Reducing Atrial Fibrillation Episodes
Atrial fibrillation occurs when the upper chambers of the heart, the atria, quiver and beat irregularly. The intermittent, or sometimes persistent, palpitations can be disabling and render the heartbeat less efficient. During fibrillation blood pools in the atria because the heart is not pumping effectively. Clots may form in stagnant blood and may break loose into the circulation. A clot can clog a blood vessel, blocking the blood flow to parts of the body. If the clot blocks an artery in the brain, the result is an ischemic stroke. Atrial fibrillation quintuples the risk of stroke.
To improve symptoms and reduce stroke risk, doctors may try to restore the normal rhythm of the heart. This can be done through electrical cardioversion or through the use of certain medications (although many of these drugs have serious side effects, including causing new heart rhythm problems). Despite treatment, atrial fibrillation recurs within six months in at least half of the patients. Studies suggest that a low-dose of the drug amiodarone may be more effective than the other antiarrhythmic drugs in restoring rhythm and preventing episodes of atrial fibrillation. Amiodarone is currently used primarily in patients who do not respond to other drugs.
A recent large, randomized study tested the long-term efficacy of amiodarone in comparison to two other drugs, sotalol and propafenone. Researchers selected 403 patients who had experienced an episode of atrial fibrillation lasting at least 10 minutes within the preceding six months. Half of the patients received amiodarone, while the other half received either sotalol or propafenone. By the start of the follow-up period, 21 days after drug treatment began, a normal heart rhythm had returned in 93% of the patients taking amiodarone and in 81% of those taking sotalol or propafenone. Researchers assessed the patients for a minimum of 12 months and measured the length of time to a first recurrence of atrial fibrillation. Over a mean of 15 months of follow-up, only 35% of the patients taking amiodarone had experienced a recurrence of atrial fibrillation compared with 63% of the patients taking sotalol or propafenone. By the end of the study period, more than half of the patients taking amiodarone remained free of a recurrence of atrial fibrillation.
These results indicate that amiodarone is more effective than sotalol and propafenone at maintaining heart rhythm. But researchers still need to demonstrate the long-term safety of amiodarone. Eighteen percent of the patients taking amiodarone discontinued the medication because of adverse side effects, whereas only 11% of those taking sotalol or propafenone discontinued for the same reason. Four patients taking amiodarone developed lung problems, and thyroid disfunction occurred in three patients taking this drug. A longer study may resolve some of the questions that remain concerning the balance between the benefit and toxicity of low doses of amiodarone.