Antiarrhythmics are medications used to prevent or terminate arrhythmias, abnormal heart rhythms resulting from a disturbance in the heart’s electrical system. These medications are used in a number of situations. They may be used to terminate an acute arrhythmia in an emergency situation, to prevent the recurrence of an arrhythmia, or to lower the risk of an arrhythmia that has not yet occurred in a high-risk patient.

These medications work in a number of ways, depending on the type of arrhythmia and kind of medication. In general, the leading class of antiarrhythmics (class I) interferes with the flow of ionized minerals through the heart. These minerals include sodium and calcium, which can cause the heart to beat too rapidly (tachyarrhythmias).  Physicians may need to experiment with a number of antiarrhythmics to find one that effectively treats a patient's particular condition.

A physician will use a particular drug (or class of drugs) based on the patient’s medical history, specific type of arrhythmia, type of underlying heart disease (if present) and current symptoms. Though antiarrhythmic medications often manage the problem quite effectively, they cannot cure it. In many cases, antiarrhythmic medications need to be taken for life.

Some forms of arrhythmia are resistant to drug therapy alone, and are best treated surgically with implanted devices such as a pacemaker or an implantable cardioverter defibrillator (ICD). Other forms of arrhythmias may be treated with radiofrequency ablation. Anti-arrhythmic medications are sometimes used in conjunction with ICDs to reduce the risk of life-threatening tachyarrhythmias.

Antiarrhythmics are medications used to treat arrhythmias, abnormal heart rhythms resulting from a disturbance in the heart’s electrical system. Antiarrhythmic medications are frequently used in the setting of rapid heartbeats. The most common tachyarrhythmias treated with antiarrhythmics include:

• Atrial tachycardia and atrial fibrillation. These conditions occur when the upper chambers of the heart (atria) beat too rapidly and at times irregularly. These tachyarrhythmias are generally not immediately life-threatening, but do increase the risk of stroke because blood clots can form in the atria and travel into the brain.
  
  
• Ventricular tachycardia. This is a rapid heart rhythm that occurs in the lower chambers of the heart (ventricles). Ventricular tachycardia can be very dangerous if it progresses to ventricular fibrillation (see below).
  
  
• Ventricular fibrillation. This occurs when the ventricles beat in a very chaotic and loosely organized fashion. Ventricular fibrillation is a serious, life-threatening condition that must be corrected immediately or death will likely result. Antiarrhythmic medications are sometimes prescribed to prevent ventricular fibrillation. In recent years, implantable cardioverter defibrillators (ICDs) have become common in the prevention and immediate treatment of ventricular fibrillation. These devices are implanted inside the chest. They monitor the heart rhythm, and in the event of ventricular fibrillation, they administer an electric shock to jolt the heart back into a normal rhythm. The device is similar to the defibrillators carried by emergency paramedic crews. ICDs and antiarrhythmic medications are often used in the same patient. ICDs are also frequently implanted in patients who are at risk of ventricle tachycardia.

Abnormally slow heart rhythms (e.g., bradycardia) are not typically treated with antiarrhythmic medications. Bradycardia can be caused by disease of the heart’s electrical system. It may also result from certain medications (e.g., beta blockers, calcium channel blockers). In trained athletes, low heart rhythms may actually be a sign of a healthy heart. When bradycardia is due to heart disease, and the patient has symptoms (e.g., dizziness, fainting), it is best treated with the implantation of a pacemaker.

Researchers continue to evaluate the role of antiarrhythmics in arrhythmia treatments, especially as ICDs become more popular. In recent years, their use has expanded, and multiple studies have been conducted to determine how antiarrhythmics fit with ICD therapy. In some cases, patients will need to take antiarrhytmics for life even after an ICD has been implanted.

There have been multiple attempts to categorize antiarrhythmic medications; the most widely accepted system is known as the Vaughan Williams classification. Although this system is not perfect, it is used to sort the various antiarrhythmic medications based on their mechanism of action. Some of the drugs exhibit multiple modes of action, however, and may belong in more than one class. The class system includes:

• Class I agents. These drugs are sodium channel blockers that slow electrical conduction in the heart. They are used to treat rapid heart rhythms that originate in the ventricles (e.g., supraventricular tachycardia, ventricle tachycardia, ventricular fibrillation). Class I is further broken down into three subclasses:
  
  

• 1a (quinidine, procainamide and disopyramide). Procainamide and quinidine can be used to convert rapid heart rhythms in the atria (atrial fibrillation) to a normal heart rhythm and help keep patients from having these arrhythmias.
  
  

• 1b (lidocaine, mexiletine, tocainide and phenytoin). These drugs  work with rapid ventricular rhythms, including ventricular tachycardia and ventricular fibrillation. They have no effect on atrial arrhythmias.
  
  

• 1c (ecainide, flecainide, moricizine and propafenone). These drugs are used for life-threatening ventricular tachycardia or ventricular fibrillation, as well as atrial fibrillation.
  
  
• Class II agents. Class II agents are conventional beta blockers. These medications reduce the workload of the heart by blocking certain hormones from binding with beta receptors in the heart, thus keeping a rapid heartbeat from being triggered. These drugs can also reduce a patient's blood pressure and heart rate. This class of of drugs includes propranolol, metoprolol, atenoiol and betaxolol. Beta blockers given after heart surgery have shown to be useful in helping to prevent atrial fibrillation, which occurs in 25 to 40 percent of patients.
  
  
• Class III agents. These drugs block potassium channels in the heart. Drugs in this class include amiodarone, azimilide, bretylium, clofilium, dofetilide, tedisamil, ibutilide, sematilide and sotalol. Sotalol is used in the treatment of ventricular arrhythmias (e.g., ventricular tachycardia). Amiodarone is used in the treatment of ventricular tachycardia or ventricular fibrillation.
  
  
• Class IV agents. Class IV agents are calcium channel blockers. This class includes vetapamil and diltaizem. These medications reduce the workload of the heart and slow its rhythm by blocking calcium ions from signaling the blood vessels to constrict or tighten.
  
  
• Class V agents. This class was created for drugs that did not fit into the other classifications. Class V antiarrhythmic agents include adenosine and digoxin (a kind of inotrope).

Certain antiarrhythmics, such as adenosine, beta blockers and calcium channel blockers, may be used in the hospital during an emergency to quickly restore a tachyarrhythmia to a normal rhythm.

One of the issues with antiarrhythmics is a relatively high incidence of side effects, including arrhythmia. Because of this, the proper choice and dosing of antiarrhythmic medication may require time while the physician and the patient experiment with different medications to see which works the best. Physicians choose which type of antiarrhythmic to prescribe based on each patient’s medical history and current symptoms/conditions. 

The following side effects are common to most antiarrhythmics. Patients should notify their physician immediately if they experience any side effects, including:

This is only a partial list of the more serious side effects antiarrhythmics may cause. Again, patients should immediately contact their physician if they experience any unusual symptom that may be a side effect from medication.

Patients should consult their physician before taking any other over-the-counter or prescription medication .This includes herbal remedies or nutritional supplements, which may contain stimulants. Of particular concern to patients taking antiarrhythmics are:

• Other antiarrhythmics. Taking these medications in combination with each other may worsen heart rhythm problems.
  
  
• Anticoagulants. These medications prevent the formation of blood clots, and some antiarrhythmics may intensify their effects and cause bleeding problems.
  
  
• Antihypertensives. Medications used to treat high blood pressure (hypertension). These include ACE inhibitors, alpha blockers, calcium channel blockers, angiotensin receptor blockers and some diuretics.
  
  
• Antimyasthenics. These medications are used to treat a rare muscular disorder called myasthenia gravis, and some antiarrhythmics can block their effects.
  
  
• Antidyskinetics. These medications are used to treat a rare disorder called Tourette syndrome, and some antiarrhythmics can block their effects.
  
  
• Antidepressants. These medications are used to treat clinical depression, and some antiarrhythmics can block their effects.
  
  
• Insulin. Certain antiarrhythmics may affect the insulin used to treat diabetes, or affect other oral medications for diabetes.
  
  
• Urinary alkalizers. These medications make urine less acidic and may cause a buildup of some antiarrhythmics in the body.

There are other conditions that may prevent an individual from using certain antiarrhythmics, including:

• Asthma or other lung problems (e.g., chronic bronchitis, emphysema)
• Atrial fibrillation
• Thyroid problems
• Liver disease
• Kidney disease
• Pregnancy or breastfeeding
• Lupus

Individuals with any of these conditions should discuss the use of antiarrhythmics with their physician.

When first taking antiarrhythmics, patients should avoid operating heavy machinery (e.g., driving) until they know how the medication will affect them. Most patients on medication to treat arrhythmias will be taking it for the rest of their lives, provided no serious side effects occur. Patients should remember that antiarrhythmics control abnormal heart rates, but do not cure them. Even if all their symptoms are relieved, patients should continue to take their medication exactly as directed. They should also keep all scheduled follow-up appointments with their physicians. In addition to taking medication, patients may be advised to make lifestyle modifications, especially concerning diet, exercise and stress management. 

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about antiarrhythmics:

1. Why do I need to take an antiarrhythmic?
   
   
2. Which drug will be prescribed for me?
   
   
3. How does this drug work for my heart condition?
   
   
4. What are the side effects of this antiarrhythmic?
   
   
5. How will you know if the drug is working?
   
   
6. How long will I need to take this medication?
   
   
7. Am I taking any other medications that may interfere with this drug?
   
   
8. Do I have any restrictions while on this medication?
   
   
9. Will I need other treatment in addition to the medication?
   
   
10. Can a different medication be used if I have a bad reaction to the drug?
    
    
11. Are there any foods or supplements that may interfere with this drug?
    
    
12. What symptoms indicate that I need immediate medical attention?