What are the cardiovascular effects of adenosine?

Cardiovascular Effects of Adenosine

Adenosine is a potent vasodilator that primarily affects the microcirculation, causes transient AV nodal blockade, and has a very short half-life of less than 10 seconds, making it valuable for both diagnostic and therapeutic cardiovascular applications. 1, 2

Mechanism of Action

Adenosine exerts its cardiovascular effects through activation of specific purine receptors:

• A1 receptors: Located in atrial/ventricular myocardium and SA/AV nodes

  • Cause negative chronotropic, dromotropic, and inotropic effects
  • Inhibit adenylyl cyclase activity
  • Activate potassium channels in cardiac tissue 2, 3

• A2 receptors: Located in coronary endothelial and smooth muscle cells

  • Produce vasodilation
  • Stimulate adenylyl cyclase activity 2, 3

Primary Cardiovascular Effects

Electrophysiological Effects

• AV nodal conduction: Causes transient AV block by depressing AV nodal conduction 4
• Chronotropic effects: Negative chronotropic effect (slows heart rate) 2, 5
• Dromotropic effects: Negative dromotropic effect (slows conduction velocity) 2
• Inotropic effects:
  • Negative inotropic effect in atrial tissue
  • Minimal direct effect on ventricular tissue, but can counteract catecholamine-induced increases in contractility 5

Vascular Effects

• Coronary circulation: Produces significant coronary vasodilation 1, 2
• Systemic circulation: Causes peripheral vasodilation leading to mild-to-moderate reduction in systolic, diastolic, and mean arterial pressure 2
• Pulmonary circulation: Causes pulmonary vasodilation 6

Clinical Applications

Supraventricular Tachycardia Management

• Highly effective in terminating AV nodal re-entrant tachycardias (78-96% success rate) 1
• Recommended dosing:
  • Initial: 3 mg rapid IV bolus with saline flush
  • If ineffective after 1-2 minutes: 6 mg
  • Maximum dose: 12 mg 4
• Should be administered via proximal IV as a rapid bolus 1

Diagnostic Applications

• Coronary artery disease assessment: Used to induce coronary vasodilation during cardiac stress testing 1, 7
• Tachycardia differentiation: Helps distinguish supraventricular from ventricular tachycardias 1, 7
• Can unmask atrial flutter or atrial tachycardia 1

Pharmacokinetics

• Distribution: Rapid cellular uptake via specific transmembrane nucleoside transport system 2
• Metabolism: Intracellular adenosine is metabolized via:
  • Phosphorylation to adenosine monophosphate by adenosine kinase
  • Deamination to inosine by adenosine deaminase 2
• Elimination: Extremely short half-life (<10 seconds) in whole blood 2, 7

Side Effects and Precautions

Common Side Effects

• Flushing
• Chest discomfort/pain
• Dyspnea
• Transient complete heart block 4, 7

Serious Adverse Effects (Rare)

• Significant hypotension
• Tachycardia
• Bronchospasm (in patients with asthma) 1, 4

Contraindications and Cautions

• Asthma: Contraindicated in severe asthma due to risk of bronchospasm 1, 4
• Drug interactions:
  • Enhanced effect with dipyridamole
  • Reduced effect with theophylline/xanthine derivatives
  • Higher rates of heart block when used with carbamazepine 1, 4

Clinical Pearls and Pitfalls

• Administration technique: Must be given as a rapid IV bolus followed by saline flush to ensure delivery to the central circulation 1
• Monitoring: Always administer in a monitored setting due to potential for transient complete heart block 4
• Diagnostic value: Continuous ECG recording during administration helps distinguish drug failure from successful termination with immediate arrhythmia reinitiation 1
• Valsalva avoidance: Patients should avoid Valsalva maneuvers during IV adenosine infusion as this can interrupt drug delivery and cause fluctuations in coronary blood flow 1
• Pre-excited tachycardias: Use with caution as adenosine may produce ventricular fibrillation in patients with coronary artery disease or accelerate ventricular response in pre-excited atrial fibrillation 1

Adenosine's unique cardiovascular profile and extremely short half-life make it particularly valuable in both diagnostic and therapeutic settings where rapid, transient effects are desired.