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Beta-Blockers

Beta-blockers inhibit beta-adrenergic receptors and reduce sympathetic stimulation of the heart and kidneys.

They are used in:

• Hypertension • Heart failure (HFrEF) • Coronary artery disease • Arrhythmias • Post-myocardial infarction

Their primary effects are reduction of heart rate, contractility, and renin release.

Mechanism of Action

Beta receptors:

• β1 – Heart & kidney (↑ HR, ↑ contractility, ↑ renin) • β2 – Bronchi & vascular smooth muscle (bronchodilation, vasodilation)

Beta-blockers:

• Block β1 (cardiac effects) • Some also block β2 • Some also block α1

Net Effects:

• ↓ Heart rate • ↓ Contractility • ↓ Cardiac output • ↓ Renin release • ↓ Blood pressure

Classification

Cardioselective (β1-Selective)

• Metoprolol • Atenolol • Bisoprolol • Nebivolol

Preferable in: • Reactive airway disease • Diabetes

Nonselective (β1 + β2)

• Propranolol • Nadolol • Timolol

Avoid in: • Asthma • Severe COPD

Combined α/β Blockers

• Labetalol • Carvedilol

Effect: • ↓ HR (β1) • ↓ SVR (α1 blockade)

Useful in: • Hypertensive emergency • Heart failure (carvedilol)

Agents with Intrinsic Sympathomimetic Activity (ISA)

• Pindolol • Acebutolol

Partial agonist activity. Less commonly used.

Indications

Hypertension

• Not first-line for uncomplicated HTN • Useful in CAD, arrhythmia, HFrEF

→ Hypertension Module

Heart Failure (HFrEF)

Mortality-reducing agents:

• Carvedilol • Metoprolol Succinate • Bisoprolol

→ Heart Failure Module

Coronary Artery Disease / Post-MI

• Reduce myocardial oxygen demand • Reduce mortality post-MI

Arrhythmias

• Rate control in atrial fibrillation • Suppress SVT

→ Dysrhythmias Module

Adverse Effects

• Bradycardia • Hypotension • Fatigue • Depression • Erectile dysfunction • Mask hypoglycemia • Bronchospasm (nonselective agents)

Contraindications

• Severe bradycardia • High-grade AV block (without pacemaker) • Cardiogenic shock • Decompensated heart failure

Use caution in: • Asthma • Severe peripheral vascular disease

Clinical Pearls

✔ Reduce mortality in HFrEF (select agents only) ✔ Not first-line for uncomplicated hypertension ✔ Cardioselective agents preferred in lung disease ✔ Avoid abrupt discontinuation (rebound tachycardia) ✔ Combined α/β agents reduce SVR and HR

Relationship to Other Classes

Often combined with:

• ACE Inhibitors • ARBs • Diuretics • Non-DHP CCBs (use caution)