ECG Interpretation: ECG Blog #287 — Sinus Tach with ST Depression?

The ECG shown in Figure-1 was obtained from a man in his 50s during hemodialysis. He complained of "chest pain" — but was hemodynamically stable at the time this tracing was recorded.

Is this Sinus Tachycardia with ischemic ST depression?
To activate the cath lab?

Figure-1: ECG from a man in his 50s with chest pain.

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

My Approach to Today's Case:

Since the patient was hemodynamically stable — there was time for systematic assessment of the rhythm. By the Ps, Qs, 3R Approach (See ECG Blog #185):

The rhythm is fast and Regular. Since the R-R interval is just over 2 large boxes in duration — I estimate the ventricular Rate to be just under 150/minute.
The QRS is narrow (ie, clearly not more than half a large box in duration) — which means that the rhythm is supraventricular.
Sinus P waves appear to be absent — because we do not see a clearly defined upright P wave in lead II. It's possible that P waves are hidden within what appears to be terminal positivity of the T wave in lead II — but this is far from certain. In cases like this, until we can demonstrate clear presence of well defined P waves — we have to assume that no sinus P waves are present.
Could there be evidence of some other form of atrial activity? (Maybe — See below).
In the absence of clearly defined P waves — the 5th Parameter in our systematic Approach (ie, Determining IF P waves are Related to neighboring QRS complexes?) is negative.

MY Impression of the Rhythm:
By the Ps, Qs, 3R Approach — We have determined that the rhythm in Figure-1 is a regular SVT (SupraVentricular Tachycardia) at just under 150/minute — but without clear sign of sinus P waves.

PEARL #1: Recognition that the rhythm in Figure-1 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 ST-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.

KEY Point: Although other entities may also produce a regular SVT (ie, sinoatrial node reentry tachycardia, junctional tachycardia) — these other entities 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 sign of sinus P waves — will greatly facilitate determining the correct diagnosis.

NOTE: For more on the causes of a regular SVT rhythm (without clear sign of normal atrial activity) — See our Audio Pearl (MP-64) at the bottom of this page in the Addendum.

PEARL #2: How Heart Rate may help in SVT Diagnosis:

Sinus Tachycardia usually does not exceed 160-170/minute in a "horizontal" adult (ie, in a patient you re 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 will probably not 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 — 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/minute rate range is for untreated AFlutter. Patients who are already on antiarrhythmic medication may present with a slower atrial rate (and therefore slower ventricuar response) for flutter.
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 will not 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. However, IF the rate of the regular SVT is close to 150/minute (ie, 140-160/minute) — then any of the 4 diagnostic entities in the above LIST could be present ( = Sinus Tach — AVNRT — AVRT — ATach — AFlutter). This is the situation in today's case — since the rate of the regular SVT rhythm in Figure-1 is very close to 150/minute.

PEARL #3: By far, in my experience — the most commonly overlooked arrhythmia (by far!) is AFlutter. The reason for this — is that the atrial activity of AFlutter will often be partially or completely hidden within the QRS complex or the ST-T wave.

As a result — the BEST way to avoid overlooking the diagnosis of AFlutter is to always Suspect AFlutter with 2:1 AV conduction whenever you encounter a regular SVT rhythm at a rate close to 150/minute, in which sinus P waves are not clearly evident.
IF you suspect AFlutter in this situation until you prove otherwise — then you will not miss the diagnosis. There are several ways you can then go about proving (or disproving) your suspicion. These include momentarily slowing the ventricular response by a Valsalva maneuver — by "chemical" Valsalva (ie, using Adenosine or other AV nodal slowing drug to see if reducing the ventricular rate brings out underlying flutter activity) — and/or by use of a special lead system, such as a Lewis Lead that may facilitate visualizing atrial activity (See Figure-4 below in the Addendum at the bottom of the page).

PEARL #4: The method that I favor to try first — is to simply LOOK 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 regular atrial activity at this fast of a rate (Atrial tachycardia will rarely be faster than 250/minute ...).

The way in which 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). The short RED lines in leads II and aVF of Figure-2 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 #5: My usual "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 small amplitude positive deflections of AFlutter in this V1 lead; iii) Lead aVR is often surprisingly helpful for identifying atrial activity; 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.
The reason the diagnosis of AFlutter is so subtle in today's case — is that except for leads II and aVF, flutter waves in other leads are almost perfectly hidden within the QRS complex!

Figure-2: I've labeled atrial activity from Figure-1 (See text).

Case CONCLUSION:

The etiology of the regular SVT at ~150/minute in today's case was AFlutter with 2:1 AV conduction. the reason for "pseudo" ST-T wave inversion was superposition of prominent "sawtooth" flutter activity throughout the cardiac cycle.

Looking at the rest of the ECG — there is slight rightward axis (S wave greater than the R wave in lead I) — and probable LVH (very deep anterior S waves in leads V2, V3) — but probably no acute ST-T wave changes once we have accounted for the prominent flutter waves.
BEST initial treatment of this patient's chest discomfort is to slow the ventricular response (and ideally convert the rhythm). Then repeat the ECG to ensure there are no acute changes once sinus rhythm has been restored.

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

Acknowledgment: My appreciation to Mohd Hatif Kamail (from Kota Bharu, Malaysia) for the case and this tracing.

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

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

Relevant LINKS to Today's Case:

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

Additional Relevant Material to Today's Case:

See ECG Blog #185 — for review of the Systematic Ps, Qs, 3R Approach to rhythm interpretation.
See ECG Blog #240 — for Review on the ECG assessment of the patient with a regular SVT rhythm (including distinction between the various types of SVT reentry).
See ECG Blog #250 — for Review of another case of regular SVT with ST depression.
ECG Blog #210 — reviews the Every-Other-Beat Method for rapid estimation of heart rate (See Video Pearl #27 in this post).
ECG Blog #220 — reviews my LIST #1: Causes of a Regular WCT and — HOW to assess Hemodynamic Stability (Listen to Audio Pearl #37 in this post).
ECG Blog #229 — reviews distinction between AFlutter vs ATach (and WHY AFlutter is so commonly overlooked).
The November 12, 2019 post in Dr. Smith's ECG Blog — in which I review my approach to a Regular SVT rhythm.

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

ADDENDUM (2/27/2022):

I've presented this material before — but it bears repeating for reference. These concepts should be automatic for assessment of the patient who presents with a regular SVT rhythm.

—

Today's ECG Media PEARL #64 (10:50 minutes Audio) — Reviews my LIST #2: Common Causes of a Regular SVT Rhythm.

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

—

—

Today’s ECG Media PEARL #45 (10:00 minutes Audio) — Why is Atrial FIutter so commonly overlooked? Reviews PEARLS regarding the ECG diagnosis of AFlutter — and — What's "New"? in the field, regarding distinction between AFlutter vs Atrial Tachycardia (5/29/2021).

For those wanting a more advanced review on some newer concepts regarding AFlutter — Check Out this article by García-Cosío F et al (Clinical Approach to ATach and AFlutter, Rev Esp Cardiol 65(4):363-375, 2012).
Cosio ( Arrhythm & Electrophys Rev 6(2):55-62, 2017).
For more on distinction between AFlutter vs ATach — Check out Figure-3 below.