Thursday, June 10, 2021

ECG Blog #232 (47) — What is Bigeminy?


You are given the ECG shown in Figure-1 — but without the benefit of any history.

  • What is the cause of the paired beats in the long lead II rhythm strip?

 

Figure-1: You are asked to interpret this ECG without the benefit of any history (See text).


 

MSequential APPROACH to this CASE:


Rate & Rhythm: The QRS complex is narrow in all 12 leads — so the rhythm is supraventricular. 

  • NOTE #1: The long lead II rhythm strip at the bottom of the tracing is not continuous with the 12-lead above it. This long lead II rhythm strip encompasses a total of 14 consecutive beats — and shows a bigeminal” rhythm (ie, there are 7 pairs of beats that occur in a repetitive pattern of alternating shorter and longer R-R intervals)
  • We KNOW that there is at least some conduction — as it appears that each of the QRS complexes at the end of each longer R-R interval is preceded by an upright P wave with a constant (albeit prolonged) PR interval.

 

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NOTE #2: At this point in my assessment — I was not certain of the etiology of the rhythm. That said, from a clinical perspective — I thought determining the precise rhythm diagnosis was not yet essential because: iWith regard to initial management of this patient — What counts most is recognition that there is a supraventricular rhythm at a reasonable ventricular rate, with at least a number of beats being sinus-conducted; andii) I could not help but notice the marked ST-T wave changes on the 12-lead that demanded more immediate attention!

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PEARL #1: As stated above — the rhythm in Figure-1 is “bigeminal”, supraventricular, and notable in that the 1st beat in each of the 7 pairs of beats is sinus conducted (albeit with a prolonged PR interval). It’s helpful to be aware of the Differential Diagnosis for a bigeminal supraventricular rhythm when there is sinus conduction of the 1st beat in each pair. This differential diagnosis includes:

  • Sinus rhythm with atrial or junctional bigeminy (ie, every-other-beat is a PAC or a PJC).
  • SA ( = Sino-Atrial) Block.
  • Mobitz I, 2nd-Degree AV Block ( = AV Wenckebach) with 3:2 AV conduction.
  • Mobitz II, 2nd-Degree AV Block.

 

PEARL #2: Although the diagnosis of Mobitz II, 2nd-Degree AV Block would be of immediate concern (because of the need for cardiac pacing) — Mobitz II is highly unlikely in Figure-1 because: i) Among the forms of 2nd-Degree AV Block — Mobitz II is extremely uncommon (ie, In my experience — at least 90-95% of 2nd-Degree AV Blocks are of the Mobitz I type); andii) The QRS is almost always wide with Mobitz II (but the QRS is narrow in Figure-1).

 

The NEXT Steps in My Assessment:

The limb leads in Figure-1 suggest there has been recent inferior MI:

  • There are Q waves in each of the 3 inferior leads. The largest Q wave is seen in lead III, which manifests a QS complex (ie, all negative QRS). Considering how tiny the QRS complex in lead aVF is — the Q wave in this lead is both deep and wide. In contrast — the q wave in lead II is small and narrow — but the fact that all 3 inferior leads manifest Q waves (with these Q waves being very large in 2 of the 3 leads) confirms that inferior MI has occurred at some point in time.
  • All 3 of the inferior leads manifest at least some degree of ST elevation. ST segments look hyperacute in leads II and aVF (straight ST segment takeoff in lead II; T waves and ST segments being more “voluminous” in both II and aVF). Relatively speaking — the amount of ST elevation in lead III is less, and it is accompanied by fairly deep T wave inversion that is consistent with “reperfusion T waves”.
  • The ST-T wave picture in high-lateral leads I and aVL is almost the mirror-image” opposite of the ST-T wave in lead III. That is — the ST segment in both of these leads is straightened (albeit not depressed) — and the tall, peaked T waves are almost the opposite of the deep T wave inversion seen in lead III.

 

IMPRESSION: There has been a recent Inferior MI. It is difficult to “date” this infarction in the absence of any history. My “guess” would be recent” (ie, perhaps 6-to-12 hours ago, up to 1-to-2 days ago) — but probably not so acute as occurring within the past 1-to-4 hours or so.

  • I based this “date estimation” on the finding of established Q waves (which are very large in leads III and aVF+ deep reperfusion T waves in lead III (which suggest that at least some time has passed) — yet withpersistence of some ST elevation in all 3 inferior leads (with hyperacute-looking ST-T waves in leads II and aVF).
  • CAVEAT: Anything is possible. On occasion — surprisingly deep Q waves can form in as little as 1-2 hours! Moreover, the course of evolving infarction is not always immediate — but sometimes can be “stuttering” — with spontaneous reopening, followed by re-closure, with this reopening and/or re-closure sometimes occurring a number of times until a final disposition develops. 

 

The CHEST LEADS in ECG #1

The chest leads in ECG #1 are consistent with recent Posterior MI — which is a common accompaniment of inferior MI. This is easiest to appreciate with use of the Mirror Test” that I illustrate in Figure-2 (See ECG Blog #193 — for more on the “Mirror” Test).

  • The mirror-image view of leads V2 and V3 (within the RED border in Figure-2— looks similar (albeit even more dramatic) to what we see in lead III in ECG #1 — namely, a modest amount of ST elevation in association with deep, symmetric T wave inversion. This is consistent with reperfusion T waves in the left ventricular posterior wall location.
  • Application of the Mirror Test in Figure-2 also provides insight into a disproportionate increase in anteriorlead R wave amplitude (that is seen in leads V2 and V3 of ECG #1). When viewed in its mirror-image — this disproportionate increase in R wave amplitude in leads V2 and V3 is seen as deepening Q waves (within the RED border in Figure-2).

  

Figure-2: To illustrate the Mirror Test — I’ve enlarged anterior leads V1V2V3 — and have placed them next to a mirror-image ( = vertically flipped) view of these leads.

 

Closer LOOK at the RHYTHM:

Now that we know this patient has had a recent infero-postero MI — it becomes EASIER to interpret the long lead II rhythm strip in ECG #1. For clarity — I have numbered the beats in Figure-3. 


Figure-3: For clarity — I have numbered the beats in the long lead II rhythm strip. WHAT is the cardiac rhythm?


 

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NOTE: Some readers may prefer at this point to listen to the 5:45 minute ECG Audio PEARL before reading My Thoughts regarding the ECG in Figure-3. Feel free at any time to review to My Thoughts on this tracing (that appear below ECG MP-47).

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Today’s ECG Media PEARL #47 (5:45 minutes Audio) — Reviews the concept of Bigeminy (which may be due to Atrial or Ventricular Bigeminy, Wenckebach conduction — or other causes).

 



MSequential APPROACH to Interpreting the RHYTHM:

In addition to recognition of recent infero-postero MI — We have already made some observations about the rhythm:

  • The QRS complex is narrow in all 12 leads — so we know that the rhythm is supraventricular.
  • There is group beating, in the form of a bigeminal rhythm (ie, there are 7 pairs of beats that occur in a repetitive pattern of alternating shorter and longer R-R intervals).
  • PEARL #3: Recognition of recent or acute inferior MI in association with group beating — should immediately make you suspect AV Wenckebach ( = 2nd-degree AV block, Mobitz Type I). This is especially true when each of the relatively longer R-R intervals ends with a conducted sinus P wave that manifests a fixed PR interval (RED arrows in the long lead II rhythm strip in Figure-4).
  • PEARL #4: AV Wenckebach that occurs in association with acute inferior MI is often associated with 1st-Degree AV Block. Therefore, the finding that the PR interval is prolonged for each of the P waves highlighted by RED arrows in the long lead II rhythm strip in Figure-4 further favors the likelihood of Mobitz I as the etiology of this rhythm.
  • PEARL #5: The atrial rhythm should be regular (or at least, almost regular) — IF there is some type of AV block. Therefore, in order to prove that the rhythm in Figure-4 is AV Wenckebach — we need to establish that the underlying atrial rhythm is regular. Use of calipers and looking in other leads facilitates accomplishing this. NOTE: Most of the time when there is AV Wenckebach — those P waves that are not readily visible can be found hiding within elevated ST segments and T waves. For example — YELLOW arrows in lead V1 highlight where P waves within the T wave of the 1st beat in each pair are hiding.

 

Figure-4: I’ve added arrows to Figure-3 to highlight P waves. The RED arrows indicate obvious sinus P waves that conduct with 1st-degree AV block. The YELLOW arrows in lead V1 clue us into the fact that P waves are hiding within the T wave of the 1st beat in each of the 2-beat groups.

 

PEARL #6: Common things are common! Admittedly — I can not clearly see indication that a sinus P wave is hiding within the T wave under each of the WHITE arrows in Figure-5. That said, these T waves do appear to be “extra” peaked and, by far — the most logical assumption based on precise “walking out” of my calipers — is that another P wave is hiding within the T waves of beats #2, 4, 6, 8, 10, 12 and 14. 

 

Figure-5: Using calipers suggests that the most logical assumption to make — is that the WHITE arrows I have added to Figure-4 highlight another hidden P wave.

 

For clarity — I’ve colored all arrows in RED to highlight the location of regular sinus P waves I believe are occurring throughout the long lead II rhythm strip (Figure-6).

  • Isn’t it now easier to appreciate Wenckebach periodicity?


Figure-6: I’ve colored all arrows in RED to highlight where I believe regular sinus P waves occur throughout the long lead II rhythm strip. 

 

LADDERGRAM:

The easiest way to illustrate the mechanism in today’s rhythm — is by drawing a laddergram (Figure-7). 

  • NOTE: For review on how to read (and drawladdergramsSee ECG Blog #188.   


Figure-7: My proposed Laddergram illustration of the Mobitz I, 2nd-degree AV block with 3:2 AV conduction, as described above in today’s case (See text).


 

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Acknowledgment: My appreciation to Bashiruddin Sayeem (from Chittagong, Bangladesh) for the case and these tracings.

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RELATED BLOG POSTS Regarding the INFARCT:

  • ECG Blog #218 Reviews when a T wave is Hyperacute (including the 5:20 minute Audio Pearl in this blog post). 
  • ECG Blog #194 Reviews how to tell IF the “culprit” artery has Reperfused, using clinical and ECG Criteria (including the 6 minutes Audio Pearl in this blog post). 
  • ECG Blog #184 — Reviews the “magical” mirror-image opposite relationship with acute ischemia between lead III and lead aVL (including the 2:15 minutes Audio Pearl in this blog post). 
  • ECG Blog #224 — Reviews this important picture to recognize (which resembles in many ways today's tracing = HOW to quickly recognize Mobitz I with Acute Inferior MI). 
  • ECG Blog #193 — Reviews a case of an acute infero-postero MI that illustrates use of the Mirror” Test.

 

RELATED BLOG POSTS Regarding the RHYTHM:

  • ECG Blog #186 — The AV Blocks (including a 4:30 minute Audio Pearl on When to suspect Mobitz I, 2nd-Degree AV Block). 
  • ECG Blog #78 — Shows a case of Atrial Bigeminy, in which every-other-P wave is a PAC that is either blocked or conducted with aberration. 
  • ECG Blog #140 — Another case study of Atrial Bigeminy, showing various forms of aberrant conduction. 
  • ECG Blog #57 — Atrial Bigeminy with blocked PACs that mimics AV block. 
  • ECG Blog #228 — Shows a case of Ventricular Bigeminy (including the challenge of assessing ST-T wave changes with this rhythm). 
  • ECG Blog #206 — A bigeminal rhythm due to a complicated AV Block.
  • ECG Blog #163 — A case if Escape-Capture Bigeminy. 
  • ECG Blog #188 — How to Read (and DrawLaddergrams.






4 comments:

  1. I thought the ST-T change in V2 V3 are definitely De-Winter T waves though. Is it possible that they are De-Winter T waves ?(though in the context of inferior wall MI, posterior involevment will be more common?)

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    1. Several people have asked if the ST-T waves in leads V2,V3 could be deWinter T waves. Without follow-up on this case (and without awareness of cath findings) — I can NOT be certain — but my strong suspicion is that the ST-T waves in leads V2,V3 do NOT represent deWinter T waves because:

      i) The rhythm is Mobitz I — and Mobitz I is VERY common with acute inferior MI (and not nearly so common with anterior MI, as would be the infarct location if these were deWinter T waves);

      ii) The “shelf-like” ST depression that we see in lead V2 very much LOOKS LIKE what you see with acute posterior MI (ie, positive “Mirror Test”, as in my Figure-2) — whereas with deWinter T waves from anterior MI — there is typically a STEEP uprise from the J-point ST depression (and you do NOT see the “shelf”-like ST depression that we see here);

      iii) Lead V1 does not look like a recent anterior MI (especially given the relative amount of ST depression that we see in lead V2!) — whereas the ST-T wave picture in lead V1 could be perfectly consistent with recent infero-postero MI with RV involvement that is now showing “reperfusion T waves”;

      and, iv) I thought the limb lead changes (seen in 5 of the 6 limb leads) were much more consistent with recent Inferior MI, now with reperfusion T waves — and even if there was LAD occlusion with “wraparound” — I just wouldn’t expect the combined picture we see here in both limb and chest leads.

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