How Do Class IC Antidysrhythmics Work?

Antidysrhythmics, also known as antiarrhythmics, are drugs used to prevent abnormal cardiac rhythms such as atrial fibrillation, atrial flutter, ventricular tachycardia, and ventricular fibrillation. These drugs work by blocking sodium, potassium, and calcium channels in the heart muscles. Some drugs show autonomic effects.

Antiarrhythmic drugs are grouped into four main classes:

• Class I, sodium-channel blockers;
• Class II, beta-blockers;
• Class III, potassium-channel blockers;
• Class IV, calcium-channel blockers; and
• miscellaneous antiarrhythmics or unclassified antiarrhythmics.

Class IC antidysrhythmics are strong sodium channel blockers with major action on open state channels and have the longest channel recovery time. These drugs do not have a significant effect on action potential, but they have the strongest effect on the initiation phase 0 of depolarization. They delay conduction, prolong P-R interval, and widen the QRS complex. These drugs have a maximum effect on His-Purkinje as well as accessory pathway conduction.

Class IC antidysrhythmics have high proarrhythmic (may cause a new arrhythmia or aggravate a preexisting arrhythmia during therapy) potential and may cause sudden death during therapy.

Antidysrhythmic drugs do not improve the survival rate among patients with nonlife-threatening arrhythmias and may increase mortality in patients with structural heart disease.

Class IC antidysrhythmics are used to treat the following:

• Paroxysmal supraventricular tachycardia (abnormal fast beating of the heart above the lower chambers)
• Atrial fibrillation and flutter (rapid and irregular heartbeats in the upper chamber of the heart)
• Last resort in refractory ventricular tachycardia (also called electrical storm, two or more episodes of ventricular tachycardia that occur with a time interval)

Serious side effects of class IC antidysrhythmics include:

• Proarrhythmogenic (these drugs are contraindicated immediately after heart attack)
• Life-threatening ventricular tachycardia (abnormal heartbeats that occur in the lower chambers)
• QT prolongation (heart muscle takes longer than usual to recover after each beat
• Congestive heart failure (heart doesn't pump blood as well as it should)
• Bronchospasm (airways go into spasm and contract)

Other common side effects include:

• Nausea and vomiting
• Blurred vision
• Headache
• Constipation
• Bitter taste

The information contained herein is not intended to cover all possible side effects, precautions, warnings, drug interactions, allergic reactions, or adverse effects. Check with your doctor or pharmacist to make sure these drugs do not cause any harm when you take them along with other medicines. Never stop taking your medication and never change your dose or frequency without consulting your doctor.

Drug names include:

• Flecainide
• Propafenone
• Rythmol
• Rythmol SR
• Tambocor