Tuesday, November 12, 2019

What is this Regular SVT?

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

MApproach 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 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 TachycardiaiiReentry 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 Tachycardiaor 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/minuteNothing 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); andiv) 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! 


  1. This post is useful for me!!! I am brazilian medical student. I want to know if is there ST depression in this tracing and how do i distinct from each other diferential diagnosis, that said, AVNRT, AVRT and Atrial Tachycardia? I am beginning to learn ekg this year, this blog is very amazing!!!

    1. Oi. Muito obrigado pelo seu coment├írio! (Hi. Thanks a lot for your comment!). If I understand your question correctly — YES, there appears to be slight ST segment depression in a number of leads in this tracing — BUT — because the rhythm is AFlutter (Atrial Flutter) — the “flutter waves” are superimposed on the ST segments, and this makes it somewhat difficult to know how much ST depression there really is. The BEST way to tell, will be AFTER the rhythm is converted — to REPEAT the ECG. Chances are there will be much LESS ST depression at that time because: i) the heart rate will be much slower (ie, tachycardia is a common cause of ST depression); and ii) there will no longer be superimposed “flutter waves” once sinus rhythm has been restored. As to your other Questions — it is sometimes difficult to distinguish between AVNRT, AVRT and Atrial Tachycardia. You may be interested in reading the 10/16/2019 case on Dr. Smith’s ECG Blog ( http://hqmeded-ecg.blogspot.com/2019/10/what-could-this-rhythm-be-and-what-is.html ) — which illustrates how the duration of the RP’ interval during the regular SVT rhythm can sometimes help in distinction between AVRT vs AVNRT (discussed in detail in My Comment at the bottom of the page). I discuss some pointers for distinguishing AFlutter from ATach at THIS LINK ( http://ecg-interpretation.blogspot.com/2016/12/ecg-blog-138-svt-av-block-atrial.html ). Finally — regarding the question of HOW to interpret ST-T wave depression, I reviewed in some detail simplified diagnostic considerations when confronted with ST depression in My Comment at the bottom of the page of Dr. Smith’s 10/21/2019 post ( = https://hqmeded-ecg.blogspot.com/2019/10/is-this-st-depression-due-to-lateral.html )

  2. Great Pearls, Ken!

    The question arises "If the ventricular rate is typically around 150/minute because the atrial rate is typically around 300/minute (with a 2:1 conduction ratio), then why is the atrial rate usually around 300/minute in just about everyone?" The answer lies in the circumference of the tricuspid valve annulus which constitutes the reentrant circuit for typical CW and CCW atrial flutter. That circumference is about the same for almost all normal-sized adults and it results in an atrial cycle length that is very close to 200 msec (or 300 beats/min).

    I also think that one of the reasons that this dysrhythmia is so often missed is because beginners are taught to look only in Lead II for P waves. V1 is very good for displaying P waves that can't be seen in Lead II. But don't forget about the other chest leads. On many occasions I've had to depend on V4 or V5 to show me the P waves.

    1. THANKS so much (as always!) Jerry for your comments! I could not agree more. Although atrial flutter is NOT an overly common arrhythmia in children — when it occurs, the atrial rate of flutter may be faster, leading to a resultant faster ventricular rate — for JUST the anatomic reasons you mention, with smaller size in the smaller hearts of children leading to a faster atrial rate. As we both emphasize — there are certain “Go To” leads, that with experience one learns exactly how to see those 2:1 atrial deflections (even when they are small and partially hidden) — but important (as you emphasize) to always be sure you search ALL 12 leads when looking for atrial activity. I like to emphasize the adage, “If you have a regular SVT at ~150/minute in an adult, without clear sign of sinus P waves — Think AFlutter UNTIL you prove otherwise — and that way you immediately become MUCH less likely to overlook this diagnosis. THANKS again for your Pearls! — :)

  3. Thank you Ken! I alway enjoy your comments!
    I have a question: I recently recorded a similar ECG. It had an atrial rate of 300 with 2:1 conduction and a ventricular rate of 150. But the atrial activity showed only in form of small blips with a normal baseline in between. P-Wave axes were distributed as in atrial flutter (negative in the inferior leads and positive in V1). So it had the the atrial rate of atrial flutter but the morphology of atrial tachycardia. Some say you can only call it atrial flutter if you do not have an isoelectric baseline. What do you say?

    1. @ Mac — THANKS for your comment! A “picture is worth 1,000 words” — so hard to make specific comments on the tracing you had without seeing it … — but to me, the rate is telling. Although in theory ATach may attain atrial rates over 250/minute — that’s just not common — so if the atrial rate in your tracing was ~300/minute — I would think that is very strong evidence favoring AFlutter as the diagnosis. I discuss differentiation between ATach vs AFlutter here — http://ecg-interpretation.blogspot.com/2016/12/ecg-blog-138-svt-av-block-atrial.html — but “Take Home” points are that: i) there are “atypical forms” of AFlutter, in which a “sawtooth” morphology may not be seen — so an isoelectric baseline does not rule out flutter; ii) Sometimes distinction between AFlutter vs ATach can only be made in the EP lab; and iii) Fortunately — this distinction is usually not essential in the short-term (ie, You’ll probably treat both rhythms quite similar in an emergency setting) — and in the longterm, if initial management is refractory — you’ll be referring the patient. Hope that helps — :)


DEAR READER: I have loved receiving your comments, but I am no longer able to moderate them. Since the vast majority are SPAM, I need to moderate them all. Therefore, comments will rarely be published any more. So Sorry.

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