Written by: Amanda Randolph, MD (NUEM PGY-1) Edited by: Jim Kenny, MD, (NUEM PGY-4) Expert commentary by: Meghan Groth, PharmD - Emergency Medicine Clinical Pharmacist, UMass Memorial Medical Center
The Case
A 37 year-old woman presents to the ED for palpitations. On the monitor, you see her heart rate is 190, but all other vitals are within normal limits. She feels anxious but is otherwise asymptomatic, breathing comfortably on room air. The rest of the physical exam is unremarkable. The patient tells you, “I think it’s my SVT again - I was just here for this last month!”
Her rhythm strip looks something like this:
https://lifeinthefastlane.com/ecg-library/svt/
SVT generally refers to any tachyarrhythmia generated above the His/Purkinje system. For simplicity, the term pSVT in this post will refer to only Atrioventricular Nodal Tachycardia (AVNRT), as it is the most common tachyarrhythmia in patients with normal cardiac structure [1].
SVT: Treatment Guidelines
You double-check the current ACLS protocol (2015) for the treatment of pSVT [2]:
Figure 1. ACLS 2015 guidelines for treatment of AVNRT
This patient is stable, so you try some vagal maneuvers, including carotid massage and Valsalva. You even try the modified Valsalva maneuver you read about in the REVERT trial (straining followed by leg elevation and supine positioning), which is described to have a 43% success rate.
Despite your best efforts, the vagal maneuvers fail, so you ask the nurse to draw up some adenosine.
At this point, the patient yells, “Absolutely no way! I’m not trying Adenosine - it makes me feel like I’m going to die! There has to be something else.”
You know Calcium Channel Blockers (CCBs) are recommended as a second line drug if adenosine does not terminate the SVT, or if adenosine is contraindicated. But what does the data say? Is it ever reasonable to jump straight to CCBs?
The Problem with Adenosine
Adenosine administration is widely recognized to produce a variety of minor side effects, as listed below4. While not quantified in any studies to date, these “minor” side effects can be extremely traumatic for patients. This distress can have lasting psychological effects that may delay or even prevent patients from seeking care [5].
- Chest pain (7-40%)
- Facial flushing (18-44%)
- Nausea (13%)
- Headache (2-18%)
- Lightheadedness/Dizziness (12%)
The Problem with Calcium Channel Blockers
Current ACC/AHA guidelines give CCBs a class IIa recommendation for use in pSVT [2]. However, most EM practitioners continue to favor Adenosine, in part because of cultural dogma, but also due to concern about inadequate data to regarding the efficacy and safety for calcium channel blocker use.
One pharmacologic difference between CCBs and Adenosine is the onset of action (100-400 seconds for CCBs compared with 21-34 seconds for Adenosine), which can create a delay to conversion [5]. However, because CCBs are only used in stable patients, this slightly longer onset is unlikely to be clinically significant [6].
More importantly, one of the most feared side effects of Calcium channel blockers is hypotension, as CCBs work by creating negative inotropy and peripheral vasodilation. In one study by Lim et al., the change in blood pressure after administration of adenosine was -2.6/-1.7, compared to -13.0/-8.1 with verapamil [9].
Of note, the duration of action is quite long for CCBs (2-5 hours), compared with adenosine (<10 seconds).7 This raises a concern that hypotension and other adverse effects of CCBs may be prolonged. For this reason, CCBs are contraindicated in patients with severe HFrEF.6,7 Additionally, CCBs are relatively contraindicated in patients taking beta blockers, as the combined effect can cause significant bradycardia and even heart block [6].
Theoretically, the use of CCBs via slow infusion instead of IV bolus may reduce the risk of hypotension,8 though there is limited data to support this. One randomized trial by Lim et al. compared the use of adenosine (n = 104) vs slow infusion of verapamil (n = 48) or diltiazem (n = 54), and reported no difference in outcomes between adenosine bolus and slow infusion of verapamil or diltiazem [9].
Calcium Channel Blockers vs. Adenosine - The Data
To date, there have been three meta-analyses comparing the efficacy and safety of CCBs to adenosine in patients with pSVT, including a recently published Cochrane review in October 2017.5,6,10 Note that the data described in these studies only refer to the use of Verapamil. Their findings are depicted below (table design inspired by a phenomenal ALiEM post) [8].
A Few Notes on Hypotension after Verapamil:
- None of these metaanalyses specifically reported their definition of hypotension, nor did they clarify whether any of these patients had clinical signs of shock.
- Holdgate and Foo reported two of three hypotensive patients subsequently reverted with adenosine and did not require any other specific treatment for their hypotension (the outcome and interventions for the third case were not reported).
- The study by Lim et al. using slow infusion of verapamil reported only one patient with clinically significant hypotension, with a drop in blood pressure from 122/81 mmHg to 74/61 mmHg after 7.5 mg of verapamil infusion. This patient’s SVT was terminated by synchronized cardioversion, after which his blood pressure improved to 103/69 mmHg.
Case Resolution
After the vagal maneuvers, you give 5mg IV Verapamil. The patient remains stable and converts to sinus tachycardia. She tells you she prefers Verapamil to Adenosine and will be “much less afraid” to come in next time.
Conclusion
Overall, both Adenosine and Verapamil are reasonable choices for termination of SVT. Anecdotally, some patients prefer Verapamil; however, there is limited evidence to support this [6]. Given the current data, physicians should discuss the pros/cons of each drug with the patient and employ shared decision-making when possible.
Take Home Points
- Start with vagal maneuvers, especially the modified Valsalva
- Adenosine and Verapamil are equally effective for SVT
- Moderate evidence by recent Cochrane review
- Class IIa by ACC/AHA
- Adenosine has a much higher incidence of minor side effects
- chest pain, facial flushing, nausea, headache, and lightheadedness/dizziness
- Verapamil has a slightly higher risk of hypotension
- Verapamil: -13/-8 mmHg; Adenosine -2.6/-1.7 mmH
- Rarely clinically significant - cases reportedly resolved with adenosine or synchronized cardioversion
- Always employ shared decision-making when possible
Expert Commentary
Thank you for your insightful post on this all-too-common conundrum we face in the ED. I think it’s incredibly important to remember, as you point out, that treatment of pSVT in the ED doesn’t have to be a “one size fits all” approach, and that we have more than just adenosine available as a treatment agent.
Most of the data for CCBs in this indication is with verapamil, but I’ve become comfortable recommending diltiazem in its place due to a lower risk of hypotension (see post for reference).
When attempting to mitigate the potential hypotension associated with calcium channel blockers, the study by Lim and colleagues that you mentioned is worth noting in more detail. Rather than the traditional 0.25 mg/kg diltiazem bolus (with 0.35 mg/kg repeat dose), subjects instead received diltiazem at a rate of 2.5 mg/min for up to 20 minutes (max dose 50 mg). This approach can optimize dose, reduce potential for hypotension, and spare the patient that “impending doom” feeling often experienced with adenosine (see further discussion on this here).
There are also some cases when adenosine should not be routinely administered, such as patients with reactive airway disease at risk of bronchospasm. A more thorough review of this topic is presented here but in such cases calcium channel blockers represent a reasonable alternative.
The strategy of using calcium channel blockers for pSVT can perhaps leave providers wanting in terms of the instant gratification that comes with adenosine administration, but agents like diltiazem or verapamil have demonstrated efficacy while avoiding some of the unpleasantries of adenosine.
For me, it comes down to recognizing that adenosine isn’t the only drug we have available for the treatment of pSVT. Calcium channel blockers like diltiazem may be used, and if we decide to try them, we can use different dosing approaches such as the slow bolus method outlined above to reduce some of the potential side effects.
Meghan Groth, PharmD
Emergency Medicine Clinical Pharmacist
UMass Memorial Medical Center
[Peer-Reviewed, Web Publication] Randolph A, Kenny J (2018, May 28 ). Treatment of pSVT: A case for calcium channel blockers. [NUEM Blog. Expert Commentary by Groth, M]. Retrieved from http://www.nuemblog.com/blog/PSVT
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References
- Burns, E., Supraventricular Tachycardia (SVT), in Life in the Fast Lane, M. Cadogan and C. Nickson, Editors. 2012.
- Page R, Joglar J, Caldwell M, et al. 2015 ACC/AHA/HRS Guideline for the Management of Adult Patients With Supraventricular Tachycardia: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society. J Am Coll Cardiol. 2016;67(13):e27-e115.
- Appelboam, A., et al., Postural modification to the standard Valsalva manoeuvre for emergency treatment of supraventricular tachycardias (REVERT): a randomised controlled trial. The Lancet, 2015. 386(10005): p. 1747-1753.
- Adenosine. Lexi-Drugs. Lexicomp. Wolters Kluwer Health, Inc. Riverwoods, IL. Available at: http://online.lexi.com. Accessed November 12, 2017.
- Delaney, B., J. Loy, and A.-M. Kelly, The relative efficacy of adenosine versus verapamil for the treatment of stable paroxysmal supraventricular tachycardia in adults: a meta-analysis. European Journal of Emergency Medicine, 2011. 18(3): p. 148-152.
- Alabed S, Sabouni A, Providencia R, Atallah E, Qintar M, Chico TJA. Adenosine versus intravenous calcium channel antagonists for supraventricular tachycardia. Cochrane Database of Systematic Reviews 2017, Issue 10. Art. No.: CD005154. DOI: 10.1002/14651858.CD005154.pub4.
- [Peer Reviewed, Web Publication] S. Brubaker and B. Long (2017 Feb 1). Treatment of Refractory SVT: Pearls and Pitfalls. [EmDocs.net, Expert Commentary by A. Koyfman]. Retrieved from http://www.emdocs.net/treatment-refractory-svt-pearls-pitfalls/
- [Web Publication] S. Rappaport and M. Groth (2016 Mar 3). Calcium channel blockers for stable SVT: A first line agent over adenosine? [AliEm Blog]. Retrieved from https://www.aliem.com/2016/03/calcium-channel-blockers-stable-svt-alternative-to-adenosine/
- Lim S, Anantharaman V, Teo W, Chan Y. Slow infusion of calcium channel blockers compared with intravenous adenosine in the emergency treatment of supraventricular tachycardia. Resuscitation. 2009;80(5):523-528.
- Holdgate, A. and A. Foo, Adenosine versus intravenous calcium channel antagonists for the treatment of supraventricular tachycardia in adults. The Cochrane Library, 2006.