that suppression of VPCs significantly reduces overall mortality in acute MI, and there is increased risk of asystole 1, 6

5. Making decisions about lidocaine response too early in chronic VPBs - response is delayed in patients with chronic ventricular ectopy compared to acute-onset VPBs; accurate assessment cannot be made in the first 8 hours 7