There are two general approaches to treating atrial fibrillation: 1) attempting to restore and maintain a normal rhythm, and 2) allowing the atrial fibrillation to persist while controlling the heart rate.
While the first method may intrinsically seem the better option, in practice it often is not. This is because the antiarrhythmic drugs that are usually necessary for restoring and maintaining a normal heart rhythm are either relatively ineffective, relatively toxic, or both. Especially concerning is the unique toxicity of antiarrhythmic drugs, which often makes them difficult to administer and to take.
Toxicity of Antiarrhythmic Drugs
The toxicity of antiarrhythmic drugs falls into two general categories: the usual kinds of side effects seen with many drugs (such as allergies, insomnia, gastrointestinal disturbances, etc.), and proarrhythmia. It is proarrhythmia that poses the major problem with antiarrhythmic drugs.
"Proarrhythmia"simply means causing cardiac arrhythmias. That is, instead of eliminating arrhythmias these drugs can actually produce them. Unfortunately, the way antiarrhythmic drugs work -- by changing the electrical properties of cardiac tissue -- inherently subjects people to the problem of proarrhythmia. Also unfortunately, many times the arrhythmias produced by these drugs (in contrast to the atrial fibrillation itself) can be fatal. Therefore, any time antiarrhythmic drugs are used, there is at least some risk of causing dangerous, potentially fatal, arrhythmias - which should make doctors and patients reluctant to use them unless truly necessary.
Some drugs are more likely to cause proarrhythmia than others, and some patients are more likely to experience proarrhythmia than others. The likelihood of proarrhythmia with a particular drug in a particular patient must be taken into account before these drugs are prescribed.
Antiarrhythmic Drugs Used for Atrial Fibrillation
Five antiarrhythmic drugs are often used to treat atrial fibrillation: Rhythmol (propafenone), Tambocor (flecainide), Betapace (sotalol), Tikosyn (dofetilide) and Cordarone (amiodarone). Therapy must be carefully individualized to minimize the risk of toxicity, but the following generalizations can be made:
- Rhythmol and Tambocor are relatively well tolerated as long as they do not cause proarrhythmia. In patients who are young and healthy, who have no underlying heart disease and are at very low risk for developing heart disease, they also cause very little proarrhythmia, and in these patients they may be the drugs of choice for trying to restore a normal rhythm in patients with atrial fibrillation. They are moderately effective in controlling atrial fibrillation. However, in patients who have any type of underlying heart disease - or who are at increased risk of developing heart disease - these drugs are extremely likely to cause life-threatening proarrhythmia, and should always be avoided.
- Betapace and Tikosyn are also relatively well tolerated as long as they do not cause proarrhythmia. However, these drugs have at least some propensity to cause life-threatening proarrhythmia in anyone, and careful precautions must be taken by doctors when these drugs are used to minimize the odds of proarrhythmia. Indeed, in the case of Tikosyn, the FDA has declared that doctors must take special training before they are allowed to administer this drug. These drugs are moderately effective in controlling atrial fibrillation.
- Cordarone is a truly unique antiarrhythmic drug. While it is more effective than any other drug in treating atrial fibrillation, and while it causes relatively little proarrhythmia, it is exceedingly likely to cause other side effects that can be quite significant and even life-threatening. As a result, Cordarone ought to be avoided whenever possible. When it is used, careful monitoring must be made for toxicity as long as the patient takes the drug - and for several months after the drug is stopped. You can read about the unique aspects of Cordarone here.
The Bottom Line
It should be clear that treating atrial fibrillation with antiarrhythmic drugs - that is, the
strategy of trying to restore and maintain a normal rhythm - can be very problematic. For this reason, added to the fact that clinical trials have shown no overall benefit to this treatment strategy, in many patients it is better to avoid antiarrhythmic drugs altogether and opt instead for a
rate-control treatment strategy.
Sources:
Fogoros, RN. Treatment of Supraventricular Arrhythmias. In: Fogoros, RN. Antiarrhythmic Drugs - A Practical Guide. Blackwell Publishing, Malden, MA: 2007.
