What is adenosine?
Adenosine is a purine nucleoside naturally occurring in the body. It plays a vital role in energy production, storage, and use. To fulfill these functions, adenosine is incorporated into adenosine-triphosphate, or short ATP, which gives energy for most of the body’s energy-requiring reactions [1].
The nucleoside also has signaling and messenger functions. Cells deprived of oxygen or blood flow release it as a stress marker [2].
An increase in adenosine in the circulation indicates cell stress. Thus, it mediates countermeasures, aiming to resolve the crisis. Among the effects it can have are vasodilation, vessel remodeling, and inflammatory reaction [2]. It also impacts the immune system [3] and the heart rhythm-controlling pathway [4].
Adenosine effects are induced by a G-protein-coupled receptor. Four types of this receptor exist: A1, A2A, A2B, and A3 [1].
The key clinical uses of adenosine are the treatment of supraventricular tachycardia and heart stress testing. Additionally, it is applied during radionuclide myocardial perfusion imaging [4, 2].
How does adenosine work for SVT?
SVT, or supraventricular tachycardia, is a rapid heartbeat that can range from 180 to 220 beats per minute [5].
The adenosine effect on the heart impairs the conduction of electric signals through the atrioventricular (AV) node [6].
It is highly effective in terminating tachycardia. In most cases of SVTs, adenosine is effective above 90% [7].
Adenosine stops the fast electric activity in the heart by acting on its receptors, which are found in the highest concentration in the heart’s AV node.
The activation of the receptors leads to a slower conduction time. More specifically, adenosine triggers potassium channels that move potassium out of the cells and stop calcium movement inside the cells [6].
All the changes in ion movement result in a hyperpolarization of the AV node and a longer depolarization, which slows down the electric impulses [6].
How do you get adenosine for SVT?
Adenosine is administered intravenously. Commonly, the treatment starts with a rapid bolus of 6 mg. If this is ineffective, two additional dosages of 12 mg each are given [8].
Every dose of adenosine is followed by a 20 ml saline flush [6].
The dosage is different in pediatric cases. The initial bolus for children is 0.05 to 0.1 mg/kg [9].
The effectiveness of the initial does very. Some sources report that only 38% of all patients respond to the first dose [10].
Research shows that a higher initial dose, 12 mg, is more effective than the 6 mg one [11].
However, the dose of adenosine for the treatment of supraventricular tachycardia may differ from the guidelines.
Doctors can adjust the dose according to other conditions, especially cardiological ones, and factors such as age, reduced ejection fraction or significant left ventricular systolic dysfunction.
For how long does adenosine stop the heart?
The use of adenosine for SVT leads to a brief period of asystole or heart stoppage.
After administration of adenosine, the SVT is typically terminated within 25 seconds, directly after the asystole period occurs [12].
The duration of this asystole varies depending on the dose of adenosine. In patients who receive 12 mg of adenosine, the heart stops for around 980 milliseconds, while in those with a higher dose of 18 mg, the asystole lasts approximately 1 second [12].
What does it feel like to be given adenosine?
The treatment with adenosine may cause many unpleasant symptoms and sensations. The most common among them is chest discomfort or even pain after administration [13].
Other symptoms that can occur after administration of adenosine are
- heat flushing in the face [14],
- shortness of breath [14],
- lightheadedness [6],
- a feeling of threatening danger [6],
- nausea [6],
- sweating [6].
Some people can also feel a short decrease in heart rate [15].
What are the complications of adenosine for SVT?
Although rare, adenosine use can lead to some heart-related complications.
For example, adenosine can lead to: