How Do Class II 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 caused by improper conduction of impulses in the heart. They 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 II antidysrhythmic drugs inhibit beta-adrenergic activation of adenylate cyclase and reduce sinoatrial node and atrioventricular node activity. They prolong atrioventricular node repolarization and increase the P-R interval. They decrease phase 4 (resting phase) slope in cardiac pacemaker cells and reduce conduction speed and blood pressure. 

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 II antidysrhythmic drugs are used to treat:

Class II antidysrhythmic drugs are used to treat:

• Supraventricular tachycardia (abnormal fast beating of the heart above lower chambers)
• Sinus tachycardia (rapid increase in the heart rate)
• Atrial fibrillation and flutter (rapid and irregular heartbeat in the upper chamber of the heart)
• Premature ventricular contractions
• Atrial premature beats
• Sympathetically mediated arrhythmias seen in pheochromocytoma (a hormone-secreting tumor that can occur in the adrenal glands)
• Anesthesia-associated arrhythmias

Common side effects include:

• Nausea and vomiting
• Disorientation 
• Hypoglycemia (low blood sugar)
• Blurred vision
• Hyperkalemia (high level of potassium in the blood)
• Depression
• Dyslipidemia (increased cholesterol levels in the blood)
• Dizziness
• Impotence 

Serious side effects of class II antidysrhythmics include:

• Severe bradycardia (low heart rate) 
• Heart failure
• Vasospastic angina (intensity of vasospasms increases)
• Worsening of chronic obstructive pulmonary disease and asthma

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

• Acebutolol
• Betapace
• Betapace AF
• Brevibloc
• Esmolol
• Hemangeol
• Inderal
• Inderal LA
• InnoPran XL
• Propranolol
• Sectral
• Sorine
• Sotalol
• Sotylize