Principles of antiarrhythmic drug therapy:
- Assess the necessity of drug therapy: Arrhythmias without organic heart disease or significant symptoms that do not affect prognosis often do not require treatment. The main goal of treating arrhythmias is to alleviate symptoms or reduce their impact on cardiac function and myocardial ischemia, rather than eliminating or reducing arrhythmias.
- Consider underlying heart disease: Address the underlying causes and triggers. Balance the importance and urgency of arrhythmia treatment, focusing on comprehensive measures that can improve prognosis, such as anticoagulation therapy for atrial fibrillation.
- Select the appropriate antiarrhythmic drug: For acute and hemodynamically unstable arrhythmias, prioritize drug efficacy to quickly terminate or improve the arrhythmia, using electrical cardioversion or temporary pacing if necessary. For chronic arrhythmias, consider drug safety and compatibility with the treatment of underlying conditions.
- Coordinate drug and non-drug treatments.
- Monitor for adverse effects: Be aware of potential adverse effects of antiarrhythmic drugs, including impacts on cardiac function, proarrhythmic effects, and effects on other organs and systems. Proarrhythmic effects, defined as new or exacerbated arrhythmias caused by antiarrhythmic drugs, occur in 5% - 10% of cases. Patients with congestive heart failure, those on digoxin and diuretics, and those with prolonged QT intervals are more prone to these effects. Most proarrhythmic effects occur within days of starting treatment or changing dosage, often manifesting as sustained ventricular tachycardia, long QT interval, and Torsades de Pointes.
Classification of antiarrhythmic drugs
Vaughan Williams classification
Based on electrophysiological effects, antiarrhythmic drugs are divided into four classes.
- Class I: Sodium channel blockers
- Ia: Drugs slowing the rate of rise of phase 0 of the action potential (Vmax) and prolonging the action potential duration, including quinidine, procainamide, and disopyramide.
- Ib: Drugs not slowing Vmax but shortening the action potential duration, including mexiletine, phenytoin, and lidocaine.
- Ic: Drugs slowing Vmax and conduction with slight prolongation of the action potential duration, including propafenone.
- Class II: β-adrenergic blockers, including metoprolol, propranolol, nadolol, carvedilol, bisoprolol, and atenolol, which have been shown to improve long-term prognosis.
- Class III: Potassium channel blockers prolonging repolarization, including amiodarone, dronedarone, sotalol, ibutilide, and dofetilide.
- Class IV: Calcium channel blockers, including verapamil and diltiazem.
The Vaughan Williams classification has been widely used due to its simplicity and practicality. However, it is too simplistic to encompass all current antiarrhythmic drugs, and many new drugs cannot be categorized within it.
Modernized classification
An updated classification expands on the original, dividing antiarrhythmic drugs into 8 categories with 32 subcategories:
- Class 0: Sinoatrial node pacemaker current (If) inhibitors
- Class I: Voltage-gated sodium channel blockers
- Class II: Sympathetic nervous system inhibitors and activators
- Class III: Potassium channel openers and blockers
- Class IV: Calcium handling modulators
- Class V: Mechanosensitive ion channel blockers
- Class VI: Gap junction channel blockers
- Class VII: Upstream target modulators
The modernized classification includes late sodium current inhibitors (Class Id) and incorporates commonly used drugs like digoxin, atropine, isoproterenol, and adenosine. It expands to include categories for abnormal heart rates (Class 0), mechanical stretch (Class V), intercellular communication (Class VI), and upstream target-related drugs (Class VII). This classification covers current pharmacological targets in cardiac electrophysiology, addressing the limitations of the traditional system, though its clinical application still requires further development.
Common antiarrhythmic drugs
Common antiarrhythmic drugs include quinidine, procainamide, lidocaine, mexiletine, propafenone, ranolazine, propranolol, nadolol, carvedilol, metoprolol, bisoprolol, esmolol, amiodarone, dronedarone, ibutilide, dofetilide, nifekalant, vernakalant, verapamil, adenosine, ivabradine, isoproterenol, digoxin, and deslanoside.