Propranolol is contraindicated in a patient with vasospastic (Prinzmetal) angina because:
- A Beta-2 blockade leaves alpha-mediated coronary vasoconstriction unopposed ✓
- B It increases myocardial oxygen demand by raising heart rate
- C It causes reflex tachycardia via baroreceptor activation
- D It increases coronary vascular resistance through beta-1 blockade
Correct answer: A. Beta-2 blockade leaves alpha-mediated coronary vasoconstriction unopposed
Explanation
In coronary arteries, sympathetic tone maintains vasodilation through beta-2 receptor activation. When propranolol blocks beta-2 receptors, alpha-1 adrenoceptor-mediated vasoconstriction goes unopposed, potentially worsening or precipitating coronary artery spasm in patients with vasospastic angina. This is why only cardioselective beta-1 blockers (and cautiously) or calcium channel blockers are preferred in Prinzmetal angina.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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