What is this Regular SVT?

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MY Comment by KEN GRAUER, MD (11/12/2019):

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My appreciation to Kenneth Khoo for this case. This patient was hemodynamically stable. There was debate among providers in his institution as to what the rhythm in this ECG was (Figure-1).

• What do YOU think the rhythm is?
• What is the differential diagnosis?
• Why can you be virtually certain what this rhythm is even before treating and before any diagnostic maneuvers?

Figure-1: The initial ECG in this case (See text).

My Approach to this Rhythm: I reviewed the basics for rhythm interpretation in the October 16, 2019 Case from Dr. Smith’s ECG Blog. In brief — once you’ve assured that your patient is hemodynamically stable (as this patient was) — We need to assess the remaining 5 KEY parameters. I favor this memory aid, “Watch your Ps, Qs and the 3 Rs”:

• NOTE: It does not matter in what sequence you address these 5 KEY parameters — and I often change the sequence I use depending on the tracing (ie, Which of these 5 parameters is easiest to assess in the tracing in front of you?).
• For the tracing in Figure-1 — the rhythm is perfectly Regular. The R-R interval is almost exactly 2 large boxes — which means that the ventricular Rate is 300/2 ~150/minute. The QRS complex is narrow — so this rhythm is supraventricular! Normal atrial activity is not seen — because there are no clear sinus P waves (ie, the P wave is not clearly upright in lead II …).

QUESTION: What does the above analysis suggest to YOU thus far?

ANSWER: We’ve established that this patient is hemodynamically stable. The rhythm in Figure-1 is a regular SVT (SupraVentricular Tachycardia) at ~150/minute without clear sign of sinus P waves. The principal differential diagnosis is similar to what we derived in the October 16, 2019 Case: i) Sinus Tachycardia; ii) Reentry SVT (either AVNRT if the reentry circuit is contained within the normal AV nodal pathway — or AVRT if an accessory pathway is involved); iii) Atrial Tachycardia; or iv) Atrial Flutter.

• PEARL #1: The major difference between this case and the case we presented on October 16 — is that the ventricular rate is very close to 150/minute. The most commonly overlooked sustained cardiac arrhythmia (by far) is AFlutter! Over the years — I’ve seen numerous cardiologists overlook this rhythm (especially those cardiologists who do not routinely use calipers for assessment of complex arrhythmias). I fully acknowledge that I've overlooked AFlutter. The BEST way never to overlook the ECG diagnosis of AFlutter is to: i) Think of this diagnosis often! — and, ii) To assume that any regular SVT rhythm in which clear sinus P waves are not seen is AFlutter until you prove otherwise — especially IF the ventricular rate of this reguar SVT rhythm is close to 150/minute (ie, ~140-160/minute range).
• PEARL #2: The reason the ventricular rate for AFlutter is so often close to 150/minute — is that: i) The atrial rate for untreated AFlutter is almost always close to ~300/minute (ie, 250-350/minute range) — and, ii) Untreated AFlutter most often conducts with a 2:1 ventricular response (ie, atrial rate ~300/minute — therefore ventricular rate ~300/2 = ~150/minute).
• PEARL #3: The expected atrial rate for flutter is likely to change IF the patient has been “treated” — in which case the ventricular rate in AFlutter with 2:1 AV conduction may be slower (if the patient is on antiarrhythmic medication) — or possibly even faster (if he/she has been treated by ablation).

QUESTION: We said that normal sinus P waves were not seen for the rhythm in Figure-1 — because there is no clearly upright P wave in lead II.

• Does this mean that there is no atrial activity in Figure-1?

ANSWER: There appear to be lots of “extra deflections” in a number of leads in ECG #1 ...

• PEARL #4: The BEST way we know to quickly determine if the “extra deflections” that we seem to be seeing in ECG #1 represent atrial activity — is to use Calipers!

We show the result of using calipers in Figure-2.

Figure-2: RED arrows indicate that the “extra deflections” are indeed regularly occurring in multiple leads (See text).

Looking for Flutter Waves: The diagnosis of AFlutter can be established in a regular SVT at ~150/minute — IF you are able to identify regular atrial activity at ~300/minute. Nothing else results in a regular atrial activity at this fast of a rate (Atrial tachycardia will rarely be faster than 250/minute ... ).

• PEARL #5: The way I look for flutter waves is to carefully set my calipers at precisely HALF the R-R interval of the regular SVT (since IF the rhythm is AFlutter — then the atrial rate should be twice the ventricular rate if there is 2:1 AV conduction). RED arrows in Figure-1 confirm that there is indeed 2:1 atrial activity in this tracing — which tells us even before application of a vagal maneuver or administration of Adenosine (or other AV blocker) that the rhythm is virtually certain to be AFlutter.
• PEARL #6: My “GO TO” leads for identifying atrial activity are: i) Lead II — which is typically the BEST lead for identifying atrial activity. In AFlutter — leads III and aVF also usually provide ready evidence of 2:1 atrial activity; ii) Lead V1 — next to lead II, lead V1 is often the 2nd-best lead in my experience for identifying atrial activity. With AFlutter — one will often see positive deflections similar to those seen in Figure-1 in this V1 lead; iii) Lead aVR is often surprisingly helpful for identifying atrial activity (RED arrows in ECG #1); and, iv) IF none of the above leads suggest atrial activity — then I’ll survey the remaining 7 leads as I look for atrial activity. That said, AFlutter will almost always provide ready evidence of atrial activity in one or more of my “Go To” leads.
• PEARL #7: On occasion — atrial activity may not be readily apparent in a hemodynamically stable patient with a tachyarrhythmia. In such cases — use of an alternative lead system, such as a Lewis Lead may enhance atrial activity and facilitate rhythm determination. Figure-3 reviews how to use a Lewis Lead. The March 20, 2018 post on Dr. Smith’s ECG Blog illustrates application of a Lewis Lead in a patient in a regular SVT rhythm.

Figure-3: Use of a Lewis Lead (See text).

Our THANKS to Kenneth Khoo (from Malaysia) for sharing this case with us!