Would you choose adenosine?

Hi sir. My name is Dr. Morgenstern. That racing feeling in your chest… it’s something we call SVT. That just means that you heart is going too fast. I’m going to get it slowed down for you. All that silly stuff we just did – getting you to blow in a syringe and raising your legs above your head – that sometimes works, but honestly, I have never seen it work myself. It’s time to stop asking you to “bear down” and move on to using medications to slow your heart down. Right now, your blood pressure is fine and you have no other problems, so we have a few options.

Option number one is a medication that works about 90% of the time, but it causes a horrible feeling when it is given. Some people describe it as chest pain. Others say is feels like they are going to die. Most people tell me it is the worst thing they have ever experienced.

Option number two is a medication that works closer to 100% of the time and doesn’t cause any pain at all.

Which would you prefer?

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When I consider the possible informed consent or shared decision making conversations around adenosine, I am often surprised it is ever used in the emergency department. Although the vignette is slightly tongue in cheek, the underlying truth is that we frequently give patients a medication that results in significant discomfort when an equally effective medication exists with none of the side effects. If our patients were aware, I think they might revolt.

First, let me start with a little bit of evidence. How does adenosine compare to its primary competitors, the calcium channel blockers?

The Evidence

The first paper I ever encountered on this topic was an RCT by Lim in 2009. In 206 adult patients with SVT, 104 were given adenosine (6mg IV push, followed by 12 mg IV push if not successful), 54 were given diltiazem (2.5 mg/min to a max of 50 mg), and 48 were given verapamil (1 mg/min to a max of 20 mg). The calcium channel blockers were better than adenosine at converting patients back to sinus rhythm (98% vs 86.5%, p=0.002, RR 1.13, 95% CI 1.04-1.23). Blood pressure did drop in the calcium channel group, but the changes (about 10 mmHg systolic) were minor and likely clinically insignificant. By 30 minutes, blood pressure had returned to pretreatment levels. They also do a cost comparison and the adenosine treatment was more expensive. 

There is also a Cochrane review on this topic, done in 2006 by Holdgate. They identified 8 RCTs comparing adenosine to calcium channel blockers. Overall, there was no difference in the rate of conversion. There were more adverse events with adenosine (10.8% vs 0.6%, p<0.001, OR 0.15, 95% CI 0.09 to 0.26). (The authors classify these as minor, but minor is not a word I have ever heard from a patient given adenosine). There were no differences in significant adverse events. Although not statistically significant, recurrent SVT occurred more often with adenosine (10% vs 2%, p=0.09).

There was supposed to be an update of the Cochrane review in 2012, but it was withdrawn because of lack of resources to get it done. The search had been completed, and 2 new trials had been found (including Lim), which did not change the overall conclusions of the review. There is a similar meta-analysis by Delaney in 2011 that essentially confirms the results of the Cochrane review.

Bottom line: The studies aren’t huge, but calcium channel blockers seem to be a better choice than adenosine as a first line agent in the management of SVT.

An important caveat: this evidence does not apply to sick patients. Patients were excluded from these studies if they had altered mental status, respiratory distress, or hypotension. Calcium channel blockers are not the ideal first line agent for patients in cardiogenic shock.

What is the best management option for a sick patient with SVT? Prompt electrical cardioversion is the best answer. A trial of adenosine might be reasonable if it will be quicker to administer than electricity, but if the patient is sick they need joules.

Of course, there is also an important role for clinical judgement when managing a patient with SVT. I am not calling for an outright ban on adenosine. There are clearly patients in whom the risk of hypotension outweighs the problem of momentary pain and suffering. We occasionally have to perform painful procedures on patients who are not fully sedated or adequately analgesed. That is emergency medicine, but we should not discount that suffering.

A couple practical points

• Hypotension seems to be more common with verapamil than with diltiazem (although I have not seen a head to head comparison). I tend to stick with diltiazem.
• Go low and go slow. Although the diltiazem dose used in the Lim study was 2.5 mg/min to a maximum of 50 mg, 75% of patients had converted by 18mg. I tend to give 15 mg of diltiazem over 10 minutes. It almost always works, but when it doesn’t I just repeat the dose.
• Always be prepared. Although SVT patients almost never crash, you should always be prepared to cardiovert any emergency department patient with an arrhythmia. At the doses I use, calcium channel blocker induced hypotension is almost never a problem. However, I am always prepared for clinically significant hypotension. My first step here would be to simply cardiovert the patient out of SVT. If that was not enough, I would start a fluid bolus with or without a dose of IV calcium, or in the worst case scenario, start a vasopressor. (This is not like the dreaded calcium channel blocker overdose.)

Why does this matter?

Is preventing suffering not a good enough reason to avoid adenosine? I really think so, but there is also an important patient safety consideration. Over the past few years I have seen a handful of patients in continuous SVT for 2 or more days before presenting to the emergency department. When I asked about the delay, they all said that they were afraid to come in. They knew that if they came in, they would be given adenosine. They had been through that before and they had suffered enough. When we forget about patient suffering – about our oaths – patients might choose to stay away and miss out on necessary medical care.

So a plea: if you are not convinced by the above – if you still want to use adenosine – please treat it like you would any other painful condition. Provide your patients with adequate procedural sedation. (Although, if the patient is sedated, I’m not sure why you would opt for adenosine over electrical cardioversion).

References

Delaney B, Loy J, Kelly AM. 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):148-52. PMID: 20926952

Holdgate A, Foo A. Adenosine versus intravenous calcium channel antagonists for the treatment of supraventricular tachycardia in adults. The Cochrane database of systematic reviews. 2006. PMID: 17054240

Lim SH, Anantharaman V, Teo WS, Chan YH. Slow infusion of calcium channel blockers compared with intravenous adenosine in the emergency treatment of supraventricular tachycardia. Resuscitation. 80(5):523-8. 2009. PMID: 19261367