ECG Blog #305 — The Cause of Palpitations?

The ECG and long lead II rhythm strip in Figure-1 — was obtained from a previously healthy middle-aged woman, with a history of intermittent palpitations over the past few months. No syncope or chest pain. She was hemodynamically stable at the time this ECG was recorded.

• How would YOU interpret the ECG in Figure-1?
• What might cause this rhythm?

Figure-1: 12-lead ECG and long lead II rhythm strip recorded on a middle-aged woman with palpitations in recent months. Hemodynamically stable.

MY Thoughts on the ECG in Figure-1:

As always — I favor starting by assessing the cardiac rhythm. Applying the Ps, Qs, 3R Approach (ECG Blog #185) — to the long lead II rhythm strip at the bottom of the tracing:

• The QRS is narrow everywhere (which we can confirm by verifying that every beat in the 12 leads above the rhythm strip has a narrow QRS).
• The rhythm is fast and irregularly irregular. But unlike Atrial Fibrillation (AFib) — there are P waves! (Figure-2).

PEARL #1: It is sometimes difficult to distinguish between baseline artifact vs different-shaped P waves. And, sometimes both artifact and different shaped P waves (PACs) may be present:

• This is not the case in today’s tracing! There is essentially no artifact in the baseline or within ST-T waves. As a result — What we see on this tracing is valid!
• There is NO doubt that an upright P wave with reasonable PR interval precedes each QRS complex that follows a short pause (ie, BLUE arrows before beats #2, 6, 7, 12, 16 and 17 in Figure-2).
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• PEARL #2: The P wave in front of beat #2 in the long lead II rhythm strip deserves special mention — because it is tiny. This is the benefit of assessing the rhythm by use of simultaneously-recorded leads! A quick look straight above beat #2, at the 2nd BLUE arrows in lead I and in lead III (vertical RED lines that correspond in timing to the P wave in front of beat #2 in the long lead rhythm strip) — confirms that there is a P wave in front of beat #2 in the long lead rhythm strip, albeit a P wave that looks different (smaller) than all other P waves in this long lead II (except for the equally tiny P wave in front of beat #1).
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• PEARL #3: I find the most helpful way to determine when and where P waves might be hiding (within their preceding ST-T wave) — is to figure out WHAT a “normal” ST-T wave looks like. In Figure-2 — I thought the ST-T wave of beats #1, 11 and 15 represent what a “normal” ST-T wave (ie, not altered by a PAC hidden within it) should look like. 
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• PEARL #4: The commonest cause of a pause is a blocked PAC! (See ECG Blog #14 and Blog #66). Awareness of this clinical reality has led me to always look carefully at the ST-T wave at the beginning of any relative pause in the rhythm — to see if there might be a P wave partially "buried" within that ST-T wave. And so, I thought the YELLOW arrows that occurred right after beats #6 and 16 clearly represented non-conducted atrial activity — with the notching under these arrows highlighting blocked PACs.

My Initial Impression of the Rhythm in Figure-2:

Having established that the rhythm in Figure-2 was supraventricular (narrow QRS) — and both fast and irregular — but not AFib because there clearly was atrial activity — I contemplated my differential diagnosis:

• P wave morphology was not consistent. For example — the tiny P waves in front of beats #1 and 2 in the long lead II rhythm strip clearly looked different than the larger and rounder P waves that precede beats #7, 16 and 17. And the P wave in front of beat #12 looked taller still, as well as being more pointed. Therefore — my initial impression of this rhythm was MAT (Multifocal Atrial Tachycardia).

And then I looked again more carefully ...

Figure-2: I've labeled atrial activity from Figure-1 with BLUE arrows. I've labeled non-conducted P waves with YELLOW arrows. The vertical RED lines illustrate PEARL #2, which describes use of simultaneously-recorded leads (See text).

Regarding MAT: What Does Not "Fit" for Today's Patient:

I have previously reviewed the ECG diagnosis of MAT (See ECG Blog #199 and Blog #65).

• MAT almost always occurs in one of 2 common predisposing settings. These 2 settings are: i) In patients with severe, often longstanding pulmonary disease; and/or, ii) In acute ill patients with multi-system disease (ie, sepsis, shock, electrolyte and/or acid base disorders). As a result — I'm hesitant to diagnose MAT in the absence of one of these 2 settings. The fact that today's patient was a previously healthy middle-aged woman is therefore against the likelihood of seeing MAT.

CONFESSION:

While labeling today's ECG for Figure-2 — I looked again at the long lead II rhythm strip. In Figure-3 — I've added a number of additional YELLOW arrows where the ST-T wave appears to be clearly deformed by additional non-conducting atrial activity. For many of these additional YELLOW arrows — we can see indication of partially hidden atrial activity of other simultaneously-recorded leads.

• LOOK AGAIN at the long lead II rhythm strip in Figure-3. If you can accept the validity of the colored arrows I've added — after the first 2 P waves in each grouping — Aren't the BLUE and YELLOW arrows that follow until the pause fairly regular?
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• PEARL #5: Not all rhythms "read the textbook". While we often think of entities such as Atrial Tachycardia and MAT as "pure" rhythm etiologies — many patients do not manifest "pure" versions of these arrhythmias. I've found it best to consider entities such as ATach, MAT, wandering atrial pacemaker, and sinus rhythm with multiple PACs as ends of a "spectrum" — with many patients manifesting more of a "mixture" between the spectrum end points for these various rhythm disorders.

MY "Revised" Rhythm Diagnosis:

While emphasizing that today's rhythm does not perfectly fit any of the rhythm etiologies that I mention above — I think it is closest to ATach.

• Remember — The atrial rate with ATach is not always regular. On the contrary — ectopic atrial tachycardia is more likely to manifest a "warm-up" phase until this rhythm gets going. Perhaps the slightly longer P-P intervals at the beginning of each grouping represent such a "warm-up" phase?
• Even with atrial impulses arising from the same site — P wave morphology may vary. Isn't it strange that the PR interval is the same for so many of the different-looking P waves in Figure-3 (ie, the P waves in front of beats #1, 2, 6, 7, 12, 13, 16 and 17). I would not expect the PR interval to remain the same for so many beats if the underlying rhythm was MAT.
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• ATach (Atrial Tachycardia) very commonly manifests Wenckebach conduction. Therefore, rather than "blocked PACs" — Perhaps the YELLOW arrows that I've drawn in Figure-3 represent non-conducted P waves from short ATach-related Wenckebach cycles?

BOTTOM LINE Regarding Today's Case:

I fully acknowledge that I do not know a definitive answer for the rhythm etiology in today's case. That said — I believe this rhythm is "clinically behaving" like an ectopic ATach in this previously healthy middle-aged woman who has intermittently been bothered by recurrent palpitations over the past few months.

• In order is a General Evaluation of this patient — to include chest X-Ray, Echo and baseline lab work (ie, thyroid function, serum electrolytes, hematocrit).
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• Verify in this patient's History the duration of her symptoms — and determine IF she is a longterm smoker (that might predispose to MAT) — and/or if there is significant alcohol, drug, caffeine or other substance use that might predispose her to a recurrent irregular SVT.
• IF these results did not yield clues to the etiology of today's rhythm — then empiric treatment with a medication such as a ß-blocker might be in order.
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• IF her palpitations (and this rhythm) persisted — referral to EP Cardiology would be in order.

Figure-3: The more I looked at this tracing — the more indication I saw of more atrial activity (additional BLUE and YELLOW arrows drawn in since Figure-2).

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Acknowledgment: My appreciation to Arjun K Budhathoki (from Kathmandu, Nepal) for making me aware of this case and allowing me to use this tracing.

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Relevant ECG Blog Posts to Today's Post:

• ECG Blog #185 — Reviews the Ps, Qs, 3R Approach to Rhythm Interpretation.
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• ECG Blog #199 — Reviews the ECG diagnosis of MAT (including a Video Pearl on this subject).
• ECG Blog #65 — Another example of MAT (vs Wandering Pacemaker).
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• ECG Blog #250 — Causes of a Regular SVT (including AFlutter & ATach).
• ECG Blog #138 — ATach vs AFlutter.
• ECG Blog #261 — Reviews a case of ATach with Wenckebach conduction.