## Management of Symptomatic Mobitz Type I AV Block **Key Point:** Atropine is the first-line pharmacological agent for symptomatic bradycardia and AV block in the acute setting, particularly in inferior MI where vagal tone is elevated. ### Mechanism of Action Atropine blocks muscarinic cholinergic receptors, reducing vagal tone and increasing AV nodal conduction velocity. In inferior MI, the right coronary artery typically supplies the AV node, and ischemia causes increased parasympathetic activity. ### Why Atropine Works Here - Mobitz type I (Wenckebach) block is typically at the AV nodal level - Vagal hyperactivity is the primary mechanism in inferior MI - Atropine rapidly restores AV conduction in nodal blocks - Dose: 0.5–1 mg IV bolus, repeat every 3–5 minutes (max 3 mg) **Clinical Pearl:** Atropine is effective only for AV nodal blocks (Mobitz I, high-degree nodal blocks). It is ineffective for infranodal blocks (Mobitz II, third-degree with wide QRS). ### When to Escalate If atropine fails or the block is infranodal: - Temporary pacemaker (gold standard for symptomatic high-degree AV block) - Isoproterenol or dopamine as bridge to pacing **High-Yield:** In acute MI with symptomatic AV block and hypotension, the sequence is: **Atropine → Pacemaker**. Vasopressors (dopamine) are adjuncts, not first-line. [cite:Harrison 21e Ch 297]
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