ECG Interpretation: ECG Blog #466 — Do You See What I See?

Saturday, January 25, 2025

ECG Blog #466 — Do You See What I See?

I was sent the ECG in Figure-1 — without clinical information.

I interpreted the rhythm as AFib (Atrial Fibrillation).

QUESTION:

Do you see anything else?

Figure-1: The initial ECG in today's case.

Take another LOOK.

To facilitate description — I've numbered the beats in Figure-2.

Figure-2: I've numbered the beats from Figure-1.

Confession: I initially looked at this tracing too quickly ...

The QRS complex is narrow. As a result — the rhythm is supraventricular.
I initially thought the rhythm was irregularly irregular, albeit with a number of baseline undulations — but no distinct P waves. I therefore interpreted the rhythm as AFib with a controlled ventricular response (with those baseline undulations representing "fib" waves).
I thought the tracing was otherwise unremarkable — other than minimal nonspecific ST-T wave changes, but nothing that looked acute.

QUESTION:

Do you agree with my initial interpretation?

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Looking Closer ...

Beginning with beat #12 — the rhythm becomes quite regular. As shown in Figure-3 — RED arrows highlight what now appears to be atrial activity that had been present all along.

Figure-3: I've labeled atrial activity in today's rhythm (See text).

QUESTION:

How can we be certain that the RED arrows in Figure-3 are truly highlighting atrial activity?

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ANSWER:

The KEY is to appreciate (and make use of) simultaneous leads. As shown in Figure-4 — the shallow negative deflection that precedes beats #11-thru-16 with a constant PR interval is a P wave. We know this — because we now clearly see distinct P waves with the same constant PR interval in simultaneously recorded leads V4,V5,V6.
And, if we look a few seconds earlier in the long lead V1 rhythm strip — no such P waves were present in lead II for the first 5 beats in this tracing (within the BLUE rectangle).
Therefore: Today's patient was in AFib at the beginning of this ECG — until there was spontaneous conversion to sinus rhythm (that began with beat #11).

Figure-4: The vertical RED line shows the presence of distinct P waves in 4 simultaneously recorded leads (leads V4,V5,V6 — and in the long lead V1 rhythm strip).

QUESTION:

Was the rhythm still AFib right before spontaneous conversion to sinus rhythm with beat #11?
HINT: Look at spontaneously recorded lead V3 ...

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ANSWER:

I thought we were seeing 4 consecutive atrial waves with a fixed P-P interval in lead V3 (BLUE arrows in Figure-5). The rate of these 4 atrial deflections is ~250/minute, which suggests that this patient began with AFib with a controlled ventricular response — then transiently developed AFlutter (or ATach) before manifesting a short pause, after which there was spontaneous conversion to sinus rhythm.

Figure-5: BLUE arrows in lead V4 highlight a 4-beat run of regular atrial activity shortly before spontaneous conversion of today's rhythm to sinus (See text).

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LESSONS to be Learned:

It's good to stay humble — as you never know when you might overlook an important finding that you should have picked up. I initially looked at today's tracing too quickly — and, as a result — I missed the spontaneous conversion of this patient's AFib to a sinus rhythm that occurred with beat #11. Today's case highlights how it's important to survey the entire rhythm strip when assessing for regularity of the rhythm.
KEY Point: One of the best clues for uncovering the mechanism of a complex rhythm (and for detecting hidden P waves) — is to Look for the "break" in the rhythm! By this I mean to look for any short pause, paying extra attention to events just before, during and just after the pause (ie, the "break" in today's rhythm is seen between beats #10 and 11, as the R-R interval is longest between these 2 beats).
NOTE: It is not common to see a patient going in-and-out of AFib during a single 12-lead recording. That said — Be aware that this can happen. AFib may spontaneously convert to AFlutter — and vice versa — sometimes passing from 1 rhythm-to-the-other multiple times.
Clinically — Although initial treatment of AFib and AFlutter is similar, there are some important different management considerations to be aware of: i) AFib is a much more common rhythm; ii) While medications to treat both rhythms are generally similar — it may be easier to control the ventricular response of AFib with medication; iii) AFlutter is typically more responsive to electrical cardioversion (and often requires much lower energies for cardioversion than does AFib); — and, iv) For persistent AFib or persistent AFlutter — the response to ablative therapy is somewhat different (typical AFlutter tends to be easier to "cure" by ablation — although in experienced centers, ablation of many cases of AFib will be successful).
Patients who go in-and-out of AFib are said to have PAF (Paroxysmal AFib). It is estimated that about half of all patients with AFib have PAF. Clinically, the risk of stroke for patients with PAF is probably about the same as the risk of stroke with persistent AFib ( = a long discussion beyond the scope of this ECG Blog).
Finally — It's good to appreciate when seeing a patient with presumably new AFib — that the overall results of literature studies suggest that if you do nothing to actively treat your patient's AFib — that ~1/2 of these patients with AFib will spontaneously convert to sinus rhythm over the next 24 hours.

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Acknowledgment: My appreciation to Sam Ghali (from Jacksonville, Florida — @EM_RESUS) 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 — Reviews the Ps, Qs, 3R Approach to Rhythm Interpretation.