ECG Blog #451 — Premature Closure ...

I was sent the ECG shown in Figure-1 — told only that the patient was a middle-aged man with septicemia.

QUESTIONS: 

• Is this rhythm too fast to be sinus tachycardia?
• Are flutter waves hidden within the QRS and T waves?
• Are we seeing the retrograde P waves of AVNRT?
• Is this ATach (Atrial Tachycardia)?

Figure-1: The initial ECG in today's case.

MY Thoughts on Today’s CASE:

In my opinion — none of the above answers are optimal to describe the rhythm in Figure-1. I say this for the simple reason that to pick any of the above 4 choices — is to imply with 100% certainty that you know the answer (or, as is implied in the title of today’s Blog post — this would be premature closure).

• Instead, I feel it preferable to openly acknowledge that — We do not know for certain what the rhythm is. 

The above said — I did have a good idea what this rhythm was most likely to be. However, until such time that we know for certain — I think it best to simply describe what we see:

• PEARL #1: Realize that for any tachycardia — there are 6 Parameters that need to be assessed. The 1st Parameter — is to ensure that the patient is hemodynamically stable. This is because IF your patient is not stable — then it no longer matters what the rhythm is (because immediate cardioversion will be needed — regardless of whether the rhythm is VT or an SVT).
• Next (assuming your patient is hemodynamically stable) — Assess the rhythm for the remaining 5 KEY Parameters — that are most easily remembered by the saying, “Watch your Ps, Qs — and the 3Rs”. With practice — it should literally take no more than seconds to assess these 5 Parameters (See ECG Blog #185 — for more on the Ps,Qs,3R Approach to rhythm interpretation).

Watch your Ps, Qs — and the 3Rs:

Regarding today's initial rhythm — I see the following:

• There is significant artifact, especially in leads V1,V2 (See Figure-2). This makes assessment of P waves impossible in these 2 chest leads. 
• That said — I thought sinus P waves might be present in the inferior leads. However, I could not with certainty distinguish between what might be a P wave? — vs a T wave? — vs a P wave hiding within the preceding T wave (ie, under the ?'s that I placed in the inferior leads).
• On the other hand — Doesn't it look like there might be 2:1 atrial activity in lateral leads V5,V6 (slanted RED lines in these leads)? As a result — I was not certain about the presence and/or nature of atrial activity.
• NOTE: My "Go-To" Leads when looking for extra atrial activity are leads II,III,aVF; aVR; and V1 — which is why I was not convinced on the basis of the RED lines I drew in Figure-2 that this truly represented 2:1 atrial activity.

Continuing with the 5 Parameters:

• The rhythm in Figure-2 is Regular — at a Rate of ~160/minute (ie, with an R-R interval slightly less than 2 large boxes in duration).
• The QRS complex is narrow in all 12 leads (ie, Not more than half a large box in any of the 12 leads).
• The last of the 5 Parameters — is whether P waves are Related to the QRS complex. But since we are not certain if there even is atrial activity? (and if so — whether such atrial activity represents sinus P waves, flutter waves, or something else?) — we can not yet address this 5th Parameter.
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• BOTTOM Line: Today's initial rhythm is a regular SVT (SupraVentricular Tachycardia) at ~160/minute, but without clear indication of the presence and nature of atrial activity.

PEARL #2: Recognition that the rhythm in Figure-1 is a regular SVT — but with uncertainty regarding atrial activity — should prompt consideration of the followling differential diagnosis LIST (See ECG Blog #240):

• i) Sinus Tachycardia (if sinus P waves are hidden below the ?'s in Figure-2 ). 
• ii) A reentry SVT (either AVNRT if the reentry circuit is contained within the AV node — or AVRT if an accessory pathway outside the AV node is involved); 
• iii) Atrial Tachycardia (ATach);
• iv) Atrial Flutter (AFlutter) with 2:1 AV conduction.

KEY Point: Although other entities may also produce a regular SVT (ie, sinoatrial node reentry tachycardia, junctional tachycardia) — they are far less common in practice. Therefore, remembering to think of the 4 entities in the above LIST whenever you encounter a regular SVT rhythm without clear indication of atrial activity — will greatly facilitate determining the correct diagnosis.

PEARL #3: Consider the History:

• Is the patient on any antiarrhythmic medication? (This is important to consider — as it may affect the rate and conduction properties of the SVT).
• Any known history of similar rhythms?
• What is the clinical situation? (ie, In today's case the patient has septicemia — therefore seemingly susceptible to sinus tachycardia!).

PEARL #4: Consider the Rate of the SVT:

• In adults — Sinus Tachycardia usually does not exceed 160-170/minute in a "horizontal" patient (ie, in a patient you are examining, who has not just been running). This is not to say that sinus tachycardia will never go faster than 170/minute — but rather to suggest that when the rate of the regular SVT rhythm you are assessing is well over this rate range — then the rhythm is less likely to be sinus tachycardia. NOTE: All bets are off in children — in whom sinus tachycardia over 200/minute is not that uncommon.
• With AFlutter — the most common ventricular response in the patient who is not being treated with an antiarrhythmic medication is ~150/minute (usual range ~140-160/minute). This is because the atrial rate in untreated AFlutter is most often ~300/minute (usual range ~250-350/minute) — and since untreated AFlutter most often presents with 2:1 AV conduction — 300/2 ~150/minute. As a result — IF the ventricular rate of the regular SVT rhythm you are assessing is over ~170-180/minute (but under ~250/minute) — then AFlutter is less likely (because this rate would be faster-than-expected for 2:1 AV conduction, and too slow for 1:1 AV conduction). 
• NOTE: This ~140-160/min. range is for untreated AFlutter. Patients who are already on antiarrhythmic medication may present with a slower atrial rate (and therefore slower ventricular response) for AFlutter.
• It is well to remember that ATach is less common as a cause for a strictly regular SVT, especially in an otherwise healthy young-to-middle-aged adult. ATach is more likely to be seen in patients referred for EP (ElectroPhysiologic testing) — and in older adults with SSS (Sick Sinus Syndrome). I include ATach in the above differential diagnosis LIST for completeness — but take into account that it won't be seen as often as AFlutter and the reentry SVTs.
• Therefore — IF the rate of a regular SVT without clear sign of sinus P waves is substantially faster than 160-170/minute — then a reentry SVT rhythm (ie, AVNRT or AVRT) becomes the most likely diagnosis. 
• But — IF the rate of the regular SVT is close to 150/minute (as it is with today's initial rhythm at ~160/minute) — then any of the 4 diagnostic entities in the above LIST could be present!

PEARL #5: Other potentially helpful considerations:  

• Look for Atrial Activity! — which we've already addressed for today's rhythm (See above). Using calipers can facilitate your search for atrial activity.
• Look for a “Break” (or subtle change) in the Rhythm! — Even a slight pause in the SVT rhythm, may be all that is needed to reveal underlying atrial activity that had been hidden by the regular tachycardia. There is no "break" in the rhythm in Figure-2. That said, it may be helpful to search Telemetry — as there may have been some change in the rhythm a little earlier in the patient's course.
• Look for the “Onset” (and/or Termination) of the Rhythm! — The KEY clue to the etiology of an SVT often lies with capturing either the beginning and/or the end of the SVT. 
• ATach often begins gradually, with progressive acceleration of the ectopic focus (ie, “warm-up” phenomenon). Then, there may be gradual slowing (ie, “cool-down”) of the rhythm as it ends. 
• In contrast — SVT reentry rhythms often start with 1 or more PACs that block conduction down one of the AV nodal pathways, which serves to set up the reentry circuit as the impulse starts down the other pathway. As a result — the onset of a reentry SVT is often abrupt (ie, accounting for the previous term used to designate this rhythm = PSVT = Paroxysmal SVT). The termination of reentry SVT rhythms is also usually quick (though this may occur over several beats).
• Finally, when Sinus Tachycardia is suspected clinically (as it is in today's case) — awareness that over time the rate of sinus tachycardia will often change (become slower or faster) as the patient's condition becomes better or worse.

 

PEARL #6: While our goal is to arrive at as precise of a rhythm diagnosis as possible — the "good news" is that for practical purposes — initial diagnostic and/or treatment measures in the field or in the ED for an undifferentiated regular SVT rhythm are similar (ie, consideration of a vagal maneuver — and/or use of an AV nodal blocking agent such as Verapamil/Diltiazem; a ß-Blocker, and possibly Adenosine).

• P.S.: If you suspect that the regular SVT rhythm is likely to be sinus tachycardia — then rather than antiarrhythmic medication, simply treating the underlying disorder may be all that is needed.

Figure-2: I've labeled the initial ECG in today's case.

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Today's CASE Continues:

The patient was treated for sepsis. A very lose dose of IV Metoprolol was given. The repeat ECG is shown below in Figure-3.

• What has happened?

Figure-3: The ECG was repeated after beginning treatment for sepsis.

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ANSWER — and CASE Conclusion: 

To facilitate comparison in Figure-4 — I've put together both ECGs in today's case.

• Following treatment for sepsis — the patient improved clinically. As a result — the heart rate in ECG #2 has now slowed just enough to allow clear distinction of sinus P waves (RED arrows in lead II of the repeat ECG).
• Clear distinction of sinus P waves is now also seen in each of my "Go-To" Leads (BLUE arrows in these leads), as well as in virtually all leads on this tracing.
• Comparing ECG #2 with the initial tracing — We can see that sinus P waves were present the entire time! Because of the very fast rate in ECG #1 — the sinus P waves were simply hidden within the terminal part of preceding T waves.
• Otherwise, on the repeat ECG — there are some nonspecific ST-T wave abnormalities (potentially rate-related) — and the possibility of large U waves (hard to tell — given the still rapid heart rate of 140-150/minute). Serum K+ and Mg++ levels need to be verified.

Figure-4: Comparison of the repeat ECG with the initial ECG (after treatment of sepsis).

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Acknowledgment: My appreciation to Sam Ghali @EM_RESUS (from Jacksonville, Florida — USA) for the case and this tracing.

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Related ECG Blog Posts to Today’s Case: 

• ECG Blog #185 — Reviews the Ps, Qs & 3Rs Approach to systematic rhythm interpretation.
• ECG Blog #188 — Reviews the essentials for reading (and/or drawing) Laddergrams, with LINKS to numerous Laddergrams I’ve drawn and discussed in detail in other blog posts.
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• ECG Blog #240 — The regular SVT ...
• ECG Blog #229 — Why is AFlutter so commonly overlooked?
• ECG Blog #138 — AFlutter vs Atrial Tachycardia. 
• ECG Blog #40 — Another regular SVT that turned out to be AFlutter.

Other sites where I've discussed similar cases:

• The March 6, 2020 post in Dr. Smith's ECG Blog.
• The October 16, 2019 post in Dr. Smith's ECG Blog. 
• Please check out the November 12, 2019 post in Dr. Smith's ECG Blog — in which I reviewed the case of a different kind of regular SVT Rhythm (AFlutter).