## Intrinsic Sympathomimetic Activity (ISA) in Beta Blockers **Key Point:** ISA is a partial agonist property that allows a beta blocker to stimulate the receptor weakly while blocking stronger agonists. This results in less bradycardia and less reduction in cardiac output at rest. ### Beta Blockers with ISA | Beta Blocker | ISA | Clinical Significance | |---|---|---| | Pindolol | **Yes** | Minimal bradycardia, preferred when HR concerns exist | | Acebutolol | Yes | Cardioselective + ISA | | Carteolol | Yes | Non-selective + ISA | | Metoprolol | No | Pure antagonist, greater bradycardia | | Atenolol | No | Pure antagonist, cardioselective | | Propranolol | No | Pure antagonist, non-selective | **High-Yield:** Pindolol is the classic example of a beta blocker with ISA. It maintains resting heart rate and cardiac output better than pure antagonists, making it useful in patients with baseline bradycardia, AV block, or peripheral vascular disease. **Clinical Pearl:** ISA beta blockers are less effective in angina and post-MI settings because the partial agonist activity may not provide adequate cardioprotection. They are preferred in hypertension with bradycardia or in patients who cannot tolerate excessive HR reduction. **Mnemonic:** **PACE** — Pindolol, Acebutolol, Carteolol, Espindolol (beta blockers with ISA).
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