Pharmacology  ·  Cardiovascular

Beta-Blockers in Angina — Receptors, Mechanism & Withdrawal

Adrenergic receptor pharmacology, dual anti-ischemic mechanism, contraindications, and withdrawal syndrome

• Beta-blockers are first-line therapy for stable exertional angina; their anti-ischemic benefit flows from beta-1 blockade in the heart, which lowers both heart rate and contractility — reducing oxygen demand while simultaneously lengthening diastole to improve coronary filling time.
• Cardioselective agents such as metoprolol and bisoprolol preferentially block beta-1 over beta-2 receptors at standard doses, reducing bronchoconstriction risk; selectivity is relative and is lost at high doses, so even cardioselective agents carry some pulmonary risk in severe asthma.
• Blocking beta-2 receptors removes a normal coronary vasodilatory influence, leaving alpha-1-mediated vasoconstriction unopposed — the mechanism that makes all beta-blockers contraindicated in vasospastic angina, regardless of cardioselectivity.
• Beta-blockers prevent the reflex tachycardia triggered by nitrates and dihydropyridine calcium channel blockers, which is the core rationale for combining them with either drug class.
• Chronic blockade causes beta-receptor upregulation; abrupt discontinuation exposes this enlarged receptor population to normal catecholamines, producing rebound tachycardia, hypertension, and potentially severe rebound angina or myocardial infarction — always taper over one to two weeks.