Adenosine is a nucleoside that occurs naturally in all the cells of the body, and is composed of an adenine molecule linked to a ribose through a β-N₉-glycosidic bond. However, this molecule has several physiological and pharmacological roles in the functioning of the normal organism, as well as in some pathological circumstances.
In the heart and blood vessels, adenosine helps to dilate or expand blood vessels, in particular coronary vessels, and therefore improves the blood supply to the myocardium. The use of adenosine enables the study of changes in blood flow within the coronary arteries, thus enabling the understanding whether there are stenoses that may have clinical significance.
Echocardiography with pharmacological stress (Ecostress with adenosine) is a diagnostic method that uses ultrasound to evaluate the anatomy and function of the heart and is performed with the intravenous administration of adenosine. The dose of adenosine administration in case of coronary perfusion test is 0.14 mg/kg infused in 6 minutes. Administration takes place only in continuous peripheral intravenous infusion.
At the level of the heart rhythm, adenosine decreases the heart rate and the speed of conduction of the heart impulse through the conduction system.
The main pharmacological effect of Adenosine is the rapid conversion of paroxysmal supraventricular tachycardias to sinus rhythm, including those associated with accessory conduction pathways (Wolff-Parkinson-White syndrome).
The adenosine test can therefore be used as a diagnostic test in patients in whom supraventricular tachycardia (SVT) is suspected, in which adenosine is used both for the induction of any arrhythmia.
The adenosine test is used specifically in the suspicion of Wolff-Parkinson-White syndrome to uncover a latent delta wave and to induce SVT.
Adenosine is also used in the ex juvantibus diagnostic sense, in the differential diagnostics of wide QRS tachycardias, since only in paroxysmal supraventricular tachycardias does Adenosine modify the electrocardiographic trace.
The adenosine test is also used for the diagnosis of sinus node dysfunction (DNS), and it has been described that in patients with DNS, episodes of syncope or presyncope were associated with a more marked inhibition of the sinus node (NS) after adenosine administration compared to normal subjects.
The adenosine test is performed after the interruption of β-blockers, calcium channel blockers and other antiarrhythmic agents for ≥ 5 half-lives. The test is carried out in the electrophysiology room, in the presence of suitable personnel and equipment for cardiopulmonary resuscitation. The test is generally practiced in the context of an electrophysiological study. The test is performed in the presence of continuous ECG monitoring during drug administration.
The pharmacological name of Adenosine is Krenosin; each 2 ml vial of Krenosin contains 6 mg of adenosine (3 mg/ml). Krenosin is intended for hospital use only in hospitals equipped with cardiorespiratory monitoring and resuscitation equipment available for immediate use.
The drug must be administered as a rapid injection I.V. in bolus according to the dosage schedule at increasing doses below. To be sure that the solution reaches the systemic circulation, administer directly into a vein or through an infusion line; the infusion must be practiced as proximally as possible and must be followed by a rapid washing with physiological solution. If administered through a peripheral vein, a large-caliber cannula should be used.
The method of administration of Adenosine are equivalent both in the diagnostic test, for the induction of SVT, and in the therapeutic use for the suppression of SVT.
Adults (for both evaluation and treatment of SVT)
initial dose: 6 mg I.V. in rapid bolus (2 seconds injection),
second dose: if the first administration does not suppress (or induce) supraventricular tachycardia within 1 or 2 minutes, a further administration of 12 mg in rapid IV bolus must be carried out,
third dose: if the second administration does not suppress (or induce) supraventricular tachycardia within 1 or 2 minutes, rapid bolus 12-18 mg IV should be administered.
No additional or higher doses are recommended. Patients who develop high grade AV block should not undergo further dose increases.
– first bolus of 0.1 mg/kg body weight (maximum dose of 6 mg)
-increases of 0.1 mg/kg body weight until suppression/induction of supraventricular tachycardia is reached (maximum dose of 12 mg).
The test is considered positive if a delta wave or SVT is sustained during the test or within 10 minutes from the end of the infusion. The infusion is immediately stopped if the test is positive.
In the case of a test carried out for the evaluation of syncopal episodes, the test is considered positive in case of induction of pauses longer than 6 seconds, or in the event that a high-grade AV block develops.
The adenosine test is carried out to evaluate the inducibility of potentially serious arrhythmias. During the administration of Adenosine, patients may develop hypotension, marked bradycardia, peripheral vasodilation, dizziness, excessive sweating, or nausea. These symptoms are transient and usually last less than a minute.
The risk of the adenosine test is, however, very controlled, and is carried out in the presence of suitable personnel and equipment for cardiopulmonary resuscitation in case of the need for the immediate treatment of any evoked arrhythmia. The risk is commensurate with the need to know the risk of developing serious arrhythmias in the individual patient.