ECG Blog #510 — Myocarditis or Acute MI?

You are shown the ECG in Figure-1 — obtained from a young adult with palpitations. Is the ST elevation in the chest leads the result of:

• an acute MI? 
• or myocarditis? 
• or is it a normal repolarization variant?

Figure-1: The initial ECG in today's case — obtained from a young adult with palpitations. (To improve visualization — I've digitized the original ECG using PMcardio).

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About the ST Elevation …

• For clarity in Figure-2 — RED dotted lines in leads V2-thru-V6 highlight the baseline for assessing chest lead ST elevation in this tracing.
• RED arrows highlight the J-point in leads V4,V5,V6 — which serves as the landmark for judging the amount of ST elevation.

QUESTIONS regarding Figure-2:

• Did YOU begin your interpretation of today’s initial ECG by assessing the rhythm?
• HINT: Why is it especially important to begin by assessing the rhythm in today’s tracing?

Figure-2: I’ve labeled the J-point in leads V4,V5,V6 — which serves as the baseline for judging the amount of ST elevation. 

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ANSWER:

The reason it’s important to first assess the rhythm in the long lead II (at the bottom of today’s tracing) — is that the shape of the P waves is not always the same, and the amount of ST elevation in this ECG varies depending on the shape of the P wave that precedes each beat.

• PEARL #1: Today’s case provides a prime example for why it is important to begin interpretation of every ECG you encounter — by spending an educated 2-3 seconds looking in front of each QRS complex to see if there is a P wave. 
• If so — Is the shape of each P wave the same? 
• Is the PR interval constant?

Depending on how your ECG machine is set up — one or more long lead rhythm strips may be displayed under the 12-lead ECG. 

• I favor systems that display a long lead II (instead of a lead V1 or other lead) — because IF upright P waves are present in lead II with a constant PR interval in front of each QRS complex — then a normal sinus rhythm is present (This is not necessarily true if a lead other than lead II is used for recording the long lead rhythm strip).

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Take another LOOK at the long lead II rhythm strip in Figure-2.

• QUESTION: Is sinus rhythm present in this tracing?

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ANSWER:

Upright P waves with a constant PR interval are present for only 3 beats in today’s tracing. As shown in Figure-3 — only beats #6,7,8 are sinus-conducted (RED arrows), albeit with a variable R-R interval.

Figure-3: RED arrows highlight the 3 sinus P waves in today’s tracing.

QUESTION:

• How many P wave shapes are there in Figure-3?
• Clinically — What does this mean?

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ANSWER:

There are at least 3 (if not 4) P wave shapes in today’s tracing. We show the most commonly occurring shape in Figure-4.

• YELLOW arrows in the long lead II highlight a run of 6 beats in a row that are preceded by large negative P waves, which have a short but constant PR interval ( = beats #10-thru-15). The R-R interval for these 6 beats is fairly constant — at a rate just under 100/minute. This suggests that these 6 beats represent an accelerated junctional focus.
• The other (less common) possibility for this 6-beat run of QRS complexes preceded by negative P waves of this size — is that beats #10-thru-15 could represent a low atrial focus.

Figure-4: Large size, YELLOW arrow P waves with a short but constant PR interval precede beats #10-thru-15.

For simplicity in Figure-4 — Let's assume that all of the YELLOW arrow P waves arise from the same accelerated junctional focus.

• We then have to explain why there are other P wave shapes in front of the remaining beats on this tracing. 
• Note that the rhythm in Figure-4 begins with a similar large-sized negative P wave ( = the first YELLOW arrow in Figure-4).

QUESTION:

I highlight the different P wave shapes in the long lead II rhythm strip with additional colored arrows in Figure-5.

• Can you explain the mechanism of today's rhythm?

Figure-5: Colored arrows highlight the different P wave shapes.

MY Thoughts on Today's Rhythm:

More than a single explanation may be possible for the unusual sequence of P wave shapes in Figure-5.

• I find it easiest to begin by looking at the 3 sinus-conducted beats ( = the 3 RED arrow P waves that highlight the upright P waves preceding beats #6,7,8 in Figure-5).
• Note that the PINK arrow P wave that precedes beat #9 manifests an intermediate P wave shape between the 3 larger upright P waves that precede sinus-conducted beats #6,7,8 — and the 6 consecutive negative P waves that precede beats #10-thru-15. 
• I suspect the reason for this intermediate P wave shape — is that the PINK arrow P wave preceding beat #9 represents an atrial fusion beat that occurs as the underlying sinus rhythm is being overtaken by the accelerated junctional rhythm that emerges with beat #10.
• Note that the rhythm in Figure-5 begins with a single junctional beat (highlighted by the YELLOW arrow that precedes beat #1).
• I'm uncertain if the 4 BLUE arrow P waves that follow in beats #2,3,4,5 represent the emergence of another atrial focus (as might be seen with a wandering atrial pacemaker) — or more likely represent additional atrial fusion beats until the slightly early-occurring sinus beat #6 briefly takes over — before being usurped by the accelerated junctional rhythm beginning with beats #9,10.

Putting It All Together:

Clincally — the details for what each differently-shaped P wave represents are less important than the overall impression of what appears to be happening.

• Today's patient is a young adult who presented for palpitations.
• The underlying rhythm appears to be sinus (beats #6,7,8).
• This sinus rhythm appears to be intermittently usurped by an accelerated junctional rhythm.
• While impossible from this single tracing to rule out interaction with a wandering atrial pacemaker — I think this is less likely than there being a series of atrial fusion beats, as control of the rhythm shifts back-and-forth between sinus beats and the accelerated junctional focus (The change in P wave morphology that is typically seen with a wandering pacemaker tends to be much more gradual than what we see here).
• PEARL #2: The reality is that accelerated junctional rhythms are not commonly seen in adults. Therefore, evaluation of this patient should consist of determing IF one or more underlying precipitating factors are present (ie, assessment of serum electrolytes, blood count, thyroid function studies, and Echocardiogram to rule out structural abnormality — as well as a careful history to rule out alcohol and/or ingestion of recreational substances that might precipitate the accelerated usurping rhythm).
• If this rhythm persisted despite a negative evaluation that fails to reveal a precipitating cause — then empiric treatment with a ß-blocker might be the simplest and most effective approach. (Unfortunately, I don't have follow-up as to the management approach selected for this patient).

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But what about the ST elevation that we saw in Figure-2?

• I highlight this ST elevation in Figure-6 — with dotted RED lines in those leads in which we see ST elevation.

QUESTION:

• Is there any relation between P wave shape — and whether the QRS complex that follows will manifest an elevated ST segment?

Figure-6: Dotted RED lines highlight which leads manifest ST elevation. Is this related to the preceding P wave shape?

ANSWER:

Today's case represents a unique illustration of the Emery Phenomenon — in which the oppositely-directed atrial repolarization wave (ie, the T of the P wave) produces a "pseudo"-ST elevation effect because of the relatively large size of the negative inferior lead P waves, with short PR interval (See ECG Blog #308).

• Most of the time — the Tp (also known as the "Ta" or atrial T wave) is hidden within the QRS complex. But on those uncommon occasions when a large negative P wave with short PR interval is seen — the resultant oppositely-directed Tp may simulate acute infarction (See My Comment in the June 3, 2020 post in Dr. Steve Smith's ECG Blog for discussion of the Emery Phenomenon in the context of a case that went to cath because of this "pseudo"-ST elevation).

To illustrate this phenomenon — I’ve adapted Figure-7, which I’ve taken from a 2015 post on the ECG Rhythms website.

• As suggested in Figure-7 — the atrial repolarization wave (ie, the T of the P wave) is always present — but with sinus rhythm, the timing of the Tp will largely coincide with the timing of the QRS complex, and therefore not be noticed on the ECG (dotted RED half circle, seen to the left in Figure-7).
• As shown in Figure-7 — the Tp will be oppositely directed to the P wave. Therefore, with normal sinus rhythm (in which by definition, the P wave will be upright in lead II) — the TP will be negative in inferior leads.
• IF the P wave in lead II is negative (as may occur with either a low atrial or junctional rhythm) — then the Tp will be upright (dotted RED half circle, seen to the right in Figure-7). If the Tp wave is large in size and upright — it may distort the end of the QRS complex, and produce the false impression of ST elevation.

Figure-7: Illustration of the Emery Phenomenon. (I have adapted this Figure from the 2015 post by Dr. Bojana Uzelac on Armel Carmona’s ECG Rhythms website).

KEY Points:

• The size of the Tp wave will be proportional to the size of its P wave. A small P wave will produce a correspondingly small Tp wave. A large P wave will produce a much bigger Tp wave.
• Actually, the effect of the oppositely-directed atrial repolarization wave ( = the Tp — also known as the "Ta" or atrial T wave) will be even larger than shown above in Figure-7 — because normal duration of the Ta wave is significantly longer (up to 2-3 times longer) than normal P wave duration (Francis). This may account for an exaggerated effect on the ST segment when the P wave is large.
• That said — I preserved the same relative proportions in Figure-7 as were seen in the original version of this Figure taken from the ECG Rhythms website. Note that the PR interval for the negative P wave in Figure-7 is almost as long as the PR interval for normal sinus rhythm. But IF the PR interval for the negative P wave is shorter (as occurs in today’s case) — then the upright Tp wave that will be seen with a junctional rhythm will be further displaced to the right, which will produce a much greater degree of pseudo-ST-elevation!

PEARL #3: The fascinating aspect of today's rhythm is that we can see this effect that the changing P wave morphology has — on the amount of ST elevation in the QRS that follows!

• Go BACK to Figure-6. Note that the amount of ST elevation is greatest for QRS complexes that follow negative P waves (ie, for the ST segments of beats #1; and #10-thru-15).
• In contrast — there is no ST elevation following sinus beats #6,7,8.
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• KEY Point: Awareness that of the Emery Phenomenon in today's case is responsible for pseudo-ST-elevation allows us to discard concern about myocarditis or acute ischemia — and focus our management on treating this patient's palpitations caused by the intermittent usurping accelerated junctional rhythm! There is no real ST elevation in today's case.

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Acknowledgment: My appreciation to Rasheed Tamimi (from Yemen, Sana'a) for the case and this tracing.

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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 #205 — Reviews my Systematic Approach to 12-lead ECG Interpretation.
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• For more on distinction between Low Atrial vs Junctional rhythm — Please see My Comment at the bottom of the page in the January 28, 2019 post in Dr. Smith's ECG Blog.
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• See ECG Blog #290 and ECG Blog #308 — for more examples of the Emery Phenomenon.
• And for additional cases of the Emery Phenomenon — Please see My Comment at the BOTTOM of the page in the June 3, 2020 post and in the February 23, 2023 post in Dr. Smith's ECG Blog.