ECG Blog #498 — Should you try Adenosine?

The ECG in Figure-1 was obtained from a middle-aged man with uncontrolled diabetes and presumed septicemia. 

• The patient's blood pressure was borderline low in association with the ECG in Figure-1. Rapid IV infusion to restore fluid volume was begun.

 

QUESTIONS:

• How would you interpret the initial rhythm in Figure-1?
• Is today's patient hemodynamically stable?
• Should you try Adenosine? 

 

Figure-1: The initial ECG in today's case — from a middle-aged man with uncontrolled diabetes and presumed septicemia. (To improve visualization — I've digitized the original ECG using PMcardio).

Is the Patient Hemodynamically Stable?

We are provided with limited clinical information on today's patient — namely, that he is a middle-aged man with uncontrolled diabetes, presumed septicemia, and a borderline low BP. Clearly, we need to find out more about what is going on ...

• The 1st Thing to do — is to LOOK at the patient! The KEY Question to address is whether or not the patient is hemodynamically stable!
• As per the 6-minute Audio PEARL in the ADDENDUM below — sometimes, "Ya just gotta be there!" in order to determine if the patient is "stable enough" to continue assessing the rhythm (ie, to distinguish between VT vs some type of SVT rhythm) — and/or — to continue with medical management without need for immediate electricity (ie, with synchronized cardioversion).
• This is because IF the patient is not hemodynamically stable because of the rhythm you are treating — then it no longer matters whether the rhythm is VT (Ventricular Tachycardia) — or some type of SVT (SupraVentricular Tachycardia) rhythm — since regardless, immediate cardioversion will be indicated!
• On the other hand — IF the patient is hemodynamically stable with the rhythm you are treating — then by definition, there is at least a moment-in-time for you to further assess the rhythm diagnosis.
• 
  
• PEARL #1: To determine hemodynamic stability — Sometimes, "Ya just gotta be there ... ".

Regarding today's initial ECG that is shown in Figure-1:

• It is hard to be certain from the verbal description we are given IF the borderline low BP of today's patient is a result of today's fast rhythm — or, if instead — this patient's precarious medical condition (with marked volume depletion from uncontrolled diabetes and septicemia) is the cause of his hypotension and tachycardia.
• That said — Let us presume since capable providers decided to treat this patient with rapid IV volume infusion — that synchronized cardioversion was not immediately needed in today's case.  

My Approach to the Rhythm in Figure-1:

Assuming that today's patient is hemodynamically stable — Let's work under the assumption that we have at least a moment-in-time to better assess the initial rhythm in Figure-1. As always — I favor the Ps, Qs,3Rs Approach (as described in ECG Blog #185).

• The rhythm in Figure-1 is fast and Regular.
• The QRS is narrow — so the rhythm is supraventricular.
• Sinus P waves are not seen (so there are no P waves to be Related to neighboring QRS complexes).
• Therefore — the rhythm in Figure-1 is a fast, regular SVT rhythm without clear sign of sinus P waves.

PEARL #2: As discussed in ECG Blog #287 — Recognition that the rhythm in today's initial tracing is a regular SVT without clear sign of sinus P waves (ie, without a definite upright P wave in lead II) — should prompt consideration of the following differential diagnosis LIST:

• i) Sinus Tachycardia (IF there is a possibility that sinus P waves might be hiding within the preceding T wave); 
• ii) A Reentry SVT (either AVNRT if the reentry circuit is contained within the AV node — or AVRT if an AP [Accessory Pathway] located outside the AV node is involved); 
• iii) Atrial Tachycardia (ATach);
• iv) Atrial Flutter (AFlutter) with 2:1 AV conduction. 

PEARL #3: Knowing the actual Rate of a regular SVT rhythm can be extremely helpful in working through the differential diagnosis of the tachycardia. This is because:

• Point #1: While not impossible — Sinus Tachycardia becomes much less likely in a non-exercising adult IF the rate of the unknown tachycardia exceeds ~170/minute.
• Point #2: Untreated AFlutter most commonly presents with a ventricular rate that is close to 150/minute (~130-170/minute range). This is because the untreated rate of flutter in the atria of adults is most commonly close to 300/minute — which with 2:1 AV conduction, results in a ventricular rate close to ~150/minute. Therefore — AFlutter also becomes unlikely when the rate of an unknown SVT rhythm exceeds ~170/minute (as this would require a ventricular rate of over 340/minute if 2:1 AV conduction was maintained).
• CAVEAT: In contrast, an SVT rhythm for which the ventricular rate is in the range of ~140-150/minute, provides NO Clue to etiology — because each of the most common diagnostic possibilities (ie, Sinus Tach — ATach — AFlutter — AVNRT/AVRT) may all present with a ventricular rate in the range of ~140-150/minute.

====================================== 

Estimating Rate when the Rhythm is Fast:

LOOK again at the rhythm in Figure-1:

• QUESTION: How fast is today’s initial rhythm?

======================================

PEARL #4: I favor the Every-Other-Beat Method for rapid estimation of a fast heart rate. I illustrate this Method with a short Video PEARL in the ADDENDUM below — but a picture is worth 1,000 words.

• NOTE: Sometimes it is easier instead of assessing the R-R interval for every-other-beat — to assess the R-R interval for every-third- or every-fourth beat.

Applying this Method to today’s initial rhythm:

• Looking every-third-beat is easiest in this example — because there is a 3-beat period in this rhythm in which a part of the QRS at the beginning and at the end of this 3-beat period falls either on (or almost on) a heavy grid line (as seen for the 2 vertical BLUE lines just under lead I of Figure-2).
• Using the Every-Third-Beat Method — the amount of time that it takes to record 3 beats (BLUE numbers in lead I) is just over 5 large boxes (RED numbers in this Figure). Therefore — ONE THIRD the rate is a little slower than 300 ÷ 5, or a little slower than 60/minute.
• Therefore — the actual rate for the rhythm in Figure-2 is a little less than 60X3, which comes to a rate of ~170-175/minute. 

Figure-2: Illustration of the every-other (in this case, every-third) beat approach for rapid estimation of a fast heart rate.

PEARL #5: By far (!) — the most commonly overlooked entity in the differential diagnosis LIST cited above in Pearl #2 — is AFlutter (Atrial Flutter). Therefore, even though the ventricular rate in today's SVT rhythm is slightly above the usual range for AFlutter — the BEST way to avoid missing AFlutter is to always at least consider this diagnosis whenever you have a regular SVT rhythm that is not excessively fast (ie, less than ~180/minute), and for which clear sign of sinus P waves is absent.

PEARL #6: Using calipers facilitates finding the diagnostic "sawtooth" pattern of AFlutter. When looking for AFlutter — I take advantage of the fact that new AFlutter most often presents with 2:1 AV conduction.

• To look for this — I simply set my calipers at precisely half the R-R interval — and then using this interval — I look for leads in which I can "walk out" 2:1 conduction.
• I have done this in Figure-3 — in which slanted RED lines that occur at precisely twice the ventricular rate can be walked out in at least 4 leads. Given the ventricular rate that we estimated in Pearl #4 to be ~170-175/minute — this corresponds to an atrial rate of ~340-350/minute.
• The "sawtooth" pattern of the baseline with AFlutter is best appreciated by stepping back a little bit from the tracing. My "Go-To" Leads when looking for subtle signs of atrial activity are leads II,III,aVF; — lead aVR — and lead V1 (with "sawtooth" flutter waves seen in 4 of these leads in Figure-3).

Figure-3: Using calipers facilitates finding "sawtooth" flutter waves that are highlighted by slanted RED lines in leads II,aVR,aVF and V1.

Should You Try Adenosine for Today's Rhythm?

To emphasize — It would not be "wrong" to give Adenosine for today's rhythm. This is because most of the time — there are no longterm adverse effects from using Adenosine, because its duration of action is so short.

• PEARL #7: Although Adenosine usually does not produce longlasting adverse effects — this drug is not entirely benign. Adverse effects are not always shortlived (See Figures-9 and -10 in the ADDENDUM below).
• Adenosine works great to convert reentry SVT rhythms such as AVNRT and AVRT — but it generally does not convert AFlutter. Instead, what the drug typically does with AFlutter is to transientlly slow AV conduction — which facilitates seeing underlying flutter waves that had previously been hidden within the QRS and/or ST-T waves.
• My Thought: The reason I would not choose Adenosine for today's rhythm — is that we are already quite certain that the rhythm is AFlutter (as shown in Figure-3) — so that there is little to learn by giving Adenosine. If on the other hand, we were less certain that today's rhythm was AFlutter — then it would be perfectly appropriate to give Adenosine as a diagnostic-therapeutic maneuver.

=============================

Today's CASE Continues:

Adenosine was given. The result is shown in Figure-4.

• What do you see?

Figure-4: Repeat ECG after IV Adenosine.

ANSWER:

The first 9 beats in Figure-4 show a continuation of the regular SVT rhythm that we saw in Figure-3. Thereafter, the rate-slowing effect of Adenosine is seen:

• Beginning with beat #10 — there is marked rate-slowing which reveals underlying flutter waves that are best seen in leads II, aVR, aVF; and V1,V2.
• Although it is not easy to see the ECG grid in Figure-4 — flutter waves appear to be regular in the above-cited leads, at a rate slightly greater than 300/minute (ie, with flutter waves slightly less than 1 large box in duration).
• We see 2 ventricular beats near the end of the tracing (beats #15,16).
• BOTTOM Line: Use of Adenosine confirmed that the rhythm in the initial ECG of today's case was AFlutter with 2:1 AV conduction, in which flutter waves were hidden within the QRS complex and the T wave that follows.

=============================

The CASE Continues:

Within 2 minutes — the rate-slowing effect of Adenosine wore off, and the rhythm returned to what we saw in Figure-3.

• With the goal of slowing the ventricular response — the patient was treated with several doses of IV Metoprolol. A dose of IV Digoxin was given.
• Clinically — the patient improved.

The repeat ECG is shown in Figure-5.

• Is the patient now in AFib?

Figure-5: The repeat ECG after IV Metoprolol and Digoxin.

============================= 

ANSWER:

The "good news" — is that the patient improved clinically. Presumably — treatment of the patients uncontrolled diabetes and septicemia contributed to this clinical improvement.

• At first glance in Figure-5, the long lead V1 rhythm strip at the bottom of the tracing "looks" like AFib. That said — there is a regular irregularity to this rhythm. This is perhaps best appreciated in the long lead II rhythm strip that appears below the long lead V1, in which 2 "families" of similar duration R-R intervals are seen (highlighted by double BLUE and double RED arrows in Figure-6).

Figure-6: Colored double arrows highlight the regular irregularity of the rhythm in the long lead II.

In Figure-7 — We look closer at the long lead II rhythm strip that appeared at the bottom of Figure-5:

• RED arrows in Figure-7 highlight that although the ventricular response is not completely regular — the underlying rhythm remains AFlutter.

Figure-7: Looking closer at the long lead II rhythm strip that we saw at the bottom of Figure-5 — We can see that the underlying rhythm of AFlutter persists, albeit with an irregular ventricular response.

=============================

Putting It All Together:

As we have seen in a number of previous ECG Blog posts — it is common for AFlutter to manifest dual-leval Wenckebach conduction out of the AV node (See ECG Blog #243  — and ECG Blog #463, among others for laddergram illustration of this phenomenon).

• I believe the group beating that the 2 families of colored double-arrows in Figure-6 suggest reflect a complex form of dual-level Wenckebach conduction in response to the AV Nodal blocking treatment that today's patient received.
• My proposed laddergram of this conduction for a portion of Figure-7 is shown in Figure-8.
• Full discussion regarding Teatment of AFlutter extends beyond the scope of this ECG Blog. A nice review of this subject is by Stiell and Eagles: Clin Exp Emerg Med 11(2):213-217, 2024. Given uncertain duration of AFlutter in today's case, and the association of AFlutter with the acute problems of uncontrolled diabetes and septicemia — medical treatment with the goal of slowing the ventricular response while addressing the patient's medical problems was perfectly appropriate.
• If this patient had been hemodynamically unstable as a result of the rapid ventricular response from AFlutter — then immediate synchronized cardioversion would have been indicated. But the patient was improving with IV Metoprolol and Digoxin, which was therefore continued. Along the way —  the initial 2:1 AV conduction in response to AFlutter slowed, with Wenckebach conduction out of the AV node. And the patient improved.

Figure-8: My proposed laddergram suggesting dual-level Wenckebach conduction for the rhythm in Figure-7.

==================================

Acknowledgment: My appreciation for today's case that was shared anonymously with me.

==================================

==================================

ADDENDUM (9/27/2025):

ECG Media PEARL #27 (3:00 minutes Video) — Reviews the Rule of 300 for estimating heart rate — and — @ 1:25 minutes in the video, the Every-Other-Beat Method for Estimating Rate with fast rhythms (from ECG Blog #210).

 

—  — 

ECG Media PEARL #37 (6:00 minutes Audio) — Reviews how to determine IF Your Patient with an Arrhythmia is Hemodynamically Stable! (from ECG Blog #220).

Regarding Adenosine:

Adenosine is a wonderful drug for emergency treatment of reentry SVTs. Even in cases in which Adenosine does not convert the rhythm — it will often facilitate rhythm diagnosis by its transient rate-slowing effect. 

• Although Adenosine is usually safe (because of its ultra-short half-life) — side effects can occur, and these are not uniformly short-lived. Therefore — Adenosine is probably best avoided for treatment of rhythms for which the drug has little to no chance of being effective (ie, If you know that the SVT you are treating is AFib or AFlutter — then its better to use some other rate-slowing or antiarrhythmic agent — rather than risking side effects from a drug that is unlikely to work).

Figure-9: Pages 1 and 2 on Pros & Cons of using Adenosine (excerpted from my ACLS-2013-ePub).

 

Figure-10: Pages 3 and 4 on Pros & Cons of using Adenosine (excerpted from my ACLS-2013-ePub).

==================================

Related ECG Blog Posts to Today's CASE:

• ECG Blog #205 — reviews my Systematic Approach to 12-lead ECG Interpretation.
• ECG Blog #185 — reviews the Ps, Qs, 3R Approach to Rhythm Interpretation.
• ECG Blog #210 — reviews the Every-Other-Beat Method for estimation of heart rate when the rhythm is very fast.
• 
  
• ECG Blog #287 — for a regular SVT that was AFlutter.
• ECG Blog #409 — another regular SVT that was AFlutter.
• ECG Blog #229 — reviews distinction between AFlultter vs ATach (and WHY AFlutter is so commonly overlooked).
• 
  
• ECG Blog #240 — reviews the approach to a regular SVT rhythm.