What are the effects of adenosine on the human body?

Effects of Adenosine on the Human Body

Adenosine is a naturally occurring nucleoside that primarily acts through specific purine receptors (A1 and A2) to cause vasodilation of the coronary microcirculation, negative chronotropic and dromotropic effects on cardiac conduction, and various other physiological effects throughout the body. 1, 2

Cardiovascular Effects

Cardiac Conduction System

• Adenosine produces direct negative chronotropic effects (slows heart rate) and negative dromotropic effects (slows conduction) through activation of A1 receptors in cardiac tissue 3, 2
• It causes transient atrioventricular (AV) nodal block, making it highly effective for terminating supraventricular tachycardias (SVT) involving the AV node, with success rates ranging from 78% to 96% 4, 3
• Adenosine suppresses cardiac pacemaker automaticity and inhibits AV nodal conduction, which is the basis for its use in treating paroxysmal SVT 3, 5

Vascular Effects

• Adenosine causes vasodilation primarily in the microcirculation with minimal effect on epicardial conduit arteries, acting through A2 receptors to increase cytosolic cyclic adenosine monophosphate 4, 1
• It decreases systemic vascular resistance and can cause mild to moderate reduction in systolic, diastolic, and mean arterial blood pressure 2, 6
• In pulmonary circulation, adenosine causes relaxation of pulmonary arterial smooth muscle, making it useful for vasoreactivity testing in pulmonary hypertension 4

Clinical Applications

Arrhythmia Management

• Adenosine is the preferred agent for acute termination of SVT due to AVNRT or AVRT, administered as a rapid IV bolus followed by saline flush 4, 3
• It can be used diagnostically to unmask atrial flutter or atrial tachycardia, though it rarely terminates these arrhythmias 4
• Continuous ECG recording during adenosine administration helps distinguish drug failure from successful termination with immediate arrhythmia reinitiation 4

Coronary Assessment

• Adenosine is used to achieve maximal coronary hyperemia for fractional flow reserve (FFR) measurement to assess the functional significance of coronary stenoses 4, 1
• It increases blood flow in normal coronary arteries with little increase in stenotic arteries, making it useful for cardiac stress testing 2, 7

Pharmacokinetics and Metabolism

• Adenosine has an extremely short half-life of less than 10 seconds in whole blood due to rapid cellular uptake and metabolism 2, 8
• It is metabolized either via phosphorylation to adenosine monophosphate by adenosine kinase or via deamination to inosine by adenosine deaminase 2
• The brief duration of action makes it ideal for diagnostic procedures and acute interventions 8

Side Effects and Precautions

Common Side Effects

• Patients commonly experience transient chest discomfort, shortness of breath, flushing, headache, throat/neck/jaw discomfort, gastrointestinal discomfort, and dizziness 4, 2
• These side effects are typically brief due to adenosine's short half-life 4, 2

Important Precautions

• Asthma is an absolute contraindication for intravenous adenosine administration due to risk of bronchospasm 1, 9
• Adenosine can cause bronchoconstriction specifically in asthmatic patients through stimulation of mast cells and release of inflammatory mediators 9
• Caution is needed in patients with Wolff-Parkinson-White syndrome due to risk of initiating atrial fibrillation with rapid ventricular rates 3
• Patients should avoid Valsalva maneuvers during intravenous infusion as this can interrupt continuous drug delivery 4, 1

Drug Interactions

• Larger doses may be required in patients taking theophylline, caffeine, or theobromine due to competitive antagonism 3
• Dose reduction is necessary in patients taking dipyridamole or carbamazepine, those with transplanted hearts, or when given by central venous access 3

Therapeutic Potential Beyond Arrhythmias

• Adenosine has cardioprotective properties during myocardial ischemia by attenuating beta-adrenergic stimulation and dilating coronary vessels 6, 7
• It may reduce ischemia/reperfusion injury by inhibiting leukocyte and platelet activation, preventing ATP depletion and calcium overload, and attenuating catecholamine release 7

By understanding adenosine's multifaceted effects on the cardiovascular system, clinicians can better utilize this agent for both diagnostic and therapeutic purposes while minimizing potential adverse effects.