Monday, January 28, 2019

What is going on here?? (The computer called it "STEMI" and "Intraventricular Conduction Delay"!!)

I was asked by my partner to interpret this ECG because the Veritas algorithm had called it "STEMI" and Intraventricular Conduction Delay (IVCD), and he could not see why.
He also was confused by what looked like possible delta waves with short PR interval.
What do you think?



This is simply an accelerated junctional rhythm at a rate of approximately 100.  It is high enough in the junction that it initiates an atrial beat before it initiates a ventricular beat, and of course it does so in a retrograde fashion.  So the P-wave is before the QRS, is inverted, and there is a very short PR interval.  The junction is going faster than the sinus node.

Alternatively, it could be a low atrial rhythm.

Usually an accelerated junctional rhythm is seen with Digoxin toxicity, but that is primarily when there is underlying atrial fibrillation: the AV node is blocked from conducting the AF impulse, and the junction is accelerated. 

See this case for AF, Dig toxicity, and accelerated junctional rhythm:

Looks like a Posterior STEMI. Is it?


If the sinus node were firing faster than 100, then it would take over, there would be an upright P-wave and a normal PR interval.

Low atrial rhythm can also have short PR interval.

Our electrophysiologist, Rehan Karim, explains this simply: 

Essentially PR interval would have 3 components:
1.       Time from impulse origin to the area of input into AV node.
2.       Time within AV node

3.       His-Purkinje system

He did not say how much is attributable to each segment, although there is no doubt that the most time is spent traversing the AV node.

There is of course no STEMI and there is no Intraventricular conduction delay (and no delta wave/no WPW!)

I found this very nice laddergram on Arnel Carmona's site (high Arnel! We have not been in touch for a long time!).


It is: http://learningecg.blogspot.com/
Our case here is analogous to (a) above.



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Comment by KEN GRAUER, MD (1/28/2019):
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Interesting case presented by Dr. Smith about the misinterpretation of a less common rhythm as being due to a “STEMI” with “IVCD”. I’ll add the following thoughts to those presented by Dr. Smith.
  • For clarity, I’ve reproduced and labeled the initial ECG in Figure-1.
Figure-1: The initial ECG in this case (See text).
==========================
THOUGHT #1 — What is the rhythm in Figure-1?
  • The rhythm in Figure-1 is not sinus — because there is no upright P wave in lead II. Instead, the P wave in lead II (as well as in the other 2 inferior leads) is negative (RED arrows). The only exceptions to the rule that “if the P wave is not upright in lead II, then you don’t have sinus rhythm” — are dextrocardia and lead misplacement. But the upright QRS in lead I and the large initial Q in lead aVR tell us the limb leads are correctly placed — and, the normal R wave progression in the chest leads tells us this is not dextrocardia.
  • The QRS complex is narrow.
  • The long lead II rhythm strip at the bottom of the tracing tells us that each QRS complex is preceded by a negative P wave in lead II with a fixed and shortened PR interval. Since this supraventricular rhythm is not sinus — there are 2 other possibilities: ian AV Nodal (or Junctional) Rhythm; or, iia Low Atrial Rhythm (often also referred to as a Coronary Sinus Rhythm).
==========================
The negative P waves in lead II of Figure-1 are the result of retrograde conduction. As schematically shown by the light RED arrows in Panels A and B of Figure-2 — atrial depolarization will be directed opposite from the +60 degree vantage point of standard lead II when impulse origin is either from the AV Node (“X” in Panel A of Figure-2) — or from a site low in the atria, such as the ostium of the coronary sinus (“Y” in Panel B).
  • Precise localization of the site of an ectopic atrial impulse is beyond the scope of this ECG Blog, and rests in the domain of the cardiology electrophysiologist. Suffice it to say that assessment of P wave morphology (positive, negative, biphasic, or null deflection) in multiple leads of the 12-lead tracing assists in location prediction. The ECG picture in Figure-1, in which inferior lead P waves are negative and P waves are positive in leads aVR and aVL (BLUE arrows) is consistent with either a Junctional or Low Atrial Rhythm.
  • What can be said — is the large size of the negative P waves in the inferior leads suggests the impulse is arising from a considerable distance away (ie, from either low in the atria or from the AV node).
  • P wave morphology in lead V1 is often helpful in further clarification of impulse origin. That said, I fully acknowledge my confusion about how to interpret P wave morphology in leads V1 and V2, as highlighted by the thin, vertical blue line in Figure-1 (which I drew corresponding to what I perceived as the end of the P wave in simultaneously-obtained lead II). BOTTOM LINE: The rhythm in Figure-1 is either Low Atrial or Junctional at a rate of ~100/minute.
Figure-2: Illustration how either a low atrial or junctional rhythm might produce the P wave morphology seen in Figure-1 (See text). Figure reproduced from Grauer K: ECG-2014-ePub (KG/EKG Press).
==========================
THOUGHT #2 — What accounts for a negative P wave in front of the QRS with AV nodal beats or rhythm?
  • I expand on the laddergram above in Figure-3. The legend explains all.
Figure-3: Laddergram of the 3 possibilities for P wave appearance in lead II with junctional beats or junctional rhythm. Panel A illustrates the normal forward conduction of sinus rhythm. The impulse originates in the SA Node — travels through the atria — slows down a bit as it passes through the AV Node — and is then transmitted down through the conduction system to the ventricles. NOTE: With junctional beats (or junctional rhythm) — the impulse originates from the AV Node. It then travels back (retrograde) to the atria, and down to the ventricles. As a result — the P wave in lead II may be negative appearing either before (Panel B) or after (Panel D) the QRS — or — no P wave at all may be seen (Panel C). Clinically — Situation C is most common, whereas it is rare to see a P wave after the QRS (situation D). NOTE: Whether a negative P wave is seen before, after, or is hidden within the QRS is determined not only by location of origin of the AV nodal impulse, but by the relative speed of conduction back to the atria compared to down the ventricles. (Figure reproduced from Grauer K: ECG-2014-ePub [KG/EKG Press]).
========================== 
THOUGHT #3 — Why did the computer interpretation call a “STEMI” with “IVCD”?
  • Computerized ECG interpretations have pros and cons. They are only as good as what they have been programmed for. The better we understand what the computerized system in our facility is capable of — the more effective we can be in using the computer. As a result — I always try to understand what the computer missed. In Figure-1 — my hunch is that the computer interpreted the negative inferior P waves as Q waves, and as a part of the QRS complex — in which case it might call an MI with IVCD. I see nothing that could be misconstrued as acute ST-T wave changes. That said — I’m not quite sure why the computer said what it did ...
  • For “My Take” on the Pros & Cons of Computerized Interpretations — and how I suggest they might best be used — CLICK HERE.
==========================
THOUGHT #4 — Clinically, regardless of whether the rhythm is junctional or low atrial — WHY is there a rate of ~100/minute?
  • Practically speaking, distinction between a junctional vs low atrial rhythm is largely academic, since clinical significance of these 2 entities is similar. In either case — the rate here is faster than anticipated ( = “accelerated” ). The point to emphasize is that there are NOT that many reasons for an accelerated junctional rhythm. As a result — recognition of this rhythm should immediately prompt consideration of the following: iDig toxicity (if a patient is on Digoxin and manifests an accelerated junctional rhythm — then almost regardless of the Dig level, they are Dig toxic!); iiIschemia/infarction; iiiPost-operative state; ivCongenital heart disease (if the patient is a child); and, v“Sick” patient.
  • Unfortunately, we are not given any History in this case. Clearly, this would be important to know before proceeding further with clinical management! All we can say is that there is an accelerated junctional (or low atrial) rhythm with LVH (R in lead V6 ≥18 mm) — but no acute ST-T wave changes.The QTc interval looks like it may be prolonged — though this is harder to interpret in view of the rapid rate and generalized ST-T wave flattening.


17 comments:

  1. Dr. Smith, so junctional tachycardia or accelerated junctional rhythm, I think its a rare one, do you know any clinical context? Thanks again for your great still active teaching platform!!

    ReplyDelete
    Replies
    1. Martin,
      Unfortunately, I don't know any clinical info on this patient.
      Thanks for the shout out!
      Steve

      Delete
  2. Wouldn't it be low atrial rhythm?

    ReplyDelete
    Replies
    1. No. A low atrial rhythm would have to traverse the entire AV node, creating a normal PR interval.

      Delete
  3. Hi Dr. Smith,

    it's perfectly clear why the computer aglorythm interpretated this as an intraventricular conduction delay (PR interval so short that kind of ""merges" with the QRS). I have two question tough:

    -In this ECG, how could you tell the difference between an accelerated junctional rythm with retrograde P waves conduction and an atrial tachycardia originating in the left atrium, really close to the AV node? (this my initial rythm interpretation, as 100 bpm is borderline but still fast enough to be called "tachycardia")

    -Obviously there is not STE, but isn't there a certain degree of STD in V1 and V2? If so, could this be a hint of an isolated posterior wall AMI?

    Thanks!

    ReplyDelete
    Replies
    1. As above, a low atrial rhythm would have to traverse the entire AV node, creating a normal PR interval.

      Delete
    2. My understanding has been that speed of conduction through cardiac tissue may affect where you see the P wave — and that the PR interval may be less than 0.12 second with some low atrial rhythms.

      Delete
  4. Dear Mr.Smith, I think a low atrial rhythm can still creates a short PR interval. Because at the time begining of inversion P wave, impulse from low atrial comes to av node. So I think we can't use PR interval to differentiate junctional rhythm or low atrial rhythm.

    ReplyDelete
    Replies
    1. You are correct and I was wrong. I have changed the post.
      Thanks!

      Delete
  5. Well I was thinking it is more specific to inferior atrial rhythm but Dr Smith and Ken have explained tremendously so learnt more detail about it

    ReplyDelete
    Replies
    1. It could be low atrial. I have changed the post:
      Low atrial rhythm can also have short PR interval.



      Our electrophysiologist, Rehan Karim, explains this simply:



      Essentially PR interval would have 3 components:

      1. Time from impulse origin to the area of input into AV node.

      2. Time within AV node

      3. His-Purkinje system

      Delete
  6. I think the computer may have interpreted it as "STEMI" due to baseline wander and artifact causing artificial ST depression in V2 and ST elevation in V4.

    ReplyDelete
  7. If the heart rate was more than 100, what would you call it ?

    ReplyDelete
    Replies
    1. Still accelerated junctional or fast low atrial

      Delete
    2. Technically, rhythms with a rate of ≥100/minute (in adults) are classified as "tachycardia" — so for those accelerated junctional rhythms with a rate of ≥100/minute, I call them junctional "tachycardia". For atrial rhythms at ≥100/minute, I call them atrial "tachycardia". That said, this is largely a semantic difference. The clinical significance of an accelerated junctional rhythm vs junctional "tachycardia" is the SAME — :)

      Delete
  8. Dr Smith
    Please explain how low atrial can create Short PR. Koch triangle is there and
    Focus location is considered above the tendon todaro or below tendon.

    ReplyDelete

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