As an ACLS-prepared clinician, it is important to understand how each drug used in the ACLS algorithm works within the body, its indications, and how to administer it properly. Adenosine is one such drug.
Although it was discovered by two Harvard Medical students years prior, the first recorded use of adenosine to treat Supraventricular Tachycardia (SVT) was in 1976. At that time, the drug was administered in the form of Adenosine Triphosphate (ATP). Since then, Adenosine has proven to be useful in certain advanced cardiac life support situations. Let’s take a deep dive into how and why Adenosine is used in ACLS situations today.
Adenosine is a purine nucleoside base. It occurs naturally in the body and is present in all cells of the body as adenosine triphosphate (ATP) and adenosine diphosphate (ADP), an important part of general metabolism. Chemically, it is 6-amino-9-beta-D-ribofuranosyl-9-H-purine.
Adenosine in the body plays an important role in signaling through various pathways in the body, by forming molecules like cyclic adenosine monophosphate (cAMP). In the brain, adenosine acts as a central nervous system depressant, promoting sleep and suppressing arousal. When the body is awake, the levels of adenosine rise each hour in anticipation of later rest.
In the heart, naturally occurring adenosine causes dilation of the coronary blood vessels to improve cardiac circulation. It also dilates the vessels in the peripheral organs. It decreases heart rate, and has an anti-platelet action in the bloodstream that, prevents coagulation.
As a drug, adenosine is found under the brand names Adenocard, Adenoscan, Adeno-jec, and My-O-Den. It is used in healthcare as both a diagnostic tool and as a therapeutic medication to treat supraventricular tachycardia (SVT). Therapeutic usage of adenosine, specifically as a part of the ACLS protocol, is the focus of this article; but it is important to acknowledge that there are other applications.
Diagnostically, adenosine is used as a part of a nuclear medicine procedure called a myocardial perfusion stress test. This process causes temporary vasodilation, which chemically induces stress on the heart, resulting in transient ischemia if coronary blockage is present. For patients with an EKG exhibiting a baseline left bundle branch morphology, it is favorable to use adenosine in cardiac testing.
The drug adenosine works through four types of purinergic adenosine receptors throughout the body. These receptors are called A1, A2a, A2B, and A3. These affect the immune, nervous, circulatory, respiratory, and urinary systems. The drug’s cardiac action comes from receptors found within the heart’s atrioventricular (AV) node tissue. It is classified outside the Vaughan-Williams Classification scheme as a miscellaneous antiarrhythmic drug.
Adenosine’s effect on cardiac conduction occurs because it acts on the AV and SA nodes. In the AV node, it specifically blocks potassium and calcium channels in the cells — in turn, slowing down the conduction. In the SA node, adenosine blocks calcium entry into the cell, inhibiting the pacemaker current and slowing the heart rate. In summary, adenosine decreases the heart rate at the SA node and reduces conduction velocity at the AV node.
Supraventricular tachycardia (SVT) is defined as any arrhythmia that originates above or at the bundle of His, excluding atrial fibrillation. SVT typically features a narrow complex and presents at a rate greater than 150 beats per minute. There are several different types of SVT. However it is often difficult to diagnose which type because of the rapid rate. In some situations, adenosine can be used to slow down the patient’s heart rate enough to assist with diagnosis. For ACLS purposes, adenosine is used for symptomatic SVT caused by AV nodal reentry (by suppressing AV node conduction). Adenosine is not effective for atrial flutter or atrial fibrillation.
The rapid administration of adenosine, when given for SVT, slows down the heart enough to effectively “reset” the electrical rhythm back to normal sinus rhythm. The heart rhythm may drastically slow or even pause for a few seconds before resuming a normal sinus rhythm (see example below).
Adenosine has a very rapid onset of action and an extremely short half-life — less than 10 seconds. Adenosine is rapidly transported into red blood cells, where it is metabolized into hypoxanthine, xanthine, and eventually uric acid that is excreted by the kidneys.
Adenosine is one of the most commonly used medications in the ACLS algorithm. It is specifically used to treat symptomatic SVT after vagal maneuvers have failed. It is given via rapid intravenous (IV) or intraosseous (IO) bolus. It is important to administer through a peripheral access, not through a central catheter line. Adenosine has such a rapid effect that if it is administered centrally, it can initiate atrial fibrillation or even ventricular fibrillation.
Adenosine comes in 3mg/mL concentrations, with 2 mL in the vial.
Dosing for adult adenosine given per ACLS protocol is as follows:
|1st dose||6 mg||IV/IO push over 1-3 seconds, immediately followed by 20mL of NS by rapid IV/IO push.|
|2nd dose (if patient is still in SVT 1-2 minutes after 1st dose)||12 mg||IV/IO push over 1-3 seconds, immediately followed by 20mL of NS by rapid IV/IO push.|
A lower dose (3mg) may be considered for patients that:
Adenosine must be administered via rapid IVP. If it is given too slowly, the drug will metabolize before it has time to reach the AV node and work effectively. This is also the reason that it is followed by a rapid NS bolus — this pushes the drug further into the bloodstream.
It may be difficult to push the drug through a small or fragile IV line, so it is recommended to give adenosine through a large bore IV located at or above the antecubital (AC).
The best way to rapidly follow the drug with a flush is to use a stopcock. Attach the adenosine syringe to one side of the stopcock and a saline syringe to the other side. Best practice is to have two people administer, as follows:
Because of the way in which adenosine works pharmacologically, there are some conditions in which the drug is contraindicated or may negatively interact with other medications in the patient’s system.
Because of its exceptionally short half-life, side effects are typically short lived and patients recover quickly.
The most common side effects of adenosine include:
While not as common, these side effects are also possible:
To become certified in Advanced Cardiac Life Support, it’s important to know how adenosine is used and how to make the best clinical decisions regarding treatment and administration. It’s also important to note that this guide is for adult administration of adenosine, and other resources should be used to study pediatric usage. Please consult the package insert to find out more about the chemical makeup of adenosine and specific prescribing information.
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