Review Question - QID 106835

Lidocaine, a class IB antiarrhythmic, preferentially binds depolarized tissue (ischemic) making it a desirable agent for treatment of post-MI arrhythmias. Toxicity includes central nervous system (CNS) effects.

This patient has experienced an inferior wall myocardial infarction (MI) as demonstrated by her EKG showing ST segment elevation in leads II, III, and aVF. The treatment discussed in the vignette was most likely immediate revascularization via endovascular cathaterization and stent placement. In the first 24 hours following an MI, patients are at increased risk for arrhythmias. Historically, class IB antiarrhythmics such as lidocaine have been used as prophylaxis because of preferential binding to (ischemic) tissue that has been damaged in the MI. While prophylaxis with these medications is now less common, there is still a role for treatment of ventricular arrhythmias with class IB antiarrhythmics in specific settings, though they must be carefully dosed and monitored as toxicity include CNS effects. This includes lightheadedness, dizziness, drowsiness and confusion in the mild cases and progresses to seizures and respiratory arrest in severe cases.

Denaro et al. examines the adverse effects seen in both therapeutic practice and accidental or premeditated overdose of class IB antiarrhythmics. They state toxicity is very common with these class IB agents and can be life-threatening. Management of toxicity is largely supportive and symptomatic and generally consists of ICU monitoring. In severe cases, hemodialysis may be effective.

Kim et al. performed a randomized control trial to compare the effect of lidocaine and dexmedetomidine infusion during off-pump coronary artery bypass graft (OPCAB). They find that lidocaine had cardioprotective effects in terms of decreased myocardial injury markers. They found that lidocaine infused at 2 mg/kg/h, but not dexmedetomidine infused at 0.3-0.7 µg/kg/h reduced postoperative myocardial injury marker levels compared with the control group. However, no other clinical benefits were observed.

Figure A is an EKG demonstrating an inferior MI as demonstrated by ST segment elevation in leads II, III, and aVF. Illustration A graphically reviews the most common post-MI complications.

Incorrect Answers:
Answer 2: Cinchonism (headache, tinnitus) is a toxicity of quinidine, a class IA antiarrhythmic.
Answer 3: Torsades de pointes is a toxicity of class IA and class III antiarrhythmics due to their prolongation of the QT interval.
Answer 4: Asthma exacerbation is a toxicity of beta-blockers (class II antiarrhythmics).
Answer 5: Flushing is a toxicity of calcium channel blockers (class IV antiarrhythmics).