How Do Class IV 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 IV antidysrhythmic drugs inhibit the slow calcium channel inward current. They decrease the slop of phases 0 and 4 and prolong phase 2 of the cardiac action potential. They reduce the conduction velocity and increase the effective refractory period (resting state in a depolarized cardiac cell) and prolong atrioventricular node repolarization and P-R interval.  

Class IV antidysrhythmic drugs are used to treat:

• Atrial fibrillation and flutter (rapid and irregular heartbeats in the upper chamber of the heart)
• Paroxysmal supraventricular tachycardia (abnormal fast beating of the heart above the lower chambers)
• Hypertension (high blood pressure)
• Multifocal atrial tachycardia (increased heart rate caused by the stimulus from multiple areas within the upper chamber of the heart)

Serious side effects of class IV antidysrhythmics include:

• Reflex tachycardia (increased heart rate in response to the stimulus of decreased blood pressure which is transmitted via the cardiac nerves)
• Heart block (an abnormal heart rhythm where the heart beats too slowly)
• Bradycardia (slow heart rate)

Other side effects include:

• Constipation
• Flushing (reddening and increased warmth due to a sudden increase in the blood flow underneath the skin)
• Edema (accumulation of fluid below the skin and soft tissue)
• Gingival hyperplasia (increased growth of gum tissue around the teeth): seen with verapamil use
• Headache

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:

• Calan
• Calan SR
• Cardizem
• Cardizem CD
• Cardizem LA
• Cartia XT
• Covera HS
• Dilacor
• Dilacor XR
• Dilatrate
• Dilt-CD
• Diltazem
• Diltazem CD
• Diltia XT
• Diltiaz
• Diltiaz CD
• Diltiaz SR
• Diltiazem
• Diltiazem CD
• Diltiazem SR
• Dilzem
• Isoptin
• Isoptin IV
• Isoptin SR
• Taztia XT
• Tiazac
• Verap
• Verapamil
• Verapamil SR
• Verelan
• Verelan PM