Adenosine

Key points

• Causes transient heart block in the AV node · A1 receptor agonist — inhibits adenylyl cyclase, reducing cAMP and causing hyperpolarization by increasing outward potassium flux
• Very short half-life of about 8-10 seconds
• Effects enhanced by dipyridamole and the '-caines' (e.g. bupivacaine) · blocked/reduced by theophyllines (aminophylline)
• Avoid in asthmatics (possible bronchospasm) · adverse effects: chest pain, bronchospasm, enhanced accessory pathway conduction → increased ventricular rate (e.g. WPW)