Medications Used to Treat Cardiac Arrhythmias

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In general, there are two reasons your doctor might want to place you on medication for a cardiac arrhythmia. First, the arrhythmia might be causing you to have symptoms, such as palpitations or lightheadedness, and treatment may be important to relieve those symptoms. Or, second, the arrhythmia may be causing harm or threatening to do so. Many arrhythmias are doing neither of these two things, and do not require treatment specifically aimed at the arrhythmia itself.

If you have an arrhythmia that requires medical treatment, there are three general classes of medications that might be useful, depending on the type of arrhythmia you have. The first group consists of the antiarrhythmic drugs — drugs specifically aimed at suppressing abnormal heart rhythms. The second consists of drugs that affect the AV node, which are mainly used for supraventricular tachycardias (SVT). The third group consists of miscellaneous drugs that have been shown to reduce the risk of sudden death from cardiac arrhythmias.

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 (arrhythmias that cause a 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 are often effective, or at least partially effective, in treating most varieties of tachycardias.

Unfortunately, the antiarrhythmic drugs as a group tend to cause a fair amount of toxicity of one kind or another, and as a consequence they 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 problems that may occur with the selected drug.

 

However, there is one unfortunate problem that is common to virtually all the antiarrhythmic drugs: Sometimes these drugs make the arrhythmia worse instead of better.

This feature of antiarrhythmic drugs — called "proarrhythmia" — turns out to be 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 better, or worse. 

Commonly used antiarrhythmic drugs include amiodarone (Cordarone, Pacerone), sotalol (Betapace), propafenone (Rhythmol), and dronedarone (Multaq).

Amiodarone is the by far most effective antiarrhythmic drug, and is also less likely to cause proarrhythmia than other drugs. Unfortunately, the other kinds of toxicities seen with amiodarone can be particularly nasty, and this drug should only be used (like all antiarrhythmic drugs) when absolutely necessary.

The bottom line is that doctors are — and ought to be — reluctant to prescribe antiarrhythmic drugs.

These drugs should be used only when an arrhythmia is producing significant symptoms, or is posing a threat to cardiovascular health.

AV Nodal Blocking Drugs

The medications known as AV nodal blocking drugs — beta blockerscalcium 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. ( Read about the normal cardiac electrical system.) This makes the AV nodal blocking drugs useful in treating SVT. Some forms of SVT (specifically, AV nodal reentrant tachycardia and the 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 the SVT known as atrial fibrillation, AV nodal blocking drugs do not stop the arrhythmia, but they do slow the heart rate to help eliminate symptoms. In fact, controlling the heart rate with AV nodal blocking 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 arrhythmias 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.

Sources: 

Grant AO. Cardiac Ion Channels. Circ Arrythm Electrophysiol 2009; 2:185.

The Sicilian Gambit. A New Approach to the Classification of Antiarrhythmic Drugs Cased 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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