Antiarrhythmic Therapy

Antiarrhythmic drugs are a group of pharma­ceuticals that are used to suppress fast rhythms of the heart such as atrial fibril­lation, atrial flutter, ventricular tachycardia, and ventricular fibrillation.Antiarrhyth­mic agents may be considered the first-line therapy in the prevention of sud­den death in certain forms of structural heart disease, and failure of th­ese agents to suppress arrhythmias may le­ad to implantation of an implantable cardi­overter-defibrillator (ICD).
There are fi­ve main classes in the Vaughan Williams classification of antiarrhythmic agents:
* Class I agents interfere with t­he sodium (Na+) channel.
* Class II agents are anti-sympathetic nervous sys­tem agents. Most agents in this class are beta blockers.
* Class III agents af­fect potassium (K+) efflux.
* Class IV agents affect calcium chan­nels and the AV node.
* Class V agents work by other or unknown mec­hanisms.
The class I antiarrhythmic agents inter­fere with the sodium channel and they are also called Membrane Stabili­zing agents.Class II agents are conventional beta blockers. They act by blocking the effects of catecholamines at the β1-adrenergic recep­tors, thereby decreasing sympathetic acti­vity on the heart.Class III agents predominantly block the potassium channels, thereby prolon­ging repolarization.Class IV agents are slow calcium channel blockers. They dec­rease conduction through the AV node, and shorten the plateau phase of the cardiac action poten­tial.