## Beta Blockers with Intrinsic Sympathomimetic Activity **Key Point:** Intrinsic sympathomimetic activity (ISA) is the ability of a beta blocker to produce partial agonist effects at beta-adrenergic receptors, resulting in less reduction in resting heart rate and cardiac output compared to pure antagonists. ### Beta Blockers with ISA | Drug | ISA | Selectivity | Clinical Use | | --- | --- | --- | --- | | **Pindolol** | Yes (high) | Non-selective | Bradycardia-prone patients | | **Acebutolol** | Yes (moderate) | β₁-selective | Arrhythmias, hypertension | | **Carteolol** | Yes (moderate) | Non-selective | Hypertension, glaucoma | | Atenolol | No | β₁-selective | Standard first-line agent | | Metoprolol | No | β₁-selective | Standard first-line agent | | Propranolol | No | Non-selective | Anxiety, tremor, thyroid storm | **High-Yield:** Pindolol is the prototype beta blocker with ISA. It causes less bradycardia and is preferred when baseline heart rate is already low or when AV conduction is compromised. **Clinical Pearl:** ISA-containing beta blockers maintain resting heart rate closer to baseline (~60 bpm) compared to pure antagonists (~50 bpm), making them safer in patients with conduction abnormalities or heart failure with reduced ejection fraction (though modern evidence favors carvedilol and bisoprolol in HFrEF). **Warning:** Do not confuse ISA with beta-1 selectivity — these are independent properties. A drug can be selective (atenolol) without ISA, or non-selective (pindolol) with ISA.
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