4 Antiarrhythmic Medications
Review antiarrhythmic drug classes, rhythm-specific treatment choices, urgent management principles, and the monitoring needed to reduce medication-related risk.
Choosing treatment safely
Antiarrhythmic drugs alter cardiac impulse formation or conduction. Their effects can also provoke a new arrhythmia or worsen an existing one, so treatment depends on the identified rhythm and the patient’s clinical context—not simply on suppressing every irregularity.
The provide a useful guide to broad drug mechanisms, but medicines grouped in the same class do not necessarily have identical effects. Drug choice should account for hemodynamic stability, cardiac structure and function, kidney function, and ECG findings.
Drug classes and broad effects
The four summarize broad mechanisms and examples:
Class I: Blocks fast sodium channels. Class IA includes procainamide, class IB includes lidocaine, and class IC includes flecainide and propafenone. Class IA drugs can prolong the QT interval. Class IC drugs slow conduction and are generally avoided after myocardial infarction or in significant structural heart disease.
Class II: Blocks beta-adrenergic effects. Metoprolol and esmolol slow heart rate and AV-node conduction; monitor for bradycardia and hypotension.
Class III: Prolongs repolarization, mainly through potassium-channel effects. Examples include amiodarone, dofetilide, and sotalol. Some agents prolong the QT interval and can cause . Dofetilide and sotalol require careful monitoring of QT, electrolytes, and kidney function.
Class IV: Blocks L-type calcium channels in the AV node. Diltiazem and verapamil slow AV-node conduction; monitor for bradycardia and hypotension.
Adenosine and digoxin have antiarrhythmic effects but are not included in these four classes.
and monitoring
Antiarrhythmics can cause . A drug’s ability to suppress an arrhythmia on an ECG does not by itself establish that it improves survival. Safety depends on patient-specific risk assessment and monitoring, including ECG intervals, heart rate, electrolytes, kidney function, medication interactions, and structural heart disease.
For atrial fibrillation (AF), rate control and rhythm control are distinct strategies. Rhythm-control drugs do not replace assessment for stroke-prevention therapy, including anticoagulation when indicated.
QT and kidney-related precautions
Dofetilide dosing depends on kidney function. Before and during treatment, correct low potassium or magnesium and monitor the ECG and QT interval, electrolytes, and renal function. Initiation requires monitored care; these measures reduce the risk of QT-related ventricular arrhythmia, including .
Dofetilide and sotalol both require careful attention to QT, electrolytes, and kidney function. A low potassium level or impaired kidney function makes careful selection and monitoring especially important.
Class IC drugs and structural heart disease
Class IC drugs such as flecainide and propafenone should not be used to maintain sinus rhythm in AF in patients with a prior myocardial infarction or significant structural heart disease, including heart failure with reduced ejection fraction. In these settings, the concerns include worsening heart failure, , and increased mortality risk.
Flecainide or propafenone can organize AF into atrial flutter. An is generally paired with a class IC drug to reduce the risk of rapid 1:1 conduction of flutter to the ventricles.
Amiodarone toxicity
Amiodarone can cause pulmonary, thyroid, and hepatic toxicity, as well as ocular, skin, neurologic, and cardiac adverse effects. Its long half-life means its effects may persist after the drug is stopped.
New cough, shortness of breath, jaundice, or symptoms suggesting thyroid dysfunction warrant prompt clinical assessment during long-term therapy.
Urgent management of tachyarrhythmias
Assess hemodynamic stability before choosing treatment. Instability—including hypotension, altered mental status, shock, ischemic chest discomfort, or acute heart failure—requires urgent action. The intervention depends on the rhythm: synchronized cardioversion is used for many unstable tachyarrhythmias, while pulseless or polymorphic rhythms require the appropriate defibrillation pathway. Follow emergency protocols.
Adenosine is not appropriate for every tachycardia, including irregular wide-complex rhythms. Treatment should follow rhythm identification rather than applying one intervention indiscriminately.
Pre-excited atrial fibrillation
In a patient with who is hemodynamically stable, clinician-directed emergency options include intravenous procainamide or ibutilide, or electrical cardioversion.
AV-nodal blockers—including diltiazem, verapamil, beta blockers, digoxin, and adenosine—are contraindicated in because they may accelerate conduction over the accessory pathway and precipitate ventricular fibrillation. If the patient is hemodynamically unstable, electrical cardioversion is indicated.