Medications Used to Treat Cardiac Arrhythmias

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Many cardiac arrhythmias, or abnormal heart rhythms, are considered harmless and don't require treatment. However, some cardiac arrhythmias--those that are severe or last a long time--can be dangerous because they may prevent the heart from pumping enough blood through the body. When this is the case, there are three general classes of medications that can be useful. 

Antiarrhythmic Drugs

Antiarrhythmic drugs are medications that that change the electrical properties of cardiac tissue, and by doing so, change the way the heart's electrical signal spreads across the heart.

Since the tachycardias (rapid heart rate) are usually related to abnormalities in the electrical signal, drugs that alter the heart's electrical signal can often improve those arrhythmias. Antiarrhythmic drugs can often be effective, or partially effective, in treating most varieties of tachycardias.

Unfortunately, antiarrhythmic drugs can be difficult to take. Each antiarrhythmic drug has its own unique toxicity profile, and before prescribing any of these drugs, it is vital that your doctor carefully explains the possible side effects. There is one side effect that is common to virtually all antiarrhythmic drugs: Sometimes these drugs make the arrhythmia worse instead of better.

This feature of antiarrhythmic drugs -- called "proarrhythmia" -- is, unfortunately, an inherent property of drugs that change the heart's electrical signal. Simply put, when you do anything to change the way the electrical signal spreads across the heart, it is possible that the change will make a tachycardia either less likely to occur, or more likely to occur.

Commonly used antiarrhythmic drugs include amiodarone (Cordarone, Pacerone), sotalol (Betapace), propafenone (Rhythmol), and dronedarone (Multaq). Amiodarone is the most effective antiarrhythmic drug, and is less likely to cause proarrhythmia than other drugs. Unfortunately, its side effects can be particularly nasty, and this drug should only be used (like all antiarrhythmic drugs) when absolutely necessary.

AV Nodal Blocking Drugs

The medications known as AV nodal blocking drugs -- beta blockers, calcium channel blockers, and digoxin -- work by slowing the heart's electrical signal as it passes through the AV node on its way from the atria to the ventricles. ( Review the normal cardiac electrical system here.) This makes the AV nodal blocking drugs useful in treating supraventricular tachycardias (SVT). Some forms of SVT (specifically, the SVTs known as "AV nodal reentrant tachycardia", and tachycardias caused by bypass tracts), require the AV node to conduct the electrical signal efficiently, and if the AV node can be made to conduct the electrical signal more slowly, the SVT simply stops.

For other forms of SVT (namely, atrial fibrillation, AV nodal blocking drugs do not stop the SVT, but they do slow the patient's heart rate while they are in the SVT. In fact, controlling the heart rate with these drugs is often the best way to manage atrial fibrillation.

Drugs That Reduce the Risk of Sudden Death

A few drugs are thought to reduce the risk of sudden death, presumably by reducing the risk of ventricular tachycardia or ventricular fibrillation, the types of irregular heart rates that produce cardiac arrest.

Research shows that beta blockers probably reduce the risk of sudden death by blocking the effect of adrenaline on the heart muscle, thus reducing the chances of developing fatal arrhythmias. All patients who have survived heart attacks or who have heart failure should be taking beta blockers.

Less easy to explain is the reduction of sudden death reported in patients taking statins, or who consume omega-3 fatty acids, but these treatments also seem to help.


The Sicilian gambit. A new approach to the classification of antiarrhythmic drugs based on their actions on arrhythmogenic mechanisms. Task Force of the Working Group on Arrhythmias of the European Society of Cardiology. Circulation 1991; 84:1831.

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