In general, people diagnosed with any type of cardiac arrhythmia like atrial fibrillation, supraventricular tachycardia (SVT), atrial premature complexes (PACs), or ventricular premature complexes (PVCs) may be prescribed certain drugs for suppressing the abnormal heart rhythm called antiarrhythmic drugs.
How do Antiarrhythmic Drugs Suppress Arrhythmia?
Briefly put, antiarrhythmic drugs suppress abnormal heartbeat by changing the characteristics of the electrical impulse of the heart. They alter the way ions (whose flow back and forth across the cardiac cells’ membranes generates the heart’s electrical impulse) travel and therefore change the electrical signal of the heart and reduce the likeliness of cardiac arrhythmias.
However, many antiarrhythmic drugs (Class I and Class III) are relatively likely to cause side effects that may sometimes outweigh their benefits. The most common potential side effect is proarrhythmia - provocation of a new arrhythmia or the aggravation of a pre-existing one. Forthat reason, doctors prescribe these drugs only if the arrhythmia is severe and disrupts the patient’s life.
How Are Antiarrhythmic Drugs Classified?
Based on the specific effects antiarrhythmic drugs have on different kinds of channels in the cardiac cell membrane, they are classified into five categories including:
Class 0Antiarrhythmic Drugs
Antiarrhythmic drugs that belong to this classification block a specific channel that is responsible for controlling the ‘pacemaker current’ in the sinus node. Currently, there’s only one drug in this class called ivabradine which is used for treating inappropriate sinus tachycardia, and fortunately, doesn’t produce proarrhythmia.
Class I Antiarrhythmic Drugs
These drugs suppress cardiac arrhythmia by blocking channels to slow down the electrical impulse of the heart when it spreads across the heart. Plus, class 1 antiarrhythmic drugsare likely to prolong the QT interval (a measurement made on an electrocardiogram used to assess some of the electrical properties of the heart).
Class I antiarrhythmic drugs include disopyramide, flecainide, mexilitine, phenytoin, propafenone, and quinidine. They are mainly used for treating reentrant arrhythmias, but as they can cause proarrhythmia, their usage has fallen off significantly.
Class IIAntiarrhythmic Drugs (Beta Blockers)
Class II antiarrhythmic drugs are commonly referred to as beta-blockers and have numerous clinical uses including suppressing arrhythmias. They slow down the production of electrical impulses in the sinus node which means that beta-blockers are beneficial for treating inappropriate sinus tachycardia. Furthermore, they reduce the conduction of the electrical signal across the atrioventricular node, so they can also treat atrial fibrillation.
Unfortunately, they aren’t suitable for treating other types of arrhythmia apart from these two even though they do not produce proarrhythmia. Common class II antiarrhythmic drugs include acebutolol, atenolol, betaxolol, bisoprolol, carteolol, carvedilol, labetalol, metoprolol, nadolol, penbutolol, propranolol, and timolol.
Class III Antiarrhythmic Drugs
The drugs in this classification include amiodarone, dofetilide, dronedarone, ibutilide, sotalol, and vernakalant. They all prolong the QT interval which is why they are considered to increase the risk of proarrhythmia. But, amiodarone and dronedarone produce very few proarrhythmia episodes.
Class IV Antiarrhythmic Drugs (Calcium Channel Blockers)
The final class is very similar to class II antiarrhythmic drugs as they help treat arrhythmias involving the atrioventricular node and sinus node. Plus, as is the case with beta-blockers, calcium channel blockers don’t tend to cause proarrhythmia. The drugs belonging to this classification are diltiazem and verapamil.
The bottom line, antiarrhythmic drugs are beneficial for treating cardiac arrhythmias. However, both doctors and patients must take precautions when prescribing and taking them, especially when it comes to Class I and Class III antiarrhythmic drugs.