From the Guidelines
Lidocaine generally does not prolong the QTc interval and is considered safe for patients with or at risk for QT prolongation. Unlike some other antiarrhythmic medications, lidocaine is a Class IB antiarrhythmic agent that typically shortens or has minimal effect on the QT interval, as stated in the 2018 AHA/ACC/HRS guideline for management of patients with ventricular arrhythmias and the prevention of sudden cardiac death 1. This makes it a preferred option for treating ventricular arrhythmias in patients with long QT syndrome or those taking other medications that prolong QTc.
Key Points
- Lidocaine works by blocking sodium channels, which affects the depolarization phase of the cardiac action potential rather than the repolarization phase that determines QT interval.
- When administering lidocaine for cardiac indications, the typical loading dose is 1-1.5 mg/kg IV followed by an infusion of 1-4 mg/min, with dose adjustments needed for patients with liver dysfunction or heart failure, as recommended in the guideline 1.
- While lidocaine doesn't typically affect QTc, it's still important to monitor patients for other potential side effects including CNS toxicity (confusion, seizures), hypotension, and bradycardia, especially at higher doses or in patients with hepatic impairment.
- The use of lidocaine in acute myocardial infarction is also supported by previous guidelines, such as the 1996 ACC/AHA guidelines for the management of patients with acute myocardial infarction 1, which highlights its role in treating life-threatening or severely symptomatic arrhythmias.
Administration and Monitoring
- The initial bolus of lidocaine is 1.0 to 1.5 mg/kg (75 to 100 mg), with additional boluses of 0.5 to 0.75 mg/kg (25 to 50 mg) given every 5 to 10 minutes if needed, up to a total of 3 mg/kg, as outlined in the guideline 1.
- A maintenance infusion of 1-4 mg/min can be used, with adjustments as necessary for patients with liver dysfunction or heart failure.
- Monitoring for potential side effects, including CNS toxicity, hypotension, and bradycardia, is crucial, especially in patients with hepatic impairment or those receiving higher doses.
From the Research
Lidocaine and QTc Interval
- The effect of lidocaine on the QTc interval has been studied in various contexts, including its use as an anti-arrhythmic drug and its potential to diagnose long QT syndrome 2, 3, 4, 5.
- A study from 1982 found that lidocaine significantly reduced the QTc interval in patients with acute anterior myocardial infarction, from 0.364 +/- 0.059 sec to 0.352 +/- 0.051 sec at 5 minutes, 0.353 +/- 0.053 sec at 15 minutes, and 0.355 +/- 0.058 sec at 30 minutes (P < 0.05) 2.
- Another study from 2004 found that lidocaine did not significantly change the QTc interval in patients with borderline QTc interval prolongation, but a subsequent potassium infusion decreased the QTc interval by 9% (P < 0.005) in patients with long QT syndrome 3.
- A study from 2008 found that intravenous lidocaine prevented the prolongation of the QTc interval induced by tracheal intubation, with no significant changes in the QTc value in the lidocaine group 4.
- A study from 2022 found that chronic continuous intravenous lidocaine was effective in reducing LQT3-triggered cardiac events in patients with malignant type 3 long QT syndrome who were refractory to standard therapy 5.
Clinical Implications
- The use of lidocaine as an anti-arrhythmic drug has been re-evaluated in recent years, with potential indications including the treatment of acute sustained ventricular tachyarrhythmias 6.
- Lidocaine's ability to block voltage- and pH-dependent sodium channels and decrease the action potential duration makes it a useful drug for interrupting life-threatening tachycardias caused by re-entrant mechanisms, especially in ischemic tissue 6.
- However, the use of lidocaine is not without side effects, and its potential benefits must be carefully weighed against its risks, including dizziness and seizures 5.