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

- Rogue Medic

Adenosine for wide-complex tachycardia – diagnostic?

ResearchBlogging.org

Adenosine is a drug that wears off very quickly, so that its side effect of asystole is not really a problem. The metabolism of adenosine takes place in the cells. If you remember the Krebs cycle, you remember how important adenosine is for the production of energy. Almost every cell has a constant demand for adenosine for energy. No circulation is needed for metabolism, as long as the person was alive when the adenosine was given (or in the few minutes before adenosine was given).
 


Image credit. Click on images to make them larger.
 

This study looks at the efficacy and safety of adenosine as a diagnostic tool for WCT (Wide Complex Tachycardia) WCT is a fast rhythm with prolonged ventricular conduction that has not had its cause diagnosed, yet. The W in WCT is its Width on an ECG (ElectroCardioGram), which is a measure of time.

The authors claim that a lack of response to adenosine will identify VT (V Tach – Ventricular Tachycardia). At least, that is what they claim that their study demonstrates.
 


WCT image from EMS 12 Lead. To find out more about this WCT, read about it at EMS 12 Lead.
 

It is expected that adenosine will 1) terminate the majority of supraventricular tachycardias (SVTs) that rely on the AV node to form a reentrant circuit; 2) cause transient AV block to permit the accurate diagnosis of atrial flutter; and 3) be unlikely to terminate most ventricular tachycardias (VTs).[1]

This is a multicenter retrospective observational study of administration of adenosine to patients with WCT (Wide Complex Tachycardia) WCT is a fast rhythm with prolonged ventricular conduction that has not had its cause diagnosed, yet. The W in WCT is its Width on an ECG (ElectroCardioGram), which is a measure of time.

A sustained rhythm was defined as continuous for at least 2 mins to minimize the risk of mislabeling spontaneous termination of a transient WCT as a response to adenosine.[1]

It often takes a couple of minutes to get everything ready to give adenosine and it is a good idea to observe a stable rhythm and to get a 12 lead ECG. Unstable patients are often cardioverted, but I will use adenosine for unstable SVT (SupraVentricular Tachycardia) rather than shock the patient without sedation.

A regular rhythm was defined as having ≤ 5% beat-to-beat variability in R-to-R interval for contiguous beats. Wide QRS tachycardia was defined as a QRS width ≥ 120 msecs and a heart rate (HR) of at least 120 beats/min.[1]

Patients who responded to 6 mg adenosine, or who received 12 mg adenosine were included. If the patient only received 6 mg adenosine, but there was no response, the patient was not included.

The underlying mechanism of the WCT rhythm was determined by the investigators using the following methods and criteria in descending order, as available: ECG evidence of AV dissociation demonstrating VT, review of the tachydysrhythmia from ICD recordings, reproduction of the dysrhythmia during an electrophysiologic study, diagnostic response to carotid massage or adenosine, such as transient AV block revealing atrial flutter waves, ECG analysis by the treating cardiology team with clear evidence of the diagnosed rhythm confirmed by the investigators, or if necessary, ECG analysis using standard criteria by an electrophysiologist investigator blinded to all clinical data.[1]

 

Let’s look at those diagnostic criteria –

1. ECG evidence of AV dissociation demonstrating VT,

That is my favorite way of identifying VT. Some people see P waves and say that is evidence of an atrial rhythm, but if the P waves are dissociated, that is evidence that the rhythm is not atrial.

2. review of the tachydysrhythmia from ICD recordings,

Meaning that this review of rhythms included a review of older rhythms and the onset of the rhythms. However, if the previous diagnosis was based on response to adenosine, is this a valid criterion?

3. reproduction of the dysrhythmia during an electrophysiologic study,

EP (ElectroPhysiologic) studies are important for patients who have had WCT, because it is sometimes difficult to identify VT.

4. diagnostic response to carotid massage or adenosine, such as transient AV block revealing atrial flutter waves,

Is adenosine diagnostic for SVT vs. VT?

Of course it is.

How do you know?

A response to adenosine was assumed to be diagnostic for SVT.

Am I being unfair to the authors?

They did include other criteria before response to adenosine or CSM (Carotid Sinus Massage – an adenosine analogue and not something that is accurately described by the word massage).

That was their last resort, so their only option was to not answer the question.

That would have been more honest/less biased, but this was not the last resort. they had other diagnostic criteria that were trumped by response to adenosine or CSM.

5. ECG analysis by the treating cardiology team with clear evidence of the diagnosed rhythm confirmed by the investigators,

Do I want to trust a response to adenosine for diagnosis or do I want to trust a team of cardiologists?

We joke that if we give an ECG to five cardiologists, we will get six interpretations.

If the cardiologists agree, should we ignore the consensus of the experts in rhythm interpretation because of a drug response that agrees with our biases?

While I do not automatically trust experts, I have much greater distrust for people who allow their biases to guide them.

Why do you believe X?

Because I want to believe X.

Or, more honestly –

Because X is consistent with my biases.

But wait.

There’s more.

Not only was that not the last resort, it wasn’t even the second to last resort.

The authors also felt that response to adenosine or CSM was better at diagnosing SVT vs. VT than the electrophysiologists.

6. or if necessary, ECG analysis using standard criteria by an electrophysiologist investigator blinded to all clinical data.

Being blinded to the clinical data may seem like a bad idea to them, but does any of it help to identify the rhythm correctly?

No.

Maybe they are correct.

Maybe a response to adenosine does prove that the rhythm is not VT.

There were no cases of VT being terminated by adenosine, so that is a reasonable conclusion.

No.

There were cases of VT terminated by adenosine in this study.
 


 

If 2 of the patients diagnosed as VT responded to adenosine, how many of the 102 tachycardia patients diagnosed as supraventricular (the SV of SVT) were diagnosed based only on response to adenosine and could have actually been ventricular (VT)?
 


 

49%
 

Allow me to round off a teens-weensy bit.

Half of the SVT diagnosed patients were diagnosed based on the response to adenosine or to CSM.

Only 1% were diagnosed based on CSM response and 48% were diagnosed based on adenosine response.

Allow me to round off a teens-weensy bit more.

Half of the SVT diagnosed patients were diagnosed based on the response to adenosine.

Patients regularly receive antibiotics for viral infections, even though the doctors know that the antibiotics will not treat a viral infection. A lot of these patients get better after they take antibiotics, no matter how non-compliant they are with the directions for taking the medication.

Do any of these doctors write papers claiming that this is evidence that the patients had bacterial infections?

I have not done a search for this, but I hope not. If they do, I hope they receive plenty of criticism.

A response to adenosine has never been demonstrated to be diagnostic.

A response to a treatment that has never been demonstrated to be diagnostic should never be used to confirm the ability of that treatment to diagnose.

Footnotes:

[1] Adenosine for wide-complex tachycardia: efficacy and safety.
Marill KA, Wolfram S, Desouza IS, Nishijima DK, Kay D, Setnik GS, Stair TO, Ellinor PT.
Crit Care Med. 2009 Sep;37(9):2512-8.
PMID: 19623049 [PubMed – indexed for MEDLINE]

Marill KA, Wolfram S, Desouza IS, Nishijima DK, Kay D, Setnik GS, Stair TO, & Ellinor PT (2009). Adenosine for wide-complex tachycardia: efficacy and safety. Critical care medicine, 37 (9), 2512-8 PMID: 19623049

Comments

  1. RVOT-VT is adenosine sensitive. Hell some VT’s are verapamil sensitive.

    A response to adenosine just proves the rhythm was responsive to adenosine 🙂

    • Christopher,

      RVOT-VT is adenosine sensitive.

      A notable exception to the lack of response of VT to adenosine is the relatively rare right ventricular outflow tract type (21, 22). Right ventricular outflow tract VT was diagnosed in 4% (three of 81) of patients in this study and was, surprisingly, unresponsive to adenosine in all cases.

      Hell some VT’s are verapamil sensitive.

      Lidocaine and verapamil make one of the best rhythm-terminating cocktails around. 😉

      A response to adenosine just proves the rhythm was responsive to adenosine 🙂

      Exactly.

      The rhythm might be SVT or it might be VT.

      The response does not diagnose.

      .

  2. So let me see if I understand this. They sought to determine whether response to adenosine is diagnostic for VT. The method for determining the rhythm in nearly half the cases was whether the rhythm responded to adenosine. Isn’t that some circular logic? That doesn’t make sense to me.

    • paul,

      So let me see if I understand this. They sought to determine whether response to adenosine is diagnostic for VT. The method for determining the rhythm in nearly half the cases was whether the rhythm responded to adenosine. Isn’t that some circular logic? That doesn’t make sense to me.

      That is the problem with this study.

      They had so many better ways to diagnose the rhythm.

      They could even conclude that the rhythm was of unknown origin.

      They chose an answer over admitting that they do not know.

      If we were to take the approach of WCT is ventricular until proven otherwise, the conclusions would be dramatically different.

      .

  3. This study should be a lesson in how little we know about this stuff. For paramedics, it is probably a good idea to cardiovert unstable WCT patients, and let the hospital figure out what’s wrong with the stable ones. For the symptomatic, but not yet unstable, it would depend on how far away the hospital is. Despite what a lot of people are taught, adenosine and amiodarone are not chicken soup. They can both leave patients worse off than if nothing was done.

Trackbacks

  1. […] and research (or lack of research) on the medications in the paramedic forumlary. This post, Adenosine for Wide Complex Tachycardia, was from earlier this month. Share Related […]

  2. […] [6] Adenosine for wide-complex tachycardia – diagnostic? Thu, 23 Aug 2012 Rogue Medic Article […]

Speak Your Mind