How Do Class V 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.

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 V antidysrhythmics (miscellaneous antiarrhythmics) include several drugs and each has its unique mechanism of action.

Adenosine binds to A1 receptors and activates G-protein. The activated G-protein after a series of pathways inhibits calcium entry into the cell by deactivating L-type calcium channels. Adenosine also inhibits the pacemaker current by acting through A1 receptors and decreases the slope of phase 4 of the pacemaker action potential. The inhibition of L-type calcium channels also decreases the conduction velocity at the atrioventricular node. Adenosine decreases the heart rate and conduction velocity that may lead to an atrioventricular block. Adenosine may increase the heart rate caused by systemic vasodilation and hypotension.

Digoxin inhibits cellular sodium/potassium-ATPases. It reduces the ability of sodium-calcium exchanger and increases sodium concentration within the cell. The increased amount of sodium in the cell increases calcium influx, thus increasing calcium concentration in the cell. This higher calcium concentration increases the contractility of the heart and decreases the heart rate.

Magnesium sulfate plays a crucial role in membrane potential. It decreases the influx of calcium and prevents early afterdepolarizations.

Class V antidysrthythmic 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)
• Digoxin toxicity (overdose of digoxin causing neurological problems, nausea, and vomiting)
• Severe systolic heart failure
• Severe heart failure with reduced ejection fraction (the heart cannot pump the blood normally)
• Coronary heart disease (Damage or disease in the heart's major blood vessels.)

Serious side effects of class V antidysrhythmics include:

• Hypertension (high blood pressure)
• Hypotension (low blood pressure)
• Bradycardia (slow heart rate)
• Bronchospasm (tightening of the muscles that line the airways in your lungs)
• Chest pain
• Asystole (a serious form of cardiac arrest)

The other common side effects may include:

• Blurring of vision
• Loss of reflexes
• Nausea and vomiting
• Abdominal pain
• Drowsiness
• Breathlessness
• Flushing

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:

• Adenocard
• Adenoscan
• Adenosine
• Digoxin
• Lanoxin
• Magnesium sulfate
• MgSO4