WHAT ARE CLASS IA ANTIDYSRHYTHMICS AND HOW DO THEY 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 I antidysrhythmics block sodium channels (bind more tightly to cardiac tissue that is depolarizing a lot) and limit the electrical conductance of sodium over the cell membrane and reduce the rate of phase 4 (resting phase) depolarization in automatic cells. They are divided into subclasses a, b, and c.
Class IA antidysrhythmics block sodium channels that are in an open state and moderately delay channel recovery time. This results in slow conduction of electrical impulse through cardiac tissue, increased duration of action potential, and decreased slop of phase 0 depolarization. This prolongation of action potential corrects any irregular heartbeat. They also increase the effective refractory period (resting state in a depolarized cell and sodium channels are inactive in this phase) in ventricular action potentials. This suppresses atrial premature depolarizations which may lead to ventricular tachycardia. They may prolong action potential by blocking potassium channels as well.
Antidysrhythmic drugs do not improve the survival rate among patients with nonlife-threatening arrhythmias and may increase mortality in patients with structural heart disease.
HOW ARE CLASS IA ANTIDYSRHYTHMICS USED?
Class IA antidysrhythmics are used to prevent and treat:
- Life-threatening ventricular arrhythmias (abnormal heartbeats that originate in the lower heart chambers)
- Atrial fibrillation and flutter (rapid and irregular heartbeats in the upper chamber of the heart)
- Supraventricular tachycardia (abnormal fast beating of the heart above lower chambers)
- Acute conversion of atrial fibrillation including Wolff-Parkinson-White syndrome (procainamide)
WHAT ARE SIDE EFFECTS OF CLASS IA ANTIDYSRHYTHMICS?
Class IA antidysrhythmics are used to prevent and treat:
Life-threatening ventricular arrhythmias (abnormal heartbeats that originate in the lower heart chambers)
- Serious side effects of Class IA antidysrhythmics include:
- QT prolongation (heart muscle takes longer than usual to recover after each beat)
- Cardiac toxicity (damage to the heart because of poisonous effects)
- Hypotension (low blood pressure)
- Drug-induced lupus erythematosus (immune system of the body attacks healthy cells and causes inflammation)
- Hypersensitivity reaction (allergies caused by an overreaction of the immune system)
- Thrombocytopenia (low platelet count)
- Sudden cardiac arrest
Other common side effects include:
- Dry mouth
- Constipation
- Urinary retention
- Blurred vision
- Nausea and vomiting
- Weakness
- Mental confusion
- Headache
- Tinnitus (ringing in the ear)
- Hearing loss
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.
