## Acute Termination of Atrioventricular Reentrant Tachycardia (AVRT) **Key Point:** Adenosine is the first-line drug for acute termination of stable narrow-complex SVTs, including AVRT and AVNRT, because of its rapid onset, short half-life, and high efficacy. ### Mechanism of Action - Adenosine causes transient AV nodal block by activating adenosine A1 receptors - Interrupts the reentrant circuit in AVRT (which depends on AV nodal conduction) - Onset: <10 seconds; duration: <30 seconds ### Dosing & Administration - IV bolus: 6 mg rapid push, followed by saline flush - If ineffective after 1–2 minutes: 12 mg IV push - Can repeat once more at 12 mg if needed ### Why Adenosine is Superior for Acute Termination | Feature | Adenosine | Verapamil | Digoxin | |---------|-----------|-----------|----------| | **Onset** | <10 sec | 3–5 min | 30–60 min | | **Duration** | <30 sec | Hours | Hours | | **Efficacy in AVRT** | 90–95% | 80–90% | 60–70% | | **Route** | IV only | IV/oral | IV/oral | | **Safety in WPW** | Safe (blocks AV node) | Avoid (may enhance accessory pathway) | Caution | **Clinical Pearl:** Adenosine is preferred in acute settings because if it causes hemodynamic compromise (flushing, dyspnea, chest discomfort), symptoms resolve within seconds due to its ultrashort half-life. **High-Yield:** Adenosine is contraindicated in patients with severe asthma or COPD (can cause bronchospasm) and in those on dipyridamole or carbamazepine (which block adenosine metabolism). ### When to Use Alternatives - **Verapamil**: Oral maintenance therapy or if adenosine fails and patient is hemodynamically stable - **Digoxin**: Chronic rate control in sedentary patients; slower onset makes it unsuitable for acute termination - **Amiodarone**: Reserved for hemodynamically unstable patients or those refractory to adenosine/verapamil [cite:Harrison 21e Ch 297]
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