Antiarrhythmic drugs, prescribed to manage both atrial and ventricular cardiac arrhythmias, are divided into four classes according to their action. (See Drug names by class.) Some antiarrhythmic drugs, such as adenosine and digitalis, can't be classified by this system.
Adverse reactions to antiarrhythmics can be serious. Most of these drugs can aggravate existing arrhythmias or cause new ones. They may trigger hypersensitivity reactions, hypotension, gastrointestinal problems (such as nausea, vomiting, or altered bowel elimination), and central nervous system (CNS) disturbances (such as dizziness or fatigue). Some antiarrhythmics may worsen heart failure and Class II drugs may cause bronchoconstriction.
Contraindications or cautions apply for the following patients:
- Patients who are hypersensitive to antiarrhythmics. Avoid their use.
- Patients with cardiogenic shock, digitalis toxicity, or second- or third-degree heart block (unless the patient has a pacemaker). Avoid or use cautiously.
- Pregnant women. Use only if the potential benefit outweighs the risk.
- Breast-feeding women. Use cautiously. Many antiarrhythmics (such as amiodarone) appear in breast milk.
- Children. Because children have a higher risk of adverse reactions, closely monitor them.
- Older adults. Use cautiously because these patients may have physiologic changes in the cardiovascular system.
- Assess your patient's apical pulse rate and rhythm before administering an antiarrhythmic.
- Monitor his cardiac rate and rhythm continuously when therapy starts or any time the dosage is adjusted.
- Check his vital signs frequently.
- Assess your patient for evidence of adverse drug events and notify the prescriber if one occurs.
- Monitor the drug level as indicated.
- Don't crush sustained-release tablets.
- Take safety precautions regarding adverse CNS reactions. For example, teach the patient to change position slowly to minimize dizziness.
- Stress the importance of taking the drug exactly as prescribed.
- Teach your patient to take his pulse before each dose and to notify his practitioner if he notes any abnormalities.
- Warn him to avoid driving or hazardous activities until the drug effects are known.
- Tell him to limit his fluid and salt intake if the drug causes fluid retention.
Drug names by class
- Class I: interfere with sodium channels to stabilize neuronal cardiac membranes
- Class IA: depress phase 0 and stabilize cardiac membranes
- Class IB: depress phase 0, shorten the action potential, and stabilize cardiac membranes
- Class IC: decrease conduction velocity but not repolarization rate
- Class II (beta-blockers)
- Class III
- Class IV (calcium channel blockers)