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).

 

MY Sequential 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: i) With 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; and, ii) 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).
• Sinus rhythm with atrial trigeminy — in which every-third P wave is a PAC that is "blocked" (non-conducted).
• SA ( = Sino-Atrial) Block.
• Mobitz I, 2nd-Degree AV Block ( = AV Wenckebach) with 3:2 AV conduction.
• Mobitz II, 2nd-Degree AV Block.

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Beyond-the-Core: Technically, there are a few additional causes of a bigeminal rhythm that need not be considered in today's case, because the rhythm is either not strictly supraventricular — or — because the 1st beat in each group is not sinus-conducted. These additional causes include:

• Ventricular bigeminy (ie, every-other-beat is a PVC).
• Atrial fibrillation, atrial tachycardia or atrial flutter with Wenckebach conduction.
• "Escape-Capture" (the 1st beat in each group is a junctional or ventricular escape beat — followed by a conducted beat).

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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); and, ii) 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 V1, V2, V3 — and have placed them next to a mirror-image ( = vertically flipped) view of these leads.

 

A 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).

 

MY Sequential 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 draw) laddergrams — See 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 (possibly with SA Block).
• ECG Blog #188 — How to Read (and Draw) Laddergrams.
• ECG Blog #206 — For review of a fascinating case of a Bigeminal Rhythm due to 3:2 AV Wenckebach with alternating Hemiblock.
• ECG Blog #144 — Escape-Capture Bigeminy with 2nd-Degree AV Block of indeterminate severity (at least 2:1 AV block, but possible higher grade).