Target localization and electrophysiology
The primary sites of action for beta-blockers are β₁-receptors, located in the cardiac pacemakers and working ventricular cardiomyocytes.
Blockade of these receptors causes a number of electrophysiological effects in the heart:
- Decreased automatism.
- Suppression of conduction.
- Decreased excitability.
- Increased effective refractory period (ERP) in all myocardial regions.
Classification and clinical spectrum
In clinical practice, drugs of this group are divided into two main categories:
- Cardioselective (acting selectively on β₁-receptors): metoprolol, atenolol, talinolol.
- Non-selective (blocking both β₁- and β₂-receptors): propranolol (also known as anaprilin).
Due to their electrophysiological action, these medications demonstrate high efficacy in both types of tachyarrhythmias — supraventricular and ventricular.
Group side effects
The use of beta-blockers may lead to adverse reactions. Common side effects for the entire group are associated with the depression of cardiac activity:
- Bradycardia.
- Conduction disorders in the form of atrioventricular block.
- Decreased myocardial contractility (negative inotropic effect).
Non-selective drugs such as propranolol are characterized by specific complications due to the extracardiac blockade of β₂-receptors: bronchospasm and peripheral vascular spasm.
Briefly: answers to topical questions
Which cardioselective beta-blockers belong to Class II antiarrhythmic agents?
Cardioselective beta-blockers belonging to Class II antiarrhythmic agents include the following drugs: atenolol, talinolol, metoprolol, bisoprolol, nebivolol, and betaxolol. These medications have a selective effect on cardiac beta-1-receptors, reducing myocardial automatism, conduction, and excitability.
- Atenolol (atenolol) — cardioselective beta-blocker
- Metoprolol (metoprolol) — cardioselective beta-blocker
- Bisoprolol (bisoprolol) — cardioselective beta-blocker
What are the absolute contraindications to prescribing propranolol?
Contraindications to prescribing propranolol include:
- Bronchial asthma — risk of bronchospasm.
- Conduction disorders — atrioventricular block.
- Pronounced bradycardia.
- Acute and severe chronic heart failure.
- Arterial hypotension.
- Vasospastic angina.
- Obliterating peripheral vascular disease.
- Pregnancy — risk of preterm labor and adverse effects on the fetus.
Which non-selective beta-blockers are used in antiarrhythmic therapy?
Among non-selective beta-blockers, propranolol is used in antiarrhythmic therapy.
- Propranolol is a non-selective beta-blocker blocking β1- and β2-receptors; also known as anaprilin.
Class II beta-blockers are effective in both types of tachyarrhythmias: ventricular and supraventricular. Propranolol, as a non-selective beta-blocker, is characterized by specific side effects: bronchospasm and peripheral vascular spasm.
Beta-blockers slow down the heart: lower rate (bradycardia), lower conduction (AV block), and weaker contractility. Non-selective ones (propranolol) also "choke" the bronchi (bronchospasm).
Class and exam questions
Which cardiac structures are targets for Class II drugs?
The targets are β₁-receptors located in the pacemakers and working ventricular cardiomyocytes.
In which types of tachyarrhythmias are beta-blockers effective?
These agents are effective in both types of tachyarrhythmias: supraventricular and ventricular.
What causes bronchospasm when taking propranolol?
Bronchospasm occurs due to the blockade of bronchial β₂-receptors, which is a specific effect of non-selective drugs.
What else to study on this topic
- Effect of β₁-receptor blockade on the action potential
- Comparison of cardioselective and non-selective blockers
- Mechanisms of negative inotropic action
- Causes of atrioventricular block during therapy
- Pharmacological features of metoprolol and atenolol
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