Wednesday, September 8, 2021

ECG Blog #250 (64) — ST Depression and a Regular SVT

The ECG in Figure-1 was obtained from a previously healthy 60-year old man who presented to the ED (Emergency Department) with palpitations and new chest pain.



  • Should you activate the cath lab?
  • What would you do first?


Figure-1: ECG from a 60-yo man with palpitations and chest pain.


My Approach to Today's Case: We are told that the patient in today's case is a 60-year old man who presents to the ED with palpitations and new chest pain. And, there is an "eye-catching" amount of ST depression seen in multiple leads in Figure-1. There is also a tachycardia ...

  • KEY Point: The 1st thing to do in the assessment of any patient in a tachycardia — is to determine IF the patient is hemodynamically stable. We have not yet been told anything about this patient's hemodynamic status.
  • As impressive as the amount of ST depression in ECG #1 is — interpretation of this tracing should follow the same Systematic Approach used for assessment of any ECG (as discussed in detail in ECG Blog #185 and Blog #205).


The Case Continues: Although this patient was having symptoms (ie, chest pain, palpitations) — it was felt that he was "stable enough" for initial assessment. Immediate cardioversion was not felt to be needed at this time. By the Ps, Qs & 3R Approach:

  • P waves are not seen in any lead.
  • The QRS is narrow (ie, clearly not more than half a large box in duration) — which means the rhythm in Figure-1 is supraventricular.
  • The rhythm is fast and Regular. I estimate the Rate of the rhythm to be ~175-180/minute (See Figure-2). Since there is no sign of atrial activity — there is no "Relation" between P waves and neighboring QRS complexes.


Figure-2: I've labeled the long lead II rhythm strip from Figure-1 to illustrate use of the Every-Third-Beat Method for estimation of the ventricular rate (as explained in Video Pearl #27 in ECG Blog #210). Starting with a QRS complex that begins on a heavy line (1st vertical RED line in the long lead II rhythm strip) — it can be seen that the time that it takes to record 3 beats (RED numbers) is just over 5 large boxes on ECG grid paper (BLUE numbers). If it would have taken exactly 5 large boxes to record 3 beats — then 1/3 of the rate would have been 300 ÷ 5 = 60/minute. This means that 1/3 of the rate is a little bit slower than 60/minute — which means that the ventricular rate in Figure-2 is between 170-180/minute.


My Thoughts Thus Far: By the Ps, Qs & 3R Approach — we've determined that the rhythm is a regular SVT ( = SupraVentricular Tachycardia) at ~175/minute, without sign of atrial activity.

  • Should you activate the cath lab?
  • What is the rhythm in Figure-2 most likely to be?


  — The Case Continues BELOW, under today's Audio Pearl ...



NOTE: Some readers may prefer at this point to listen to the 10:50-minute ECG Audio PEARL before reading My Thoughts regarding the ECG in Figure-1. Feel free at any time to refer to My Thoughts on this tracing (that appear below ECG MP-64).


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


NOTE: I allude to a number of important concepts in arrhythmia interpretation in today's Audio Pearl. For easy reference — I list below LINKS with more on these concepts.

  • ECG Blog #185 — reviews the Ps, Qs & 3R Approach (Listen to Audio Pearl #3 in this post).
  • 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 andHOW 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 — Listen to Audio Pearl #45).
  • The November 12, 2019 post in Dr. Smith's ECG Blog — in which I review my approach to a Regular SVT rhythm.





The Case Continues:

Although there is marked, diffuse ST depression in ECG #1 — the highest priority at this time is to determine the rhythm because:

  • The rhythm does not appear to be sinus (since upright P waves are not seen in lead II).
  • If sinus rhythm and rate control could be established — it’s possible that much (most) of the ST depression might resolve. It may be that the ST depression we see in today's tracing is not the result of an acute coronary syndrome.
  • Even if this patient did have an acute coronary syndrome — it would not be advisable to activate the cath lab until after the arrhythmia was diagnosed and rate control was reestablished.


LIST #2: Common Causes of a Regular SVT Rhythm:

We have described the rhythm in today’s case as a regular SVT (SupraVentricular Tachycardia) at ~170-180/minute, without clear sign of atrial activity. As discussed in the above Audio Pearl (ECG-MP-64) — the LIST that I favor for the differential diagnosis consists of 4 Causes:

  • Sinus Tachycardia (Sinus Tach).
  • Atrial Flutter (AFlutter).
  • Reentry SVT (ie, AVNRT or AVRT).
  • Atrial Tachycardia (ATach).

PEARL #1: Of the 4 Causes that I’ve listed for a regular SVT rhythm without sign of atrial activity — the least common in my experience is Atrial Tachycardia (ATach)ATach may result in a regular SVT rhythm with either 1:1 or 2:1 AV conduction. The atrial rate may vary from anything over 100/minute — to 240 per minute (or rarely, even faster than this).

  • ATach with Block used to be a common manifestation of Digitalis toxicity. With dramatic reduction in the use of Digitalis in recent years (and with lower doses being used in most of those patients who still are receiving this medication) — ATach with Block is seen much less often than in the past.
  • When ATach is seen — it will often present with group beating from Wenckebach conduction. As a result — there will commonly be changing conduction ratios, with periodic short pauses — and IF the rhythm is ATach, then P waves that conduct will usually be seen before the first beat at the end of such pauses. Although for completeness, I list ATach as one of the 4 Causes in my SVT LIST — ATach will not commonly present as a strictly regular SVT rhythm without any P waves.

PEARL #2: Determining the heart rate may provide an important clue to the etiology of a regular SVT without clear sign of atrial activity.

  • In a supine adult (ie, an adult who has not just exercised) — it is not common for sinus tachycardia to exceed ~170/minute. This is not to say that you will never see sinus tachycardia this fast in a non-exercising adult — but rather to suggest that the very rapid heart rate in today’s case (ie, ~175/minute) makes sinus tachycardia less likely.
  • Untreated AFlutter most commonly presents with 2:1 AV conduction, in which the atrial rate of flutter is close to 300/minute (ie, ~250-to-350/minute range) — and the ventricular rate close to half that, or ~150/minute (ie, ~130-to-160/minute range). The ventricular rate of ~175/minute in today's case would imply an atrial rate of 175 X 2 = 350/minute, which is faster than the usual atrial rate for AFlutter.
  • From these points — it can be seen that when the rate of a regular SVT rhythm is not more than 150-160/minute — any of the entities on the SVT LIST could be operative. However, when the ventricular rate is greater than ~170/minute — a reentry SVT rhythm becomes much more likely!

FOLLOW-UP in Today's Case:

By the process of elimination — the rhythm in today's case was diagnosed as a reentry SVT — and treated with Adenosine. This promptly converted the rhythm to sinus — with resolution of the patient's symptoms and resolution of much of the ST depression.

  • Cardiac cath was performed given the patient’s age and the presenting symptom of chest pain, in association with such marked and diffuse ST depression. Cardiac cath showed no more than minimal coronary disease.


Final PEARL #3: An important ECG pattern to recognize — is diffuse ST depression (in ≥7 leads) that occurs in association with ST elevation in lead aVR. It should be emphasized that this ECG pattern is not a sign of acute coronary occlusion. Instead, it suggests diffuse Subendocardial Ischemia, which may be due to one of the following:

  • Severe Coronary Disease (due to LMain, proximal LAD, or severe 2- or 3-vessel disease) — which in the right clinical context may indicate ACS (Acute Coronary Syndrome).
  • Subendocardial ichemia from another Cause (ie, sustained tachyarrhythmia; shock/profound hypotension; GI bleeding; anemia; etc.).


KEY Learning Points from Today's Case: 

It is good that despite profound ST depression in the initial ECG — the cath lab was not activated. Instead, initial management appropriately focused on diagnosis and treatment of the cardiac rhythm. 

  • The finding on cardiac cath of no more than minimal coronary disease provides insight how even profound and diffuse subendocardial ischemia may sometimes not be the result of severe coronary disease. 
  • Finally — persistent tachycardia can be the cause of marked ST depression.




ADDENDUM (September 8, 2021): The 2 LISTS that I favor for the diagnosis of cardiac arrhythmias assist in assessment of regular wide and narrow tachycardias. Discussion in today's blog post focused on LIST #2 = the Causes of a Regular SVT.

  • I've added Figure-3 below, as review of the Causes in my LIST #1.



Figure-3: Shown here is my LIST #1: Causes of a Regular WCT ( = Wide-Complex Tachycardia) Rhythm of Uncertain Etiology (ie, without clear sign of sinus P waves). This list is discussed in detail in ECG Blog #220.




Related ECG Blog Posts to Today’s Case: 

  • ECG Blog #185 — Reviews the Ps, Qs & 3R Approach to Systematic Rhythm Interpretation
  • ECG Blog #205 — Reviews my Systematic Approach to 12-lead ECG Interpretation.
  • ECG Blog #210 — Reviews a case of a Regular WCT Rhythm (Media Pearl #27 in this blog post is a Video that reviews the Every-Other-Beat Method for estimation of heart rate when the rhythm is fast).
  • ECG Blog #220 — Reviews the differential diagnosis for List #1: Causes of a Regular WCT Rhythm without clear sign of atrial activity (Media Pearl #37 in this blog post is an Audio that reviews assessment to determine IF the patient is Hemodynamically Stable).
  • ECG Blog #229 — reviews distinction between AFlutter vs ATach (and WHY AFlutter is so commonly overlooked — Listen to Audio Pearl #45).
  • The November 12, 2019 post in Dr. Smith's ECG Blog — Reviews another case of a Regular SVT rhythm
  • The October 16, 2019 post in Dr. Smith's ECG Blog — My Comment (at the bottom of the page) reviews my approach to another case of a Regular SVT rhythm

  • ECG Blog #196 — Reviews "My Take" on assessing the Regular WCT (Wide-Complex Tachycardia) — with tips for distinguishing between VT vs SVT with either preexisting BBB or aberrant conduction.