Dawn's picture

To continue a recent theme, we offer this ECG, which appears on quick glance to be an atrial bigeminy.  On closer inspection, we do not see ectopic P' waves in the second conducted beats of each pair.  In fact, the P waves look the same in both the first and second beats. However, if you look very closely (we enlarged the screen), you may notice that the second T wave of each pair is slightly larger with a slightly different morphology than the first T wave.  If this distortion of the second T waves represents a PAC, the PAC is non-conducted and concealed in the T wave. If that concealed P wave is able to penetrate and depolarize the sinus node, we might expect the sinus node to be reset, and the next P wave and QRS combination is right on time.

So, what looks like an "atrial bigeminy" might actually be an "atrial trigeminy" - albeit with non-conducted PACs.

Also notable is the subtle ST elevation in V1, V2, and V3, which should be evaluated with clinical data. Unfortunately, we do not have information about the patient.  Also, V2 and V3 do not represent normal or expected R wave progression.  The chest leads should have rS patterns, and they should progress from small r waves and deep S waves in V1 with gradually taller R waves and shorter S waves across the chest wall.  V6 should be, finally, all upright.  We suspect lead reversal between V2 and V3, or misplacement of the electrodes in general.  Also, the q waves in those leads seem misplaced, without the usual configuration of pathological Q waves in those leads.

We would love to hear your opinions about this interesting rhythm.


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ekgpress@mac.com's picture

     As per my Comment Title - there is LOTS to speculate on for this interesting tracing. Unfortunately - due to no history - no additional tracings on the patient - and baseline artifact - we'll never know for certain.

  • As per Dawn - there is a bigeminal rhythm. We know the underlying rhythm is sinus - as determined by the upright P wave with fixed PR interval preceding beats #2,4,6,8,10,12 and 14.
  • Every other P wave does look similar - though there is just enough baseline artifact AND a relative pause following beats #1,3,5,7,9,11 and 13 for me not to be certain.
  • It looks like the PR interval preceding every-other beat (ie, preceding beats 1,3,5,7,9,11,13) is slightly longer than the PR interval for each of the even beats. The difference in PR interval between even and odd beats is small enough - that I'm hesitant to definitively call this .... IF this is correct - then there is a component of AV Wenckebach - but not "true AV Wenckebach" because the P-P interval is clearly not regular throughout this tracing ...
  • As per Dawn - the 2nd T wave in each pair IS different. That said - I do not see the usual "telltale notching" I'd expect if a PAC was hidden within. This is NOT to say that there is no hidden PAC within the T waves of beats #3,5,7,9,11, and 13 - but only that I'm just not comfortable calling this (though I'd still entertain it as a possibility). There IS another possible reason for change in P wave morphology of the 2nd beat in a pair - namely that this sometimes "happens" (previously postulated as a reflection of underlying ischemia, though I have seen this phenomenon without ischemia). Without a cleaner tracing and some consecutively conducted sinus beats - I don't think we can know for certain ...
BOTTOM LINE re the RHYTHM: I'm left with a bunch of unknowns. We have underlying sinus rhythm with a bigeminal rhythm of uncertain cause (atrial bigeminy; atrial trigeminy with blocked PACs; AV Wenckebach with blocked PACs interrupting the cycle; combined SA and AV block; other reason ... ).
  • Clinically - I think the most important lesson regarding this rhythm is that there are times when you KNOW what the rhythm is - and other times when you just can't be certain. It is OK not to be able to be certain - with best policy (in my opinion) to state what is known and what is speculated. We simply need: i) some history; ii) a cleaner tracing; and iii) additional rhythm strips. That said - it is FUN to speculate! 
The REST of the ECG: As per Dawn - there are a lot of intriguing findings - once again without certain conclusion:
  • rSr' pattern in lead V1 with a narrow s in V6 but not in lead I - so therefore not fulfilling criteria for "incomplete" RBBB. I account for this by just stating, "rSr' in lead V1".
  • As per Dawn - there is unusual (unreal) R wave progression. I strongly suspect significant lead placement error - though not simple misplacement of V2 and V3, since exchanging those leads would still result in an unfathomable progression of T wave morphology. Something is probably off with lead placement ....
  • Without the ability to repeat the ECG with verified lead placement - I have no idea if the Q waves we see in V1,V2,V3 are real and indicative of anteroseptal infarction at some point - nor if the seemingly isolated hyperacute T wave in lead V3 is real. I also have no idea if the QRST pattern we see in leads V1,V2 is real and reflects a Type II (non-diagnostic) Brugada pattern or not (Click HERE for brief review of Brugada patterns).
  • Finally - Note slight change in QRS morphology for beats #7,11 and 13 - so there is slight aberrant conduction in this tracing for these early beats.


Ken Grauer, MD  www.kg-ekgpress.com   [email protected] 

This looks like a 2˚ HB Mobitz II, because... I'm not seeing multiple underlying P-waves. I don't see a marching of P's and a firing of QRS's or Aberantly conducted QRS... its dropping a beat, without a increase in the P-R interval... so that's why I go with a 2˚ Mobitz II

Dave Richley's picture

I strongly suspect that his is atrial bigeminy. Admittedly the T wave of the 2nd beat of each pair is different from that of the first, but the QRS is different too. Slightly different depolarisation = slightly different repolaristaion. I think if there were a P wave on this T wave it would be more apparent, particularly in V1. With reference to Scott's comments, it can't be Mobitz II because we don't see non-conducted sinus P waves before the pauses. It's interesting how an apparently straightfroward ECG can generate so much discussion!

Dave R

What a great 12-Lead...everyone has already covered the questions about lead placment etc. and bigeminy vs trigeminy. I can only report what I see and am left wondering about the alternating voltage in the T waves...Could it be T wave Alternans? The fact they are probably having an MI could be an indicator. I might be splitting hairs, but it also appears as though V4 is about 1 mm elevated...one more thing some type of incomplete BBB...V1 - V4 ST elevation and a BBB...not a good day for this patient.

Also appears to fit criteria for P mitrale. 

Jerry W. Jones MD FACEP's picture

It's unfortunate that we don't have two consecutively conducted sinus beats. I certainly don't think that we are seeing a Mobitz II block because there are no obvious non-conducted P waves in areas where one would expect them to conduct. Also, I would expect the QRS complexes to be a bit wider. The precordial leads, I suspect, have not only been switched (V2 and V3) but probably placed an interspace or two too high on the chest wall (hence the r' in V1). I agree with Dr. Grauer that there are just too many unknowns here to make a definitive diagnosis. However, in trying to avoid sounding like a radiologist, I would call this an atrial bigeminy and thus also agree with Dr. Richley.

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