Without evidence of benefit, an intervention should not be presumed to be beneficial or safe.

- Rogue Medic

Happy Adenosine Day


 

6-12-12
 

The dosing of adenosine (Adenocard) for PSVT (Paroxysmal SupraVentricular Tachycardia or just SVT – SupraVentricular Tachycardia) is 6 mg, followed by an immediate 20 ml flush, wait a minute, 12 mg, followed by an immediate 20 ml flush, wait a minute, and then another 12 mg, followed by an immediate 20 ml flush.

This only comes twice a century according to the Gregorian calendar. Once in the US style and once in the European style (December 06, 2012 – where the month comes after the day).
 

Wait!
 

O frabjous day! Callooh! Callay!

The AHA (American Heart Association) has decided that we should be able to celebrate Adenosine Day twice a year, rather than twice a century.
 

Adenosine. If PSVT does not respond to vagal maneuvers, give 6 mg of IV adenosine as a rapid IV push through a large (eg, antecubital) vein followed by a 20 mL saline flush (Class I, LOE B). If the rhythm does not convert within 1 to 2 minutes, give a 12 mg rapid IV push using the method above.[1]

 

Where is the third dose?

Is it wrong to give a second dose of 12 mg? No, but it also isn’t wrong to celebrate Adenosine Day twice a year. 😉

It never did make sense to wait a minute to repeat the same dose of a medication that is supposed to be completely metabolized in less than a minute. Unless there is something cumulative about the administration, the same dose should produce the same result.

Since the second dose of 12 mg occasionally has been followed by a change in rhythm, maybe the metabolism of adenosine is not as fast as we expect.

I have seen a strip of over a minute of asystole following adenosine administration – the initial 6 mg dose. Apparently, that patient did not metabolize adenosine as rapidly as we would expect.
 


Click on images to make them larger. Image credit.[2] This is not the actual strip, but a strip of an adenosine pause edited to produce more asystole.
 

What should we do for that asystole?

Check a pulse.

Yes. There is no pulse. The leads are connected. The axis of the heart has not suddenly changed, so checking another lead will not change anything, but feel free to satisfy do your protocol thing.

Check for responsiveness.

The patient states that she feels awful and wants to know what you did to her.

Begin CPR?

Not on an awake and talking patient.

Give epinephrine?

Hell No!

Epinephrine, if it provides any benefit, only helps the chest compressions of CPR to perfuse. We are not starting CPR, so we are not giving epinephrine.

What dose would we give to this living patient? the appropriate dose for a living patient 0.002 mg (2 μg) to start or the dead person dose of 1 mg (1,000 μg)?

What was the initial rate?

Very very fast.

How quickly is adenosine metabolized?

Very very quickly.

What do we expect the rate to be when the adenosine wears off and the epinephrine kicks in?

If the hear can go any faster before it quits, it will, but epinephrine (heart failure in a syringe) is only going to make the heart fail sooner.

The only thing to do is to wait at least a minute for the adenosine to wear off. This is a good time to review the medications the patient is taking for drugs that alter the effective period of adenosine –
 

Adenocard is antagonized competitively by methylxanthines such as caffeine and theophylline, and potentiated by blockers of nucleoside transport such as dipyridamole. Adenocard is not blocked by atropine.[3]

 

Benzodiazepines can also potentiate adenosine.[4] If we have any expectation of cardioversion, we should sedate early. Benzodiazepines are not the best, or second best, or even the third best sedative for cardioversion, but benzodiazepines are all that some of us have. Also, I have been told by one person that cardioversion is less painful that adenosine. If cardioversion is preferable to adenosine, maybe we should consider giving a sedative before adenosine for some people.

And then there is the myth that adenosine diagnoses SVT. This is not true. Some V Tach (Ventricular Tachycardia) does respond to adenosine,[5] just as some V Tach does respond to amiodarone.

The only questions are –

Do more V Tach patients respond to adenosine than to amiodarone?

Should we finally give up the ineffective amiodarone (barely more effective than placebo, but with the potential for more harm – hypotension, QT segment prolongation, torsades, et cetera – and it is the only commonly used antiarrhythmic banned for pregnant patients) and sedate the patient in preparation for cardioversion?

Almost all of the patients who receive amiodarone will receive cardioversion because of the ineffectiveness of amiodarone. Why do we treat patients as if amiodarone will work this time?

Because we are hopeless optimists who do not understand what we are doing. 😳

Footnotes:

[1] Adenosine
2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care
Part 8: Adult Advanced Cardiovascular Life Support
Part 8.3: Management of Symptomatic Bradycardia and Tachycardia
Free Full Text from Circulation

[2] Atrioventricular Re-entrant Tachycardia
Thumbnail Guide to Congenital Heart Disease
edited version of their adenosine ECG strip
Article

[3] ADENOCARD (adenosine) solution
[Astellas Pharma US, Inc.]

DailyMed
FDA Label

[4] Therapeutic concentrations of diazepam potentiate the effects of adenosine on isolated cardiac and smooth muscle [proceedings].
Clanachan AS, Marshall RJ.
Br J Pharmacol. 1980 Jan;68(1):148P-149P. No abstract available.
PMID: 7357161 [PubMed – indexed for MEDLINE]

Free Full Text from PubMed Central

[5] Effects of adenosine triphosphate on wide QRS tachycardia. Analysis in 18 patients.
Hina K, Kusachi S, Takaishi A, Yamasaki S, Sakuragi S, Murakami T, Kita T.
Jpn Heart J. 1996 Jul;37(4):463-70.
PMID: 8890760 [PubMed – indexed for MEDLINE]

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Comments

  1. It may not diagnose SVT accurately, but it does help distinguish reentry tachycardia from automatic focus tachycardia.

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