Supraventricular tachycardia (SVT) is defined as a dysrhythmia that originates proximal to (or ‘above’) the atrioventricular (AV) node of the heart. It commonly manifests as a regular, narrow complex (QRS interval < 120ms) tachycardia in affected patients. It is most frequently attributable to re-entrant electrical conduction through accessory pathways in the heart, with typical Electrocardiogram (ECG) findings depicting ventricular rates of 150 to 250 beats/min without the preceding P wave usually seen in sinus tachycardias. [1,2]
In the stable adult patient presenting with SVT, where no ‘red flags’ such as shock, altered mental state, ischemic chest pain or hypotension are present, management typically begins with an attempt to convert the rhythm back to its baseline sinus state using vagal manoeuvres. Vagal manoeuvres such as the carotid sinus massage and the Valsalva manoeuvre are effective first-line therapies, terminating approximately 25% of spontaneous SVTs, with the newer, modified Valsalva manoeuvre showing even greater efficacy of 43% conversion. When these fail or are otherwise not feasible to use in patients, management involves the administration of a drug called Adenosine.
The Evolution of Adenosine Use for SVT
In 1927, studies found that the injection of extracts from cardiac tissue into animals appeared to decrease heart rates and that this effect was attributable to an ‘adenine compound’. This compound was later identified as Adenosine, comprised of the purine-based nucleobase Adenine attached to a ribose sugar. Fifty years after its initial discovery, Adenosine began to emerge as a treatment for stabilizing SVTs and has remained a mainstay in its management ever since.
Current guidelines recommend Adenosine for the management of SVT, usually administered through a peripheral intravenous (IV) access initially as a 6 mg bolus. Adenosine has an extremely short half-life (less than 10 seconds) and is therefore rapidly metabolized soon after it enters the body. Therefore, IV dosage is commonly followed by a 20 mL rapid saline flush to facilitate the drug’s transport to cardiac tissue where it can act before being broken down into inactive metabolites. If the 6mg dose does not convert the SVT back to sinus rhythm, subsequent doses are given at 12 mg, also followed by 20-mL saline for rapid infusion.
Pro-Tip: Single syringe technique
Before we dive into the concept of the single syringe method of administering Adenosine, take a look at the segment above. How would you give 6 mg of Adenosine through an IV site, making sure a total of 20 mL saline follows right after, in enough time to make sure you don’t waste that precious 10-second half-life of Adenosine? In many places, one of the two methods are used to make this happen:
- Use an IV line to push Adenosine > remove syringe > push 10 mL saline using a pre-filled syringe > remove syringe > push 10mL saline using a second pre-filled syringe.
- Fancier places use what’s known as a stopcock, a device usually with 3 ports attached to the IV site. Adenosine syringe is attached to one port and a 10 mL saline flush is attached at a separate port. The process looks something like this: Push adenosine through stopcock port > turn stopcock to open saline port’s access to IV site > push 10 mL saline flush > push an additional 10 mL saline using second syringe or remainder of a 20 mL prefilled syringe.
Now we all know that nurses are indistinguishable from ninjas at times when handling IV medication. However, even the most experienced practitioner is not immune to the occasional stumble when switching between the various syringes and swivels required in the methods above. In fact, a study in 2018 found that, in pediatric patients, adenosine given using the stopcock method delivered suboptimal doses.
In an attempt to improve administration time, a potential work-around was proposed where adenosine could be combined with the flush solution in one 20 mL syringe and pushed altogether. This potentially eliminates any time wasted changing syringes and manipulating stopcocks, but does it still work the same? Fortunately, a few studies have demonstrated the feasibility of the single syringe method, with non-inferior efficacy compared to standard methods of drug administration.[11,12]
Caveats: Coffee Conundrums
Let’s talk a bit about dosage. We mentioned above that guidelines recommend starting at 6 mg and moving to 12 mg for subsequent dosages. These dosages assume uninhibited action of adenosine at its receptors which, unfortunately, may not always be the case in patients. What would inhibit adenosine’s activity, I hear you ask? You’ll want to put down that Caramel Macchiato because the answer (pause for dramatic effect) … is coffee – caffeine to be exact.
Caffeine is known to work by antagonizing adenosine receptors, thereby decreasing adenosine’s biologic effect. A component in many frequently consumed beverages, such as coffee, tea, energy drinks and sodas, and with a half-life of approximately 4-5 hours, caffeine is very likely to be present in the bloodstreams of many Emergency Department patients (and doctors). A 2010 multi-centre study in Australia found that recent ingestion of caffeine less than 4 hours prior to a 6 mg adenosine bolus significantly reduced its effectiveness in treating SVT. 
This makes it all the more important to not only include information on any known recent beverage consumption during history taking for patients presenting with SVT, but also to potentially increase dosage for patients with a confirmed or suspected recent ingestion of caffeine. In such cases, it would be reasonable to start at 12 mg adenosine as the first dose, followed by 18 mg subsequent dosages to manage SVT.
References and Further Reading
- Bibas, L., Levi, M., & Essebag, V. (2016). Diagnosis and management of supraventricular tachycardias. CMAJ : Canadian Medical Association journal = journal de l’Association medicale canadienne, 188(17-18), E466–E473. https://doi.org/10.1503/cmaj.160079
- Mahtani, A. U., & Nair, D. G. (2019). Supraventricular Tachycardia. The Medical clinics of North America, 103(5), 863–879. https://doi.org/10.1016/j.mcna.2019.05.007
- Advanced Cardiac Life Support Provider Manual, American Heart Association, Mesquite 2016
- Lim, S. H., Anantharaman, V., Teo, W. S., Goh, P. P., & Tan, A. (1998). Comparison of Treatment of Supraventricular Tachycardia by Valsalva Maneuver and Carotid Sinus Massage. Annals of emergency medicine, 31(1), 30–35.
- Appelboam, A., Reuben, A., Mann, C., Gagg, J., Ewings, P., Barton, A., Lobban, T., Dayer, M., Vickery, J., Benger, J., & REVERT trial collaborators (2015). Postural modification to the standard Valsalva manoeuvre for emergency treatment of supraventricular tachycardias (REVERT): a randomised controlled trial. Lancet (London, England), 386(10005), 1747–1753. https://doi.org/10.1016/S0140-6736(15)61485-4
- Drury, A. N., & Szent-Györgyi, A. (1929). The physiological activity of adenine compounds with especial reference to their action upon the mammalian heart. The Journal of physiology, 68(3), 213–237. https://doi.org/10.1113/jphysiol.1929.sp002608
- Delacrétaz E. (2006). Clinical practice. Supraventricular tachycardia. The New England journal of medicine, 354(10), 1039–1051. https://doi.org/10.1056/NEJMcp051145
- Kazemzadeh-Narbat, M., Annabi, N., Tamayol, A., Oklu, R., Ghanem, A., & Khademhosseini, A. (2015). Adenosine-associated delivery systems. Journal of drug targeting, 23(7-8), 580–596. https://doi.org/10.3109/1061186X.2015.1058803
- Weberding, N. T., Saladino, R. A., Minnigh, M. B., Oberly, P. J., Tudorascu, D. L., Poloyac, S. M., & Manole, M. D. (2018). Adenosine Administration With a Stopcock Technique Delivers Lower-Than-Intended Drug Doses. Annals of emergency medicine, 71(2), 220–224. https://doi.org/10.1016/j.annemergmed.2017.09.002
- Hayes, B.D. (2019). ‘Trick of the Trade: Combine Adenosine with the Flush’. Academic Life in Emergency Medicine Blog Post https://www.aliem.com/trick-of-trade-combine-adenosine-single-syringe/
- Choi, S.C., Yoon, S.K., Kim, G.W., Hur, J.M., Baek, K.W., & Jung, Y.S. (2003). A Convenient Method of Adenosine Administration for Paroxysmal Supraventricular Tachycardia. Journal of the Korean society of emergency medicine, 14, 224-227.
- McDowell, M., Mokszycki, R., Greenberg, A., Hormese, M., Lomotan, N., & Lyons, N. (2020). Single-syringe Administration of Diluted Adenosine. Academic emergency medicine : official journal of the Society for Academic Emergency Medicine, 27(1), 61–63. https://doi.org/10.1111/acem.13879
- Ribeiro, J. A., & Sebastião, A. M. (2010). Caffeine and adenosine. Journal of Alzheimer’s disease : JAD, 20 Suppl 1, S3–S15. https://doi.org/10.3233/JAD-2010-1379
- Cabalag, M. S., Taylor, D. M., Knott, J. C., Buntine, P., Smit, D., & Meyer, A. (2010). Recent caffeine ingestion reduces adenosine efficacy in the treatment of paroxysmal supraventricular tachycardia. Academic emergency medicine : official journal of the Society for Academic Emergency Medicine, 17(1), 44–49. https://doi.org/10.1111/j.1553-2712.2009.00616.x
- Hayes, B.D. (2012). ‘Is the 6-12-12 adenosine approach always correct?’ Academic Life in Emergency Medicine Blog Post https://www.aliem.com/is-6-12-12-adenosine-approach-always/