ECG Blog #398 — Uncontrolled Graves Disease ...

The ECG in Figure-1 was obtained from a middle-aged woman who presented with "palpitations". Of note — she has a history of untreated hyperthyroidism.

QUESTIONS:

• How would YOU interpret the rhythm in Figure-1?
• Can you explain the atrial activity in this rhythm strip?

Figure-1: The initial long lead II rhythm strip in today's case.

MY Approach to the Rhythm in Figure-1:

As per ECG Blog #185 — I favor the Ps, Qs, 3R Approach for interpretation of the cardiac rhythm — beginning with whichever of these 5 KEY Parameters is easiest to assess for the tracing in front of me:

• At least in the single lead II rhythm strip seen in Figure-1 — The QRS complex appears to be narrow.
• P waves are present (See PEARL #1 below).
• The rhythm in today's tracing is not Regular. The Rate of the rhythm varies because of this irregularity — but the overall ventricular rate is a bit over 100/minute (ie, most R-R intervals are slightly less than 3 large boxes in duration). 
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• NOTE: For the moment, I will defer addressing the last of the 5 KEY Parameters — which is to determine if P waves are (or are not) Related to neighboring QRS complexes.

PEARL #1: After considering the 5 KEY Parameters — the EASIEST next step for determining the mechanism of a complex rhythm — is to label the P waves.

• RED arrows in Figure-2 — highlight those P waves that we can readily identify.
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• I've colored the 1st and 3rd arrows in Figure-2 in PINK, because while not as obvious — it should be apparent that these PINK arrows also highlight "extra" deflections that are P waves (ie, in the partially seen T wave at the very onset of this rhythm strip and distorting the initial upstroke of the R wave of beat #2).
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• Isn't it EASIER to at least assess the rhythm in Figure-2 — now that all P waves are labeled?

NOTE: Although the most common cause of unexpected pauses in a rhythm is the occurrence of one or more blocked PACs — I do not see distortions in any ST-T wave of this single-lead rhythm strip that might be consistent with blocked PACs.

• Instead — the P wave morphology in Figure-2 that we see highlighted by each of the arrows is the same. This suggests that we are dealing with a single atrial focus that is both irregular and firing rapidly!
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• In support that the underlying atrial rhythm is ATach (Atrial Tachycardia) — is that we see 3 P waves in a row with similar P wave morphology and a similar P-P interval at the beginning of the tracing (between beats #1-to-#3) — and then 4 P waves in a row with similar P wave morphology and a similar P-P interval near the end of the tracing (between beats #8-to-10).
• That said — there clearly is variation in the P-P interval in other parts of today's tracing.

PEARL #2: It is important to be aware that "not every arrhythmia obeys the rules!" As a result — We sometimes need to think "out of the box" in order to come up with the most plausible explanation for a given arrhythmia. 

• Examples of conditions notorious for producing arrhythmias that "do not obey the rules" include: i) Hyperkalemia (See ECG Blog #275); ii) Cardiac arrest; and, iii) Vagotonic Block (See ECG Blog #61).
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• Today's case, in which the patient had untreated hyperthyroidism — presents one more condition that may be associated with unusual forms of common arrhythmias that "do not obey the usual rules".

PEARL #3: Although ATach is usually a fairly regular atrial rhythm — there may at times be some irregularity. That said — I do not recall ever seeing as much irregularity in the atrial rhythm of a patient with ATach as we see in today's tracing.

• As noted in Pearl #2 — it is likely that the reason for this excessive degree of irregularity in today's ATach rhythm, is the result of this patient's uncontrolled hyperthyroidism.
• Use of ß-blocker therapy (oral and IV as needed for rate control) — is the usual treatment of choice for sinus tachycardia and/or other SVT rhythms associated with hyperthyroidism. The "good news" — is that once this patient's thyroid condition comes under control — the atrial tachyarrhythmia will probably resolve.

Figure-2: I've added RED arrows to Figure-1 — to highlight those P waves that we can readily identify. The 1st and 3rd arrows (in PINK) — highlight deflections produced by partially "hidden" P waves (See text).

What Then is the Rhythm in Figure-2?

So far — We have only interpreted part of the rhythm in today's tracing. What we know thus far:

• This patient has uncontrolled hyperthyroidism — and as a result (as per Pearl #2) — arrhythmias associated with this condition "may not obey the usual rules".
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• That said — WHY is the ventricular rhythm so irregular?

PEARL #4: It is extremely common to see Wenckebach conduction in patients with ATach. As a result — I always look for this possibility whenever I see irregularity in a patient with ATach. What we know:

• The PR interval before beats #4, 5 and 11 looks to be the same — which strongly suggests that at least these 3 beats are conducting!
• There are other PR intervals (ie, the PR interval before beat #3) — that are slightly longer — which makes me consider the possibility of some form of Wenckebach conduction in this patient with ATach.

NOTE: I wish I had a simultaneously-recorded 12-lead tracing. Lacking this — I assumed that all 12 QRS complexes seen in today's rhythm strip were supraventricular, even though some of these beats are noticeably taller than others in this single monitoring lead.

• BOTTOM Line: At this point in the process — I suspected that today's rhythm represented an unusual form of ATach, in which there was marked irregularity in the atrial rhythm (as a result of this patient's uncontrolled hyperthyroidism) — with some form of Wenckebach conduction accounting for much of the rhythm irregularity and variation in PR intervals.
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• To EMPHASIZE: The above "Bottom Line" interpretation of today's rhythm, which is admittedly general — is enough for appropriate clinical management. The reason that this is all that is needed clinically — is the knowledge that today's rhythm will probably resolve once this patient's hyperthyroidism is treated.
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• The said, in my intellectual desire to better understand the likely mechanism of today's rhythm — I thought the best way to explore this would be to devise a Laddergram. 

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LADDERGRAM Illustration:

• Sequential legends over the next 5 Figures illustrate my thought process as I derived the laddergram that I propose in sequential Figures-3 thru -7. (See ECG Blog #188 for review on how to read and/or draw Laddergrams).
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• To EMPHASIZE — Today's laddergram was not easy to draw — because as emphasized above, today's rhythm does not obey the usual rules. That said — my hope is that even clinicians with limited experience reading laddergrams will be able to follow these sequential figures. Stay with me!

Figure-3: It is usually easiest to begin a laddergram by marking the path of sinus P waves through the Atrial Tier (RED lines drawn directly below the onset of each of the P waves — as shown by the large BLUE arrows). Note that these RED lines in the Atrial Tier are nearly vertical — since conduction of sinus P waves through the atria is rapid. As mentioned earlier — the atrial rhythm is not regular.

Figure-4: The most challenging part of most laddergrams is construction of the AV Nodal Tier — so I typically save that for last. Therefore, after drawing in all P waves into the Atrial Tier — It's easiest to next add indication of all narrow (ie, conducting) QRS complexes into the Ventricular Tier. The large BLUE arrows show that I use the onset of each QRS as my landmark. Note that the RED lines in the Ventricular Tier are also nearly vertical — since conduction of these narrow QRS complexes through the ventricles is rapid.

Figure-5: It's time to begin "solving" what we can in the laddergram. I do this by connecting P waves in the Atrial Tier that might logically be conducting — to narrow QRS complexes in the Ventricular Tier. 
—  —  —  —
Because of the complexity of today's rhythm — I had to make assumptions that would need to be "tested out". As per PEARL #4 — I thought it most logical that beats #4,5,11 are conducted to the ventricles (because the PR interval preceding each of these beats is the same — and that is unlikely to occur by chance). I added some additional light BLUE lines (before beats #1,2,3; 6; and 10 — because I thought it logical that the P waves preceding these beats would also be likely to conduct).

Figure-6: As more and more of the AV Nodal Tier is filled in — the possibilities for alternatives lessen. I therefore added the 4 new light BLUE lines that we see in Figure-6. Even though the PR intervals proposed in this laddergram for beats #7,8,9 are long — I see no alternative explanation for P waves h,i,j and o — than for these P waves to be conducting to produce QRS beats #7,8,9 and 12.
—  —  —  —
This leaves the 4 BLUE arrow P waves ( = P waves c,k,l and p). I thought it logical to propose that P waves c and p do not make it out of the AV Nodal Tier. This leaves us with the remaining 2 BLUE arrow P waves ( = P waves k and l).

Figure-7: Step back a bit from this laddergram: Doesn't the generally increasing PR intervals seen for beats #5-thru-9, followed by non-conduction of P wave k — make for a credible Wenckebach sequence? Similarly — Doesn't the increasing PR interval from beats #11-to-12, followed by non-conduction of P wave p — make for a credible 3:2 AV Wenckebach sequence?
—  —  —  —
This leaves us with P wave l — which is a P wave without any possibility of conducting. Retrograde conduction from P wave k (the dotted BLUE line ending in a butt end) could account for failed conduction of P wave l.

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Putting It All Together:

• PEARL #5: On occasion — certain complex arrhythmias will defy precise description of their mechanism from the surface ECG. The "Pearl" — is to realize that this does not matter! What counts — is the "theme" of the rhythm. 
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• The "theme" of today's rhythm — is that in this patient with uncontrolled hyperthyroidism — there is a markedly irregular ATach with periods of Wenckebach conduction out of the AV Node. Because today's rhythm does not obey the usual rules — it is probably not worth the time and effort trying to attain a more precise rhythm diagnosis.
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• As noted above for the other conditions I cite in Pearl #2 — IF the underlying (causative) condition can be corrected — the arrhythmia will usually resolve! This is especially true in today's case, in that IF this patient's thyroid condition can be controlled — both the irregular ATach and the intermittent Wenckebach conduction will probably resolve.

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Acknowledgment: My appreciation to Hao Nguyen (from Cao Lãnh, Vietnam) for the case and this tracing. 

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Related ECG Blog Posts to Today’s Case:

• ECG Blog #205 — Reviews my Systematic Approach to 12-lead ECG Interpretation.
• ECG Blog #185 — Review of the Ps, Qs, 3R Approach for systematic rhythm interpretation.
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• ECG Blog #188 — Reviews how to read and draw Laddergrams (with LINKS to more than 90 laddergram cases — many with step-by-step sequential illustration).

ADDENDUM (10/7/2023):

I have just received an email from H.S. Cho = 조현석 (from Seoul, Korea) — in which he questions whether instead of P wave "m" conducting beat #10 — perhaps it is really P wave "l" that conducts. This is a reasonable theory — given that the PR interval from m-to-beat #10 does appear to be slightly less than the PR intervals that precede beats #4 and 5 (and we know that P waves e and f are conducting).

• What I also find very plausible about H.S. Cho's theory — is that laddergram events in beats #9 and 10 now look similar to laddergram events in beats #2 and 3.
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• BOTTOM Line: As I emphasized earlier — the precise mechanism of this fascinating tracing is elusive. That said, regardless of which laddergram is "correct" — the "theme" of today's rhythm remains that in this patient with uncontrolled hyperthyroidism — there is a markedly irregular ATach with periods of Wenckekbach conduction out of the AV Node.
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• My THANKS to H.S. Cho for his very valid suggestion!

Figure-8: I've redrawn my Figure-7 — to illustrate H.S. Cho's alternative theory for events in the latter part of this tracing.